GB2252567A - Metal/ceramic protective coating for superalloy articles - Google Patents

Abstract

A metal/ceramic protective coating as illustrated in Fig 1 for superalloy articles comprises an outer ceramic layer (1) comprising metal oxides; an oxidation-resistant layer (2) comprising an M-Cr-Al-Y alloy, where M comprises Ni, Co, Fe, or a combination thereof, with an Al content in the oxidation-resistant layer (2) of 7.5-14.0% by weight; and an inner plastic layer (3) comprising an M-Cr-Al-Y alloy, where M comprises Ni, Go, Fe, or a combination thereof, with an Al content in the inner plastic layer of 2.5-5.5% by weight, lying between the oxidation-resistant layer (2) and the surface of a superalloy article (4), wherein the ratio of thicknesses of the oxidation-resistant layer (2) and the inner plastic layer (3) is 4.0-1.0. The ceramic layer may be formed of yttria-stabilized zirconia which may contain TiB2, ZrB2, HfB2, or Ce2S3. In addition there may be an aluminide layer between the inner plastic layer and the surface of the superalloy article. The coated product finds use as gas turbine blades or in parts for internal combustion engines. <IMAGE>

Description

9 r- - 2252567 METAL/CERJAMIC PROTECTIVE COATING FOR SUPERALLOY ARTICLES

The present invention relates to digd-temperature coatings for metallic materials, and more particularly to a protective coating of the metallceramic type for articles from superalloysq for example, gas turbine blades and parts of internal combustion engines.

The claimed invention finds application as a protective coating on blades and vanes of aircraft and marine gas turbines, hot parts of industrial gas turbines, for piston crowns of high-pover diesel engines, and parts used in units for the production of synthetic f uels.

Parts of moaern nigh-temperature equipment made from superalloys, e.S. blades of gas turbines, in tae process of operation, are subjected to high-temperature and low-temperature corrosion, as well as to the actioa of cyclically caaaging thermal and mechanical loads. Compounds of sulfur, sodium salts, chlorides, lead, vanadium impurities, solid particles (carbon) contained in a gas flow cause growing corrosion and erosion failures of the working surface of noa-protected parts.

Knowa in the art is a monola7er metal coating composed of M-Cr-AI-Y (where It is nickel, cobalt, iron tatcea separately or in combination).

4 tendency to an increase of power, economy and ecological purity of modern engines and units aas led to an increase of temperature of a gas flow (over 1,3<)COC) r-\ 1 - 2 and, accordingly, to a rise of working temperature of cooled parts. In connection with this, employment of the existing types of monolayer metal coatings becomes low efficient because of their fast failure, corro5 sion and erosion.

The effect of an aggressive high-temperature gas flow on a superalloy can be limited by developing thermal barrier coatings of the metal/ceramic type. Structurally, such coatings reprL-serit a two-layer system in which an oxidation-resistant layer composed of M-Cr-Al-Y is applied onto a protected part made from a SUDeralloy; an outer ceramic layer made from a low Leat-conducting oxide (as a rule, on the basis of stabilized zirconia) is applied onto the frst layer.

A low Leat conduction of the outer ceramic layer (by an order lower than that of the metal oxidationresistant layer and of the superalloy - the part's material) in the employment of thermal barrier coatings makes it possible to lower the temperature of the part's metal, thus enhancing its life time or, maintaining the temperature of the metal's surface at the same level, to increase the temperature of gas,, thereby increasing the engine power.

The basic functions of the oxidatio n-resis taut, layer in the two-layer thermal barrier coating of the metal/ceramic type reside in protection against oxida tion and corrosion and providing an adhesive contact 1 1,1 with ceramics, while those of the outer ceramic layer reside in limitin6 the heat flow coming from tile combustion products to the material of a part, preventing access of the aggressive gas-slag medium to the surface of the oxidation-resistant layer and in protecting it against erosion dama6e.

The main difficulty on the way of broad employment of coatings of the metal/ceramic type is an insufficiently ai6a thermal cyclic life time (thermal shock resistance) of such coatings, ile. ability of the outer ceramic layer to endure cyclic temperature changes without delamination.

Residual stresses occurring due to mismatch between coefficients of thermal expansion of the outer ceramic layer(CZro 2 10-10-60 C 1) and oxidation-resistant layer (cLI_Cr_Al_y 13-15 10-6o C-1) can lead to spalling of ceramics. Known in the art is a protective coating and a method of its obtaining (plasma spraying) in which, in order to decrease residual stresses occurring due to mismatch between coefficients of thermal expansion of ceramics and metal, transition from the oxidation-resistant layer to the outer ceramic one occurs stepwise, i.e. the content of the oxide phase varies from 0 (at the surface of the oxidation-resistance layer M-Cr-Al-Y) to 100% (at the surface of the outer ceramic layer). In the course of operation of the abovementioned coating, oxidation of metal particles present in a ceramic matrix - 4 is accompanied by expansion of their volume and finally results in a failure of the ceramic layer.

To prevent polymorphic transformations in the ceramic layer of zirconia (accompanied by considerable volumetric changes and cracking), use of yttria as a stabilizing oxide is most preferable owing to its high thermal stability, as compared with other oxides.

As a rule, the content of yttria in zirconia equals 6 - 207o by mass. The data available testify to the fact triat the highest thermal stock resistance of ceramic coatings is attained at introducing 6-8% by mass of jttria in zirconia.

The key role in ensuring a high thermal cyclic life time of tne outer ceramic layer is played by its 15, microstructure, which is determined by a method of deposition of coatings.

For plasma-sprayed coatinGs characteristic is a lamellar microstructure of the outer ceramic layer. Coatings obtained by evaporation and condensation in vacuum have a microstructure in the form of columnar grains orientated along the normal to the surface on whicLi they are deposited. It has been established that in its ability for resistance without failure of deformation arid for relaxation of arising stresses. as well as in thermal shock resistance, the vapor-deposited ceramic coatinGs surpass thosb obtained by plasma-spraying.

Known in the art is a thermal barrier coating - 5 which is a two-layer system obtained by electron-beam evaporation and vapour-deposition in vacuum. An outer ceramic layer from yttria -stabilized zirconia, 125.blm thick, applied over the oxidation-resistant layer (Ni - 23% by mass Co 18% by mass Cr - 12.5% by mass Al - 0.375 by mass Y), owing to its microstructure, sur passes in thermal shock resistance a similar plasma sprayed coating more than 20 times. Deposition of the outer ceramic layer is done on an alumina layer (Al 10 3)$ 0.25-2.5gm thick, preliminarily formed by oxidizing tde oxidation-resistant layer (Ni-Co-Cr-Al-Y), wLich increases adhesion bond between the oxidation-resistant layer and the outer ceramic layer owing to processes of solid solubility.

Along witri a high deformation ability, the vapour deposited cdramic coatings have a disadvantaGeg connected with the fact that the surrounding medium can penetrate through intercolumnar gaps to the surface of the oxidation resistant layer, rendering it oxidized and corroded.

It has been established that the main reason for delamination and spalling of the outer ceramic layer is oxidation of the surface of tae oxidation-resistant layer, formation and growing of a layer of alumina AI 2 0.3 on the metal/ceramic interface. At reaching a definite critical thickness, the layer of alumina 412-03 starts de lamination at thermal cycles, under the action of high compressive stresses, from the surface of the oxida- c tion-resistant layer M-Cr-Al-Y and spalling toGether with the outer ceramic layer.

It is an object of the present invention to create such a protective coating of the metal/ceramic type for articles made from superalloys which possesses an enhanced thermal cyclic and corrosion life time.

The above object is accomplished due to the fact that claimed is a protective coating of the metal/ceramic type for articles made from superalloys, which is a multilayer system containin6 an outer ceramic layer on the basis of metal oxides and an oxidation-resistant layer from the alloy M-Cr-Al-Ye where M is Nil Co. Fe, takeen separately or in combination, with the content of aluminium in the oxidation-resistant layer of 7.5-14. 096o by mass, which, according to the invention, also con- 0 tains an inner plastic layer from the alloy M-Cr-Al-Y, where M is Nil Col Fe, taicen separately or in combination, with a content of 2.5-5.5% by mass of aluminium in the inner plastic layer located between the abovemen- tioned system, comprising the outer ceramic layer and the oxidation- resistant layer, and the surface of an article made from a superalloj, the relation of thicknesses of the oxidation-resistant layer and the inner plastic layer being 4.0-1.0.

Ttle claimed coating ensures extension of the service life of articles made from superalloys, e.g. blades of gas turbines by 1.5-2.0 times as compared with the c 7 earlier used known two-layer coatings of tkie metal/ce ramic type due to increased thermal stability and rela xation ability of the three-layer coatiagg retardation of the rate of growing of the layer of alumina Al 2 0 3 on the metal/ceramic interface.

In case when the outer -ceramic layer on the zirconia basis contains yttria as a stabilizer, it is recommended that the layer should also contain one of diborides of metals of the subgroup IYa of the Mendeleev's periodic system of elements (titanium diboride, or zirconium diboride, or hafnium diboride), with the following relation of components, jo by mass:

TiB 21 or ZrB 21, or HfB2 - 0.3 - 6.0; Y203 - 5.0 - 25.0i Zr02 - ttle balance.

Employment of t1aree-layer coatin6s having a modified outer ceramic layer with additions of diboride of a metal of trie subgroup IYa of the Periodic system of elements renders it possible to increase thermal shook resistance of coatings 2-3 times, as compared with non-modified outer ceramic layer of the three-layer coatings, and 3-4 times, as compared with the known tow-layer coatings of the metal/ceramic type.

In case of employment of yttria-stabiiized zirconia as an outer ceramic layer, it is also recommended that it siould additionally contain cerium sulfide, with the following relation of components, % by mass.- Ce2s 3 0.5-5.0; 0 - 8 Y2 0 3 6.0-25.0; Zr02 - the balance.

Employment of tiaree-layer coatiars with a modified outer ceramic layer, containing cerium sulfide, increases thermal cyclic life time of coatings 1.5-2.5 times, as compared with the knowa two-layer coatings.

It is also desirable that the outer ceramic layer on the yttriastabiiized zirconia basis should contain metallic zirconium in the form of interlayers 0.5-4.Ojtm thick, located in tiae outer ceramic layer parallel to the article surface, the minimum distance between each of the interlayers, as well as the distance between the surface of the oxidation-resistant layer and the nearest to it interlayer of metallic zirconium being equal to 6.01m, and the number of interlayers of metallie zirconium bein6 equal to at least one.

It is expedient that the outer ceramic layer of tL-.e yttria-stabilized zirconia basis should contain at least four interlayers of metallic zirconium, the thickness of each of which being equal to 2.5-3.0.,uml and the distance between each of tue iaterlayers, as well as the distance between the surface of the oxidationresistant layer and the nearest to it interlayer being equal to 20-23 M. 6 The thermal cyclic life time of the three-layer coatin8s with an outer ceramic layer, containing interlayers of metallic zirconiums is 2.5-3.5 times higher than that of the i:nown two-layer coatings of the metal/ceramic type.

1 1 0 9 Besides, it is also possible that the coating should contain a 5-45gm thick aluminide layer with 15-35% by weight aluminium located between the inner plastic layer and the surface of an article made from a superalloy.

Employment of such four-layer coatings for the protection of blades of gas turbines, operating under conditions of sulphide-oxide corrosion, enhances their thermal cyclic and corrosion life time 3-5 times, as compared with the earlier employed known two-layer coatings of the metal/ceramic type.

The invention will be further explained by a detailed description by way of example only, with reference to the accompanying drawings, wherein:

Figure 1 shows an article made from a superalloy with a protective coating applied thereon; Figure 2 shows an outer ceramic layer of the protective coating shown in Figure 1; Figure 3 shows a variant of the protective coating; The protective coating of Figure 1 for articles made from superalloys is a multilayer system, containing an outer ceramic layer 1 on the basis of metal oxides, eg. zro 2' Al 2 0 3' TiO 2 and Y 2 0 31 an oxidationresistant layer 2 from the alloy M-Cr-Al-Y, where M 0 is Ni, Co, Fel taken separately or In combination, with the content of aluminium in this layer of 7.5-14.0% by mass, and an inner plastic layer 3 from the alloy M-Cr-Al-Y, where M is NI, Co, Fe, taken separately or in combination, with the content of aluminium in this layer of 2.5-5.5% by mass. The inner plastic layer 3 is located between the oxidationresistant layer 2 and the surface of an article 4 made from a superalloy. The relation of taicknesses of the oxida- tion-resistant layer 2 and the inner plastic layer 3 is 4.0 - 1.0.

The coating is produced by way of an electron beam-physical vapour deposition of various alloys M-Cr-Al-Y and ceramic materials with their vapour- deposition in vacuum on protected articles.

Deposition of coatings is performed by means of industrial electron-beam units, equipped with multicrucible evaporators. The articles to be coated are placed in special fixtures Intended for rotating the articles in a vapour flow of the evaporated material with a speed of 4-12 rpm. The articles are heated in a vacuum chamber by an electron beam to a temperature of 830 9800C. The temperature of the articles in the process of deposition of layers of M-CrAl-Y depends on the chemical composition of the superalloy from which an article Is made. The pressure of residual gases in tae vacuum chamber is maintained not over 1. 3. 10-2 Pa.

An ingot of the alloy M-Cr-Al-Y is placed in a 1 c 11 water-cooled crucible of the evaporator. The electron beam melts the ingot, forming a molten metal pools and the vapour flow of the evaporated alloy starts condensation on the article surface, thus forming a protective coating.

The alloys Ni-Cr-Al-Y and Ni-Co-Cr-Al-Y are widely us-ed for application of an oxidation-resistant layer owing to their phase stability. They are used, mainly, for the protection of blades of aircraft gas turbines, operating at a temperature of the gas exceeding 1s300 0 C, under conditions of frequent thermal Cycles.

The systems of alloys Co-Cr-Al-Y and Fe-Cr-Al-Y are used for application of coatinGs operating under conditions of mainly sulfide-oxide corrosion, e.g. on blades of gas turbines of ma:bine power units and on blades of gas- pumping units.

Application of a coating is started from deposition on tue article's surface an inner plastic layer, containing 2.5-5.51o' by mass aluminium from the alloy M-Cr-Al-y.

Tiae chemical composition of the inner plastic layer is selected, as a rule, close to that of the oxidationresistant layer and differs from the latter only in a low content of aluminium, approximately corresponding ( 0.5% by mass) to the content of aluminium in the superalloy, from which the article is made. The initial microstructure of the inner plastic layer must be close 0 12 to a single-phase on-, i.e. practically, it should have no P-phase of MAl.

The thickness of the inner plastic layer is determined by the time of evaporation of the alloy.

Employment of a multicruci ble evaporator makes it possible to apply an oxidation-resistaat layer of the alloy M-Cr-AI-Y immediately after obtaining the inner plastic layer of the necessary thickness without extraction of articles from the vacuum chamber. The fixtures with articles are moved and placed over another crucible, wherein an ingot of the superalloy M-Cr-Al-Y was placed preliminarily. After that started is the process of deposition of the oxidatioa-resistant layer of the necessary thickness. The technological para- meters of the process of application of the oxidationresistant layer are identical to taose employed in deposition of the inner plastic layer.

The rate of condensation of the inner plastic layer and oxidationresistant layer on a rotating article depends on ta-e ctlemical composition of the alloys M-Cr-Al-Y and equals 5-8J.tm/min- Upon applcatioa of the inner plastic layer and oxidation-resistant layer, the articles are removed from ttie vacuum chamber. Further on, they are subjected to a diffusion heat-treatment in vacuum at a temperature of.1,040-1,1300C for two hours, shot peening with metallic microballS9 and then - to a repeated diffusion 0 - 13 beat treatment in vacuum for two-four hours at a tempe rature of 1,040-1v130 0 C (depending on the chemical com position of the superalloy from which the article is made).

Tde last stage is the formatio nj on the surface of the oxidation-resistant layer, an outer ceramic layer from yttria-stabilized zirconia. The main tectinological operations of articles' preparation are similar to those describ,:d above.

Tae fixtures with articles rotated at a speed of 4-12 rpm are arran6ed over the crucible of the evaporator, wnerein located are the discs of compacted ceramics of stabilized zirconia. The temperature of articles in tLe course of deposition of the outer ceramic layer is maintained at the level of 850-1,0800C (V;V,klici:L is deter- mined by the chemical composition of evaporated ceramics and by the edemical composition of the superalloy from which an article is made).

Evaporation of ceramics is conducted at a rate of 0.9-3.5Lm/min. The outer ceramic layer consists of columnar grains and has a general porosity of 16-20%. 'Itie time of evaporation of the outer ceramic layer determines its necessary ttlickness on an article depending on functional tasks.

It rias been established that introduction of the inner plastic layer M-Cr-Al-Y, containing 2.5-5.5% by mass aluminiums between the oxidation-resistant layer 1 If. 11.

11) - 14 11-Cr-Al-Y, containing 7.5-14.0% by mass aluminium, and the superalloy from which an article is made, considerablj (2-4 times) increases thermal cyclic life time of the coating owingto retardation of the rate of 6;ro-vtki of a layer of scale Al 2 0 31 which is formed on the surface of the oxidation-resistant layer on the metal/ceramic interface, and relaxation of thermal stresses occurring in the three-layer system.

The obtained effect of increasing the thermal cyclic life time of the three-layer coating, as compared with the &nown two-layer coatin6, is explained by the following mechanism:

- presence of the inner plastic layer retards the interdiffusion action of the oxidation-resistant layer with the superalloy, the thickness of the diffusion zone, formed between them, being lowered. This consideraoly entiances thermal stability of the oxidationresistant layer. A lower diffusion mobility of elements of trie oxidation-resistant layer facilitates retarda- tion of the rate of growth of a layer of alumina A1 2 0 3; - owing to its high plasticity because of a low content of aluminium, the inner plastic layer ensures relaxation of thermal stresses occurring at the metal/ceramic interface. In the long run, this increases the tnermal cyclic life time of the coating.

The necessity of ensuring the maximum possible oxidation resistance and corrosion resistance of the 1 C) f oxidation-resistant layer requires the presence of chromium (up to 24-26% by mass) and aluminium (up to 12-147o by mass in it). However, at such amounts of these metals, resistance of ttlermal fatigue ttle alloys M-Cr-Al-Y is lowered, especially so when the content of aluminium exceeds 14.ol by mass as a result of a temperature riseof the dictile-brittle temperature transition. Introduction of the inner plastic layer ma;ces it possible to improve thermoplastic characteristics of the three-layer system. Owing to the ability of the inner plastic layer to retard thermal fatigue microcracks originating in the oxidation-resistant layer, the resistance of articles provided with such coatings to thermal fati6ue is iticreased.

The necessary level of resistance to oxidation and corrosion is ensured at the introduction of 7.5-1475 by mass aluminium into the oxidationresistant layer.,'ihen the content of aluminium in the oxidationresistant la-ier is less then 7.5% by mass, its resistance to v oxidation at the operating temperature of over 1,000 0 0 sharply drops.

The minimum content of aluminium in the inner plastie layer is 2.575 by mass, which is brougnt about by the fact that at lower amounts of it the exchange diffusion processes between the inner plastic layer and oxidationresistant layer start to proceed intensitvely. The inner plastic layer loses the function of a diffusion 0 16 barrier, which lowers the effect of its employment.

With a content of aluminium in the inner plastic layer in excess of 5.5% by mass. due to a drop of plasticity, it loses relaxation properties, as a result of which its positive effect on the thermal cyclic life time vanishes.

The content of aluminium in the amount of 2.5-5.5% by mass in the inner plastic layer ensures a better thermal stability of the oxidationresistant layer, as compared with tde known two-layer coating of the metal/ce ramic type. The growth of a layer of alumina AI 2 03 is retarded and relaxation of thermal stresses occurring in the coating is facilitated, owing to which fact the thermal cyclic life time of the three-layer system is extended.

The outer ceramic layer of the three-layer coating, having a columnar microstructure with intercrystalline pores, is permeable for the surrounding oxidation medium.

" the outer ceramic Owing to a decreased gas permeability oL layer, there appears a possibility to retard the rate of growth of tae layer alumina Al 2 0 3 and to increase the thermal stability of the protective coating.

Various oxides, such as e.g. Cao, L,1go, GeO 2 and Y203 can be used as stabilizers of zirconia. In case of its stabilization by yttria, in order to decrease gas permeability of the outer ceramic layer, introduced into it is one of diborides of the metals of subgroup IVa 17 of tile Periodic system of elements, with the folloviing relation of the abovementioned components, % by mass TiB 2 or ZrB 2 or HfB 2 0.3-6.0; Y203 5.0-25.0; ZrO, the balance.

Application of the coating is performed similarly to that described above, the only difference being that ttie evaporated ceramic discs contain a preliminarily in-roduced diboride of the metal of subgroup IVa of the Periodic system of elements.

The teednology of producing ceramic discs is the following: the initial powders ZrO29 Y 2 0 3 and (TiB 2 or ZrB or HfB), taken in the necessary per cent 2 2 proportion, are mixed and compacted.

The temperature of an article in the process of application of Cie outer ceramic layer is at the level of 850-1,0800C and is determined by the chemical compo sition of ceramics and superalloy, from wLieL the article is made.

The deposited outer ceramic layer ZrO Y203 (TiB 2 or ZrB 2 or HfB.) has disperse particles-of the introduced diboricLe uniformly distributed throughout the entire volume of ceramics, 'Said particles being mainly released alont, the borders of columnar crystallines.

In the course of operation of the coated articles, 0 at heatine the outer ceramic layer over 900 C, there occurs oxidation of diboride particles with the forma- 0 18 tion of molten boric anhydride B 2 0 3 in the form of accumulations of a vitreous film along the borders of columnar crystallines, microcracks and pores. This film creates a diffusion barrier for penetration of the agGres- sive medium along the borders of columnar crystallines through the outer ceramic layer. Its gas permeability is decreased, the growta of a layer of alumina Al 2 03 on the metal/ceramic interface is retarded, as a result of which the general taermocyclic life time is increased.

Besides, owing to a modifying effect of diborides, the microstructure of the outer ceramic layer becomes more disperse. The number of columnar crystallines is increasedt while the size of the cross section of a single crystalline is decreased. This impedes the spread of microcracks in the outer ceramic layer, appearing unaer the action of thermal stresses.

The percentaGe of in6redients of the outer ceramic layer is determined by the operating conditions of articles and chemical composition of the oxidation- resistance layer.

With a content of diboride of one of tLe metals of sub6roup IVa of the Periodic system of elements less than 0.3 and more than 6.01/15 by mass, the positive effect of increasing thermal stability practically boiled down to minimum. This is associated with the fact that with content of titanium diboride (or zirconium diboride or hafnium diboride) in excess of 6.0% by mass, tkiere 0 19 occurs an increase of the volume fraction of diboride particles released in the ceramic matrix, their size is increased, brinGing about the appearance of micro6aps in the outer ceramic layer. With a content of one diboride of ttie metals of subgroup Va of the Periodic system of elements less then 0.3% by mass, the amount of released aisperse particles is too small for creating diffusion barriers on the way of the oxidation medium in the outer ceramic layer.

Lowering of gas permeability in the outer ceramic layer from yttria-stabilized zirconia can also be attained at introducing cerium sulfide in it, with the following percentage of componentss Vo by mass: Ce ?- S 3 0.4-5.0; Y, 10 3 6.0 - 25.0; ZrOp - the balance.

Application of the coating is performed similarly to taat described above, tue only difference being tuat tlie evaporated ceramic discs contain cerium sulfide introduced preliminarily.

Taken in the necessary percentage, the initial pow- 2-0 ders of zirconia, yttria and cerium sulfide are mixed and compacted into ceramic discs.

Tfte temperature of an article in the process of application of t1ae outer ceramic layer is at the level of 850 - 1,0800C and is determined by the claemical com- position of ceramics and superalloy from which the article is made.

The positive effect of cerium sulfide resides inensuring the formation of dense intercrystalline inter- 0 - 20 faces of the outer ceramic layer. Acting W a plasticizing phase that reduces microhardness of the outer ceramic layer, cerium sulfide- noticeably makes the structure finer and increases uniformity of axes of columnar crystalliaes, due to which fact tiaey Srow togetfter more closely. There are no discontinuities along intercrystalline interfaces. As a result, gas permeability of the outer ceramic layer becomes less, the growth of a layer of alumina A1203 is retarded, and thermal shock resistance of the outer ceramic layer is increased.

With the content of cerium sulfide in the outer ceramic layer less then 0. 5% by mass, a sufficiently dense interp.;rowth of columnar crystallines is riot en- sured, whereas with the amount of it in excess of 5.0;7o by mass, the structure of tile outer ceramic layer becomes excessively dense. Microcrackcs appear in the outer ceramic layer which decrease resistance to oxidation and ta-ermal shock resistance of the coating.

Further increase of thermocyclic life time of the outer ceramic laTer owin6 to lowering of gas permeability is asociated with a change (violation) of its columnar structure, This is accomplished by that the outer ceramic layer I (Fig. 2) applied on the oxidation-resistant layer 2, also contains at least one interlayer 5 of metal lic zirconium with a thickness of 0-5-4.0km arranged 0 - 21 parallel to the articlej the distance I between each of interlayers 5 of metallic zirconium and the distance.1 between the surface of tiae oxidation-resistance layer 2 and the interlayer 5 of metallic zirconiumg nearest to 5 the la3?er 2, must equal 6 pm, or more.

Introduction of interlayers 5 from metallic zirconium makes it possible to increase triermal cyclic life time of three-layer coatints. Especially efficient is introduction of such interlayers into the outer ceramic layer from yttria-stabilized zirconia, witi a modifying addition of one of diborides of metals of sub,roup IVa of the Periodic system of elements, or cerium sulfide.

Application of the coating is performed according to tie tecanolo,y described above, tkie only difference bein-- t4at in the deposition of theouter ceramic 1 ayer I, periodically (depending on tiae required amount of interlayers 5 of metallic zirconium) stopped is evaporation of ceramics and displaced is the fixture with articles, which is arran6ed over the crucible that conains metallic zirconium. Zirconium is melted by means of an electron beam and an interlayer 5 of the required thickness is deposited. Then evaporation of metallic zirconium is stopped, the fixture with articles is displaced and located over the ceramics, and depo ition of tue outer ceramic layer I is resumed. After a definite period of time (required for application of the outer 0 - 22 ceramic layer with a thickness equal to the distance 1 between the neighbouring interlayers) tile whole technological.cycle of deposition of the next interlayer 5 of metallic zirconium is repeated.

Introduction of interlayers of metallic zirconium Dreaks the columnar structure of grains and decreases porosity of the outer ceramic layer. Owing to this, gas permeability of the outer ceramic layer is lowered, while tue rate of formation and growth of a layer of alumina Al 2 0 3 on the metal/ceramic interface is retarded.

In tae course of operation of an article with the claimed coating, as a result of penetration of an oxidizinG medium, there occups a subsequent (bejinning from the interlayer nearest to the surface of the outer ceramic layer) oxidation of interlayers of metaiiic zircOnium and their transformation into interla7ers of zirconia. The interlayers of zirconia, taus formed, serve as barriers on the way of penetration of an aggressive gas medium and retard the process of oxidation and corrosion of the oxicLation-resistant layer. Thereby, accomplished are retardation of the rate of growth of a layer of alumina Al 2 0 3 and extension of the thermal cyclic life time of the coating. An interval of tniciiness of each of the interlz:xye.rs 5 of metallic zirconium of 0.5-4.OjCm is determined by the type and conditions of operation of an article made from a superalloy, as well as by the thickness of the outer ceramic layer. At a thickness 0 23 of the interlajer exceeding 4.0 J.1m, a probability arises of appearance of a local separation of ceramics from metallic zirconium in the process of operation. At a thickness of the interlayer of metallic zirconium less than 0.5)1m, the effect from their introduction into the outer ceramic layer sharply drops, since they are already not a sufficiently effective barrier on the way of the oxidation medium owin6 to its small thickness.

If the distance between interlayers of iaetallic zir10 conium and tne distance between the surface of the oxidation-resistant layer and the interlayeR nearest to it becomes less then 6.kIm, a danger appears of delamination of tLe outer ceramic lajer at thermal cycles because o:C trie appearance of considerable thermal 15 stresses in the outer ceramic layer.

The number of introduced interlayers 5 is determined by the b--eometry of the surface and operating conditions of an article subjected to coatin6, as well as by t'L.Le thickness of a sin61e interlajer and tlae taickness 20 of tt.Le outer ceramic layer.

For the articles of a complex shape with inner cavizies, with a view to enhance resistance to oxidation and taermalc cyclic life time, offered is a multilayer coating, containing in addition to the abovementioned outer ceramic layer I (Fi6. 3), the oxidation-resistant layer 2 and tae inner plastic layer 3, an aluminide layer 6, witia the ttlicKness of 5-45),Lm, having 15-35% by mass aluminium and located between the superalloy from which 0 the article 4 is made, and the inner plastic layer 3. The aluminide layer 6 is produced by a diflusion saturation, as well as by means-of other known technologies.

The technology of deposition of a three-layer coating on the surface of an article made from a superalloy, having an aluminide layer, does not differ from that described above.

A positive effect of the aluminide layer is brought about, first of all, by reducing thermal stresses in the oxidation- resistant layer on the metal/ceramic interface, which enhances the thermal cyclic life time of the coatinE. This is accomplished owing to the appearance in tile aluminide layer, when cooled, residual comp- ressive stresses. since its coefficient of thermal expansion is lower than that of the superalloy. 'v-V'hen the oxidation-resistant and inner plastic layers are cooled, residual tensile stresses appear in these layers, since trieir. thermal coefficient of linear ex- panzion is greater than that of the superalloy. AS a result of a mutual compensation, the general level of stresses in such four-layer system is lowered, which fa cilitates the increase of the thermal cyclic life time of the coating.

Resides, the aluminiae layer acts an an additional diffusion barrier, materially limiting tne diffusion in teraction of the three-layer coating with the superalloy, which increases the thermal stability and life time of the coating.

C) - 25 The maximum content of aluminium in the aluminide layer (35% by mass) is determined by the fact _ttlat exceeding of this level leads to worsening of mecrianical chLaracteris ties of the superalloy, in tile first 5 place, of the thermal fatigue ones.

The minimum value of content of aluminium in the aluminide layer (1575 by mass) is associated with the factUlat at a lower concentration the aluminide layer lowers its oxidation resistance at a temperature exceeding 9500C. At a thickness of the aluminide layer iess than 5.Um, its action practically is not felt because of inability to redistribute residual stresses.

At a thickness over 45?m the aluminide layer --ay start cracKing because of considerable compressive stresses acting therein.

Employment of the coating to protect blades of a gas turbine of a marine power unit operating at a temperature over 9200C under conditions of a sulfileoxide corrosion makes it possible to extend tneir service life almost twice, as compared with two-lajer metal/ceramic coatings employed ealier.

Employment of three-layer coatings wittl an outer ceramic layer from yttria-stabilized zirconia, containin6 stabilizing additions (one of dibori(les of tne metals of subgroup 1Va of the Periodic system of ele=encs or cerium sulfide) to protect bladee of an aircraft. t:as turbine operatin6 at a temperature of a gas flow oil C 1,300OC-plus makes it Possible to increase their thermal cyclic life time three times in comparison with blades protected by the known two-layer metal/ce ramic coating.

Application of three-layer coatings with an outer ceramic layer containing interlayers of metallic zir conium on piston crowns of an adiabatic diesel en6ine with an elevated temperature of fuel combustion products increases their thermal cyclic life time 3.5 times, as compared with piston crowns protected by the known twolayer metal/ceramic coating.

Employment of the coating, having an aluminide layer, on blades of gas turbines operating under copditions of a sulfideoxide corrosion$ extends tneir tkiermal cyclic and corrosion life time four times, as compared with the known two-layer coatings of the metal/ceramic type. Given below are concrete examples, illustrating the invention. 20 EXAMPLE I. A three-lajer coating of the metal/ceramic typeg containing an inner plastic layer NI 17.2% by mass Cr - 5.5 % by mass A1 - 0.1% by mass Y, 5Cim taick, an oxidation-resistant layer Ni - 17.4% by mass Cr - 14.0% by mass AI - 0.1% by mass Y, 50 -',j4m thick, and an outer ceramic layer ZiO 8% by mass and Y 2 0 3' 100.44m thick, is applied on a group of blades of an aircraft has turbine (the len6th of the blade fin is 90 mm) made from an alloy, containings IS by mass:

IC) - 27 Cr 8.0 - 9.5; W 9.5 11-0; Co 9.0 - 10.5; Al 5.1 - 6.09 Mo 1.2 2.4; Ti 2. 0 2.9; Nb 0.8 - 1.2 Fe < 1.0; C 0.13 - 0.22; Ni - the balance.

Application of the coating is performed by means of an industrial electron-beam unit on blades rotatinr in a vapour cloud of the evapoaated material at a speed of 6 rpm. Deposition of the inner plastic and oxidation-resistant layers is performed by way of a successive electronbeam evaporation of inGots 68.5 mm in diameter made from tiae alloys Ni-Cr-Al-Y of the respective chemical composition. The temperature of heating the blades in the process of deposition of metallic layers of the coatin6 is 830+250C, the rate of concLensation of tc,,e layers Ni-Cr-Al-Y being 5.8Lm/min. The vacuum in the workinS chamber should not exceed 1-3 010-2 Pa.

Upon application of thie inner plastic and oxicla tion-resistant layers, tae blades are subjected to a diffusion heat treatment in vacuum at a temperature of 19040 0 C during 2 hours, after which, in order to obtain a dense, non-porous structure of the oxidation-resis tant layer, triey are subjected to shot peening with steel microballs 200,Um in diameter. Next, the blades are subjected to a repeated diffusion heat treatment in vacuum at a temperature of 1,0400C durin6 2 hours.

Appiication of the outer ceramic layer on the blades having the layers Ni-Cr-Al-Y is performed by way of an electron-beam evaporation of ceramic discs 684,5 mm in G - -28 diameter. In the process of deposition of ceramics, the temperature of blades is maintained at the level of 950250C. the rate of deposition of the outer ceramic layer being 1.9,,Um/min, and vacuum in the working cham- ber being not in excess of 1.3-10-2 Pa. Upon application of the outer ceramic layer, the blactes are subjected to a diffusion heat treatment in vacuum at a temperature of 1,0500C during 2 tiours. The general porosity of tile outer ceramic layer, as measured by a gravimetric metlaod is 19;iO, and an avera6e diameter of a sinrle columnar grain is 4. 3 "1 mo Thermal cyclic tests of tile coated blades are performed in the open by way of heating them to a temperature of 1.1000C during 3 minutes, keeping them at tais temperature during 5 minutes, and coolinb to a temperature of 1000C during 0.5 minute. Appearance of the first cracks and spallin6 of the outer ceramic layer is considered a failure of the coating.

For the purpose of comparison, subjected to testing are the blades with a two-layer coating of tne metal/ceramic type, including an oxidation-resistant layer Ni - 17.3% by mass Cr - 14.0% by mass Al - 0.1% by mass Y loo,ktm thicK, and an outer ceramic layer ZrO 2 - 81% by mass Y203, 100,tm thick. The technological parameters of application of coatings are similar to those employed in application of three-layer coatin6s.

The averate thermal cyclic life time of the blades with a three-layer coatind is over 70 thermal cycles - 29 (without failure) and that of the blades with two layer coatings is only 23 thermal cycles.

EXA:vIPLE 2. A three-layer coating of the metal/ce ramic type, includin6 an inner plastic layer Co - 24.0% by mass Cr - 4.3% by mass Al - 0.1% by mass Y, 25 'i #m taick, an oxidation-resistarit layer Co - 28.0% by mass Cr - 10.2915 by mass Al - 0.1% by mass Y, 100JUm thick, and an outer ceramic layer ZrO 2 - 12Yo by mass Y 2 0 3' 180),Lm thick, is applied onto cylindrical samples 7 mm in diameter (the length of ttie working part of ttle samples is 60 mm) made from a superalloy of tae followin6 composition, 5-o by mass: Cr - 18.0; Co - 5.6 Al 4.5; W - 4.0; Mo - 4.0; Ti - 2.6; Pe - 2.3 Ni the balance.

Deposition of the coating is performed according to the tecinology described in Example 1. The general porosity of the outer ceramic layer is 21%.

Tests for thermal shock resistance are conducted in the open, observing tae following conditions: heating of trie coated samples to a'temperature of 1,1000C durinG 4 minutes 9 keepin6 them at tile maximum tempera ture during 20 minutes, and cooling by a flow of air to a temperature of 40 0 C during 6 minutes. Spalling of the outer ceramic layer on an area of 50% of the sample surface is considered a failure of the coating.

The thermal cyclic life time of the samples with a three-layer coating is 175 thermal cyclest wriereas the samples made from the similar alloy with a two-laver - 1 0 - 30 coating, including an oxidation-resistant layer Co 28.07o by mass Cr - 10. 1% by mass Al - 0.1% by mass Y. 125)im thick, and an outer ceramic layer ZrO. - 12% by mass Y 2 0 3' 180jm thick, applied with the use of the Same tec!2nolo6ical parameters, endure only 90 thermal cycles.

Tests of the samples with two-layer and three-layer coatings for oxidation resistance (oxidation in the open at a temperature of 1,OOOOC) during 500 houvs show that the thickness of a layer of alumina Al 2 0 3 formed at the metal/ceramic interface of the three-layer coatin,-s is 2.0 'M v while in the two-layer coatings it is equal to 3-0)),16.

The thickness of a diffusion zone between the oxi- dation-resistant layer and the inner plastic layer of tiae three-layer coatin.-s 20.Imt and of thet between the oxidation-resistant layer and ttie superalloy of the two-layer coating - 45Am.

aAMIPLE 3. A three-layer coatin6 of ttie metal/ce- ramic type, including an inner plastic layer Co - 24.87o by.mass Cr - 4.0% by mass Al - 0.1% by mass Y, 40Am thick, an oxiaatiori- resistant layer Co - 26.9% by mass Cr 11.775 by mass Al - 0.1% by mass Y, 50,pp thick, and an outer ceramic layer ZrO 2 - 1275 by mass Ceo., 110úm thick, is applied onto wedge-sklaped samples, simulatin6 a leading edge of a blade (the leading edge corner radius of the samples being 0.7 mm, height - 80 mm, length 43-47 mm) made from a superalloy of the 0 - 31 composition given in Example 29 on whose surface on alumini-e layer (30% by mass Al), 30Am thick, was applied earlier b37 the gas-phase deposition method.

The technolosy of deposition of the three-layer coating is similar to that described in Example 2.

The rate of condensation of metallic layers of the coatin6 is 5.0km/min, and taat of the outer ceramic layer - 2.2),tm/min. The general porosity of the outer ceramic layer is 2317o.

The samples are subjected to taermal cyclic tests on a -as-d.7namic stand in the diesel fuel combustion products, containin6 0.25% by mass sulfur. The maximum temperature of the blade leading edSe of the samples is 1, 0000C. The time of heatin8 up to this temperature is 60 S., the time of cooling down to a temperature of 400 OC is 70 S. The amplitucie of tuermal stresses (a sum of temile and compressive stresses), owing to different length of the sapples, is equai. to 815-955 IMPa.

The formation of a thermal fati6ue crack, 0.5 mm lonE, on a leading edee is considered a start of tue coating failure, waile the life time is determined by the number of tkiermal cycles up to the formation of such a crack.

The taermal cyclic life time of the three-layer coatinE;s is 790 thermal cycles, whereas the wedGeshaped samples with an aluminide layer, 30Jim tr, :LCKP carrying a two-layer vapour-deposited overcoatin;, including an oxicLation-.resistant layer 90'km thick, similar in composition to the oxidation-resistant 1 ay er 0 of the three-layer coating mentioned above, and an outer ceramic layer Zro 2 - 12% by mass CeO., 100.,Um tiaicK, could endure only 400 thermal cycles.

A metalloeraphic analysis of the failed samples 5 has shown that the thickness of a layer of alumina A1203 which forms on the metal/ceramic interface of the three-la7er coatin6s, does not exceed 2.5)tmo which is almost 1.5 times less in comparison with tae thicKness of a la7er of alumina AlpO 3 that forms in two-layer coatings. EXAASLE 4. A taree-layer coatin; of the metal/ceramic t37pe, includin6 an inner plastic layer Ni 10.5% by mass Co - 17.476 by mass Cr - 4.8% by mass Al - 0.27o by mass Y, 40)Im thick, an oxidation- resistant layer 15 Ni - 11.2O by mass Co 18.7;o7 by mass Cr - 8.016 by mass Ai - 0.11o by mass Y, 60,Um thick, and an outer ceramic layer ZrO 2 - 6% by mas s Y203' 95vum t"'01" is applied on smali-size (the length of tde blade fin is 25 mm) blades of an aircraft gas turbine from a superal20 loy, includinE;, % by mass: Cr 10.0 - 12.0; Al - 5.06.0; W 4.5 - 5.5; Co 4.0 - 5.0; Mo 3.5 - 4.8; Ti - 2.53.2; Fe 2.0; C - 0.1 - 0.2 and Ni- the balance. The technology of application of the coating is similar to that described in Example 1, the only difference bein6 tiaat the temperature oif -the samples in the process of deposition of the outer ceramic layer is 920 + 25 OC. - 0 The rate of condensation of metallic layers of the coating is 5.6,Xm/min, and that of the ceramic layer 1 - 5,Wmi n Me thermal cyclic tests of the blades are conducted unuer condition6 similar to those described in Example 2.

lue thermal snock resistance of tae claimed three- la,,er coatings is 460 thermal cycles, waich is 1.7 times ai6aer in comparison wita tae tiaeriaal sliockc resistance of tiae icnown two-layer coatinLs, including an oxidationresistant layer, 100 If),tm thick, and an outer ceramic laFer, 95,)m tiaicic, similar in composition and conditions of application to the same system of a threelayer coatin&.

Rie tL.ickness of a layer of alumina Al 2 0 3 in a tlaree-la.yer coating of tiae tested samples is 2.0,,Uml and tiat in a two-layer coating - 2.5, 1AM.

E.kLaPLE 5. A three-layer coatinb, includinb an inner plastic layer Ni 15.0,7,6 by mass Cr - 4.27o by mass Al - 0.1% by mass Y, 40).tm thick, an oxidation-re sistant layer Ni - 17.8/5 by mass Cr - 10.7% by mass Al 0.1,Zo by mass Y, - 50)),m thick, and an outer ceramic layer Al 0 10% by mass ZrO,>, 80.,zm thicK., is applied 2 3 on the samples made from a superallo7 (the saape of tue saL4ples and composition of the superalloy ave gven in Example 2).

Deposition of the coat-Lng is performed according to 0 - 34 the technoloGy described in Example 1. 'The temperature of the samples in the process of deposition of the outer ceramic layer is 990+25'C",. the rate of conden sation of the-outer ceramic layer - 1.2/Am/min.

Tile methods of testin6 for thermal shock resis tance are described in Example 2.

The thermal cyclic life time of the samples with a ttiree-layer coating is 58 taermal cycles, whereas the safflples made from trie similar alloy with a two-layer coatin,,, including an oxidation-resistant layer Ni - 17.7:b by mass Or - 10.6% by mass AI - 0.1% by mass Y1 go v - 10% JLtm thick, and an outer ceramic layer AI d03 by mass ZrO;,,, applied under the same teennological parameters endure only 37 thermal cycles.

EXAAPLE 6. A coating of the metal/ceramic type2 incluc-.,ing an inner plastic layer Fe - 20.27a by mass Ni - 16.1;75 by mass Or - 2.5% by mass AI - 0.1; by mass Y 30)11m thicK, an oxidation-resistant layer 1P.e 27.315 by mass Or - 7.5% by mass AI - 0.1,c,5 by mass Y, 60 Atil ttic,:, and an outer ceramic layer ZrO 2 - 2070' by mass Y2032 125.Um thick, is applied on the cylincrical samples, described in Example 2, made from a superalloy of the following composition, ra by mass: Ni 33-37; Or 14-16; W 2.8 - 3.5; Ti 2.4 - 3.2; AI 0.7 1.4;1.11n <0.o; Si.:!-0.6; S,-'-0.02; P,-'-0.035; B,-<-0.02; C,< 0.08 $.

Fe - the balance.

- 35 The technological parameters of application of the coating are similar to those described in Example 1. The General porosity of the outer ceramic layer is 22%. Tne thermal - cyclic tests are performed under condi5 tions described in Example 2.

TLe triermal snock resistance of the three-layer coatinG is 180 thermal cycles, which is 1.8 times dibher than that of the two-layer coating of the metal/ceramic type, having an oxidation-resistant lajer with a thickness of 901" and an outer ceramic layer with a thickness of l.:5ym, whose compositions are similar to those of the three- layer system.

EXA1,2LE 7. Applied on the samples made from a supe-L.alloy, whose composition and dimensions are similar to t-,-.o;se described in Example 2, is a three-layer vapourdeposited coating of the metal/ceramic,7pe, incluaing an inner plastic layer Ni - 17.4,/7o by mass Cr - 3.77,5 by mass Al - 0.15-15 by mass Y, 35JU thick, an oxidationresistant layer Ni - 17.9% DY mass Cr - 10.3% by mass AI - 0.1% by mass Y, 60),.,-m thick, and an outer ceramic layer ZrO, - 8% by mass Y203 - 1.6 by mass TiB;,,, gottm thick.

The teennological parameters of deposition of the ti,.ree-la,7er coating are similar to those described in Example 1. Application of the outer ceramic layer by way of an electron beam evaporation of tUe ceramic material, containing ' zirconia, jttria and titanium 1 0 diboride, preliminarily mixed and compacted into discs 68.5 mm in diameter, located in one of the crucibles of the evaporator of the electron-beam unit.

The rate of condensation of metallic layers of the coating is 5.9 Am/min, and that of the outer ceraaic layer - 2.5 Zim/min. The:.eneral porosity of the outer v ceramic layer is 17%, the avarate diameter of a single columnar grain is 2.2,Um.

The tests for thermal shock resistance are performed under conditions described in Example 2.

The thermal shock resistance of the samples with a taree-layer coatint, whose ceramic layer contains titanium diboride, is 710 thermal cycles, while that of a threelayer coating without titanium diboride in the outer ceramic layer is 350 thermal cycles, the thermal shock resistance of a two-layer coating, includin6 an oxiuation-resistant layer Ni - 17.7% by mass Cr - 10.37o by mass Al - 0.175 by mass Y, 95,Atm thick, and an outer ceramic laver ZrO - oyo by mass Y..O. 90 ilm thick is 4 220 thermal cycles.

J The metallographic analysis of the samples tested for oxidation resistance under conditions described in Example 2 has shown that the thickness of a layer of alumina A1203' which is formed in the three-layer coating with an outer ceramic layer from ZrO 2 - Y23 - TiB 2 does not exceed 1.8im, which is 1.5 tiaes less than that in the t4ree-layer coatingg whose outer ceramic layer does 0 37 not contain titanium diboride, and 1.8 times less than that in the two- layer coating.

EXA.2LE 8. Applied on cylindrical samples made from a superalloy, whose dimension and composition are given in Example 2 and whose surface has a previously deposited aluminide lajer, 45Am chick, containing 155 by mass aluminium, is a three-layer coating, including an inner plastic layer Go -23.375 by mass Cr - 3.1% by mass A1 - 0.175 by mass Y, 40,um thick, anoxidation-resistant, layer Go - 27.1% by mass Cr - 11.4% by mass Al 0.1,1 by mass Y, 50jkra thicK, and an outer ceramic layer ZrO2 - 575 by mass Y-O - 6-16 by mass ZrB,q 55jtm thick.

2 3 The technological parameters of deposition are similar to those described in Example 1. The tempera- ture of tije samples in the process of deposition of the outer ceramic layer is 900 + 25 OC. The rate of conden ,-ation of. metallic layers of the coating is and that of the outer ceramic layer The General porosity of the outer ceramic layer is 19%. the averabe cliameter of a single grain is 2.11Ltm.

Tae tests for thermal shock resistance have been performed under conditions described in Example 2.

Simultaneously, subjected to testin6 were the samples with the abovementioned three-layer coatinp,,, applied onto samples which had no aluminide layer, the samples with a four-lajer coating (includin6 the aluminide layer) similar in composition and thickness to the coatin6 0 0.1 38 described in this Example, in whose composition of the outer ceramic layer there were no zirconium diboride5 as well as the samples with a twolayer coating of the metal/ceramic type, containing an oxidationresistarit layer, 90Atm thick, whose composition is similar to that used in the three-layer coating, and an outer ceramic layer ZrO 2 - 5% by mass Y2 0 3' 55.#m thick.

The thermal shock resistance of the four-layer coating with an outer ceramic layer, containing zirconium diboride. is 480 thermal cycles. The same coating, but without an aluminide layer, withstands 422 thermal cycles. The life time of the four-layer coating, whose outer ceramic layer contained no zirconium diboride, is 390 thermal cycles. The least thermal shock resistance (305 thermal cycles) has a two-layer coating of the metal/ceramic type.

EXAMPLE 9. Applied on the wedge-shaped samples made from a superalloy is a four-layer coating of the metal/ceramic type (the form of the samples. composition of the superalloy, composition and thickness of the coating are given in Example 3).

The coating differs only in that the thickness of the aluminide layer is 5,gm (the amount of aluminium is 35% by mass), and in that the outer ceramic layer has a composition Zr02 - 8% by mass Y 2 0 3 - 1.9% by mass Ce 2 S 3 Application of the coating is performed according to the technology described in Example 1.

39 Application of the outer ceramic layer is performed by way of an electron- beam evaporation of a ceramic material, containing zirconia, yttria and cerium sulfide, preliminarily mixed and compacted into discs 68.5 mm in diameter, which are placed in one of the crucibles of the evaporator.

The rate of deposition (condensation) of metallic layers of the coating is 5.9,qm/min, of the outer ceramic layer - 2.1jim/min. The general porosity of the ouzer ceramic layer is 16%, and an average diameter of a single grain 2.1.1-4m The tests for thermal cycling have been perf=e under conditions described in Example 3. The anplitUe of thermal stresses is 565-620 Ua.

The thermal cyclic life time of four-layer coaLiigs equals 1,600 cycles, which is by 550 cycles more than the life time of the same ccating, but withou-: a--d-tions of cerium sulfide into the outer ceramic layer. The thermal cyclic life time of a three-layer coating (Aiitho,.it an aluminide layer), containing cerium sulfide 4-n. the outer ceramic layert is.920 thermal cycles, and ther two-layer coating of the metal/ceramic type (its composition and thickness are given in Example 3, but oiith, the outer ceramic layer composed of ZrO 2 - 8% by 7ass Y 2 0 3) is 740 cycles.

EXALIPLE 10. Applied on the plate-shaped samples.

measuring 120xlOxl.5 mm, made from a superalloy, con- f a 0 - 40 taining, % by mass: Cr 22.5; W 7.0; Co 6.0; Mo 4.5; Pe 4.5; A1 3.0; Ti 1. 3; and Ni - the balance, is a threelayer coating, including an inner plastic layer Ni - 17,2% b by mass Cr - 3.0% by mass Al - 0.1% by mass Y, 40,blm thick, an oxidation-resistant layer Ni - 17.6% by mass Cr - 13.1% by mass A1 - 0.1% by mass Y, 50,Am thick, and an outer ceramic layer Zr02 - 25% by mass Y 2 0 3 - 0.3% by mass TiB 21 90,Mm thick. The outer ceramic layer also contains two interlayers of metallic zirconium, 4.01, Affl thick each, arranged parallel to the surface of the sample made from a superalloy. The distance from the surface of the oxidation-resistant layer to the nearest interlayer is 20jim, and that between the interlayers 1.

The technological parameters of application of the coating are similar to those described in Example 7. In application interlayers of metallic zirconium, the process of deposition of the outer ceramic layer is interrupted, the rotating fixtures with samples are positioned over the crucible, where a zirconium ingot is placed, and by way of its evaporation obtained is an interlayer of metallic zirconium on the samples, after which the process of evaporation of ceramics is resumed.

The rate of condensation of metallic zirconium is 1.0.,Um/min, and that of the outer ceramic layer - 3.m/min. The general porosity of the outer ceramic layer is 15%.

The conditions of testing for thermal shook resis- to 41 tance are described in Example 2.

In comparison with a coating of the similar thickness and composition, but without interlayers of metallic zirconium, the instant coating has a 104-times greater thermal cyclic life time - 584 thermal cycles. A threelayer coating of the same composition, but I without titanium diboride in the outer ceramic layer, has failed after 330 thermal cycles. A two-layer coating, containing an oxidation- resistan't layer Ni - 17.6% by mass Cr 13.1% by mass Al - 0.1% by mass Y, 90),,Zm thick, and an outer ceramic layer ZrO 2 - 25% by mass Y 2 0 3' 90 um, thick, has endured 170 thermal cycles. A coating, containing interlayers of metallic zirconium in the outer ceramic layer had on the metal/ceramic interface, after testing for oxidation-resistance at a temperature of 1,000 0 C during 500 hours, a layer of alumina Al 2 0 3 1. 9'Atm thick, whereas a traditional two-layercoating 3-8,am- EXAMPLE 11. Applied on the plate-shaped samples made from a superalloy (the form and composition are given in Example 10) is a three-layer coating, whose thickness and composition are given in Example 10. The only difference is the fact that the outer ceramic layer, 110,UM thick, has a composition ZrO 6% by 2 mass Y2 0 3 0.5 by massCe 2SY' The technology of deposition of the coating is given in Example 9. The rate of condensation of metallic 1 layers of the'coating is 5.6jtm/min, and that of the outer ceramic layer - 1.9Am/min. The general porosity of the outer ceramic layer is 17%. the average diameter of single grains - 3-3ltme The conditions of performing the thermal cyclic tests are given in Example 2.

The thermal shock resistance of the present coating is 390 thermal cycles, whereas that of the same coating, but without sulfide in the outer ceramic layer - 355 thermal cycles. A two-layer coating of the metal/ceramic type, containing an oxidation-resistant layer Ni - 17.6% by mass Cr - 13.1% by mass Al - 0.1% by.

mass Y, 90,um. thick, iand an outer ceramic layer Zr02 - 6% by mass Y203' 110.,4tm thick, has failed after 250 thermal cycles.

EXAMPLE 12. Applied on the cylindrical samples made from a superalloy (the form of the samples and composition of the superalloy are indicated in Example 2) is a three-layer coating, into an outer ceramic layer of which introduced are four interlayers of metallic zirconium. The coating includes an inner plastic layer Co -24.0% by mass Cr - 4.1% by mass Al 0.1% by mass Y, 45,am thick, an oxidation-resistant layer Co - 27.7% by mass Cr - 10.5% by mass Al - 0.1% by mass Y, 50ktm thick, and an outer ceramic layer ZrO 8% by mass Y203' 123jtm thick.

The thickness of an interlayerv nearest to the 2 0 surface of the outer ceramic layer, is 3.04m, the other interlayers having a thickness of 2.5,im each. The distance between the surface of the oxidationresistance layer and the nearest interlayer of metallic zirconium is 23/LM, and between each of the interlayer 21 U m. - j The technological parameters of deposition of the coating are given in Example 1.

The rate of condensation of metallic layers of the coating is 5.1 Am/min, that of the outer ceramic layer - 2.1,im/min, and that of metallic zirconium 1.0 A m/min. The general porosity of the outer ceramic layer is 14%.

The tests for thermal shock resistance have been conducted under conditions described in Example 2.

The thermal shock resistance of the three-layer coating, containing interlayers of metallic zirconium in the outer ceramic layer, covers 593 thermal cycles. A similar coating without interlayers in ceramics has failed after 425 thermal cycles. A two-layer coating, containing an oxidation-resistant layer Co - 27.7% by mass Cr - 10.5% by mass Al - 0.1% by mass Y, 95jum. thick, and an outer ceramic layer ZrO 2 - 8% by mass Y 0 120tm. thick, has withstood 320 thermal cycles.

2 3' The metallographic analysis of the samples withdrawn from the tests after 400 thermal cycles has shown that the thickness of a layer of alumina Al 2 0 3 in 0 44 a three-layer coating, whose outer ceramic layer contains interlayers of metallic zirconiums is 3.0,Um, whereas in a three-layer coating of the same compoc;ition and thickness, but without interlayers of metallic zirco- nium, the thickness of a layer of alumina A12 0 3 equals 4.5.,Um.

EXAh,TLE 13. Applied on small-size blades of an aircraft gas turbine (their dimensions and composition of the superalloy are given in Example 4) is a three- layer coating, in whose outer ceramic layer of ZrO 2 - 25% by mass Y 2 0 3 - 5.0% by mass Ce 2 0 3 50JtM thick, introduced are seven interlayers of metallic zirconium, 0.5j,tm thick each. - The distance between the surface of the oxidation- resistant layer and the interlayer of metallic zirconium, nearest to it, as well as the distance between each of the interlayers is 6,um.

The thickness and composition of metallic layers of the coating are given in Example 4. Special f.eatures of the coating deposition technology are given in Example 10.

The rate of condensation of the outer ceramic layer is 2.5.#m/min, and that of metallic zirconium - MjLm/min. The general porosity of the outer ceramic layer is 17%.

The conditions of carrying out thermocyclic tests of blades with coatings are given in Example 4.

Subjected to testing are also a three-layer coating I- 0 without interlayers of metallic zirconium and containing no cerium sulfide in the outer ceramic layer, and a two-layer coating described in Example 4, having an outer ceramic layer of ZrO 2 - 25% by mass Y 2 0 3' According to the results of the thermal cyclic tests, they are classified as follows:

(1) a three-layer coating with interlayers of metallic zirconium - 435 thermal cycles; (2) a three-layer coating without interlayers of metallic zirconium 375 thermal cycles; (3) a three-layer coating without interlayers of metallic zirconium and without cerium sulfide - 320 thermal cycles; (4) a two-layer coating - 264 thermal cycles.

EXAhTLE 14. Applied on cylindrical samples (the size is given in Example 2) made from a superalloy of the following composition, % by mass: Cr 16.0; Mo 4.1; W 9.5; A1 1.4; Ti 1.4; a 0.06 and Ni - the balance, is a three-layer coating of the metal/ceramic type, including an inner plastic layer Co - 22.3% by mass Cr - 2.5% by mass A1 - 0.1% by mass Y, 35,,Um thickg an oxidation-resistant layer Co - 27.2% by mass Cr 10.5% by mass Al - 0.1% by mass Y, 45itm thick, and an outer ceramic layer, 65jLm thick. On the-first group of samples applied is an outer ceramic layer Zr02 - 80f by mass Y2 0 3' on the second group ZrO 2 - 8% by mass Y 2 0 3 - 1.8% by mass TiB 2 1 on the third group Zr02 - 1 1 U 46 - 8% by mass Y2 0 3 2.5% by mass Ce2S3. and on the fourth grouP.Zr02 8% by mass Y 2 0 3 with two interlayers of metallic zirconium, each 2)4m thick (the distance between interlayers and between the surface of the oxidation-resistant layer and an interlayer nearest to it, is 20)tm).

Special features of the technology of application of the coating are given in Example 1. The rate of deposition of metallic layers of the coating is 5-3/Lm/min, that of the outer ceramic layer- 2.0 + 0.3jtm/min, and that of metallic zirconium 1.0.)-Im/min.

The corrosion Life time of the abovementioned coatings is determined by way of an isothermic oxidation of the samples,on whose surface applied is a mixture of salts, imitating an ash of the gas turbine fuel of the following composition, % by mass: Na 2 so 4 66.2; Fe 2 0 3 20.4; NiO 8.3; CaO - 3.3; V 2 0 5 - 1.8. The ash in the form of a suzpension, prepared on ethanol, is applied on the coatings. The specific concentration of the ash on the surface of the outer ceramic layer 2 is 10-12 mg/cm Tests are conducted at temperatures of 750 and 8500C during 9-18 thousand hours. A layer of ash is renewed every 250 hours. The corrosion resistance of coatings is evaluated by means of metallographic analyses and by a weighing method by losses of mass of the samples in case of spalling of the outer ceramic layer. The time required till starting a failure of the metallic U 47 ocidatio.n-resistance layer is considered a life time of the coating.

Considered as a base coating is a two-layer con densation system, comprising an oxidation-resistant layer Co - 27.2% by mass Cr - 11.6% by mass Al - 0.1% by mass Y, 80)tm thick, and an outer ceramic layer ZrO - 8% by mass Y 2 0 3' 65),tm thick. The test results are given in the Table below.

Corrosion life time thousand hours Coating (outer ceramic layer) Test temperature 750 0 c 850 OC Base, two-layer (ZrO 2 - 8% by mass Y 2 0 3) 14 6.5 Three-layer (ZrO 2 - 8% by mass Y 2 0 3) 18 10.5 Three-layer (ZrO 2 8% by mass Y 2 0 3 1.8% by mass TiB2) 18 12.8 Three-layer (ZrO 2 - 8% by mass Y 2 0 3 2.5% by mass Ce 2 S 3) 18 11.5 Three-layer (ZrO - 8% by mass Y 0 with two iRterlayers of Zr 3 not failed. Tests are stopped.

18 13.7 - L_.

48 The present invention has been described above purely by way of example, and modifications can be made within the scope of the invention.

1 f) k_ 11 49

Claims (16)

1. A metal/ceramic protective coating for superalloy articles, comprising an outer ceramic layer comprising metal oxides; an oxidation-resistant layer comprising an M-Cr-Al-Y alloy, where M comprises Ni, Co, Pe, or a combination thereof, wherein the A1 content of the oxidation-resistant layer is 7.5-14.0% by weight; and an inner plastic layer comprising M-CrAl-Y alloy, where M comprises Ni, Co, Fe, or a combination thereof, lying between the oxidation-resistant layer and a surface of a superalloy article, the Al content of the inner plastic layer being 2.5-5.5% by weight, and wherein the ratio of the thickness of the oxidation-resistant layer and the inner plastic layer is 4.0-1.0.

2. The protective coating according to Claim 1, wherein the outer ceramic layer comprises yttria-stabilized zirconia.

3. A protective coating according to Claim 2, wherein the outer ceramic layer also comprises a subgroup IVa metal diboride, with the following ratios of components, % by weight:

TiB 2 or ZrB 2 or MB 2 - 0.3 6.0; Y 2 0 3 - 5.0 25.0; zro 2 - the balance.

4. A protective coating according to Claim 2, wherein the outer ceramic layer also comprises cerium sulphide, with the following ratio of components, % by weight:

Ce 2 S 3 Y 2 0 3 ZrO 2 0. 5 5. 0; 6. 0 2 5. 0; the balance.

5. A protective coating according to Claim 2, 3 or 4, wherein the outer ceramic layer also comprises metallic zirconium in the form of interlayers, 0.5-4.Ogm thick, lying in the outer ceramic layer, parallel to a surface of the article, the minimum distance between the surface of the oxidation-resistant layer and an interlayer of metallic zirconium nearest to it being 6.Ogm, wherein there is at least one interlayer of metallic zirconium.

6. A protective coating according to Claim 5, wherein the outer ceramic layer comprises at least four interlayers of metallic zirconium, the thickness of each interlayer being 2.5 - 3.0im, and wherein the distance between each of the interlayers is 20-23gm, and the distance between the surface of the oxidation-resistant layer and an interlayer nearest to it is 20-23gm.

7. A protective coating according to Claims 1 to 6, further comprising an aluminide layer with an aluminium 4 U 51 content of 15 - 35% by weight, and a thickness of 5.0 45.Ogm, lying between the inner plastic layer and a surface of a superalloy article.

8. A protective coating of the metal/ceramic type for articles from superalloys, comprising an outer ceramic layek on the basis of metal oxides, an oxidation-resistant layer from an alloy M-Cr-Al-Y, where M is Ni, Co, Fe, taken separately or in combination, with a content of Al in the oxidation-resistant layer of 7.5-14.0% by mass, and an inner plastic layer from an alloy M-Cr-Al-Y, where M is Ni, Co, Fe, taken separately or in combination, arranged between the oxidation-resistant layer and a surface of an article from the superalloy, with the content of Al in the inner plastic layer of 2.5-5.5% by mass, the ratio of thicknesses of the oxidation-resistant layer and the inner plastic layer being 4.0-1.0.

9. A protective coating according to Claim 8 wherein the outer ceramic layer on the basis of yttria-stabilized zirconia also comprises one of diborides of metals of subgroup IVa of the Periodic system of elements, with the following ratio of components, % by mass:

Ti B 2 or zrB 2 or MB 2 - 0. 3 - 6. 0; Y 2 0 3 - 5.0 - 25.0; zro 2 - the balance.

1 M_ U 52

10. A protective coating according to Claim 8, wherein the outer ceramic layer on the basis of yttria-stabilized zirconia also comprises cerium sulfide, with the following ratio of components, % by mass:

Ce 2 S 3 Y 2 0 3 ZrO 2 0. 5 5. 0; 6. 0 2 5. 0; the balance.

11. A protective coating according to Claim 8 or 9 or 10, wherein the outer ceramic layer on the basis of yttria-stabilized zirconia also comprises metallic zirconium in the form of interlayers, 0.5-4.Olim thick, arranged in the outer ceramic layer, parallel to an article surface, the minimum distance between the surface of the oxidation-resistant layer and an interlayer of metallic zirconium, nearest to it, being 6.0[Lm, and the number of interlayers of metallic zirconia - at least one.

12. A protective coating according to Claim 11, wherein the outer ceramic layer on the basis of yttria-stabilized zirconia, comprises at least four interlayers of metallic zirconium, the thickness of each interlayer being 2.5 - 3.Ogm, and the distance between each of the interlayers, as well as the distance between the surface of the oxidation-resistant layer and an interlayer, nearest to it, being 20-23gm.

9 p 1 i ,- -1 53

13. A protective coating according to Claims 8 to 12, wherein it also comprises an aluminide layer with the content of aluminium 15 - 35% by mass, 5.0 - 45.Ogm thick, arranged between the inner plastic layer and the surface of an article from a superalloy.

14. A protective coating according to any of the preceding Claims, as identified in the description, examples and accompanying drawings.

15. A protective coating substantially as herein described with reference to the accompanying drawings.

16. A protective coating substantially as herein described with reference to any of the foregoing examples.