US3597241A

US3597241A - Metallo-ceramic compositions,having at least three components,for the production of protective coatings for ferrous and non-ferrous metallic surfaces

Info

Publication number: US3597241A
Application number: US596400A
Authority: US
Inventors: Giancarlo Perugini
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1965-11-29
Filing date: 1966-11-23
Publication date: 1971-08-03
Anticipated expiration: 1988-08-03
Also published as: JPS4815777B1; CH488819A; GB1105199A; NL6616433A; FR1505659A

Abstract

A PROCESS FOR PROTECTING FERROUS AND NON-FERROUS METALS AGAINST HIGH TEMPERATURE AND ACTING AS A THERMAL BARRIER, ANTI-OXIDANT BARRIER AND/OR ELECTRO-INSULATING BARRIER. THE COMPOSITION USED AND COATINGS PRODUCED ARE ALSO SHOWN. THE COMPOSITION ILLUSTRATED CONTAINS 15 TO 60% CR, 10 TO 50% NI AND 10 TO 40% OF A CERAMIC OXIDE HAVING A MELTING POINT$1900*C.

Description

United States Patent O 3,597,241 METALLO-CERAMIC COMPOSITIONS, HAVING AT LEAST THREE COMPONENTS, FOR THE PRO- DUCTION OF PROTECTIVE COATINGS FOR FERROUS AND N ON-FERROUS METALLIC SURFACES Giancarlo Perugini, Merano, Italy, asslgnor to Montecatini Edison S.p.A., Milan, Italy No Drawing. Filed Nov. 23, 1966, Ser. No. 596,400 Claims priority, application Italy, Nov. 29, 1965, 26,449/ 65 Int. Cl. C23c 7/00 U.S. Cl. 106-1 13 Claims ABSTRACT OF THE DISCLOSURE A process for protecting ferrous and non-ferrous metals against high temperature and acting as a thermal barrier, anti-oxidant barrier and/ or electro-insulating barrier. The composition used and coatings produced are also shown. The compOsition illustrated contains 15 to 60% Cr, to 50% Ni and 10 to 40% of a ceramic oxide having a melting point 21900" C.

DESCRIPTION Generally related to this application are my applications Ser. No. 552,490 filed May 24, 1966, now Pat. No. 3,390, 292, Ser. No. 570,283, filed Aug. 4, 1966; Ser No. 596,409, filed Nov. 23, 1966.

The present invention refers to a particular metalloceramic composition, having at least three components, in the form of a powder mixture phase or sintered rod, for producing protective coatings on ferrous and non-ferrous metallic surfaces.

The present invention has among its objects a method of applying said metallo-ceramic compositions in protecnve treatments on ferrous and non-ferrous metallic surfaces, various typically protective treatments highly resistant to high temperatures and the articles with the protective coatings thus obtained.

Particularly, the various metallo-ceramic compositions with at least three components, and the various protective treatments obtainable therewith together with ceramic oxides, make it possible to obtain coatings resistant to thermal oxidation (anti-oxidant barrier), highly insulating and thermo-resistant coatings (thermal barrier) and electroinsulating coatings for high temperatures (electro-insulating barrier), useful for the protection of ferrous and non-ferrous metallic surfaces.

The problem of obtaining new materials able to resist heat oxidation and thermal yielding, is very critical. Upon the availability of such materials depends the development of high temperature technologies, which assume more and more importance both in the industrial sector and in that of scientific and technical research in relation to the problem of space navigation.

The demand of special materials for the construction of cracking chambers at higher temperatures, compartments for jet engines, blades for gas turbines, expansion nozzles, ogives and various elements for missiles, is already felt. In the field of said problems concerning the resistance of the materials, part of research activity is in the field of the superficial protection of the common materials by means of protective coatings realized with special materials.

Various processes for the deposition of coating of various special materials having particular thermoresistant characteristics and therefore protective functions on ordinary materials are known in the general field of protective coatings for metallic and non-metallic surfaces. The pro- ICO tective coatings thus obtained are nevertheless unsatisfactory both as to effectiveness and duration. Among such processes are electrochemical deposition (such as chromium plating, nickel plating, etc.), metallization under vacuum, thermochemical deposition (such as the chromium plating in the vapor phase), immersion in a molten bath, and finally spray in the molten state.

This last technique dates back to the time in which Schoop used the process for projecting materials in the molten state in order to obtain various coatings on various base materials. This technique underwent successive and gradual improvements until today it is greatly improved and divided in various specific techniques. Among the latter are various processes for projecting the materials to be applied in the form of wire, sintered rod or powder, into an oxy-acetylene jet.

A recent development are the processes of projection into the arc of a plasma jet. These processes are subdivided depending upon the various forms of the materials to be applied, e.g. wire, sintered rod or powder.

The spray in the molten state technique which, without doubt, is the newest technique of protective coating, offers various advantages over the other processes. These advantages are determined by the possibility that this technique gives of depositing non-metallic materials. These materials can be oxides, carbides, borides, etc., either alone or in admixture with each other, in metallic, ceramic and metallo-ceramic compositions.

This technique, nevertheless, possesses less favorable characteristics or clifiiculties in the realization and application stage of the protective coatings. The success and effectiveness of the same coatings is dependent upon overcoming these difficulties. The deposition of a layer of ceramic oxide or of another material cannot accidentally cause the desired protective effect against the thermal oxidation or against another damaging phenomenon, since the physical characteristics of the base material must be reconciled to those of the coating material, particularly to their coeflicients of thermal expansion, in order to avoid cracking and detaching of the coating at its first thermal test, because of thermomechanical stresses not suitably resolved. Another cause which can negatively affect the utilization of said protective coatings is the porosity of the applied coating. In general, this varies from 5 to 10% of the volume. It is known in fact that diffusion of corrosive gases through the said porosity alters the adhesion characteristics of the coating to the metal base, thus causing the separation of the coating after a short time. In conclusion, while the spray in the molten state techniques offer wide possibilities of solution of the problems concerning the resistance of the materials, many and divergent difiiculties are encountered, on the other hand, which are prejudicial to the realization and success of the protective coatings obtained by these techniques.

I have now found the solution to the problems concerning the realization and the success of difierent types of protective coatings for ferrous and non-ferrous metallic surfaces which are exposed to oxidizing atmosphere and high temperatures. More particularly, and this is one of the objects of the present invention, I have found that the afore-mentioned inconveniences can be completely eliminated by employing, as protective material against thermal oxidation of ferrous and non-ferrous metallic surfaces, metallo-ceramic compositions of three or more components, such as those resulting from the combination of one or more metal oxides of a ceramic nature, with I mixtures of chromium and nickel, in a ratio of 15 to 60 parts by weight of chromium, from 10 to 50 parts by weight of nickel and from 10 to 40 parts by weight of a ceramic oxide or of a mixture of at least two ceramic oxides, for each parts by weight of metallo-ceramic mixture.

The ceramic components of the above-mentioned metallo-ceramic compositions are chosen from the simple or complex metal oxides, having a melting point not lower than 1900 C., such as the oxides of: aluminum, A1 in the alpha-form; zirconium, ZrO in the form stabilized with calciumor magnesiumor yttrium-oxide; magnesium oxide MgO; aluminum and magnesium oxides (spinel); calcium zirconate, CaZrO zirconium silicate, ZrSiO However the simple oxides are preferably employed.

According to the present invention, the various metalloceramic compositions, within the above-mentioned percentage limits of the metallic and ceramic components cited, are prepared by means of mixture of the powders of the components, within a granulometric range between l20 and +600 mesh, and preferably within a range of 230 and +325 mesh.

The invention includes the method of application of the special protective materials used in the various treatments considered by spraying in the molten state. More particularly, the projection of the particles of the special materials in the molten state is generated by a controlled feeding of the materials to be applied, as a powder or sintered rods, into a jet of chemical or electric flame, preferably into an electric plasma arc-flame.

A suitable generator of electric plasma flame, such as that to which the present invention refers, briefly consists of a tungsten cup cathode and a copper nozzle anode, supported and connected by an electro-insulating interelectrodic element. The electric arc darting between the electrodes is stabilized and blown as a flame jet at very high temperatures (300015000 C.) by a suitable gas (argon, or nitrogen, or hydrogen, or their mixtures) which is introduced in suitable quantity into the interelectrodic cavity. An example of such generator can be found in my application Ser. No. 552,490.

The material to be applied, preferably fed as a powder, and injected into the plasma jet by means of eolic transport, is dynamically molten and projected at high speed onto the surface to be coated, previously cleaned by sanding. When the material to be applied is a sintered rod, it is statically molten. However, the use of metallo-ceramic compositions in the powder state is preferable.

Although the Whole range of the above-defined components of possible metallo-ceramic compositions gives sure and eflicacious results, the use of the eight types of metallo-ceramic compositions listed herebelow is preferable for applying the protective treatments to ferrous and non-ferrous metallic surfaces.

(1) 50% by weight of chromium, 25% by weight of nickel, 25% by weight of magnesium oxide. The composisition is particularly suitable for the protection of iron, steel, copper and brass.

(2) 30% by weight of chromium, 30% by weight of nickel, 40% by weight of 0: aluminum oxide. The composition is particularly suitable for the protection of iron, brass and copper.

(3) 50% by weight of chromium, 25% by weight of nickel, 25 by weight of magnesium oxide. The composition is particularly suitable for the protection of iron, steel and copper.

(4) 25 by weight of chromium, 50% by Weight of nickel, 25 by weight of magnesium oxide. The composition is particularly suitable for the protection of iron, steel, copper and brass.

(5) 30% by weight of chromium, 35% by weight of nickel, 20% by weight of alpha-type'aluminum oxide, 15% by weight of magnesium oxide. The composition is particularly suitable for the protection of iron, steel, copper and brass.

(6) 30% by weight of chromium, 35% by weight of nickel, 20% by weight of magnesium oxide and 15% by weight of or type aluminum oxide. The composition is 4 particularly suitable for the protection of iron, steel, copper and brass.

(7) 30% by weight of chromium, 35 by weight of nickel, 20% by weight of magnesium oxide and 15% by weight of zirconium oxide stabilized with calcium oxide. The composition is particularly suitable for the protection of brass.

(8) 30% by weight of chromium, 35 by weight of nickel, 20% by Weight of zirconium oxide stabilized with calcium oxide and 15% by weight of or aluminum oxide. The composition is particularly suitable for the protection of steel and brass.

The above metallo-ceramic compositions are applied by spraying in the molten state, using an electric plasma flame jet and feeding the material to be applied in the powder state, thereby depositing coatings whereby the treated ferrous and non-ferrous surfaces receive an eflicacious and undestroyable antioxidant protection. This is true even when the metallic elements reach, in mass, temperatures up to 800900 C., while being exposed to oxidizing surroundings. The antioxidant barrier coatings are applied in a thickness between 0025-05 mm. and preferably of 0.2 mm.

A further object of the present invention is to apply protective coatings which, besides being a barrier against the destructive action of thermal oxidation, also constitute a thermoresistant insulation. That is, the coating is capable of withstanding higher surface temperatures while simultaneously containing the amount of heat transmitted through the wall of the protected metal element. Such coatings, generally called thermal barriers, are known and are obtainable through metal oxide coatings of a ceramic character. Zirconium oxide is preferred. As indicated above, it is difficult, however, to anchor properly the ceramic coating because of the damaging effect of thermomechanical stresses which causes its separation. These stresses are particularly evident when the piece is brought up to the severe thermal working conditions. This invention has as an object to overcome this difficulty. The antioxidant barrier coatings obtained by using the above-mentioned metallo-ceramic compositions hereof represent a very good base layer for an effective and lasting bond of the thermal barrier coatings.

It is therefore possible to obtain, on both ferrous and non-ferrous metallic surfaces, protective coatings having combined characteristics of antioxidant and thermal barrier. This is achieved by applying a two-layer coating; the first layer having an antioxidant character, is obtained by using one of the eight metallo-ceramic compositions, specified above, by applying the same modalities mentioned for the realization of the thermal barrier protective coating. The second layer, having an antithermal character, is also realized through spray in the molten state by using a coating material consisting of one or more metal oxides deposed in admixture and/o1 singularly, selected from those having a melting point not lower than l,900 C. and a low coeflicient of thermal conductivity. The said second layer having antithermal character, can consist of two or more hemi-layers or stratified films, obtained from mixtures of oxides and/or from one or more oxides, taken singularly and deposited.

This second coating layer which is exclusively of ceramic character is obtained also by use of a chemical or electrical flame jet, preferably an electric plasma jet flame, using the operative modalities already described in the case of the protective treatment with a coating consisting of a single typical layer, as antioxidant barrier.

The ceramic material required for the realization of the second layer of the coating is selected from aAl O ZrO stabilized with calcium oxide, magnesium oxide or yttrium oxide; ThO MgO or from composite oxides such as: spinel (MgO-Al O calcium zirconate; zirconium silicate (ZrSiO and preferably consists of stabilized zirconium oxide and/or aluminum oxide in the alpha form, which can be deposited in admixture and/0r singly.

Electro-insulating barrier protective coatings are also obtainable by the present invention. These coatings like the thermal barrier type have very good bonding and temporal resistance, due to the utilization of the base layer obtained by using the special above-specified metallo-ceramic compositions. By electro-insulating barrier is meant a coating having a ceramic character which represents an electric insulation and is effective at ordinary temperature and at high temperature up to 800-900" C. and above. Stabilized zirconium oxide is also included in the materials suitable for this purpose, but the material generally known to be the most suitable for this purpose is aluminum oxide. This is due to its dielectric characteristics and stability at both low and high temperatures. Many difliculties are encountered in obtaining a stable electro-insulating barrier coating on the metal surface when high temperatures are to be used. The percentage of failure is high, particularly at higher temperature values, for the same reasons specified in the case of thermal barriers." 0n the other hand, it is possible according to the present invention to carry out highly effective protective treatments on ferrous and non-ferrous surfaces having not only electro-insulating characteristics but also jointly the nature of antioxidant and electro-insulating barrier. I utilize coatings with two typical layers, the first layer having antioxidant character, is obtained by using one of the metallo-ceramic compositions described above and the second layer having electroinsulating character, is obtained by using a ceramic material. This can also consist of alpha type aluminum oxide alone or also of two oxides, preferably consisting of aluminum oxide a form, and of stabilized zirconium oxide and solely applied as hemi-layers one upon the other or vice versa.

The invention therefore also offers the possibility of realizing protective coatings having combined antioxidant, antithermal and electro-insulating characteristics. When in the second layer, having a ceramic character, that is an hemi-layer of zirconium oxide upon which is superimposed a covering aluminum oxide hemi-layer, is thus applied, the protective coating essentially assumes the electro-insulating characteristics which, however, are associated to the antithermal characteristics of the lower hemi-layer (zirconium oxide) and to antioxidant characteristics of the first chromium-nickel-ceramic oxide(s) layer.

If vice versa, in the second layer having a ceramic character, the aluminum oxide hemi-layer is first applied with the covering zirconium oxide hemi-layer superimposed thereon, the protective coating essentially assumes the antithermal characteristics of this last oxide, which however are associated to the electro-insulating characteristics of the lower hemi-layer (of aluminum oxide) and to the antioxidant characteristics of the first metallo-ceramic chromium-nickel-oxide (s) ceramic layer.

The present invention, therefore, relates not only to the special metallo-ceramic chromium-nickel-oxidets), the corresponding method of application and the relevant antioxidant barrier treatment but also to the treatments as antioxidant-thermal barrier, as antioxidant-electroinsulating barrier, as antioxidant-thermal-electro insulating barrier and as antioxidant-electro-insulating-thermal barrier.

All the treatments of the various barriers have in common the application of metallo-ceramic layer of chromium-nickel oxide(s) in direct contact with the ferrous and non-ferrous metallic surface on which it exerts the antioxidant protection. The treatments of the bivalent or trivalent barrier type have the common characteristic of applying a second layer having a ceramic character, in which one or more metal oxides having a melting point not lower than 1,900 C. are deposited.

It is again stressed that for deposition of the second layer having a ceramic character relating to bivalent or trivalent barrier treatment, recourse can be made to the use of more than one oxide. In this case, two or more oxides can be applied either in the form of a compound projection, using a mixture of the components either in powder from or as a sintered rod, or in the form of hemi-layers or stratified films consisting of one comuponent using the single components in powder form or as a sintered rod. The deposition of hemi-layers or of stratified films in which zirconium oxide is laid on aluminum oxide or vice versa, is preferred, With the materials being fed as a powder.

The material of the second layer having a ceramic character in the plurivalent (multi-purpose) barrier treatment is selected from the simple or compound oxides mentioned above and is preferably fed as a powder in granulometric compositions between and +600 mesh, and preferably between -230 and +325 mesh. The thickness of this second layer is comprised between 0.052.5 mm. 011 the basis of the characteristics relating to the conditions of use and to the geometry of the piece to be protected, the most suitable thickness is selected within this range. As general criteria for the selection it should be taken into account that, above a thickness of 0.5 mm., the more the mass temperature of the protected element decreases below 1000 C., the more increasing values can be usefully applied. The higher the surface temperature is above 1500 C., and not above 2500 C., the more the thickness of 0.5 mm. will be reduced to a minimum of 0.2 mm.

The invention thus forms a considerable extension of the possibilities of employment of the usual metallic ferrous and non-ferrous materials as the construction material of industrial equipment and plant, where high temperatures are encountered. The invention appears particularly interesting for the protection of internal surfaces in contact with flames, of the elements forming the reactor of petrochemical plants for the production of acetylene for cracking of gaseous and/or liquid hydrocarbons.

The following non-limitive examples are given to further illustrate the invention.

Example 1 Application of the protective treatment.Onto one side of a flat, rectangular iron sample of 60 x 50 x 4 mm. has been applied, after previous sanding, and using the spraying in the molten state technique with an electric flame argon plasma jet with a power of 14 kw., the antioxidant barrier treatment, consisting of a sole quaternary composite layer of a thickness of about 0.2 mm. was applied. A mixture of powders, containing 35% by weight of nickel, 30% by weight of chromium, 20% by weight of MgO and 15% by weight A1 0 of alpha form, in a granulometric fraction comprised between 200 and +325 mesh, was injected into the plasma jet by means of colic transport by nitrogen.

Testing against thermal oxidation under homogeneous heating conditions in a muflle furnace.After application of the protective treatment, the metal specimen was placed into a mufile, under air atmosphere, at a temperature of 800 C. and kept there for 400 hours. After extraction from the mufile, the coating applied onto the test piece was observed to have excellent characteristics of resistance to thermal oxidation. The coating remained perfectly anchored to the base surface excellently protecting the latter, while the surface of the base metal on the other non-protected side had undergone a strong corrosion by heat oxidation.

Result.Positive, with suitability of the applied treatment for the protection of iron against corrosion by heat oxidation.

Example 2 Application of the protective treatment.--Onto one side of a fiat, rectangular steel specimen of 60 x 50 x 4 mm., after previous sanding, using the spraying in the molten state technique with an electric flame argon plasma jet with a power of 14 kw., the antioxidant-thermal barrier treatment, consisting of two layers, was applied. The following working conditions were used.

The first layer (composite ternary), of a thickness of about 0.2 mm., was obtained by using a mixture of powders containing 35% by weight of Ni, 30% by weight of Cr, 20% by weight A1 of alpha form and 15% by weight of MgO, in a granulometric fraction comprised between 200 and +325 mesh;

The second layer (simple), of a thickness of about 0.1 mm., has been obtained by using only ZrO powder (stabilized with about of CaO), in a granulometric fraction comprised between 270 and +325 mesh.

In both cases, the powders were injected into the plasma jet by means of eolic transport by nitrogen.

Testing against thermal oxidation under homogeneous heating conditions in a muflle furnace.After application of the protective treatment, the metal specimen was placed into a muflle furnace, in air atmosphere, at a temperature of 800 C. and kept there for 320 hours. After extraction from the muffle furnace, the coating applied onto the metal test specimen was observed to have excellent characteristics of resistance to thermal oxidation. It had remained perfectly anchored to the base surface, perfectly protecting the latter, while the surface of the base metal, on the opposite non-protected side, had undergone a strong corrosion by thermal oxidation.

Result.Positive. The antioxidant thermal barrier type protective coating is suitable to substain the tensions determined by a massive heating and to assure an excellent protection of iron against heat oxidation.

Example 3 Application of the protective treatment.0nto one side of a flat, rectangular brass specimen of 60 x 50 x 4 mm., after previous sanding, using the spraying in the molten state technique using a jet of electric argon plasma flame with a power of 14 kw., the antioxidant thermal barrier treatment, consisting of two layers, was applied according to the following working conditions:

The first (composite ternary) layer, of a thickness of about 0.2 mm., was obtained using a mixture of powders containing 50% by weight of Cr, 25% by weight of Ni and 25% by weight of aAl O in a granulometric fraction comprised between 200 and +325 mesh;

The second (simple) layer, of a thickness of about 0.1 mm., was obtained using the sole ZrO powder (stabilized with about 5% of CaO), in a granulometric fraction comprised between 200 and +325 mesh.

In both cases, the powders were injected into the plasma jet by means of colic transport by nitrogen.

Testing against thermal shock.After application of the protective treatment, the metal specimen was placed in front of an oxyacetylene jet (0.275 1./ sec. of C H 0.265 l./sec. of 0 at 17 C. and 746 mm. Hg), at a distance of 5 cm. from the specimen surface. The metallic mass was brought to a temperature of 800 C. At this point, a sudden cooling ensued by means of a spout of water at 15 C. The specimen surface was then subjected to repeat cycles of heat and cold jets. After having subjected the test piece to thermal shock for a number of 20 cycles, it was observed that the protective coating had not undergone any cracking and that its adhesion to the metallic base surface had not suffered at all.

Result.Positive. The treatment applied as thermal barrier proved to possess an excellent resistance to stresses caused from a sudden thermal shock and to be suitable for applications on brass.

Example 4 Application of the protective treatment-Onto the face of a copper micro-oxygen-nozzle, provided with a jacket for cooling by water circulation, of the size of 36 mm. diameter and 85 mm. length, after previous sanding using the spraying in the molten state technique with a jet of electric argon plasma flame of a power of 14 kw., the antioxidant thermal barrier treatment, consisting of two layers was applied according to the following working conditions:

The first (composite ternary) layer, of a thickness of about 0.2 mm., was obtained using a mixture of powders containing 50% by weight of Cr, 25 by weight of Ni and 25% by weight of A1 0 alpha-form, in a granulometric fraction comprised between +200 and +325 mesh;

. The second (simple) layer, of a thickness of about 0.1 mm., was obtained by using only ZrO powder (stabilized with about 5% of CaO), in a granulometric fraction comprised between 200 and +325 mesh.

Testing of the resistance to thermal oxidation under the action of an oxyacetylene jet.-After the application of the protective treatment, the micro-nozzle has been subjected to the action of an oxyacetylene jet (0.275 l./ sec. of C H and 0.265 l./sec. of 0 at 17 C. and 746 mm. Hg) kept with the head against the coated face, while a flow of 0 was fed through a series of holes made in the face of the micro-nozzle, creating a highly oxidizing atmosphere all around. The cooling water, with a power of 1.0 l. per minute had a temperature of 11.9 C. when entering, and of 36 C. when leaving. The protective coating was in superficial incandescence.

Result.Positive. The applied treatment presents itself unaltered after a 10 hours working, during which also various (13) thermal shocks took place, due to stoppings, showing to possess an excellent resistance to continuous stress and assuring an excellent protection of copper against heat oxidation.

Example 5 Application of the protective treatment.Onto one side of a flat, rectangular iron sample of the size of 60 x 50 x 4 mm. has been applied, after previous sanding, by spraying in the molten state technique, using a jet of argon plasma electric flame with a powder of 14 kw., the antioxidant-electro-insulating barrier treatment, consisting of two layers, was applied according to the following working conditions:

The first (composite ternary) layer, of a thickness of about 0.2 mm., was obtained using a mixture of powders containing 40% by weight of A1 0 alpha-form, 30% by weight of Cr and 30% by weight of Ni, in a granulometric fraction comprised between 200 and j+325 mesh;

The second (simple) layer, of a thickness of about 0.1 mm. was obtained by using only a powder of A1 0 in alpha-form in a granulometric fraction comprised between 270 and +325 mesh.

Testing against thermal oxidation under homogeneous heating conditions in a mufile furnace-After application of the protective treatment the metallic sample has been put into a rnuflle furnace, in air atmosphere, at a temperature of 800 C. and kept there for 250 hours. After extraction from the muffle furnace, the coating applied onto the test piece was observed to have excellent characteristics of resistance to thermal oxidation. It had remained perfectly anchored to the base surface, perfectly protecting the latter, while the surface of the base metal on the opposite not protected side had undergone a strong corrosion by heat oxidation.

Moreover, the applied coating presents excellent electro-insulating characteristics at high temperatures, due to the ceramic A1 0 layer.

Result.P0sitive, with suitability of the applied treatment for the protection of iron against corrision by heat oxidation and with electro-insulating characteristics at high temperatures.

Example 6 Application of the protective treatment-Onto one side of a fiat, rectangular iron specimen 60 x 50 x 4 min, after previous sanding, by spraying in the molten state technique, using a jet of electric argon plasma flame with a power of 14 kw., the electro-insulating-heat barrier treatment, consisting of two layers realized, was deposited according to the following working conditions:

The first (composite ternary) layer, of a thickness of about 0.2 mm., was obtained by using a mixture of powders, containing 50% by weight of Cr, 25% by weight of Ni, and 25% by weight of A1 alpha-form, in a granulometric fraction comprised between 200 and +325 mesh;

The second (simple) layer, was obtained by using aluminum oxide and zirconium oxide in the form of stratified films of one component, depositing a thickness of 0.2 mm. of aAl O in a granulometric fraction comprised between 270 and +325 mesh, and subsequently apply onto said film a thickness of 0.15 mm. of Zr0 (stabilized with about 5% of CaO) in a granulometric fraction comprised between 270 and +325 mesh.

In each case, the powders were injected onto the plasma jet by means of colic transport by nitrogen.

Testing against thermal oxidation under homogeneous heating conditions in a mufiie furnace-After application of the protective treatment the metaallic specimen was placed into a mufiie furnace, in air atmosphere, at a temperature of 800 C. and kept there for 250 hours. After extraction from the mufiie furnace the coating applied onto the sample was observed to have excellent characteristics of resistance to thermal oxidation. It had remained perfectly anchored to the base surface, perfectly protecting the latter, while the surface of the base metal, on the opposite non-protected side, had undergone a strong corrosion by heat oxidation. Moreover, the applied treatment presents excellent electro-insulating characteristics at high temperature, together with a high efiicacy in barring the heat, characteristics proper of the double ceramic layer.

Result.Positive, with suitability of the applied treatment for the protection of iron against the corrosion by thermal oxidation, and with electro-insulating characteristics at high temperature and characteristics of heat barring.

I claim:

1. Metallo-ceramic compositions for application as a coating by means of spraying in the molten state technique, for the protection of ferrous and non-ferrous metallic surfaces against thermal wear and thermal oxidation, comprising 15 to 60% by weight of chromium, to 50% by weight of nickel, and 10 to 40 by weight of at least one ceramic oxide, having a melting point 1900 C.

2. Metallo-ceramic coating composition according to claim 1, wherein the ceramic oxide is selected from the group consisting of A1 0 alpha-form, ZrO -type stabilized with calcium oxide, with magnesium oxide and with yttrium oxide or MgO.

3. Metallo-ceramic coating composition according to claim 1, wherein the ceramic oxide is selected from the group consisting of MgO.Al O in the form of spinel, calcium zirconate and ZrSiO 4. Metallo-ceramic coating composition in the powder state according to claim 1, having a granulometric field between and +600 mesh.

5. Metallo-ceramic coating composition in the powder state according to claim 4, wherein the granulometric field is between 230 and +325 mesh.

6. Metallo-ceramic coating composition according to claim 1, containing 50% by weight of chromium, 25% by Weight of nickel and 25% by weight of aluminum oxide A1 0 alpha-form.

7. Metallo-ceramic coating composition according to claim 1, containing 30% by weight of chromium, 30% by weight of nickel and 40% by weight of aluminum oxide A1 0 alpha-form.

8. Metallo-ceramic coating composition according to claim 1, containing 50% by weight of chromium, 25% by weight of nickel and 25 by weight of magnesium oxide, MgO.

9. Metallo-ceramic coating composition according to claim 1, containing 25% by weight of chromium, 50% by weight of nickel and 25 by weight of magnesium oxide, MgO.

10. Metallo-ceramic coating composition according to claim 1, containing 30% by weight of chromium, 35% by weight of nickel, 20% by weight of aluminum oxide A1 0 alpha-form and 15% by weight of magnesium oxide, MgO.

11. Metallo-ceramic coating composition according to claim 1, containing 30% by weight of chromium, 35% by weight of nickel, 20% by weight of magnesium oxide, MgO, and 15% by weight of aluminum oxide, A1 0 alpha-form.

12. Metallo-ceramic coating composition according to claim 1, containing 30% by weight of chromium, 35% by weight of nickel, 20% by weight of magnesium oxide, MgO, and 15% by weight of zirconium oxide, ZrO in the form stabilized with calcium oxide.

13. Metallo-ceramic coating composition according to claim 1, containing 30% by weight of chromium, 35% by weight of nickel, 20% by weight of zirconium oxide, ZrO in the form stabilized with calcium oxide and 15 by weight of aluminum oxide, A1 0 alpha-form.

References Cited UNITED STATES PATENTS 3,044,867 7/ 1962 Edstriim 75206X 3,110,571 11/1963 Alexander 1l7-l60X 3,129,093 4/ 1964 Alexander et 'al. 75.5AB 3,254,970 6/ 1966 Pittrich et al. 75.5BC 3,388,010 6/1968 Stuart et al. 75206X LORENZO B. HAYES, Primary Examiner US. Cl. X.-R.