AU645758B2

AU645758B2 - Workpiece coated with a solid solution layer, method for its production, use of the workpiece, and apparatus for carrying out the method

Info

Publication number: AU645758B2
Application number: AU61122/90A
Authority: AU
Inventors: Roland Schmid
Original assignee: Balzers AG
Current assignee: OC Oerlikon Balzers AG
Priority date: 1989-08-21
Filing date: 1990-08-20
Publication date: 1994-01-27
Anticipated expiration: 2010-08-20
Also published as: DE58909591D1; KR910004837A; KR0148355B1; ATE133718T1; CA2023049C; JPH0382748A; CA2023049A1; CN1049688A; CN1039354C; EP0413853B1; EP0413853A1; AU6112290A; JP3388736B2; BR9004095A

Abstract

The mixed crystal layer (C, D) of metaloids on a workpiece, applied by means of reactive physical coating, has an incorporation ratio of metaloids which changes continuously in the thickness direction. The mixed crystal layer (C, D) is present on a separation layer (A) of the workpiece. For the production of the metal layer (C, D), titanium is evaporated in a crucible, which is moved to and fro in front of the workpiece surfaces to be coated, in a vacuum chamber, and two gases which have different affinities to the vaporised titanium are passed in. To produce a first part layer (C) of the mixed crystal layer (C, D), the incorporation ratio of the gases is continuously changed. During coating, the workpieces rotate so that their surface sometimes faces the crucible and sometimes faces away. The coated workpieces are distinguished by high flank wear resistance and crater wear resistance. <IMAGE>

Description

14SBii Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority i 01 Related Art: Name of Applicant Address of Applicant: Actual Inventor Address for Service BALZERS AKTIENGESELLSCHAFT 9496 Balzers, Liechtenstein ROLAND SCHMID WATERMARK PATENT TRADEMARK ATTORNEYS.

LOCKED BAG NO. 5, HAWTHORN, VICTORIA 3122, AUSTRALIA Complete Specification for the invention entitled: WORKPIECE COATED WITH A SOLID SOLUTION LAYER, METHOD FOR ITS PRODUCTION, USE OF THE WORKPIECE, AND APPARATUS FOR CARRYING OUT THE METHOD The followinq statement is a full description of this invention, including the best method of performing it known to US H57-0C2 US -1 WORKPIECE COATED WITH A SOLID SOLUTION LAYER, METHOD FOR ITS PRODUCTION, USE OF THE WORKPIECE, 0 o 0 0 AND APPARATUS FOR CARRYING OUT THE METHOD FIELD AND BACKGROUND OF THE INVENTION The present invention relates in general to the field of vapor deposition and in particular to a new and useful coated workpiece, a method for its production, uses for the coated workpiece and an apparatus for carrying out the method.

A method of this type and a workpiece coated by the method in order to increase its hardness and toughness are known from European Patent document A 0191554. Such workpieces are used e.g. as cutting tools. The known coating is carried out by means of a PVD process at temperatures between 200 and 700 0 C. Up to four discrete layers of titanium carbide, titanium nitride and titanium carbonitride are applied, a titanium nitride layer being always applied directly over the surface to be coated.

L *~YLL U -2- SUMMARY OF THE INVENTION It has now been found that during application of the carbon-containing titanium compounds as coating layers, pure carbon is incorporated into the respective layer as well. These carbon inclusions significantly reduce the adhesivity of the layer on its substrate, as well as the toughness of the coating.

An object of the present invention is to remedy this situation. By the invention, the problem is solved by providing a coated workpLece, as well as a method for the production of the coated workpiece, in which the applied layers adhere well to the workpiece surface and have a high toughness.

S. The invention includes various preferred forms of the coated workpiece and preferred embodiments of the method for producing the coated workpiece.

Accordingly, a further object of the present invention is to provide a coated workpiece having a solid solution layer of metalloids which are applied by means of a reactive physical coating process, wherein the inclusion ratio of the metalloids in the solid solution layer vary continuously over a majority of a thickness of the layer.

Another object of the present invention is to provide a method of producing a coated workpiece wherein a material to form a component of the coating is vaporized in a vacuum chamber and condensed in the form of a solid solution layer on the workpiece, a first gas and a second gas being supplied to the vacuum chamber during the condensation of the vapor, with the flow of the first gas steadily decreasing and the flow of the second gas steadily increasing.

A still further object of the present invention is to utilize the coated workpiece as a cutting or forming tool.

Another object of the present invention is to provide an apparatus for carrying out the method which includes a vapor source for depositing one component of the coating on the workpiece, and means for moving the vapor source past the workpiece.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure.

C For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and ep descriptive matter in which the preferred embodiments of the invention are illustrated.

C

BRIEF DESCRIPTION OF THE DRAWINGS

*O

0 e In the following, an example of the method according to the invention and workpieces coated according to the invention are explained more specifically with reference to drawings, in which: I. FIG. 1 is a schematic representation of a vapor deposition installation; FIG. 2 is a composite illustration showing the time response of various parameters during application of layers on workpieces according to the invention; and FIG. 3 is a composite illustration showing percentages of the vapor-deposited material over the layer thickness.

I. I -4- DESCRIPTION OF THE PREFERRED EMBODIMENTS

S

S* S S 0 0 *0 0 *54 0 Fig. 1 shows an example of a vapor deposition installation for carrying out the method of the invention for the production of coated workpieces 2. The system has a vacuum chamber 1 with an evacuation connection 3 and a glow cathode chamber 5 with a glow cathode 6 connected to the vacuum chamber 1 via an opening 7. The glow cathode 6 is powered by a current supply unit 9. Approximately over the center of the bottom 10 of the vacuum chamber 1 is a coolable, vertically displacable crucible 11, in which titanium 13 is brought into its gaseous state by vaporization. The crucible 11 is shown in broken lines in Fig. 1 raised by a distance d from its lowest position which is shown in solid lines. The displacement takes place through a vertically displacable movement system shown at 14. System 14 consists of three cylinders telescoping by a spindle mechanism (not shown). In the vacuum chamber 1 are twelve supports 15 rotatable about the longitudinal axis of the chamber, of which two are shown, and on. which the workpieces 2 to be coated are held on a mount 17 for each. The glow cathode chamber 5 further has a coolant duct, to cool its walls during operation.

Gas feed lines 21 and 22 lead into the glow cathode chamber and into the vacuum chamber 1 respectively. Line 22 divides in the vacuum chamber 1 into several branches 24a, 24b provided with openings 23. Two branches are shown.

Inside the vacuum chamber 1, the branches and openings 23 produce a uniform distribution of the gas or gas mixture which is admitted through the gas feed line 22. Two schematically represented magnet coils 25 are located below the bottom 10 and above a cover part of the vacuum chamber 1 in rotational symmetry to the crucible 11 to create an approximately parallel vertical magnetic field therein.

To produce the coated workpieces 2, the workpieces are fastened on the mounts 17 of the supports 15, and titanium 13 is placed in the crucible 11. In a first process step thie vacuum chamber 1 is closed, evacuated, and through the gas feed line 21 the rare gas argon is admitted until a partial pressure of 200 mPa is reached.

For heating and ion etching the workpiece surfaces, a low-voltage 'arch burns in the argon atmosphere from the Sglow cathode 6 to the surfaces of the workpieces 2. For uniform heating and cleaning of the workpieces 2 arranged around the support 15, the supports rotate at about one revolution in five seconds.

The time sequence of the individual process steps

S

Sfor the production of the coating after the cleaning and heating step is shown in Fig. 2. The layers produced during one of the process steps, namely a bottom layer A, a separating layer B, a first partial and predominant portion or layer C of a solid solution layer and a second partial and subordinant portion or layer D of the solid o solution layer, which forms the topmost layer of the S coating, are plotted on the abscissa. In Fig. 2, graph a indicates the time-current curve Iac of the current arc strength of the low voltage arc, graph b is the response of the negative bias Usub at the workpieces 2, graph c is the distance d of Fig. 1 for crucible 11 from its lowest position on the bottom 10 of the vacuum chamber 1, S graph d is the gas flow of argon Ar into the vacuum chamber 1 through gas feed line 21, graph e is the gas flow f -6of acetylene C 2

H

2 through the gas inlet 22, and graph f is the nitrogen gas flow N 2 Each of the graphs are correlated in time with each other.

Following the heating and cleaning of the surfaces of the workpieces 2, in a next process step a

O

titanium bottom layer A of approximately 1000 A is applied directly onto the surfaces of the workpieces 2.

The materials deposited on the surface of the workpieces 2 during the entire process are plotted in Fig.

3 in their percent composition by weight at a selected distance a from the original workpiece surface. In Fig.

3, graph a, the titanium nitride content TiN is plotted, in Fig. 3, graph b, the titanium carbide TiC content is S* plotted, and ir Fig. 3, graph c, the content of pure titanium Ti is plotted.

For applying the pure titanium layer A (see Fig.

.*.ebb 3, graph c, and Fig. a low-voltage arc 27 from the t glow cathode 6 to the crucible 11 burns with a current (Fig. 2, graph a) of approximately 80 A. The workpieces 2 are at a potential with respect to the crucible 11 (Fig.

2, graph b) of about -100 V. The vaporizing titanium Ti is ionized in the gas discharge and attracted by the surfaces of the workpieces 2. For obtaining a uniform Stitanium layer, the crucible 11 is moved toward the glow cathode 6 and away from the bottom 10 of vacuum chamber 1 to a maximum distance dma x along the workpieces 2 attached to the supports 15 (see Fig. 2, graph The time for the production of this titanium bottom layer A is chosen so that the surfaces of the rotation workpieces 2 face the crucible 11 several times as the supports rotate.

The titanium bottom layer having been vapor deposited in a thickness of approximately 1000 A, in a next process step nitrogen N 2 is admitted through the gas inlet 22 with the low-voltage arc 27 burning (Fig. 2, graph a nitrogen partial pressure of 50 mPa being adjusted so as to have a sufficient supply of nitrogen atoms and ions available for complete reaction with the vaporized titanium Ti, the vaporization being increased by increasing the current (Fig. 2, graph a) of the low voltage arc 27 to about 200 A. Through the branches 24a, 24b, etc. the nitrogen N 2 distributes itself uniformly in the vacuum chamber 1 and forms with the titanium vapor Ti titanium nitride TiN, which deposits on the surfaces of the workpieces 2. From the workpieces 2 a current of approximately 20 A flows after reduction of the negative bias (Fig. 2, graph b) to -50V. The workpieces 2 rotate also during this process step. The crucible 11 (Fig. 2, S graph c) is moved from its topmost position downward Stoward the bottom 10 and toward the end of this process step once more upward and again downward, to obtain a uniform coating with titanium nitride TiN.

•After vapor deposition of the separating layer B of titanium nitride TiN of a thickness of about one micrometer (the thickness can be varied depending on the purpose of use for the workpieces acetylene C 2

H

2 *4e as a carbon-releasing gas, and as shown in Fig. 2, graph e, is admitted together with the nitrogen N 2 through the gas inlet 22 in a further process step and distributed evenly in the vacuum chamber 1 through the branches 24a, 24b etc. In proportion as the percentage of acetylene C2H 2 increases in the vacuum chamber 1, the nitrogen S percentage N is reduced as seen in Fig. 2, graphs e and a, f. The acetylene C 2

H

2 is dissociates and the dissociates carbon is ionized in the vacuum chamber. The ionized carbon as well as the ionized nitrogen combine -8with the' titanium vapor Ti to titanium nitride TiN and titanium carbide TiC respectively. The inflow of acetylene is increased and the inflow of nitrogen decreased until there is 70% nitrogen N 2 and acetylene C2H 2 in the vacuum chamber 1. The inflow of argon continues (see Fig. 2, graph During the increase of the acetylene inflow, the crucible 11 (see Fig. 2, graphs c) is moved back and forth twice. During the back and forth movement a solid solution layer forms the partial layer C, with a layer thickness of about two micrometers of titanium carbide TiC and titanium nitride TiN. Depending on the purpose of use for the workpieces 2, the layer thickness is preferably 1.2 to 2 times the layer thickness of the separating layer B.

After the acetylene inflow has reached 30% compared to the nitrogen inflow, in a further process step a partial layer D about one micrometer thick (thinner partial S" layer D of the solid solution layer) forms with this constant nitrogen-acetylene ratio and forms TiC 0 .3N 0.7* Depending on the purpose of use for the workpieces 2, this layer thickness is between one fifth and one half of the preceding layer C.

*te Surprisingly, due to the above described rotation of the workpieces 2, as well as the up and down movement of the crucible 11, the carbon inclusions that impair S adhesivity and toughness disappeared in the applied layers C and D. Also it was observed on the basis of prepared microsections on coated workpieces 2 that superposed on a steady increase of the titanium carbide content of the applied layer C were concentration fluctuations k of titanium carbide TiC to titanium nitride TiN which are shown in Fig. 3 and are in agreement with the movements of the crucible 11. Superposed on these fluctuations were additional concentration fluctuations s which correlate with the rotation of the supports Fig. 3 shows the concentration of pure titanium Ti (graph titanium nitride TiN (graph a) and titanium carbide TiC (graph b) according to a microsection of a coated workpiece. The fluctuation of small amplitude s and small period in the thickness zone C and D (see also Fig. 2) are due to the rotation of the workpieces 2 on the supports 15. The two fluctuations of large amplitude k and large period in zone C, as well as the one fluctuation in zone D are attributable to the two up and down movements of the crucible 11 during the vaporization of the layer in zone C and the one up and down movement in zone D.

The broken lines gl and g 2 in fig. 3, graph a and respectively j and j2 in Fig. 3, graph b indicate the percent titanium carbide TiC and respectively titanium nitride content TiN of the vapor-deposited layer if no crucible movements and no workpiece movements had taken S place. The course of lines m I to m 4 for the titanium nitride TiN and nl to n 4 for the titanium carbide TiC indicates the response of the percent titanium nitride TiN and titanium carbide content TiC of a vapor-deposited layer if the rotation of the workpieces 2 around support SV 15 had been dispensed with. The indices used are S* identical with the indices of the movement of the crucible 11 in Fig. 2, graph c. The curves shown in Fig. 3 apply to workpieces 2 near the bottom 10. For workpieces 2 near the cover parts 26 the line m i is flapped up symmetrically to line gl, and the line g down symmetrically to line j, the equivalent applies to the lines m 2 and n 2 Line m3 then lies above line gl or g 2 and line n 3 helow line jl and jf Kespetitively.

As known already from European Patent document A 0191554, workpieces which are coated only with titanium nitride TiN are, due to their reduced hardness, less resistant to flank wear than workpieces which are coated only with titanium carbide TiC. However, a workpiece coated only with titanium carbide TiC has, because of the low chemical resistance, greater crater wear. In European Patent document A 0191554 the attempt was made to combine both advantages by applying on a titanium nitride layer TiN a titanium carbide TiC or titanium carbonitride layer TiCN.

It has now been found that the coating made according to the method of the invention, in which there 9.

are no longer any discrete individual layers but only layers whose inclusion ratio fluctuates continuously over the layer thickness, have a significantly higher adhesivity on the workpiece and the workpieces have a significantly higher toughness than those coated according to the known 9.

method.

In long-term tests it was possible to cut 7000 threads with an uncoated MS tap. With a tap coated with TiN 25,000 threads could be cut, and with a tap with a coating according to the invention 75,000 threads were cut. With a punch of 1.0334 material, 20,000 stampings were obtained for uncoated material, 62,000 for TiN-coated, and 140,000 for material coated according to the invention.

The concentration fluctuations within the coating g ~can very likely be explained by the different affinity of ionized carbon and nitrogen to titanium vapor. As long as only nitrogen is present, the nitrogen combines with the titanium. If ionized carbon is present, the carbon combines preferably with the titanium, that is, the zone -11directly around the crucible 11 is depleted of carbon, as the carbon has combined with the titanium. Therefore, with decreasing distance of a workpiece surface from the crucible 11 more titanium nitride TiN precipitates on the surface thereof.

Instead of using acetylene C2H 2 as the carbon-releasing gas, ethylene C2H 4 or other carbon-releasing gases can be used.

Instead of the two fluctuations in the first partial layer C of the solid solution layer, several fluctuations can be produced by a greater number of crucible movements; preferably one to five fluctuations per two micrometers of layer thickness are produced. Also the rotation of the workpieces 2 around the supports can be varied in the range of from 5 to 100 period per crucible movement cycle.

Instead of transforming the titanium 13 in crucible 11 into the gaseous state with a low-voltage arc, cathode sputtering, plasma-supported vaporization, or cathodic arc vaporization may be used.

While specific embodiments of the invention havbeen shown and described in detail to illustrate the application of the principles of the invention, it will be e understood that the invention may be embodied otherwise 0 without departing from such principles.

S S S @5 *e

Claims

1. Workpiece having a surface being coated by a reactive physical vapor deposition method with a solid solution coating D) of at least two metalloids, wherein the concentration ratio of the metalloid composition of the at least two metalloids in said solid solution coating D) is changing continuously in a predominant portion region only in the direction uoon the surface normal of said surface between at least three relative extreme values of said concentration ratio.

2. A coated workpiece according to claim 1, wherein said solid solution coating includes a solid solution layer region and a separating layer region, said solid solution layer region lying upon said separating layer region, and wherein said separating layer region comprises only one of said metalloids and whc :ein the transition between the concentration ratio of said separating layer region and said solid solution layer region changes steadily, the thickness of said solid •go• solution !ayer region being from 1.2 to 2 times the thickness of said separating layer region.

3. A coa'ed workpiece according to claim 2, wherein said solid solution layer region consists of a first layer portion and a second layer portion, said first layer portion lying adjacent to said workpiece surface and wherein the value of the concentration ratio of the metalloid composition changes continuously, said second layer portion lying adjacent to the coating surface, the thickness of said second layer portion being less than the thickness of said first layer portion, said second layer portion having an at least approximately constant concentration ratio, wherein the transition between the concentration ratio of said first Ika.yer portion region and said second layer portion changes steadily and the thickness of said first layer portion is from 2 to 5 times the thickness of said second layer portion. 13

4. A coated workpiece according to claim 1, wherein said concentration ratio of said metalloid composition within said solid solution coating changes periodically in a direction normal to said surface between relative extreme values of said concentration ratio. A coated workpiece according to claim 1, wherein a second variation of the concentration ratio of the two metalloids is superposed to the first variation of said concentration ratio of one metalloid to the other one within said solid solution coating which is either increasing or decreasing in a direction normal to said surface, but is not constant.

6. A coated workpiece according to claim 1, wherein the value of said concentration ratio of one metalloid to the other within said solid solution coating fluctuates periodically between relative extreme values in a direction normal to said surface, preferably 1 to 5 times per two micrometers of layer thickness.

7. The coated workpiece according to claim 4, wherein said concentration ratio of said metalloids within said solid solution coating is composed of a first and a second periodical fluctuation train, said second periodical fluctuation train having a smaller spatial period and smaller concentration differences between 0:0 adjacent relative extreme concentration values than said first periodical fluctuation train, caid second periodical fluctuation train having 5 to 100 fluctuation periods within one first fluctuation period.

8. A coated workpiece according to claim 2, having a bottom layer lying upon said workpiece surface and underneath said separating layer region, said bottom layer preferably having a thickness of 0.01 to 0.5 micrometers.

9. A coated workpiece according to claim 1, wherein said solid solution coating consists of a nitride-carbide solid solution crystal. A coated workpiece according to claim 1, wherein said solid solution coating consists of a solid solution crystal of essentially titanium nitride and titanium carbide.

11. A coated workpiece according to claim 8, wherein said separating layer region consists essentially of titanium nitride.

12. A coated workpiece according to claim 8, wherein said bottom layer consists essentially of titanium.

13. A coated workpiece according to claim 3, wherein said second layer portion consists of a solid solution crystal with approximately 30% by weight titanium and 70% by weight titanium nitride.

14. A method of producing coated workpieces by a reactive physical coating process; comprising providing a workpiece portion having a surface and a solid solution coating of at least two metalloids on said surface, the coating being deposited by transferring a metal to the gaseous state by a vapor source i: (11) within a vacuum chamber said workpieces being moved relative to said vapor source said metal in said gaseous state is reacted with gaseous reaction means introduced into said vacuum chamber at said surface, wherein a first and a second gas are used as the gaseous reaction means, said first gas is introduced into said vacuum chamber with steadily reducing inflow and said second gas is introduced into said vacuum chamber with steadily increasing inflow, said surface of said workpiece being moved relative to said vapor source such that the distance and/or the angular position of said surface changes periodically with respect to said vapor source with such a velocity that a solid solution coating comprising a first and a second metalloid is created, said first meta!!old being created by a chemical composition of said first gas and said metal in the gaseous state, said second metalloid being created by a chemical composition of said second gas and said metal in the gaseous state, I j course of the concentration ratio in the direction normal to said workpiece surface having at least three relative extreme values being a superposition of the periodical distance variation of said surface to the vapor source (11) and the variation of the inflows of said first and said second gas. Method according to claim 14, wherein the metal is vaporised from said vapor source by an arc, especially a low voltage arc.

16. A method according to claim 14, wherein the first and second gases are selected to have different affinities for the vaporized metal, the vaporized metal being supplied from said vapor source in the vacuum chamber, and further comprising moving the workpiece portion with respect to the vapor source periodically during condensation of at least part of the solid solution coating for periodically varying the concentration ratio of the at least two metalloids in the solid solution coating.

17. A method according to claim 14, wherein the vaporized metal is supplied from the vapor source in the vacuum chamber, and including periodically moving the vapor source along the surface of the workpiece portion for changing the concentration ratio of the at least two metalloids in the solid solution coating and in the direction of movement of the vapor source with respect to the workpiece portion.

18. A method according to claim 14, wherein the vapor source is moved at a lower speed than the workpiece portion.

19. A method according to claim 14, including forming a separating layer region comprising only one metalloid formed by only one of the gases and the metal, by vaporising the metal in the vacuum chamber and initially supplying only one of the gases to the vacuum chamber, the solid solution coating being formed subsequently by introducing the other of the two gases into the vacuum chamber. 16 A method according to claim 19, including forming a portion of the solid solution coating by reducing the flow of one of the two gases with respect to the other of the two gases during formation of the solid solution coating, and subsequently forming a remaining portion of the solid solution coating by admitting both of the gases into the vacuum chamber and at a constant ratio.

21. A method according to claim 14 of producing a coated workpiece according to claim 3, wherein in a first step during transferring said metal into the gaseous state only the first gas is introduced into the said vacuum chamber for producing upon the surface of said workpiece a separating layer region, said separating layer region comprising no chemical composition of said second gas, in a second step for creating a first layer portion of said solid solution coating *o said second gas is introduced into said vacuum chamber wherein the inflow of said first gas is steadily reduced, in a third step the inflow of said first and said second gases is maintained approximately constant to produce a second layer portion of the solid solution coating.

22. A method according to claim 14 or 21, wherein one of the two gases is nitrogen and the other of the two gases is a carbon releasing gas, the metal Scomprising titanium. 9*Gt t S 23. A method according to claim 21 or 22, wherein the inflow of said first and second gases into said vacuum chamber is adjusted so that the second layer portion comprises Tico. 3 No.7.

24. A method according to claim 1, wherein the coated workpiece is used as one of a cutting and forming tool. An apparatus for producing a coated workpiece made of a workpiece portion having a surface and a solid solution coating of at least two metalloids on the surface, the coating being deposited by a reactive physical coating process and having a concentration ratio of the at least two metalloids in the coating thickness which varies continuously in a direction normal to said surface between relative extreme values, the apparatus comprising means for forming a vapor source for vaporizing a metal for use in reactions with gases to form the at least two metalloids, and means for moving the vapor source with respect to a workpiece portion for producing the coated workpiece. *e BALZERS AKTIENGESELLSCHAFT *o DATED THIS 28th day of September of 1993 *THE ATRIUM 290 B ROAD *HAWTHORN VICTORIA 3122 WATERMARK PATENT USTRALIADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA