US 3640689 A
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Description (OCR text may contain errors)
United States Patent Glaski et al.
[ 51 Feb. 8, 1972  COMPOSITE HARD METAL PRODUCT  Inventors: Frederick A. Glaski; Robert A. l-lolzl;
Richard B. Kaplan, all of Pacoima, Calif.
 Assignee: Fansteel Inc., North Chicago, Ill.
 Filed: Mar. 4, 1970  Appl. No.: 16,349
Scales et al.
3,552,939 1/1971 Darnell et al. ..29/l95 Primary ExaminerL. Dewayne Rutledge Assistant Examiner--E. L. Weise Attorney-Bames, Kisselle, Raisch & Choate ABSTRACT A method of chemical vapor deposition (CVD) of a hard layer on a substrate such as cemented tungsten carbide and the product resulting from such method; the method involves a more rapid and more easily controlled CVD of a hard metal such as titanium carbide, by providing an intermediate layer of a refractory interface barrier such as refractory metal on the cemented carbide materials to prevent deleterious interaction between the substrate and the hard metal layer and to obtain a hard wear surface with good composite strength characteristics and bond to the substrate; the product is the resulting composite substrate with the interface metal and the face metal.
6 Claims, 3 Drawing Figures fAIENTEDFEB 8 I912 3.640.689
M, W .-%W m ATTORNEYS COMPOSITE HARD METAL PRODUCT This invention relates to a a Hard Metal Product and more particularly to one comprising a relatively hard substrate of cemented carbide or other hard metal composition and a tenaciously adherent layer of hard and wear resistant material selected from Group lVB metal carbides.
HISTORY OF THE ART Since the introduction of hard metal cutting tools, wear parts and drawing dies, there has been a constant search for compositions and methods which would produce harder, more wear-resistant parts, with a longer life, greater transverse rupture strength and which can lead to higher cutting speeds, greater resistance to destruction from vibration and abrasion and deeper cuts. Typical hard meta] compositions of the type referred to are cemented carbides and other cast or sintered cobalt-hard metal base materials having high concentrations of Group VlB metal and carbon.
in a U.S. Pat. to Ruppert et al., No. 2,962,388, which issued Nov. 29, 1960, the existing art of chemical vapor deposition of titanium carbide was discussed, more particularly the coating of ferrous and nonferrous materials and possibly hard metal alloys, the above patent, together with a U.S. Pat. to Ruppert et al., No. 2,962,399, issued Nov. 29, 1960, disclosed certain improved methods to accomplish such coating, suggesting certain low-range temperatures and reactive gas compositions as desirable to achieve improved results.
PRESENT INVENTION lt is an object of the present invention to improve the adhesion characteristics of the surface layer to the substrate.
In the selection of a process for the application of a thin layer of a metallic carbide to a hard metal substrate, there are several facts to be considered. Due to the thinness of the coating to be applied, and the fragile nature as well as the frequency of irregular shapes in the substrates, the mechanical pressing-on of the material is impractical. On the other hard, physical vapor deposition or sputtering and even electrochemical plating processes or the fused salt process are inappropriate because of the nature of the material to be deposited, namely, carbides of Group lVB. Also, the flame and plasma spray-coating processes exhibited relatively poor properties of adhesion and cohesion. Accordingly, these are not satisfactory.
By far, the most appropriate process for the purpose has proved to be the process called chemical vapor deposition or gas plating or vapor plating." The medium or solvent to use a parallel to electrodeposition of metal is a chemically reactive gas mixture which is thermally activated to deposit material, usually by heating a substrate to a temperature higher than that of the reactive gas mixture. Chemical vapor deposition has the ability to deposit an extremely thin layer uniformly on relatively complex shapes and it has the advantage of a more rapid rate of deposit as distinguished from electrodeposition or physical deposition.
The adherence and coherence of the layer deposited by chemical vapor deposition is excellent in quality even for hard mechanical use such as cutting edges and surfaces of a cutting tool, and the process is also well suited to the deposition of compounds having desirable characteristics for the intended purpose.
In the process when the substrate is hotter than the so-called feed, that is, the source of the material to be deposited, the feed gas can be thermally activated to deposit the desired material as an overlayer.
ln this connection, the volatility of the feed material is an important practical consideration. Materials which are normally gaseous at room temperature, or at room temperature and reduced pressure, are the most easily transported without decomposition. WF and MoF, are typical chemically vapor deposited compounds falling into this category which are used as sources to deposit tungsten and molybdenum metal. TiCl by contrast, is a liquid at room temperature but has a relatively high vapor pressure and can therefore be transported in a dry inert or reducing carrier gas at reduced pressures. Metal carbonyls such as W(CO) and Mo(CO) are solids at room temperature and can be sublimed with only slight heating but they are very unstable compounds and will decompose in transit upon slight overheating. More difficult feed materials to transport are the less volatile metal chlorides such as WCl TaCl and HfCl, which are solids at room temperature and boil above 300 C. A hot carrier gas feed system is required to transport these materials, resulting in system sealing problems and metering problems. These problems are obviated by the use of in situ direct chlorination of the metal and this technique will be described in conjunction with the description of the figures which are part of this specification.
The in situ chlorination can also be applied to TiCl feed systems.
In the normal utilization of CVD processes, mechanical cleaning and/or degreasing of the substrate with conventional solvents prior to their introduction to the plating chamber, and then an elevated temperature treatment of the surface of the substrate in hydrogen, have been employed to clean and prepare the surface for deposition.
The firing process is often more effective when conducted at reduced pressures in order to remove volatile impurities from the surface of the substrate as is taught in the Ruppert et al. U.S. Pat. No. 2,962,388.
These cleaning procedures and the commonly known processes for CVD are generally satisfactory for the deposition of Group IVB metal carbides on various substrates. However, if it is desired to operate the process above l,l0O C. and preferably above l,200 C. in the range where significant increase in deposition rate and simplicity of process control are achieved, major problems are experienced. In this range vigorous interaction occurs between the free cobalt in the substrate and the metal species of the plating gas, resulting in an uncontrollable diffusion as evidenced by the formation of a liquid phase with the production of a weak brittle layer on freezing and a substantial population of Kirkendall holes. The resultant-product is rendered inferior as a cutting or wear tool.
If the higher temperature range and the more rapid rate of deposition are to be maintained, it is essential that this deleterious effect be avoided while achieving the ultimate overlay of the desired refractory metal carbide with a good bond and solid base. This has been accomplished by the present invention by introducing a selected barrier material as an interface which not only solves the above problem but also provides many distinct additional advantages.
The selected barrier material must have the characteristics of:
a. withstanding the deposition temperature without melting;
b. withstanding the deposition temperatures without forming a liquid phase by combinations either with the substrate or the overlayer;
c. Being readily amenable to vapor deposition;
d. Providing good strength and hardness under final product use temperature; and
e. Serving as an efficient impurity getter either as a reactant gas or as the deposited material.
In addition, desirable characteristics of the barrier material are:
1. Expansion qualities compatible with both the substrate and the final overlay and preferably intermediate between the two, and/or,
2. Reasonable ductility as deposited in order to distribute stresses due to mismatch in thermal expansion between the substrate and the overlay.
Thus, an object of the invention is the selection and application of an interface material for the final chemical vapor deposition of the face material.
Other phases of the method include the selection and use of a suitable temperature-material combination to accomplish the deposition in a relatively short time of the barrier and the overlay materials which are compatible with the constituent ingredients contained in the substrate and at the same time avoiding detrimental interaction between the substrate/barrier and barrier/overlay materials.
Another object of the invention is the provision of a proper pressure and flow control coordinated with temperature to achieve proper depositions on the selected substrate.
Other objects and features of the invention will be apparent in the following description and claims wherein the principles of the invention are set forth together with the best mode presently contemplated for practicing the invention.
Drawings accompany the disclosure and the various views thereof may be briefly described as:
FIG. 1, a view of a substrate together with a barrier material and an overlay deposit, the dimensions being enlarged for the purposes of clarity.
FIG. 2, a diagrammatic presentation of a flow circuit which can be used in the chemical vapor deposition.
FIG. 3, a view of a reaction chamber and reactant feed configuration where both interlayer and overlayer are deposited from less volatile chlorides.
In accordance with the invention, the substrate can be any of the alloys or composites of cobalt and hard metals. Frequently employed in industrial use for cutting tools and wear-resistant parts are cemented refractory metal carbides, such as tungsten carbide, with a matrix of cobalt of up to approximately 25 percent. These materials are typically made by cold pressing and less frequently by sintering, hot pressing, or liquid metal infiltration. Also of important industrial use are multiphase alloys containing up to approximately 65 percent cobalt having a dispersed phase of hard metals with an alloy matrix. These materials are sometimes made by powder metallurgy techniques but are most frequently cast. The selected substrates in accordance with the invention are described in Volume 1 of the Metals Handbook, 8th edition, pages 659 through 679, published by the American Society for Metals, Metals Park, Ohio, 1961.
The ultimate and final overlayer which is relatively thin, is selected for chemical vapor deposition on the substrate and is preferably a carbide of a metal from the Group IVB, namely, titanium, zirconium and hafnium. The superior performance of the carbides of these metals as surfaces for cutting or wearresistant parts is well known and is based on their high hardness even at elevated temperatures, their low coefficient of friction against the materials to be worked such as iron, steel, and nickel alloys, and their superior chemical inertness both to the work material and the environment. The ultimate in the desired tool characteristics is a substrate having superior bulk mechanical properties, i.e., strength, toughness and elastic modulus, with a surface layer having the desirable properties above noted.
In order to achieve successful chemical vapor deposition of the overlayer on the substrate, a barrier material must be vapor deposited on the substrate in advance of the final overlayer. The desirable characteristics of this barrier material have been outlined above. Since both the deposition temperature for the final wear overlay and a typical maximum cutting edge temperature are above l,200 C., the material available for the barrier is significantly limited. Suitable interlayer materials are metals of Group VB, namely, vanadium, columbium, tantalum; Group VIB namely, chromium, molybdenum, tungsten; and nitrides of Group IVB, namely, titanium, zirconium, hafnium, and of Group VB. These materials can each be deposited at temperatures not greater than the temperatures at which the final overlay surface is put down. Thus, any selected material can be deposited in a sequential operation as a prelude to the final deposition as will be described below.
It should be understood, however, that when depositing the Group IVB metal carbide overlayer, during which a carbonbcaring gas is used, there is measurable migration of carbon from the substrate as well as from the overlayer material into the previously deposited metal barrier material, resulting in at least a partial conversion of said barrier material to a refractory carbide.
In considering possible candidate materials which might qualify as acceptable barriers, the Group VIII noble metals, namely, ruthenium, rhodium, palladium, osmium, iridium, platinum, as well as rhenium from Group VIIB, could be included from the point of view of chemical properties. However, the use of these materials is not considered to be practical from an economic standpoint.
In order to assure a tenaciously bonded overlayer, certain conditions must be fulfilled. The general problem is the codeposition of various species. For example, in the case of the deposition of a metal carbide, the timing of the flow of gases is important. If the carbon-bearing gas impinges the surface of the part to be coated first, there is a propensity to form a weak, in fact, even an amorphous, deposit of carbon. Therefore, in the codeposition of a metal carbide, it is necessary that the metal bearing gas impinge the surface first. Another limitation is hereby imposed. The metal from this metal-bearing gas must not, under the deposition conditions, react with the substrate to form a solution or intermetallic compound with the substrate, which results in a low melting eutectic or liquid phase. This is the reason for introducing certain metallic or metallic compound barrier materials as an interlayer between the hard metal carbide and the substrate.
There are hard metal compounds which can be deposited; however, this should be 'done only where the above problem does not exist, i.e., where the nonmetal species is under no circumstances solid. This would be true in the case of oxygen or nitrogen. Oxygen, however, if it impinges the heated surface first, will degrade the substrate in a different way, namely, the oxidation of the various species of the substrate thereby degrading the mechanical integrity. Nitrogen therefore represents a unique situation. If nitrogen impinges the surface to be coated first, no substantial reaction occurs and there is no degradation of this surface.
If the nitrogen-bearing gas impinges the surface first, no elemental nitrogen will be deposited since nitrogen is gaseous under the deposition conditions. The implication of this consideration is that nitrides intrinsically are good candidate materials as barrier layers since, in the deposition, when using the nitrogen bearing gas, i.e., nitrogen or ammonia (unlike a carbon bearing gas) either in the presence of hydrogen or without hydrogen, there is no concern about initial weak or nonadherent coating. The metal species can follow the injection of the nitrogen-bearing gas, such that a metal nitride is formed without any danger of undue reactivity of that metal species with the cobalt of the substrate. To repeat them, of all the metallic compounds which may have physical properties which make them desirable, the nitrides are to be preferred as that first deposit to be put on the surface to be coated. Thereafter, the metal carbide overlayer having the desirable properties may be applied with impunity on the inert metal nitride interlayer.
The apparatus which can be used in connection with the performance of the process above described is illustrated partially in diagrammatic form in FIGS. 2 and 3. With reference to FIG. 2, an induction heater coil 20 surrounds a 1.8 inch diameter quartz or vycor grade glass tube 22 supported on a seal 24 in a base 26 which serves as a primary condensate collection chamber. This base is preferably formed of stainless steel. Also supported centrally on the base of the tube 22 is a graphite furnace chamber 28 having a graphite or tungsten rod support system 30 for a carbide insert 32. Above the induction heater coil 20 is a nichrome resistance heater 34 which in the unit which has been used has been about 2 inches in internal diameter and 4 inches long. (One or two heaters simultaneously have been used.) At the top of the tube 22 is a brass seal ring 36 which serves as a support for a cylindrical 1% inch-diameter quartz or vycor grade glass chamber 38 which depends into the tube 22 into the area surrounded by the resistance heater 34. At the top of the tube 38 is an upwardly flared wall 40 which supports a brass seal plate 42 having on its underside a seal 24. A downwardly flared flange 46 supports the tube 38 on the ring 36. Centrally of a seal 41 is a thermocouple well 48 which projects downwardly into the tube 38 in the area of the resistance heater 34. The bottom of the tube 38A is intended to receive and support a quantity of metal chips 50 which in the present example will be tantalum chips. Outside of the induction heater is a pyrometer 52 for checking temperature.
Connected to the condensate chamber 26 is a condensate trap 54 surrounded by a suitable water-cooling coil 56, this trap being connected through a valve 58 to a mechanical pump 60 and being connected through a valve 62 to a water aspirator 64 serving as an alternate vacuum system. The seal plate 42 has a connection through a line 66 and a valve 68 to a flowmeter 70 and a Cl source 72, there being a gauge 74 for pressure reading.
Another opening in the ring 42 is connected to a line 80 through a valve 82 to a line 84 controlled by a valve 86, this line having a flowmeter 88 and a gauge 90 and serving as a source of hydrogen. Lines 80 and 84 are manifolded into a line 92 which connects to the manifold ring 36, this line 92 being connected to a valve 94 and a flow meter 96 to serve as a source of a carbon containing gas such as C 11 Line 92 also connects to a line 98 valved at 100 with a flowmeter 102 connected to a source of molybdenum fluoride (MOFG) or tungsten fluoride (WF A fourth line 104 connected to the line 92 is valved at 106 and controlled by a flowmeter 108. This line has a bubbler unit 110 which can serve as a source of titanium chloride (TiCl The end of this line 104 has a gauge 112 and is connected to a source of hydrogen (H or helium (He) as a carrier gas source for the titanium chloride. A fifth line 114 connected to line 92 is valved at 116 with a flowmeter 118 and is connected to a source of argon (A) or helium (He) as an optional source of inert gas diluent to the deposition system. At the top of the heater 34 is a steel heat shield 120 which prevents heat loss by convection between the chamber at the bottom of the tube 22 and the resistance heaters 34.
Referring to FIG. 2, the deposition chamber at the bottom of the tube 22 is initially evacuated through the graphite furnace 28 with the pump system 60 or 64. Hydrogen is then turned on from the source through pipe 84, metered by the flowmeter 88 and controlled by the valve 86, this hydrogen flowing through the chamber 28 and through the bypass 80 to the chlorinator chamber in tube 38, while the furnace 28 containing the carbide insert specimen 32 on rack 30 is heated by the induction coil 20. At the same time the chlorinator chamber tube 38 containing tantalum chips 50 supported by a suitable tantalum screen 38A is heated by the resistance heaters 34. The temperature of the tantalum chips 50 is measured by thermocouple 48 placed in the tube 38 and the temperature of the furnace 28 is monitored by the radiation pyrometer 52.
The reaction chamber at the bottom of the tube 22 is sealed from the exterior atmosphere by a proper grade rubber gasket 24 at each end of the tube assembly and at the manifold ring 36 as well as by the brass seal plate 42 at the top of the assembly.
When a proper chlorinator temperature is obtained for the chips 50 and a proper tantalum deposition temperature is obtained on the carbide insert 32, the bypass hydrogen from lines 84 and 80 to the chlorinator tube 38 is turned off and hydrogen is only flowed from pipe 84 to the reaction chamber through the manifold ring 36. The system pressure is adjusted by vacuum source 60 in the pressure range below 40 torr or by vacuum source 64 in the pressure range of 40 to 150 torr, and the chlorine source through line 66 is turned on, metered by the flowmeter 70 at a pressure indicated by gauge 74 and controlled by valve 68 through line 66 into the chlorinator 38 and tantalum chloride generation begins.
Tantalum deposition takes place by tantalum chloride/hydrogen reduction reaction for about three minutes before the valve 68 is closed ofi" and the carrier gas from the hydrogen or helium source at line 104 is turned on. This gas is metered by the flowmeter I08 bubbled through the titanium chloride reservoir and controlled by valve 106 and flowed through the line 92 and the manifold ring 36 into the reaction chamber in tube 22. The carbon source gas through line 97 is then turned on by operating the control valve 94 with flow through the meter 96, this carbon source gas also flowing through the manifold ring 36 into the reaction chamber. Titanium chloride deposition proceeds by reaction between the titanium chloride and the carbon source gas for about 30 minutes at which time all gases except the helium or argon source through line 114 are turned off. The system is then allowed to cool.
During a deposition run, the primary condensate chamber 26 is employed to trap readily condensable chlorides, and the cold trap 54 cooled by the coil 56 is used to trap any remaining condensables before they can enter and plug either the exhaust lines or the vacuum systems 60 and 64 beyond the condenser. The argon (A) bleed controlled by the valve 116A trims the system pressure by variably matching the capacity of the vacuum system 60 or 64 to the volumetric throughput of reactant and product gases flowing in the system. When tungsten fluoride or molybdenum fluoride are used as reactants to produce a tungsten or molybdenum barrier on the specimen 32, they are provided by the source through line 98, metered through the meter 102, and controlled by valve 100.
In FIG. 3, there is illustrated a binary chlorination system which is used when the interlayer and the Group IV carbide overlayer are both derived from less volatile chloride species. It should be recognized that when tungsten fluoride or molybdenum fluoride is used for the interlayer deposition prior to the deposition of hafnium carbide or zirconium carbide, only one less volatile species is present and the single chlorination system shown in FIG. 2 is sufficient. The binary system shown in FIG. 3 pertains only to the chlorinator and deposition chamber and assembles readily to the chemical vapor deposition apparatus shown in FIG. 2.
With reference to FIG. 3, the bottom of the tube 22 is shown with the induction heater coil 20, the graphite furnace 28, the specimen support 30 and the specimen 32. In FIG. 3, the branch tubes I30 and 132 extend to the right and to the left of the central quartz or vycor grade glass chamber. Tube has a suitably supported inner quartz or vycor grade glass tube column 134 for containing tantalum chips 136, there being a resistance heater 138 surrounding this area and in the left-hand tube 132 the supported tube 140 containing hafnium or zirconium chips 142 is surrounded by the resistance heater 144. The sources of the various gases is shown at the top of the drawing and suitable flowmeters and control valves would be utilized as shown in FIG. 2.
Referring to the system illustrated in FIG. 3 where both the interlayer metal and the overlayer carbide, that is, zirconium carbide or hafnium carbide, or as an optional titanium carbide system, that is, a Group IV metal of the barrier metal, are deposited from less volatile chlorides, a sequence similar to that of FIG. 2 is used while employing the different reaction chamber design, that is, the branch systems 130 and 132. The barrier metal such as tantalum is placed in the chlorinator chamber 136 and the overlayer Group IVB metal is placed in the chlorinator chamber 142, each chlorinator being heated by the respective heaters 138 and 144 to the optimum chlorination temperatures.
The depositions then proceed as previously described, first flowing hydrogen through line 148 and then the chlorine through line 146 through the tantalum chips 136 for about 3 minutes, followed by a turning off of lines 146 and 148 and a turning on of the chlorine through the Group IVB metal in chamber 142 through a line 150. Also the hydrocarbon is flowed through line 152 and the hydrogen through line 154 for about 30 minutes to deposit the Group IVB metal carbide and inert gas source for argon or helium at 156 and suitable seals 160 are provided at the top of the chamber. It should be pointed out that the chlorination systems above described are applicable also to bromide and iodide systems and since bromine and iodine have lower vapor pressures at room temperature than chlorine, they require either a gas carrier to transport the liquid bromine to a brominator in the same manner as TiCl, is transported or a hot feed line to the iodinator to maintain the normally solid iodine in the vapor state.
In connection with the parameters for the deposition conditions, certain limits can be set up. For example, the deposition temperature is preferably between 2,l50 F. and up to 2,550 F. approximately 1,174 to l,400 C. In connection with the deposition of titanium carbide, it appears preferably to operate in the range from 2,300 F. to 2,400 F. approximately l,260 to l,316 C. HfC and ZrC are best deposited in the range 2,4002,500 F. (1,3 l6l ,372"). With respect to pressures, the most desirable range seems to be 40 to 70 torr for TiC deposition. These pressure ranges may go as low as 4 and as high as 150 but a more acceptable product is achieved in the above indicated preferred range. HfC or ZrC deposition proceeds more favorably at a somewhat lower pressure, preferably 2040 torr. With respect to the mixture ratio of the carbon containing gas such as propane, the limits are preferably from about 22 standard cc./min. to 175 standard cc./ min.
As an example of the parameters in a successful deposition utilizing a tantalum barrier layer on a cemented tungsten carbide insert and laying down a titanium carbide overlayer, the following can be outlined:
l. TiC Deposition temperature2,250-2,300 F. (1,232
to l,260 C.);
2. H flows1,000 standard cc./min.;
3. He flow through liquid TiCl l ,000 standard cc./min.;
4. TiCl, carried in He- 1 .65 gram/min.;
5. System pressure-40 torr.; and
6. Time for each deposition-3 min. Ta and 30 min. TiC.
The following specific examples of run conditions for applying titanium carbide as an overlayer with a tantalum barrier are illustrative of successful operations;
l. Best run conditions for TiC with Ta barrier a. Heat carbide insert to l,900l ,950 F. (1,038 to 1,066 C.) in H b. Deposit Ta for 3 minutes i. Insert temperature 1 ,038l ,066 C. ii. Chamber pressure540 torr. iii. Cl to chlorinator275 standard cc./min. iv. H l ,000 standard cc./min.
c. Reduce chamber pressure to 50 torr.
d. Turn off Cl e. Increase carbide insert temperature to 1,232-1 ,260 C.
f. Deposit TiC for 30 minutes i. H carrier through TiCl., l ,000 standard cc./min. ii. H additional 1 ,000 standard cc./min. iii. C H,,45 standard cc./min.
g. After total time of 30 minutes, turn off TiCl and C H and cool part in H Result: Thickness: 0.003 inch (more typical) to 0.006 inch (average many runs, both sides total).
Hardness 2,5002,700 DPH Vickers scale (average many runs).
2. Same as example 1 but TiC deposition temperature 1 ,400 C. Result: Thickness: 0.007 inch both sides. Hardness: 2,800-3, 200 DPH Vickers.
3. TiC without any H Ta barrier used a. Heat carbide insert to 1,038l ,066 C. in H2. b. Deposit Ta for 3 minutes i. Insert temperature-- 1 ,038-l ,066 C. ii. Chamber pressure-540 torr. iii. C1 to chlorinator275 standard cc./min. iv. H 1 ,000 standard cc./min. c. Reduce chamber pressure to 50 torr. d. Turn off Cl e. Raise temperature of carbide insert to 2,200-2,250 F.
(l,204l ,232 C.)
f. Deposit TiC for 20 minutes i. He carrier through TiCl., l ,000 standard cc./min. ii. He additionalstandard cc./min. iii. C H,,45 standard cc./min.
g. After 23 minutes total, turn off TiCl, and C ll and cool in He Results: 0.0035-inch thick deposit, both sides.
2,4002,600 DPH Vickers hardness Using hafnium carbide as the overlayer, the following examples are pertinent:
4. HfC Deposit with Ta barrier a. Heat insert to l,038l ,066 C. in argon b. Deposit Ta for 4 minutes i. Insert temperaturel ,038-1,066 C. ii. Chamber pressure-5 torr iii. C1 to chlorinator275 standard cc./ min. iv. H 1 ,000 standard cc./min. c. Increase chamber pressure to 30 torr d. Turn off Cl e. Increase part temperature to 2,400" F. l ,3 1 6 C.) f. Deposit HfC for 15 minutes i. Cl to chlorinator360 standard cc./min. ii. H 1 ,000 standard cc./min. iii. CH -290 standard cc./min. g. After 19 minutes total, turn off C1 H and CH and cool in argon. Results: 0.002 inch thick (both sides).
Hardness2,5002,600 DPH Vickers,
Another example utilizing titanium carbide as an overlayer and a tantalum barrier on a cast Co alloy insert such as Tantung G manufactured by VR/Wesson Division of Fansteel Inc. is as follows:
5. TiC on Tantung G-Ta barrier All conditions identical to Example 1.
A further example utilizing titanium carbide as an overlayer and a tungsten barrier on a carbide insert is as follows:
6. TiC with Tungsten barrier a. Heat carbide insert to l,600 F. (871 C.) in H for 5 minutes to clean. b. Reduce temperature to l,200 F. (649 C.) and apply a flash coating of tungsten for 15-30 seconds. i. Chamber pressure50 torr. ii. WF 1050 standard cc./min. iii. H l ,000 standard cc./min. c. Turn off WF d. Increase temperature to 1,232 C. e. Deposit TiC for 30 minutes i. Chamber pressure-50 torr ii. H carrier thru TiCl., 1 ,000 standard cc./min. iii. Additional H 1 ,000 standard cc./min. iv. C H -45 standard cc./min. f. After total time 30.5 minutes shut off all gases but H and cool in H Results: 0.002 inch 0.005 inch thick coating both sides (average many runs). Hardness: 2,400-2,600 DPH Vickers Utilizing a titanium carbide overlayer with a titanium nitride barrier, the following is an example:
7. TiC with TiN barrier a. Heat insert to l,232 C. in H and N i. N 40O standard cc./min. ii. PI -1,000 standard cc./min. b. Deposit TiN for 10 minutes by turning on TiCl source i. Insert temperature-1,232 C. ii. Chamber pressure50 torr. iii. H l ,000 standard cc./min. iv. N 400 standard cc./min. c. Turn off N source only at 10 minutes (I. Turn on C H source and deposit TiC for 30 minutes i. C H 45 standard cc./min. e. After 40 minutes total time, turn off all gases except H and cool in H Results: 0.002 inch-0.004 inch thick coating both sides (average many runs). Hardness: 2,400-2,600 DPH Vickers With regard to the thickness of the coatings, satisfactory results in cutting tests have been obtained with coating thicknesses ranging from 0.0001 inch to 0.004 inch, this including the total barrier layer plus the overlayer. Effective thicknesses of barrier layers for such coatings have been less than 0.0002 inch.
It may be mentioned that the analyses of samples utilizing an electron microprobe has verified the fact that utilizing tantalum as a barrier isolates any cobalt binder in the substrate from the final titanium carbide overlayer, thus indicating that the tantalum barrier, for example, effectively isolates the substrate from the final overlayer while insuring an effective bond between the substrate, the interface layer, and the overlayer.
It has been discovered, for example, in examining the products with an electron microprobe that the interlayer, utilizing tantalum can be quite thin in the neighborhood of 2-6 microns; and yet it still serves effectively as a barrier against any eutectic formation with the cobalt, while permitting some of the tungsten of a substrate to migrate into the interlayer and the overlayers, thus creating an extremely effective bond between all the materials. Thus, in a sense, the tantalum barrier effectively isolates the cobalt in a substrate while serving as a window for the tungsten to the extent that a unique bond is obtained.
The ultimate coating for the substrate is intended to have good friction, wear, and chemical characteristics relative to the worked material. With good friction characteristics, there will be a reduction in the temperature of operation, and, in the case of cutting, the temperature of the chips. The wear characteristics are improved by these lower temperatures and also by the fact that there is no binder in the coating to spall out. The term good chemical characteristics" has reference to the ability of the cutting or wear material to resist chemical interaction and alloying with the worked metal at high working temperatures. One of the primary problems with uncoated hard metals is the chemical interaction with the worked metal or hot chips causing local loss in mechanical integrity of the wear part resulting in what is commonly known as cratering.
1. A laminate article for cutting and wear parts comprising a substrate of cobalt-hard metal alloy or composite, a chemically vapor deposited overlay face material on said substrate comprising a carbide of a metal selected from Group lVB hav ing good friction, wear and chemical characteristics, and a chemically vapor deposited barrier material between said substrate and said overlay material to control diffusion during chemical vapor deposition and to provide resistance to the formation of a low melting liquid phase between the metal of said overlay and the constituents of said substrate at temperatures of at least l,200 C.
2. A laminate article for cutting and wear parts comprising a substrate of cobalt-hard metal alloy or composite, a chemically vapor deposited overlay face material on said substrate comprising a carbide of a metal selected from Group IVB having good friction, wear and chemical characteristics, and a chemically vapor-deposited barrier material between said substrate and said overlay material to control diffusion during chemical vapor deposition and to provide resistance to the formation of a low melting liquid phase between the metal of said overlay and cobalt at temperatures of at least l ,200 C.
3. A laminate article for cutting and wear parts comprising a substrate of cobalt-hard metal alloy or composite, a chemically vapor-deposited overlay face material on said substrate comprising a carbide of a metal selected from Group lVB having good friction, wear and chemical characteristics, and a chemically vapor-deposited barrier material selected from the group of metals in Groups VB, W8 and nitrides of Groups W8 and VB between said substrate and said overlay material.
4. A laminate article for cutting and wear parts comprising a substrate of cobalt-hard metal alloy or composite, a chemically vapor-deposited overlay face material on said substrate comprising a carbide of a metal selected from Group [VB having good friction wear and chemical characteristics, and a chemically vapor-deposited overlay of tantalum as a barrier material between said substrate and said overlay material 5. A laminate article for cutting and wear parts comprising a substrate of cobalt-hard metal alloy or composite, a chemically vapor-deposited overlay face material on said substrate comprising a carbide of a metal selected from Group lVB having good friction, wear and chemical characteristics, and a chemically vapor deposited layer of tungsten as a barrier material between said substrate and said overlay material.
6. A laminate article for cutting and wear parts comprising a substrate of cobalt-hard metal alloy or composite, a chemically vapor-deposited overlay face material on said substrate comprising a carbide of a metal selected from Group [VB having good friction, wear and chemical characteristics, and a chemically vapor deposited layer of titanium nitride as a barrier material between said substrate and said overlay material.