IE52544B1 - Prepferentially binder enriched cemented carbide bodies and method of manufacture - Google Patents

Abstract

Cemented carbides with a binder enriched surface are made by adding a metal, hydride, nitride or carbonitride of a Group IVB or VB transition metal (Ta, Nb, Ti, Hf, Zr, V) into the powder mixture prior to sintering. The binder enriched surface may be coated with a refractory oxide, nitride, boride and/or carbide.

Description

Th· present Invention patUlna to th· fields of cemented carbide parti, having cobalt, nickel, iron or their alloys as a binder materiel, and Che manufacture of these parts. More particularly, the present invention pertains to cemented carbide metal cutting Inserts having a hard refractory oxide, nitride, boride, or carbide coating on their surface.

In the past, various hard refractory coatings have been applied to the surfaces of cemented carbide cutting inserts to improve the wear resistance of the cutting edge and thereby Increase the cutting lifetime of the insert. See, for example, United states Patent Specification Nos. 4,035,541 (assigned to applicant corporation); 3,564,683; 3,616,506; 3,882,581; 3,914,473; 3,736,107; 3,967,035; 3,955,038; 3,836,392; and Reissue 29,420. These refractory coatings, unfortunately, can reduce the tough15 ness of cemented carbide inserts to varying degrees. The degree of degradation depends at least in part on the structure end composition of the coating and Cha process usad for its deposition. Therefore, while refractory coatings have improved the wear resistance of metal cutting inserts, they have not 2o reduced the susceptibility of Che cutting edge to failure by chipping or breakage, especially in interrupted cutting applications.

Previous efforts to Improve toughness or edge strength in coated cutting inserts revolved around the production of a cobalt enriched layer extending inwardly from the substrate/ coating interface. It was found that cobalt enrichment of the -2surface layers In certain C porosity substrates could be achieved during vacuum sintering cycles. These cobalt enriched zones were characterized by A porosity while most of the bulk of the substrate had C porosity. Solid solution carbide s depletion was usually present to varying depths and degrees in the areas of cobalt enrichment. Cobalt enrichment is desirable in that it is well known that increasing cobalt content will increase the toughness or Impact resistance of cemented carbides. Unfortunately, the level of enrichment produced is difficult to control in C porosity substrates. Typically, a coating of cobalt and carbon was formed on the surface of the substrate.

This coating of cobalt and carbon was removed prior to deposition of the refractory material on the substrate, in order to obtain adherent bonding between the coating and substrate.

At times, the level of cobalt enrichment in the layers beneath the surface of the substrate was so high that it had an adverse effect on flank wear. As a result, sometimes the layer of cobalt*enrichment on the flank faces of the substrate were ground away leaving cobalt enrichment only on the rake faces and 20 the possibility of C porosity material on the flank face. In comparison with A or B type porosity substrates, C porosity substrates are not as chemically homogeneous. This can result in less control over the formation of eta phase at the coating substrate interface (a hard and brittle phase affecting tough!5 ness), a reduction in coating edherency and an increase in nonuniform coating growth. -3By way of definition, the porosity observed in cemented carbides may be classified into one of three categories recommended by the ASTM (American Society for Testing and Materials) as follows: Type A for pore sizes less than 10 microns in diameter.

Type B for pore sizes between 10 microns and 40 microns in diameter.

Type C for irregular pores caused by the presence of carbon inclusions. These Inclusions are pulled cut of the sample during metallographic preparation leaving the aforementioned irregular pores.

In addition to the above classifications, the porosity observed can be assigned a number ranging from 1 through 6 to indicate the degree or frequency- of porosity observed. The I5 method of making these classifications can be found in Cemented Carbides by Dr. P. Schwarzkopf and Dr. R. Kieffer, published by the MacMillan Co., Mew York (1960) at Pages 116 to 120.

Cemented carbides may also be classified according to their binder carbon and tungsten contents. Tungsten carbide-cobalt alloys having excess carbon are characterized by C porosity which, as already mentioned, are actual free carbon inclusions. Tungsten carbide-cobalt alloys low in carbon and in which the cobalt is saturated with tungsten are characterized by the presence of eta phase, a Mj^C or M^C carbide, where M represents cobalt and tungsten. In between Che extremes of C porosity and eta phase, there is a region of intermediate binder alloy compositions which contain tungsten and carbon in solution co - 4 varying level», but such that no free carbon or eta phaaa are present. The tungsten level present In tungsten carbide cobalt alloys can also be characterised by the aagnetlc saturation of the binder alloy, since the aagnetlc saturation of the cobalt alloy la a function of lta composition. Carbon saturated cobalt ia reported to have a aagnetlc saturation of 158 gauaa-ca/ga cobalt and la indicative of C type porosity, while a aagnetlc saturation of 125 gauss-ca /ga cobalt and below Indicates the presence of eta phase.

According to the present invention, there is provided a proceaa for producing a body of tungsten carbide ceaented with a metallic binder material, said IS process coaprislng the steps of coapactlng a powder aixture of tungsten carbide, said binder material, and a cheaical agent selected from nitrides and carbonitrides of transition aetals whose carbides have a free energy of foraatlon more negative than that of tungsten carbide at a teaperature above the aelting point of the binder aaterial, denslfying the coapact ao formed, and sintering said denalfied compact at a liquid-phase sintering teaperature, said cheaical agent being tranaforaed during said sintering step 2s or during a aubsequent heat treataent into a aeeond carbide in solid solution with said tungsten carbide, thereby to increase the content of eaid binder alloy aaterial near a peripheral surface of said body. - 5 In accordance with the praaant Invention, thia process nay ba used to produce a layer of binder enrichment near a peripheral surface of a ceaented carbide body having substantially only A to B type porosity g throughout said body.

Preferably, the binder alloy aay ba cobalt, nickel, iron or their alloya, but ia, nost' preferably, cobalt.

Preferably, the cheaical agent is aalaetad froa the nitrides, and carbonitrides of the Group IVB and VB element! and ia, preferably, added in a aaall but effective amount, aoat preferably, O.S to 2 weight percent of the powder charge. Nost preferably, the cheaical agent ia titanium nitride or titanium carbonitride.

Ceaented carbide bodies produced in accordance with the present Invention have also bean found to have a layer, at least partially depleted in solid solution carbide, near a peripheral surface of the body. Ceaented carbide bodies produced in accordance with the present invention have also been found to have a layer beneath aaid depleted solid aolutlon layer which ia enriched in qplld solution carbides.

The ceaented carbide bodies produced aocording to the present invention, preferably, have a cutting edge at the Juncture of a rake face and a flank face with a hard dense refractory coating adherently bonded to these faces. The binder enriehed layer aay be ground off the flank face prior to coating.

The refractory coating is preferably coapoaed - β of on· or nor· layer· of a natal oxide, carbide, nitride, boride or carbonitrida.

BBIgF DESCRIPTION OF THE PRAWIHGS The exact nature of the present invention will 5 becoae aore clearly apparent upon rafaranca to tha following detailed specification, reviewed in conjunction with tha accompanying drawings, in which: Figure X is a achaaatlc, cross section through an aabodiaent of a coated aatal cutting insert produced according to tha present invention.

Figure 2 is a graphical representation of tha typical lavals of cobalt anriehaant produced in a ceaantad carbide body produced according to tha present invention · a function of dapth balow it· IS raka surface·.

Figure 3 is a graphical representation of tha variation In binder and solid solution carbide· ralativa concentrations ·· a function of dapth balow tha raka surface in an Kxaapla H aaapla. it has baan found that tha layer of aatarlal adjacent to tha periphery of a ceaantad tungsten carbide body can ba consistently binder enriched and, usually, at laaat partially solid solution carbide depleted during sintering or reheating at a taaparatura above tha aalting point of tha binder alloy by incorporating Group IVB and VB nitride and/or carbonitrida additlone to tha powder charge. 53544 - 7 During sintering, these Group IVB and VB additions react with carbon to fora a carbide or earbonitrida.

Thaaa carbides or carbonitrides may ba present partially or wholly in a solid solution with tungsten carbide and any other carbides present· The level of nitrogen present in the final aintcrad carbide ia typically reduced froa the level of nitrogen added aa a nitride or carbonitride since these additions are unstable at elevated taaparaturea above and below 10 the binder alloy salting point and will lead to at least partial volatization of nitrogen froa the aaaple if the sintering ataoyphere eontaina a concentration of nitrogen less than ita equilibrium vapor praaaura.

Tha nitrides and earbonitridee of tantalus, tltaniua, niobiua or hafniua can ba used alone or in coabination to proaota consistent cobalt enrichment via sintering or subsequent heat treating of tungsten carbide-cobalt baas alloya having a wide range of carbon. Additions totalling up to approximately weight percent have bean found to ba useful. It is believed that tha nitrides and carbonitridaa of xlrconiua and vanadlua are also suitable for this purpose. In A and B porosity alloya and carbon deficient alloya containing ate phase, cobalt anrlehaant occurs without tha parlpharal cobalt or carbon capping, thus eliminating tha need to -aremove excess cobalt and carbon from the cemented carbide surfaces prior to refractory coating.

Additions of approximately 0.5 to 2 weight percent, especially of titanium in the form of titanium nitride or titanium carbonitride, to tungsten carbide-cobalt base alloys are preferred. Since titanium nitride is not completely stable during vacuum sintering, causing at least partial volatilization of the nitrogen, it is preferable to add one-half mole of carbon per mole of starting nitrogen to maintain the carbon level necessary for a tungsten lean cobalt binder alloy. It has been found that cobalt enrichment via heat treating of tungsten carbide-cobalt base alloys occurs more readily when the alloy contains a tungsten lean cobalt binder. The tungsten lean cobalt binder preferably should have a 145 to 157 gauss-cm / gn cobalt magnetic saturation. Titanium nitride additions along with the necessary carbon additions to tungsten carbide-cobalt base powder mixes promote the formation of a 145 to 157 magnetic saturation cobalt binder alloy which is ordinarily difficult to achieve. Although a cobalt binder alloy having 145 to 157 gauss-cm^/gm cobalt magnetic saturation is preferred, alloys containing tungsten saturated cobalt binder alloys (less than 125 gauss-csr/gm cobalt) can also be enriched.

It has been found that a layer of cobalt enrichment thicker than six microns results in a significant improvement in the edge strength of refractory coated cemented carbide inserts.

Uhile cobalt enrichment as deep as 125 microns has been achieved, a cobalt enriched layer having a thickness of 12 to 50 microns -9is preferred for coated cutting insert applications. It is also preferable that the cobalt content of the cobalt enriched layer on a refractory coated insert be between 150 to 300 percent of the mean cobalt content as measured on the surface by energy dispersive·x-ray analysis.

It is believed that binder enrichment should occur in all tungsten carbide-binder-cubic carbide (i.e., tantalum, niobium, titanium, vanadium, hafnium, zirconium) alloys which do not sinter to a continuous carbide skeleton. These alloys containing binder from 3 weight percent and above should enrich utilizing the disclosed process. However, for cutting insert applications, it is preferred that the binder content be between 5 and 10 weight percent cobalt and that the total cubic carbide content be 20 weight percent or less. While cobalt is the preferred binder, nickel, iron and their alloys with one another, as well as with cobalt, may be substituted for cobalt. Other binder alloys containing nickel or cobalt or iron should also be suitable.

The sintering and heat treating temperatures used to obtain binder enrichment are the typical liquid phase sintering temperatures. For cobalt base alloys, these temperatures are 1285 to 1540 degrees Centigrade. Sintering cycles should be at least 15 minutes at temperature. Results can be further optimized by the use of controlled cooling rates from the heat treating temperatures down to a temperature below the binder alloy melting point. These cool down rates should be between 25 to 85 degrees Centigrade/hour, preferably 40 to 70 degrees Centigrade/hour. Most preferably, the heat treat cycle for 2 544 -10cuttlng insert cubetratea having a cobalt binder le 1370 to 1500 degrees Centigrade for 30 to 150 ainutea, followed by a 40 to 70 degrees Centlgrade/hour cool down to 1200 degrees Centigrade. Pressure levels during heat treating can vary froa 10”^ torr up to and including those elevated presaures typically usad In hot isoatatlc pressing. The preferred prasaura level la .1 to .15 torr. Since nitride or carbonitride additions ere being utilised, the vapor preaaure of the nitrogen in the sintering ataoaphere is preferably below lta equilibrium preaaure, ao as to allow volatilization of nitrogen froa the substrate.

While initial enrlehaent will occur upon sintering, subsequent grinding steps in the aetal cutting insert fabrication procaaa aay raaova the enriched tenea.

In these situations, a subsequent heat treatment in accordance with the above parameters can ba utilized to develop a new enriched layer beneath the peripheral aurfacas.

Binder enriched subatrataa to ba usad In coatad cutting inserts can have binder enrlehaent on both the rake and flank faces However, depending on insert style, the binder enrlehaent on the flank face aay eoaetiaee be removed, but thia is not necessary to achieve optimum performance in all cases.

The binder enriched subatrataa can ba coated using the refractory coating tachniquea wall known to those -11ekllled In the art. While the refractory coating applied can have one or more layers coaprieing materials selected froa the Group IVB and VB carbides, nitrides, borides, snd carbonitrides, and the oxide or the oxy5 nitride of sluainua, it has been found that a combination of good cutting edge- strength and flank wear can be achieved by combining a substrate having a binder enriched layer produced according to the. present invention with a coating of: aluminum oxide over an inner layer of titanium carbide; or an inn«r layer of titanium carbide bonded to an intermediate layer of titanium earbonitride, which is bonded to an outer layer of titanium nitride, or titanium nitride bonded to an inner layer of titanium carbide. A cemented carbide body having a binder enriched layer produced according to the present invention in combination with a titanium carbida/aluminum oxide coating la most preferred. In thia caaa, the coating should have a total coating thlcknaas of 5 to 8 aicrona.

Referring now to Figure 1, an embodiment of a eoatad metal-cutting insert 2 produced according to the present invention is schematically shown. The insert 2 is comprised of a substrate or cemented carbide body 12 having a binder enriched layer 14, and a binder depleted layer 18 over the bulk IB of the substrate 12 which haa a chemistry substantially equal to the chemistry of the original powder blend. -12A binder enriched layer 14 la present on the rake faces 4 of the ceaented carbide body and haa been ground off the flank faces 6 of the body. Located Inwardly of the binder enriched layer 14 aay be a S binder depleted sone 16. This binder depleted zone 16 has been found to develop along with tha binder enriched layer when ceaented carbide bodies are fabricated according to the disclosed procaaa. -13The binder depleted zone 16 is partially depleted in binder material while being enriched in solid solution carbides. The enriched layer 14 is partially depleted in solid solution carbides. Inwardly of the binder depleted zone 16 is bulk substrate material 18.

At the junction of the rake faces and flank faces 6, a cutting edge 8 is formed. Uhile the cutting edge 8 shown here is honed, honing of the cutting edge is not necessary for all applications of the present invention. It can be seen in Figure 1 that the binder enriched layer 14 extends into this cutting edge area and is, preferably, adjacent to most, if not all, of the honed edge 8. The binder depleted zone 16 extends to the flank surface 6 just below the cutting edges 8. A refractory coating 10 has been adherently bonded to the peripheral surface of the cemented carbide body 12.

These and other features of the invention will become more apparent upon reviewing the following examples.

EXAMPLE NO. 1 A nix containing 7000 grams of powders was milled and blended for 16 hours with a paraffin, a surfactant, a solvent and cobalt bonded tungsten carbide cycloids, in the amounts and proportions shown below: .3 .85 0.2 8.5 1.5 w/o* w/o* w/o* w/o w/o* 2.5 w/o liter gram Ta(C) Ti(C) Nb(C) Co Ti(N) - 102.6 grams UC + C to produce a 2 w/o - 7000 gm U - 98 w/o Co binder alloy paraffin (Sunoco 3420)(Sun Oil Co.) solvent (perchloroethylene) surfactant (Ethomeen S-15) (Armour Industrial Chemical Co.) 53544 -14*weight percent of metal added.

Square insert blanks having dimensions of 15.1 mm x 15.1 nm x 5.8 to 6.1 am and a weight of 11.6 grams were pill pressed using a force of 8200 kilograms. These inserts were vacuum sintered at 1496 degrees Centigrade for 30 minutes, and then cooled under ambient furnace conditions. After sintering, the inserts weighed 11.25 grams and were 13.26 nm x 13.26 mm x 4.95 nm in size. These inserts were then processed to SHG433 ground dimensions as follows: (this identification number is based on the insert identification system developed by the American Standards Association and which has been generally adopted by the cutting tool Industry. The International designation is: SNGN 12 04 12) 1. Tops and bottoms (rake faces) of the inserts were ground to a thickness of 4.75 nm. 2. The inserts were heat treated at 1427 degrees Centigrade for 60 minutes undpr a 100 micron vacuum, then cooled at a rate of 56 degrees Centigrade/hour to 1204 degrees Centigrade, followed by cooling under ambient furnace conditions. 3. The periphery (flank faces) was ground to produce a 12.70 nm square and the cutting edges honed to a 0.064 nm radius.

A titanium carbide/titanium carbonitride/titanium nitride coating was then applied to the ground inserts using the following chemical vapor deposition (CVD) techniques in the !5 following order of application: -15TABLE I Coating Coating Reactions Type Temperature Pressure TiC 982-1025eC —1 atm.H2 T1CL4CB, rf TiC, .+4HC1 4 4*- (s) TiCN 982-1025’C atm.H2 TiCl4+CH4+l/2N2 TiCN(s)+4HCl TIN 982-1050°C -~1 atm. TiCl4+2H2+l/2N2 Ti»(a)44HCl Processed along with the above inserts were inserts made from the same powder blend but without the TIN and its attendent Microstructural data obtained from the coated carbon addition. inserts are shown below: Porosity Cobalt Enriched Zone Thickness Solid Solption Depleted Zone Thickness TiC/Substrate Interface Eta Phase Thickness Coating Thickness TiC TICK TIN EXAMPLE NO. 2 EXAMPLE 1 EXAMPLE 1 without TiM with TIN Al Al, B2 (non-enriched bulk) Al (enriched) None —22.9 microns (rake face only) None —22.9 microns (rake face only) 4.6 microns *3.3 microns 5.6 microns 5.0 microns 2.3 microns 3.9 microns 1.0 microns 1.0 microns Green pill pressed inserts were fabricated according to Example 1 utilizing the Example 1 blends with and without the TIM and its attendent carbon additions. These inserts were sintered at 1496 degrees Centigrade for 30 minutes under a 25 micron vacuum and then cooled under ambient furnace conditions. They were then honed (0.064 ton radius), and subsequently TiC/TiCN/TiM CVD coated according to the techniques shown in -1610 Table I. In this example, it should be noted the cobalt enriched layer was present on both flank and rake faces. The coated inserts were substantially evaluated and the following results were obtained: EXAMPLE 2 EXAMPLE 2 without TIN with TiH Porosity A-l edges A-2 enriched zone A-3 center A-4 bulk Cobalt Enriched Zone Thick- Hone up to 22.9 microns ness Solid Solution Depleted Zone Hone partial and inter- Thickness mittent up to 21 microns TiC/Substrate Interface Eta up to 5.9 3.3 microns Phase Thickness microns Coating Thickness TiC 2.0 microns 1.3 microns TiCN 1.7 microns 1.0-microns TIN 8.8 microns 7,9 microns Average Rockwell A 91.2 91.4 Hardness (Bulk Material) Coercive Force, He 138 oersteds 134 oersteds EXAMPLE NO. 3 A mix comprising Che following materials was charged inCo a cylindrical mill, with a surfactant, fugitive binder, solvent and 114.kilograms of cycloids: fwc (2-2.5 micron particle size) 15,000 grams 85.15 w/o ή (WC (4-5 micron particle size) 27,575 grams 5.98 w/o TaC 2,990 grams 2.6 w/o TIN 1,300 grams 6.04 w/o Co 3,020 grams 0.23 w/o C (Ravin 410-a product of 115 grams Industrial Carbon Corp.) _ 50,000 grams The powder charge was balanced to produce 6.25 weight percent total carbon in the charge. The mix was blended and milled for 90,261 revolutions to obtain an average particle size of 0,90 microns. The blend was then wet screened, dried and -17hammer milled. Compacts were pressed and then sintered at 1454 degrees Centigrade for 30 minutes followed by cooling under ambient furnace conditions.

This treatment produced a sintered blank having an over5 all (i.e., measurement included bulk and binder enriched «J material) magnetic saturation of 117 to 121 gauss-cm /gm cobalt Microstructural evaluation of the sintered blank showed: eta phase to be present throughout the blank; porosity to be A-2 to B-3; the cobalt enriched zone thickness to be approximately 26.9 microns; and the solid solution depleted zone thickness to be approximately 31.4 microns.

EXAMPLE NO. 4 The following materials were added to a 190 na Inside -diameter by 194 am long mill jar lined with a tungsten carbide cobalt alloy. In addition, 17.3 kilograms of 3.2 mm tungsten carbide-cobalt cycloids were added to the jar. These materials were oiilled and blended together by rotating the mill jar about its cylindrical axis at 83 revolutions per minute for 72 hours (i.e,, 367,200 revolutions).

CHARGE COMPOSITION 283 grams ( 4.1 wt. X) TaC 205 grams ( 3.0 wt. X) NbC 105 grams ( 1.5 wt. X) TIN 7.91 grams ( 0.1 wt. X) C 381 grams (5.5 wt. X) Co 5946 grams (85.8 wt. X) WC 105 grams Sunoco 3420 14 grams Ethomeen S-15 2500 milli- liters Perchloroethylene -18This mix was balanced to produce a 2 w/o W - 98 w/oCo binder alloy. After milling and blending, the slurry was wet screened to remove oversized particles and contaminants, dried at 93 degrees Centigrade under a nitrogen atmosphere and then 5 hammer milled to break up agglomerates in a Fitzpatrick Co.

J-2 Fitzmill, Using this powder, compacts were pressed snd then sintered at 1454 degrees Centigrade for 30 minutes snd cooled under ambient conditions, The top and bottom (i.e., the rake faces) of the insert were then ground to final thickness. This was followed by a heat treatment at 1427 degrees Centigrade wider an 100 micron vacuum. After 60 minutes at temperature, the inserts were cooled at a rate of 56 degrees Centlgrade/hour to 1204 degrees Centigrade and then furnace cooled under ambient conditions.

The peripheral (or flank) surfaces were then ground to a 12.70 mm square and che insert cutting edges honed to a 0.064 nm radius.* These treatments resulted in an Insert substrate in which only Che rake faces had a cobalt enriched and solid solution depleted zone, these zones having been ground off the flank faces.

The inserts were then loaded into a coating reactor and coated with a thin layer of titanium carbide using the following chemical vapor deposition technique. The hot zone contain25 ing the inserts was first heated from room temperature to 900 degrees Centigrade. During this heating period, hydrogen gas was allowed to flow through the reactor at a cate of 11.55 -19liters per minute- The pressure within the reactor was maintained at slightly less than one atmosphere. The hot zone was then heated from 900 degrees Centigrade to 982 degrees Centigrade. During this second heat up stage, the reactor pressure was maintained at 180 torr. and a mixture o£ titanium tetrachloride and hydrogen, and pure hydrogen gas entered the reactor at flow rates of 15 liters per minute and 33 liters per minute, respectively, The mixtures of titanium tetrachloride and hydrogen gas was achieved by passing the hydrogen gas through a vaporizer holding the titanium tetrachloride at a temperature of 47 degrees Centigrade. Upon attaining 982 degrees Centigrade, methane was then allowed to also enter the reactor at a rate of 2.5 liters per minute. The pressure within the reactor was reduced to 140 torr. Under these conditions, the titanium tetrachloride reacts with the methane in the presence of hydrogen to produce titanium carbide on the hot Insert surface. These conditions were maintained for 75 minutes, after which the flow of titanium tetrachloride, hydrogen and methane was terminated. The reactor was then allowed to cool while Argon was being passed through the reactor at a flow rate of 1.53 liters per minute under slightly less than one atmosphere pressure.

Examination of the microstructure in the final insert revealed a cobalt enriched zone extending inwardly up to 22.9 microns and a cubic carbide solid solution depletion zone extending inwardly up to 19.7 microns from the substrate rake surfaces. The porosity in the enriched zone and the remainder of the substrate was estimated to be between A-l and A-2. 53544 EXAMPLE NO, 5 The material in this example was blended and milled using a two stage milling process with the following material charges: Stage I (489,600 revolutions) 141.6 grams ( 2.0 wt. %) TaH 136.4 grams ( 1.9 wt. %) TIN 220.9 grams ( 3.1 wt. X) NbC 134.3 grams ( 1.9 wt. %) TaC 422.6 grams ( 5.9 wt. %) Co 31.2 grams ( 0.4 wt. %) C 14 grams Ethomeen S-15 1500 milliliters Perchloroethylene Stage II (81,600 revolutions) (84.9 wt. %) 6098 140 1000 grams grams milliliters WC Sunoco 3420 Perchloroethylene This was balanced to produce a 2 w/o V - 98 w/o Co binder alloy.

The teat inserts were then fabricated and TIC coated in accordance and along with the test blanks described in Example No. 4.

Microstructural evaluation of the coated inserts revealed the porosity in the cobalt enriched as well as the bulk material to be A-l. The cobalt enriched zone and the solid solution depleted zone extended inward from the rake surface to depths of approximately 32.1 microns and 36 microns, respectively.

EXAMPLE NO. 6 The following materials were charged into a 190 mm inside diameter mill jar: 283 grams ( 4.1 w/o) TaC 205 grams ( 3.0 w/o) NbC 105 grams ( 1.5 w/o) Till 7.91 grams ( 0.1 w/o) C 381 grams ( 5.5 w/o) Co 5946 grams (85.8 w/o) wc 140 grams Sunoco 3420 14 grams Ethomeen S-15 2500 milliliters Perchloroethylene This mix was balanced to produce a 2 w/o W - 98 w/o Co binder alloy.

In addition, cycloids were added to the mill. The mixture was then milled for four days. The mix was dried in a sigma blender at 121 degrees Centigrade trader a partial vacuum, after which it was Fitzmilled through a 40 mesh sieve.

SNG433 inserts were then fabricated using the techniques described in Example 4. The inserts in this Example, however, were CVD coated with a TiC/TiN coating. The coating procedure used was as follows: 1. T-iC coating—The samples in the coating reactor were held at approximately 1026 to 1036 degrees Centigrade under a 125 torr vacuum. Hydrogen carrier gas flowed into a TiCl^ vaporizer at a rate of 44.73 liters/minute. The vaporizer was held at 33 to 35 degrees Centigrade under vacuum. TiCl^ vapor Was entrained in the carrier gas and carried into the coating reactor. Free hydrogen and free Methane flowed into the coating reactor at 19.88 and 3.98 liters/minute, respectively. These conditions were maintained for 100 minutes and produced a dense TiC coating adherently bonded to the substrace. 2. TIN coating—Methane flow into the reactor was discontinued and N2 was allowed into the reactor at a rate of -222.98 litera/mlnute. The*· condition* were maintained for 30 alnutee and produced a dense TIN coating adherently bonded to the TIC coating.

Evaluation of the coated Insert* produced the following results: Porosity Cobalt Enriched Zone Thicknese Solid Solution Depleted Zone Thickneae TiC/Substrate Interface Eta Phase Thicknese Coating Thickness TIC TIN A-l throughout 17.0 to 37.9 micron· up to 32.7 micron· up to 3.9 micron· 3.9 microns 2.6 microns IS Average Rockwell A Hardness of Bulk Coercive Force, He 91.0 oersteds EXAMPLE NO. 7 A 260 kg blend of powder, having carbon balanced to C3/C4 porosity in the final substrata, was fabricated using the following two stag· blending and milling procedure: STAGE I The following charge' composition was milled for hours: ,108 gtlQS TaC ( 6.08 w/o Carbon) 7,321 grams NbC (11.28 w/o Carbon) 3,987 grams TiN 1,100 grains C (Molocco Black—a produce of Industrial Carbon Corp.) 16,338 grama Co 300 grams EChoatan S-1S 364 STAGE 11 kilograms 4.8 nm Co-UC cycloids Naphtha Th* following was added co eha above blend, and Che mixtuza Billed foe an additional 12 hours: 221.73 kilograms WC ( 6.06 w/o Caxbon) 3.0 kilograms Sunoco 3420 Naphtha The final blend waa Chen wee screened, dried, and Fiex15 milled.

Insere blinks were Chen pressed end later sintered at 1434 degrees Centigrade for 30 oinutes. Thia sintering procedure produced a cobalt enriched zone overlying bulk oaterial having a C3/C4 porosity. The sintered blanks ware chan ground and hontd to SNG433 insert dimensions, resulting ia removal of the cobalt enriched zona.

The ainterad inserts were then packed with flake graphite inside of an open graphite canister. This assembly was than hot isostatically pressed (HIPed) at 1371 to 1377 degrees fl A Centigrade for one hour under a 8.76 x 10 dynas/cez amaosphere of 23 v/o and 73 v/o Ha. Microstruetural examination of a HIPed sample revealed that a cobalt enriched zona of approximately 19.7 microns in depth had been produced during HIPing. About 4 microns of surface cobalt and 2¼ surface of carbon were also produced due to the C type porosity substrate utilized. -24EXAMPIX NO, 8 λ bacch containing the following materials was ball allied: .0 w/o WC (1.97 micron average particle size) 750 kg 51.4 w/o WC (4.43 micron average particle size) 1286 kg 6.0 w/o Co 150 kg 5.0 w/o WC-T1C solid aolutioa carbide 124.5 kg 6.1 w/o TaWC solid solution carbide 152 kg 1.5 w/o W 37.5 kg This nix was charged to 6.00 w/o total carboa. Thasa materials were allied for 51,080 revolutions with 3409 kllogrns of cycloids sad 798 liters of naphtha. A final particle else of 0.82 microns waa produced.

Five thousand grans of powder were spile froa the blended and allied batch and tha following materials added to It: 1.9 w/o TIN (prsmllled to approximately 1.4 to 1.7 ailerons) 96.9 gm 0.2 w/o C (Ravia 410) 9.4 gm 1500 ml Ferchloroathyleae These materials wera then milled In a 190 aa Inside diameter tungsten carbide lined mill jar containing 50 volume percent cycloids (17.3 kg) for 16 hours. Upon completion of milling, the lot waa vet screened through a 400 aeeh screen, dried under partial vacuum in a sigma blender at 121 degreee Centigrade, and then Fitzmllled through a 40 mesh slave.

SNG433 blanks were pressed using a force of 3600 kilograms to produce a blank density of 8.24 gm/ce and a blank height of 5.84 to 6.10 ma.

The blanks were sintered at 1454 degrees Centigrade for 30 minutes on a NbC powder parting agent under a 10 to 25 micron vacuum and then allowed to furnace cool. The sintered samples -25had «inured dimensions of 4.93 ms x 13.31 sxs square, a density of 13.4 gm/cc and an overall magnetic saturation value of 146 co 130 gauss-cs?/ga Co, Microstrueeural evaluation of the samples shoved A porosity throughout end a cobalt enriched s layer approximately 21 microns thick.

The Cop and bottom of the inserts vara Chan ground to a total thickness of 4.73 ms. The inserts vara than heat treated at 1427 dagraas Centigrade for 60 minutes under a 100 micron vacuum cooled to 1204 dagraaa Centigrade at a rata of 36 degrees Candgrade/hour and then furnace cooled.

Tha flank faces of each insert vara ground to- a 12.70 on square and the edges honed co a 0.064 ms radius.

The inserts vara subsequently CTO coated with titanium caxbida/alusinuss oxide using tha folloving techniques.

The inserts vara placed in a coating reactor and haatad to approximately 1026 to 1030 dagraas Centigrade and held under an 88 to 123 toxz vacuum. Hydrogen gas ac a race of 44.73 Hears/ miauta was passed through a vaporizer containing TiCl^ ae 33 to 38 degrees Centigrade under vacuum. TiCl^ vapor was entrained in tha hydrogen and diractad into tha coating reactor.

Sinsilraneoualy, hydrogen and “methane vara flowing into tha reactor at rates of 19.88 and 2.98 liears/mlmita. These conditions of vacuum, temperature, and flow rata vara maintained for 180 minutes producing an adherent TiC coating on the inserts Hydrogen flow co the vaporizer and methane flow into the reactor were then terminated. Hydrogen and chlorine were nov allowed to flow to a generator containing aluminum particles at 380 to -2610 400 degrees Centigrade and O.S pal preseure. The hydrogen and chlorine flowed Into the generator at rates of 19.88 liter*/ minute and 0.8 to 1. Hear/minute, respectively. The chlorine reacted with the alumlnua co product A1C1.J vapor* which war· than directed Into the reactor. While the hydrogen and A1C 1^ wera flowing Into the reactor, COj at a rata of 0.5 litere/ minute vae also flowing Into the reactor. Thaia flow rates were maintained for 180 minuets during which time the Insert* were held at 1028 to 1028 degress Centigrade under a vacuum of approximately 88 eorr. This procedure produced a denee coating of AljOj adherently bonded co a TIC inner coating.

Evaluation of Cha coated lneart* produced the following results: Porosity Al In enriched zone, Al with scattered B In the bulk material Cobalt Enriched Zone Thick- approximately 39.3 microns nass (taka surface) Solid Solution Depleted Zona up to 43.2 micron* Thickness (rake surface) Coating Thickness .9 microns 2.0 microns 91.9 170 oersteds TIC Al2O3 Average Bulk Substrata Rockwell A Hardness Coercive Force, He EXAMPLE SO, 8 An additional 5000 grams material ware split from die Initial batch of material produced in Example t. Premilled TICK in the amount of 95.4 gram* (1.9 w/o) end 1.98 grams (.02 w/o) Ravin 410 carbon black wara added co this materiel, mixed for 16 hours, screened, dried, and Fitzmllled, as per Example 8. -27Test pieces were pill pressed, vacuum sintered ae 1496 degrees Centigrade Cor 30 minutes, sad Chen Cumae* cooled at Cha ambient furnace cooling rata. samples produced the following Porosity Cobalt Enriched Zone Thickness Solid Solution Depleted Zone Thickness Average Bulk Substrate Rockwell A Hardness Magnetic Saturation Coercive Force (He) Evaluation of the sintered results: A-l throughout approximately 14.8 microns up to 19.7 microns 92.4 130 gauss-cm^/go Co 230 oersteds EXAMPLE KO, 10 An additional 5000 grams of material were split from the initial batch mada in Example 8. Freoilled TiCl? in the amount of 95.4 grams (1.9 w/o) was added, mixed for 16 hours, screened, dried and Fitzmilled as per Example 8. Test pieces were than pressed and alntarad at 1496 degress Centigrade with the Example 10 test places.

Evaluation of the alntarad samples produced the following results.· Porosity Cobalt Enriched Zone Thickness Solid Solution Depleted' Zona Thlcknasa Average Bulk Rockwall A Hardness Magnetic Saturation Coercive Force, He EXAMPLE HO. li Al, with heavy eta phase throughout approximately 12.5 microns up to 16.4 microns 92.7 120 gauss-cm /gm Co 260 oersteds The following mix was charged using the two stags milling cycle outlined below: -28throughout and a solid eolutlon depletion zona ehickneea of approximately 25.8 microns.

Subeequently, Cha (ample was reprepared and examined by energy dispersive x-ray lint scan analysis (EDX) ac various S distances from the rake surface. Figure 3 ahowa a graphical representation of the variation of nickel, tungsten, titanium and tantalum relative concentrations as a function of distance from the rake surface of the temple. It can ba dearly seen that there is a layer near the surface in which the titanium and tantalum, forming carbides which arc in solid solution with tungsten carbide, are at least partially depleted. Thia solid aolutlon depleted sone extends inwardly approximately 70 microns. The discrepancy between this value and eha value reported above are believed' to be due to the fact thee the sample was reprepared between evaluations io that different planet through the samples were examined in each evaluation.

Corresponding with the titanium and tantalus depletion la an enriched layer of nickel (eee Figure 3. The nickel concentration in the enriched layer decraaaea at the distance from the rake surface decreaaea from 30 to 10 mlerona. Thia indicates that the nickel in this zona wae partially volatilized during vacuum a in caring. .

The (pike in titanium and tantalus concentration se 110 microns is believed to be duetto the scanning of a random lug· grain or grains having a high concentration of these elements. -29The following materials were added co a 181 ns Inside dissieter by 194 am long WC-Co lined mill Jac with 17.3 kg of 4.6 cm WC-Co cycloids. The mill Jac was rotated about Its cylindrical axis at 83 revolutions pec minute for 48 hours (244,800 revolutions). 455 grass ( 6.5 wt. X) Hl 280 grass ( 4.0 wt. X) TsH 112 grass ( 1.6 wt. X) TIN 266 grass ( 3.8 vt. X) HbH 42.7 grass ( 0.6 vt. X) Carbon 14.0 grass Hthomssn S-13 1500 milliliters Perehloroethylene Stage II The following were then added to the mill jar and rotated an additional 18 hours (81,600 revolutions): 5890 grams (83.6 wt. X) WC 105 grams Sunoco 3420 1000 milliliters Farchloroechylane This mix was balanced to produce a 10 w/o V - 90' w/o Hi binder alloy. After discharging the mix slurry from the mill Jar, it was wet screened through a 400 swsh sieve (Tylar), dried at 93 degrees Centigrade under a nitrogen atmosphere, and Fitzmilled through a 40 mesh sieve.

Test samples vara pill pressed, sintered at 1430 degrees Centigrade for 30 minutes*under a 6.9 x 10^ dynes/ca2 nitrogen atmosphere, and then furnace cooled at the ambient furnace cooling race. Following sintering, the samples wars HIFsd at 1370 degress Centigrade for 60 minutes In a 1 x 10® dynes/ca^ helium atmosphere. Optical metallographic evaluation of the HIPed samples showed the material to have A-3 porosity -30The two parallel horizontal llnee ehow the typical scatter obtained in analysis of the bulk portion of the semple around the nominal bland chemistry.

EXAMPLE SO. 1¾ The following mix was charged using the two stage milling cycle outlined below: Stage I The following materials were milled per Stage I of Example 12: 455 grams ( 6.4 w/o) Ml 280 grams ( 3.9 w/o) TaH 112 grams ( 1.6 w/o) TIN 266 grams ( 3.7 w/o) MbH 61.6 grams ( 0.9 w/o) C Ravin 410, 502 14 grams Ethomeen S-15 2500 mlllllltsrs Perchloroethylene ££!£*-££ The following were then added to the mill Jar and rotated an additional 16 hours: 5960 grams (83.6 v/o) WC 140 grams Sunoco 3420 This mix was balanced to produce 10 w/o W - 90 w/o Ml binder alloy.

After discharging the mix, It was screened, dried and Fitzmllled per Example 12.

Pressed test samples were vacuum sintered at 1466 degrees Centigrade for 30 minutes under a 35 micron atmosphere. The sintered samples had an A-3 porosity throughout end a solid solution depletion zone up to 13.1 microns thick. -31- .

EXAMPLE HO. 13 A batch of material having a competition equivalent to the Example a batch was blended, milled and pressed Into Insert blanks. Tha blanks vara then sintered, ground, heat treated and ground (flank faces only) In substantial accordance with tha procedures used in Example a . However, a 69 degrees Centigrade/ hour cooling rata was used In the final heat treataenc.

An Insert was analyzed by EDX line scan analysis st various distances from the insert raka surfaces. Tha results of thia analysis is shown in the Figure 2 graph. It indicates Che existence of a cobalt enriched layer extending Inwardly from tha rake surfaces to a depth ot approximately 23 microns followed by a layer of material partially depleted in cobalt extending inwardly to approximately 90 microns from tha rake IS surfaces. While not shown In the Figure 2 graph, partial solid solution depletion has bean found in the cobalt enriched layer and solid solution enrichment has been found in Che partially depleted cobalt layer.

Tha two horizontal lines indicate the typical 'scatter in analysis of tha bulk material around the nominal bland chemistry Tha preceding description and detailed examples have been provided co illuatrace some of the possible alloys, products, processes and uses that art within the scope of this invention as defined by Che following claims.

Claims (12)

1. CtAIMS

1. A proc·»» for producing a body of tungsten carbide cemented with a metallic binder material, aaid process comprising the steps of compacting a powder mixture of tungsten carbide, eaid binder material, and a cheaical agent selected froa nitrides and carbonitrides of transition aetala whose carbides have a free energy of formation more negative than that of tungsten carbide at a temperature above the melting point of the binder material, denelfying the compact so formed, and sintering said densifled compact et a liquid-phase sintering temperature, said chemical agent being transformed during said sintering step or during a subsequent heat treatment into m second carbide in solid solution with said tungsten carbide, thereby to increase the content of aaid binder alloy material near a peripheral surface of said body.

2. A procaaa aa claimed in Claim 1 in which aaid cemented tungatan carbide body is of substantially A type porosity, in which aaid compact comprises powders of tungsten carbide, cobalt and a natal compound selected froa the nitrides and carbonitrides of Group IVB and VB transition matala, milled and blended together.

3. A proeeea as claimed in Claim 2' wherein said powdera further comprise a second carbide powder selected from IVB and VB metal carbides and their -33eolld solutions in an amount aubatantially lees than said tungsten carbide.

4. A proceaa according to Claim 2 or Claim 3 further 5 comprising the step of at least partially velatixing nitrogen during the sintering step.

5. A process according to any one of Claims 2 to 4 further comprising the addition of free carbon during aaid milling and blending. 10

6. A proceaa according to any one of the preceding Claims further coaprieing the step of removing said binder enriched layer in selected areas of said body.

7. A process according to Claim 6 further comprising the step of depositing on aaid peripheral surface 15 an adherent hard wear resistant refractory coating having one or more layers.

8. A process according to Claim 7 wherein the material eoapriaing the or each layer is selected froa the group consisting of the carbides, borides, 20 nitrides and carbonitrides of titanium, zirconium, hafnium niobium, tantalum and vanadium, and the oxide and oxynitride of aluminium.

9. A process according to any one of the preceding Claims wherein aaid binder material is selected froa 25 the group consisting of cobalt, nickel, iron and their alloys. 53544 -3410. A process according to any one of tha preceding Claims wherein eald chealcel agent la tltenlua nitride.

10. 11. A proceas for producing a eeaented tungaten carbide body substantially as hereinbefore deacrlbed with 5 reference to, and ae illustrated in, the aeeoapanylng diagraaaatic drawings or aa described with reference to any of the Exaaplee.

11.

12. A eeaented tungsten carbide body produced by a proeeee ae claimed in any one of Cleiae 1 to 11.