CA2156828A1

CA2156828A1 - Complex multi-phase reaction sintered hard and wear resistant materials

Info

Publication number: CA2156828A1
Application number: CA002156828A
Authority: CA
Inventors: Ellen M. Dubensky; Edward E. Timm; Julie L. Board; Ann Marie Mccombs
Original assignee: Individual
Current assignee: Dow Chemical Co
Priority date: 1993-03-18
Filing date: 1993-03-18
Publication date: 1994-09-29

Abstract

A powdered admixture of a boron, carbon, nitrogen or silicon derivative of a first metal is combined with at least one other reactant that is selected from (a) a boron, carbon, nitrogen or silicon derivative of a second metal wherein the derivative differs from that of the first metal, (b) a source of a second metal and a source of a third metal, or (c) a source of the second metal and a densification promoting amount of an iron group metal, subjected to densification (heat and pressure), partially reacted and converted to a hard, wear resistant material. The wear resistant material contains an amount of the first metal derivative as well as at least one material of varying stoichiometry that is the partial reaction product. The material may also contains residual unreacted portions of components other than the first metal derivative. Articles formed from this material can be useful in wear resistant applications.

Description

~ 2 8 WO 94121574 PCTtUS93/02443 COMPLEX MULTI-PHASE REACTION SINTERED HARD AND
WEAR RESISTANT MATERIALS.
Technical Field This invention generally concerns a product prepared from an incomplete reaction of a mixture of a boron, carbon, nitrogen or silicon derivative of a fi rst metal, a source 5 of a second metal, an iron group metal or a source of a third metal, and, optionally, boron, carbon, nitrogen or silicon. This invention also concerns a process for preparing such products.
This invention further concerns wear resistant articles formed from such materials.
Backaround Art Tungsten carbide cemented with cobalt is a material of widely known util ity for10 useincuttingtoolsandinotherapplicationsrequiringhighhardness. Forexample,tungsten carbide/cobalt is used in abrasive waterjet cutting nozzles. Unfortunately, cobalt is a strategic material. As such, its price and availability can be subject to political factors. These considerations, among others, provide a basis for many long standing programs aimed at finding replacements for tungsten carbide/cobalt.
Itwould bedesirabletohaveoneormorenonstrategicmaterialswhichwould provide improvements in terms of hardness over tungsten carbide/cobalt, but at a lower cost than diamond. It would also be desirable to have a process which allowed production of complex, near net shapes which cannot be made by casting molten carbides or by hot pressing.
Disclosure of Invention One aspect of the present i nvention is a material suitable for use i n fabricati ng articles of manufacture requiring high degrees of hardness or wear resistance that comprises a substantially fully dense, complex, multi-phase, fine grained product of an incomplete reaction among components of a powdered admixture of AX, an optional amount of X and at least one other reactant that is selected from (a) BY, (b) a source of B and a source of C, or (c) a source of 25 B and a densification promoting amount of E, AX and the other reactant(s) each having a melting point, the incomplete reaction taking place under pressure and at an elevated temperature that is less than about three fourths of the lowest of the melting points of AX and the other reactant(s), said product having minimal grain growth and containing at least one compound AX and at least one compound that is a product of varying stoichiometry selected 30 from (A, B)XY, (A, B)X and (A, B)Y when the selection of other reactant(s) is (a), (A, B, C)X, (A, B)X, (A, C)X and (B, C)X when the selection of other reactant(s) is (b), and (A, B, E)X when the selection of other reactant(s) is (c), wherein A and B are different materials selected from titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, X and Y are different materials selected from boron, carbon, silicon and nitrogen, E is 35 selected from iron, cobalt and nickel.
If the other reactant is (c), the incomplete reaction product desirably contains no residual E. In other words, the amount of E is desirably less than that which would leave a WO 94/21574 ~ l ~ 6~ g PCTIUS93/02443 residual ad~nl~*e~-v~it~ fhe compound (A, B, E)X. The reaction product may, however, contain an amount of the source of B if it is not completely consumed in forming the compound(s) (A, B, E)X.
If the other reactant is (b), the source of B, the source of C or both may not be 5 chemically identical with AX. In other words, the source of B could be BY wherein BY is as defined herein. The source of C could also be CY, where Y is as defined herein, or CZ where Z is selected from the same group as X and Y, but is different from either X or Y. The foregoing list of products of varying stoichiometry is readily expanded where the source of B is BY or the source of C is either CY or CZ.
A second aspect of the present invention is a method of prepari ng a material suitable for use in fabricating articles of manufacture requiring high degrees of hardness or wear resistance that comprises subjecting a powdered admixture of AX, an optional amount of X and at least one other reactant that is selected from (a) BY, (b) a source of B and a source of C, or (c) a source of B and a densification promoting amount of E, AX and the other reactant(s) each having a melting point, to a temperature that is less than about three fourths of the lowest of the melti ng poi nts of AX and the other reactant(s) and a pressure sufficient to produce a substantially fully dense, consolidated product of an incomplete reaction between AX, the other reactant(s) and, optionally, X, said product having minimal grain growth and comprising at least one compound AX and at least one compound that is a product of varying 20 stoichiometry selected from (A, B)XY, (A, B)X and (A, B)Y when the selection of other reactant(s) is (a), (A, B, C)X, (A, B)X, (A, C)X and (B, C)X when the selection of other reactant(s) is (b), and (A, B, E)X when the selection of other reactant(s) is (c), wl1erei n A and B are different materials selected from titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, X and Y are different materials selected from boron, 25 carbon, silicon and nitrogen, E is selected from iron, cobalt and nickel. The comments fol I owi ng the fi rst aspect al so appl y to the second aspect.
The term ndensification promoting amount" of an element means that amount which will result in substantial Iy complete densification of the product of an incomplete reaction between AX and a source of B at a temperature which is less than that at which said 30 product is densified i n the absence of the element with substantially no degradation of hardness and wear properties of the resultant densified product.
It is believed that temperatures in excess of three fourths of the lowest melting point lead to excessive grain growth and drive the reaction toward a complete reaction of AX
with the other reactant(s). These results are believed to be undesirable. The consolidated 35 product suitably has a Vickers hardness of at least about 1900 kg/mm2 measured using a 1 kg load. The Vickers hardness is beneficial Iy at least about 2200 kg/nnm2. The process may further comprise one or more preliminary steps such as forming the powdered admixture of AX and ~ 2~828 the other reactant(s), and converting the admixture into a shaped greenware article. The process may also comprise one or more finishing steps subsequent to densification.
The materials of the first aspect may be used to form wear resistant articles.
Suitable wear resistant articles include: nozzles such as waterjet cutting nozzles or mixing 5 tubes, abrasive blast nozzies, water blast nozzles, spray dry nozzles, and paint spray nozzles;
orifices such as choke valves and flow meter parts; bushings; pump and valve parts; ti les, `` sleeves, chutes, tubes and other parts used in handling abrasive materials such as coal or mineral slurries; cutting tools such as indexable inserts, end mills, router bits, reamers, drills, saw blades, and knives used, where appropriate, for machining or cutting materials such as 10 metals, plastics, wood products and composites; dies, capstans, rollers, guides, punches, forming tools and other tools used for wire drawing, tube drawing, extrusion, molding, textile manufacturing and other operations requiring hardness or wear resistance; powdercompacting dies; EDM current contacts and guides; sporting equipment; and precision parts for timepieces, computers, guns, and gyroscopes. This listi ng of suitable appl ications is solely 15 for purposes of illustration and is not intended to be a definitive listing of all potential applications. Other uses should be readily apparent without undue experimentation.
Detailed Description The present invention employs a material AX wherein A is selected from titanium,zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten and 20 X is selected from boron, carbon, sil icon and nitrogen. A is beneficial Iy tungsten, hafni um or titanium, desirably tungsten or hafnium and preferably tungsten. X is beneficially carbon, silicon or nitrogen, desirably carbon. As such, tungsten carbide (wC) is a prefel .ed, commercially available material. The WC has an average grain size which is suitably about ten ~lm or less, beneficially about five llm or less, desirably about one llm or less and preferably 25 fromO.4toO.811m. Thegrainsizeisdesirablyasfineaspossible. Suchasizeisnotalways commercially available. As such, the commercially available powders may have to be used as is or, if possible, reduced in size by attrition or another suitable process. Acceptable grain sizes for other materials of the formula AX approximate those for tungsten carbide and are readily determined without undue experimentation. The material AX is preferably in powder or 30 particulate form.
In one aspect of the present invention, the presence of an iron group metal, designated herein as " EN, is a necessary component of at least a portion of the incomplete reaction product. In other words, the incomplete reaction product has varying stoichiometry and is generically represented by formula (A, B, E)X. E is an element selected from the group 35 consisting of iron, cobalt and nickel. E is preferably cobalt.
A densification promoting amount of E provides satisfactory results. The amount must be sufficiently high to promote substantially complete densification of the product of the incomplete reaction. It also must be sufficiently low to substantially preclude its presence as an WO 94/21574 ~ PCT/US93102443 unreacted material in the densified product. It is desirably low enough to minimize, preferably eliminate, use of E as a binder metal in the sense of a traditional cobalt bound tungsten carbide hard metal. The amount is suitably from 0.01 to 2.0 percent by weight (\~vt-%), based upon the combined weight of A, B and X.
Densification beneficial Iy occurs at a temperature that is 1 00C or more lowerthan that needed in the absence of E. In addition, such densification desirably accompanies mai ntenance of hardness and wear properties equivalent to those obtai ned at said higher temperature. The actual temperature needed for densification and the effect of E vary with choices for A, B, E and X. By way of illustration composites wherein AX is tungsten carbide and 10 the source of B is Mo2C can be consol idated to near theoretical density at temperatures as low as 1 400C in the absence of E and at lower temperatures with an appropriate amount of E.
Substituti ng Cr3C2 for Mo2C increases the te,. ,pe. d lure for consolidation to theoretical density to tem peratures in excess of 1 500C. Use of the densification promoti ng amount of E lowers the consol idation temperature to 1 400C or even lower and avoids pitfalls such as excessive grain growth.
In other aspects of the present invention, addition of one or more auxiliary or binding metals, such as those of the iron group, while permissible provided they do not adversely affect physical ,orope, lies of resultant compositions, is believed to be unnecessary.
Although cobalt is not an essential component, inadvertent addition of trace amounts is 20 believed to be unavoidable if milling or attritor media used to form powdered mixtures contain an amount of cobalt. Cobalt, in particular, aids in forming mixed carbides which may lower densification temperatures to about 1 400C or lower, depending upon the composition.
However, cobalt is not believed to be essential for complete densification. One need only use higher temperatures in the absence of cobalt to approach or achieve complete densification.
The present invention also employs a source of B. B, like A, is selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten. B is not, however, the same as A. In other words, when A is tungsten, B may be any of the aforementioned materials other than tungsten. Certai n aspects of the present invention favor choices of B which differ from those of other aspects. When the 30 reactants are AX and a source of B, or AX, a source of B and E, B is beneficially molybdenum, vanadium, zirconium, chromium, and, when A is not tungsten, tungsten. B is desirably molybdenum or chromium, and preferably molybdenum. When the source of B is BY, B is desirablytitanium. When the reactants are AX, a source of B, a source of C and, optionally, an amount of X, the source of B is beneficially chromium carbide or titanium carbide. The source 35 of B is preferably in powder or particulate form.
The source of B includes the aforementioned metals as well as the boron, carbon,silicon and nitrogen derivatives thereof. Other than the aspect wherein the source of B is BY, derivatives of B, where used, are desirably chemically consistent with AX. That is, if X is carbon, WO 94/21574 21~ 6 ~ 2 8 PCT/US93/02443 the source of B is desirably a carbide or subcarbide of B. By way of illustration, sources of molybdenum include molybdenum metal, molybdenum carbide (MoC), and molybdenum subcarbide (Mo2C). If B is an elemental powder, such as molybdenum metal, one may, if so desired, add an amount of X, carbon in this instance, which is desirably less than or equal to 5 that amount needed to equate stoichiometrically with other sources of molybdenum such as MoC and Mo2C. Addition of more than a stoichiometric equivalent, while possible, may leave residual unreacted X, carbon in this instance, which, in turn, may adversely affect physical properties, such as Vickers Hardness, of resultant densified materials.
A preferred source of molybdenum isthe subcarbide Mo2C. Mo2C is believed to 10 serve asa source of both molybdenum and carbon for preparation of the mixed carbides. A
suitable, but less prefe, red, source of molybdenum is molybdenum metal. Another suitable, but even less preferred, source of molybdenum is molybdenum carbide (MoC). Combinations of two or more sources of molybdenum also provide satisfactory results. The molybdenum source is preferably in powder or particulate form.
The source of B is beneficially employed in an amount sufficient to allow the formation of at least one compound of varyi ng stoichiometry. Depending upon components of the incomplete reaction, the compound will be (A, B)X, (A, B)Y, (A, B)XY, (A, B, E)X, (A, B, E)Y, (A, C)X, (B, C)X or (A, B, C)X, wherein A, B, C, E, X and Y are as defined herein. The amount is desirably sufficient to form said compound(s) without providing such a large residuum that 20 physical properties or performance of the reaction product are degraded enough to cause the reaction product to have no practical utility. The amount is also desirably less than that which would fully react all of AX. Such amounts vary depending upon the source of B, but are readily determined without undue experimentation.
By way of illustration, the source of B, when B is molybdenum, is beneficially 25 employed in an amount sufficient to allow the formation of at least one tungsten-molybdenum mixed carbide. The molybdenum source is desirably employed in an amount sufficient to provide the final composition with a molybdenum content of about one weight percent or more. When the molybdenum source is Mo2C, the amount is suitably from one to 30, desirably from three to 20, and preferably from six to 10, wt-%, based upon the 30 weight of the total amount of Mo2C and WC starting materials.
When the source of B is BY, Y differs from X, but is selected from the same group as X. By way of illustration, when X is carbon and Y is nitrogen the incomplete reaction product may be a carbonitride such as (W, Mo)CN.
The present invention, in one aspect, also includes a source of C. C is selected35 from the same group of elements as A and B provided, however, that A, B and C are al I
different elements. Like B, the source of C may be an elemental material or a boron, carbon, silicon or nitrogen derivative thereof. For some applications, the source of C is desirably chemically consistent with AX and the source of B. In other words, X is carbon and the sources 2~ ~828 of B and C are both metal carbides. For other applications, the source of C need not be consistent with AX, the source of B or both. As such, the source of C may be CY or CZ
depending upon whether i~ is to differ chemically only from AX or both AX and BY. The source of C is also desirably in the form of a powder. It is employed in an amount of sufficient to form 5 at least one compound (A, B, C)X without an excessively large residue of unreacted material. In other words, some residual source of C may be present without substantial Iy reduci ng desirable properties of resultant materials. Other compounds, such as (A, B)X, (A, C)X and (B, C)X, may be formed concurrently with formation of the compound (A, B, C)X. An amount is considered excessively large if it degrades physical properties such as hardness to a point where the 10 resultantmaterial hasnopractical utility.
The process of the present invention suitably comprises subjecting a powdered admixture of reactants to densification conditions sufficient to produce a consolidated product of an incomplete reaction between or among the reactants. The product comprises at least one compound AX and at least one compound of varying stoichiometry. The latter compound is generically represented as (A, B)X, (A, B)Y, (A, B)XY, (A, B, E)X, (A, C)X, (B, C)X or (A, B, C)X
depending upon selection of components for said powdered admixture. The variables A, B, C, E, X and Y are as defined herein. Incorporation of Z by way of CZ expands the list of compounds of varying stoichiometry to include compounds such as (A, B, C)XY and (A, B, C)XYZ. The densification conditions are selected to minimize grain growth and include a 20 temperature which is less than about three fourths of the lesser of the melting points of AX and the remaining components of the admixture other than E, but greater than a temperature at which no appreciable consolidation occurs. The temperature may exceed the melting point of E where an iron group metal such as cobalt is present. A temperature in excess of the melting point of E is not, however, always necessary or even desirable. The conditions also include a 25 pressure sufficient to achieve a desirable degree of densification. The reaction product is preferably substantially fully dense.
As used herein, the terms "incomplete reaction", "incomplete reaction product"
and "product(s) of an incomplete reaction" all refer to the reaction of AX with the other components of the powdered admixture wherein at least a portion of AX does not react with 30 said other components. As a consequence, that portion is admixed with the incomplete reaction product(s) (compound(s) of varying stoichiometry) and, optionally, a small amount of the other components in products prepared in accordance with various aspects of the present invention.
When A is tungsten, B is molybdenum and X is carbon, the densification 35 conditions are beneficially sufficient to produce a material having a Vickers hardness, measured using a 1 kg load, of at least about 2200 kg/mm2. The Vickers hardness is desirably more than about 2300 kg/mm2 and preferably more than about 2400 kg/mm2. Lower Vickers hardness values of 1900 kg/mm2 or less, are readily attainable if the material isto be used in applications WO 94/21574 2 ~ 5 6 8 2 8 PCT/US93/02443 wherein the higher hardness values are not needed. One means of attaining such lower values is to select molybdenum metal as the molybdenum source.
When elements other than tungsten, molybdenum and carbon are substituted, respectively, for A, B and X, om~vhen the source of B is BY or when one or more of reactants E
5 and C are employed, the resultant densified materials can provide Vickers hardness values as lowasabout 1000 kg/mm2. Thewearresistance of a 1000 kg/mm2 Vickers hardness material should, however, be much lower than that of a 2400 kg/mm2 Vickers hardness material.
Because of chemical compatibility or other reasons, the lower hardness materials may, however, still show exceptional utility in certain applications.
The powdered admixture may be prepared by any one of a number of conventional mixing processes so long as a generally uniform admixture is obtained and no adverse effects upon physical properties of the resultant material are observed. The use of an attritor, wherein balls of hard material are used to facilitate mixing, provides particularly satisfactoryresultsevenifsmall portionsoftheballs,typicallyformedfromatungsten carbide/cobalt material, are abraded therefrom during mixing and added to the admixture.
The presence of a minor amount of cobalt in reaction products or final materials does not adversely affect the physical properties of the densified material. The use of balls formed from the same material as that being mixed. If E is included as a reactant, the amount of cobalt added via abrasion of the attritor or mulli ng media may, if desired, result i n reduction of the 20 amount of E added as an element.
The starting materials, AX, the source of B, the source of C, E and, optionally an amount of X, are beneficially in particulate or powder form before they are converted to an admixture. It is believed that small particles offer more advantages than large particles, at least in terms of hardness, wear and residual unreacted starting materials. Small particles, as a 25 general rule, also require less mixing time than large particles. As such, the powders desirably have an average particle size of less than about 2 llm. Based upon factors such as availabi I ity, larger particle sizes may have to be used as received or, if necessary, subjected to size reduction operations before use.
Mixing of the powders in an attritor is beneficially accomplished with the aid of a 30 liquid such as heptane. In order to facilitate greenware formation subsequent to mixing, a binder such as paraffin wax can be added during the final stages of attrition. Desirably, the attrited mixture is dried before further processing. Particularly satisfactory results are obtained by screening or classifying the attrited and dried mixture to remove unwanted agglomerates and fines.
The process of the present invention may also comprise a second preliminary stepwherein the attrited, dried and classified mixture is converted to a preform. Preforms can be prepared using technology known in the powder metals or ceramics industries. U.S. Patent WO 94/21574 PCTIIlS93/02443 i 2 ~ 8 4,446,100 and Modern Ceramic Enqineerinq, Chapter 6, pages 178-215 (1982) describe such technology.
A typical procedure for converting a particulate material, which can contain oneor more of reinforcements, fillers, densification aids, binders, lubricants, dispersants and 5 flocculants, into a preform begins by forming or shaping the powder into a desired configuration using uniaxial pressing, isostatic pressing, slip casting, extrusion, injection moldingoranysimilartechnology. Theresultingarticleisthenpreparedfordensificationby thermal or chemical debindering, pre-sintering, green machining, re-isopressing, and the like.
A protective coating can be applied to the resulting article to prevent reaction with the 10 environment. In extreme cases, the article can be "canned", or placed in an impervious container, to permit handling without atmospheric contamination. The resulting article, as prepared for densification, is referred to herein as "greenware".
When B is molybdenum, densification is suitably conducted at a temperature of less than about 1 600C. Temperatures i n excess of 1 600C, such as 1 650C, offer no appreciable advantages in terms of an increase in density. Such temperatures do, however, provide a significant disadvantage in that they promote grain growth which is believed to adversely affect performance of the densified material i n practical considerations I i ke hardness.
Temperatures which are too low to achieve adequate densification are unacceptable. It is believed that adequate densification cannot be achieved much below about one-half the 20 melting temperature of the molybdenum source. Of the three preferred molybdenum sources, molybdenum metal, Mo2C and MoC, molybdenum metal has the lowest melting point at2617C. As such, a reasonable lowertemperature limitfordensification isabout 1300C. In the absence of a densification aid such as an iron group metal, densification at temperatures as low as1300Crequiresoptimumconditions. Suchconditionsincludeveryfineandwellmixed 25 powders. The range of tem peratu res for densificati on i s desi ra bl y from 1 350C to 1 500C.
Temperature ranges for other combinations of AX and other reactants are readily determined without undue experimentation.
The greenware is subjected to pressure assisted densification using one of several techniques known to those skilled in the art wherebythe greenware is desirably subjected to 30 pressure at elevated temperatures to produce a desired article. These techniques include hot pressing, hot isostatic pressing (HlP'ing) and rapid omnidirection31 compaction (ROC).
Although any of these techniques may be used with varying degrees of success, particularly suitableresultsareobtainedbytheROCtechniquewhichemploysmechanicallyinduced pressure, e.g., that generated by using a forging press, as a means of densifying greenware.
A desirable method of converting the greenware into a satisfactory densified article is described in U.S. Patent 4,744,943 at column 5, line 13 through column 6, line 33 and column 7, line 21 through column 10, line 40. When such a method is employed, the pressure is suitably applied for a period of time of less than about one hour. The period of time is WO 94/21~74 215 6 8 2 8 PCT/US93/02443 preferably less than about 30 minutes, desirably less than about one mi nute and preferably less than about 30 seconds. In order to facilitate recovery of resultant densified parts, the greenware is beneficially wrapped in graphite foil or some other substantially inert material priortobeingplacedinaglasspocketfluiddieorotherdensificationmedium.
U . S. Patent 4,081,272 discloses a glass-encapsulated H IP process. U . S. Patent 3,622,313 discloses a HIP process. If the glass-encapsulated process is used, a desirable modification includes evacuating the glass capsule containing a part to be densified and eliminating the use of powdered glass. Application of pressure suitably occurs over a period of one hour or less.
The densified article prepared in the manner described hereinabove is a complex,multi-phase, fine-grained composite containing, as principal components, at least one compound of varying stoichiometry and at least one compound AX. The compound of varying stoichiometrywill have a composition which reflectsthe choice of reactants. In otherwords, it will be represented as (A, B, E)X, (A, B)X or both where the reactants are AX, a source of B and E; as (A, B)XY, (A, B)X, (A, B)Y or mixtures thereof where the reactants are AX and BY; and as (A, B, C)X, (A, B)X, (A, C)X, (B, C)X or mixtures thereof where the reactants are AX and sources of B and C. If the reactants are AX, BX and CY or AX, BY and CZ, the compounds of varying stoichiometry wi ll be represented by variations of the foregoi ng. By way of i l l ustration, when A istungsten, B is molybdenum and X is carbon, the reaction productwill contain tungsten 20 carbide and at least one mixed carbide of tungsten and molybdenum (W, Mo)C. If the source of B and, where appropriate, E or the source of C, are not fully converted to the compound of varying stoichiometry, the reaction product will also contain an amount of the source of B and, where appropriate, the source of C. The amount may vary from as little as a trace amount (about 0.01 wt-% or less) to much larger quantities depending upon a variety of interrelated 25 variables. Such variables include starting material selection, adequacy of mixing, and densification parameters. Finally, if an attritor is used for mixing and the balls contained therei n are formed at least partially from a material other than the starti ng materials, such as cobalt, that material may be incorporated into the composite as, for example, part of an additional mixed carbide phase.
The densified article exhibits surprisingly improved hardness and wear resistance in comparison to a like article formed from tungsten carbide/cobalt. The Vickers hardness of an article representative of the present invention is suitably at least about 220û kg/mm2 measured using a 1 kg load. The Vickers hardness is beneficially at least about 2300 kg/mm2, and desirably at least about 2400 kg/mm2. As noted hereinabove, lower Vickers hardness vaiues on 35 the order of 1900 kg/mm2 or even lower may be acceptable for some appl ications. Also as noted hereinabove, those hardness values are readily attainable with the process of the present invention. The article wherein A in tungsten, B is molybdenum and X is carbon suitably exhibits an abrasion wear resistance of at least about 500 cm-3 measured by the ASTM G65-80 method.
g WO 94t21574 $~ PCT/US93/02443 The abrasion wear resistance is desirably at least about 550 cm-3. The article beneficially exhibits an erosion wear rate of no more than about 3X10 3 mm3/g of abrasive measured at a 30 degree angle measured by the ASTM G76-83 method. The article desirably exhibits an erosion wear rate of no more than about 2X10-3 mm3/g of abrasive measured at a 90 degree angle 5 measured by the ASTM G76-83 method. Although lower wear rates would clearly be desirable, measurement of such rates with currently available equipment is quite difficult, if not impossible. Skilled artisans will recognize that hardness and wear resistance vary depending upon the materials represented by A, B, X and where appropriate, C, E and Y. Skilled artisans will recognize that wear resistance is proportional to hardness and that softer materials may 10 provide an abrasion wear resistance below 500 cm 3. These materials may be suitable in extreme temperatures or in chemically aggressive environments.
The densified article suitably has a fine-grained structure with an average grain size of less than about 10 llm. The grain size is beneficially less than about five ~m and desirably less than about one llm.
The articles of this invention generally have a density of about 85 /0 of theoretical density or greater. The density is beneficially more than about 90 %, desirably more than about 95 % and preferably about 100 % of theoretical density. "Theoretical density", as used herein, is a calculated value based upon volume fraction and density of the starting components. "High density", as used herein, refers to a density of at least about 90 % of 20 theoretical density. Another measure of adequate densification is porosity of the articles of this invention. The porosity is suitably minimized to attain optimum hardness. As such, the porosity is beneficial Iy less than about 5 /0 percent by volume (vol-% ), based upon total article volume. The porosity is desirably less than about 3 vol-% and preferably less than about 1 vol-%. As used herein, the term "substantially fully dense" means either a density of 99 % or 25 more of theoretical density or a porosity of less than about 1 vol-% . The material of the i nvention is particularly useful for the fabrication of cutti ng tools and nozzl es, such as waterjet cutting nozzles.
SPecific Embodiments of the Invention The following examples and comparative experiments illustrate the present 30 invention and should not be construed, by implication or otherwise, as limiting its scope. All parts and percenlages are by weight and al I temperatures are i n centigrade (C) unless otherwise indicated. Examples of the present invention are designated by Arabic numerals whereas comparative examples are identified by capital letters.
Example 1 - Preparation of Densified material Usinq Tunqsten Carbide as AX and Titanium 35 Nitride as BY
The starting powderwas a mixture of 96.4 % tungsten carbide powder (average particle size of 0.8 ~m) and 3.6 percent titanium nitride (average particle size of about 1.5 llm).
The mixture was attrited, in the presence of heptane, for four hours with a 7 kilogram (kg) load WO 94/21S74 ~15 6 8 2 ~ PCT/US93/02443 of tungsten carbide-cobalt (WC-Co) balls. About 2-3 percent paraffin wax was added as a binder during the last thirty minutes of attritor mixing.
The resultant mixture was dried and screened through a 20 mesh (850 ~m) screen.
Greenware parts were made by cold-pressing the mixture which passed through the screen in steel tooling at 5,000 pounds per square inch (psi) (35 MPa). The cold-pressed parts were then cold isostatically pressed at30,000 psi (210 MPa). The resultant partswere dewaxed under vacuum at 350C. The greenware was then wrapped in graphite foil (GRAPHOIL~ from Union Carbide), placed i nto a glass pocket fl uid die, or isostatic d ie assembly, preheated i n a nitrogen atmosphere to 1650C at a rate of 10C/minute, held at that temperature for 15 minutes, and 10 then isostatically pressed at 120,000 psi (830 MPa) for 10 seconds. The pressing procedure is described in more detail in U.S. Patents 4,744,943 at column 5, line 34 through col umn 6, line 15 and column 9, line 51 through column 10, line 3; 4,428,906 at column 4, line 61 through column 6, line 32; and 4,656,002 at column 4, line 41 through column 5, line 6. The fluid die was cooled in air and the parts were recovered and sand blasted. The parts weighed 25 grams (9) and were cyl i ndrical i n shape havi ng a d iameter of 1.85 cm and a length of 1.19 cm.
Analytical work involved the use of metallography, light microscopy, analytical scanning electron microscopy (ASEM), electron probe analysis (EPA), analytical transmission electron microscopy (ATEM), and x-ray diffraction (XRD). Microstructures were observed under the SEM, ATEM, and light microscopes. Determination of the presence of a reaction phase 20 made use of XRD. Composition of the reaction phase was determined by EPA and ATEM.
Volume fraction of phases was determined by stereology of BSE images, and grain counting in ATEM. The parts were also subjected to Vickers Hot Hardness testing in accordance with the procedure described by B. North in Enqineerinq Applications of Brittle Materials, page 159 (1985). Thetestingusedaonekgloadandatensecondindenttimeatvarioustemperatures.
Physical properties of recovered parts were as follows: a) density - 14.54g/cm3 (99.7 percent of theoretical); b) Hardness, Rockwell A - 95.6; c) Vickers hardness - 2602 kg/mm2;
and d) Palmqvist toughness - 23.9 kg/mm. The recovered parts had a hot hardness, measured as i n Example 1, of 10.74 G Pa at 1200C.
Examples 2-4 - Preparation of Densified material Usinq Tunqsten Carbide as AX and Titanium 30 Nitride as BY
The process of Example 1 was, save for using a smallerattritorwith a 3.5 kg loadof WC/Co balls, increasing the preheat temperature to 1800C and the time at pressure to 30 seconds and varying the pressure and time at pressure as shown in Table 1, replicated for Examples 2-4. The density, Hardness, Rockwell A, Porosity (ASTM B-276-79) and Vickers 35 hardness are also shown in Table 1.

~,~5~

Table I Physical Properties of Examples 2-4 Exam- Pres- Density Hardness Vickers Poros ple sure Denslty % Theor- Rockwell Hardlness it No. (MPa) (9/~)etical A (kg/mm2) Y
2 828 14.66 100.6 95.1 2450 A04 3 414 14.69 100.8 95.0 2374 A04 4 207 14.69 100.8 94.9 2393 A06, Examples 5-6 - Preparation of Densified Material Usinq Tunqsten Carbide as AX and Tantalum Nitride as BY
The process of Example 1 was, save for changing the composition to a mixture of 5 89.6percentofthesametungstencarbideasin Example l and 10.4percenttantalum nitride (average particle size of about 1 llm) and varying the preheat temperature as shown in Table ll, replicated for Examples 5 and 6. The density, Hardness, Rockwell A and Vickers hardness are also shown in Table ll.
Table ll Physical Properties of Examples 5-6 2~

Exam- Preheat Density Hardness Vickers ple Temper Denslty/O Theor- ROckwell HardneSs No. ( C) etical A (kg/mm2) 2 5 1650 15.70100 95.1 2425 6 1800 15.74100.3 94.6 2270 Similar results are expected with titanium nitride and tantalum nitride contentsrangingfrom 1 to50percent,preheattemperaturesof 1400Cto2000Candvariationsintime at pressure as well as pressure level. Similar results are also expected with other combinations of materialssuchashafniumcarbidewithtitaniumnitride,zirconiumnitrideortantalum nitride and tungsten carbide with zirconium nitride.
Example 7 - Preparation of Densified Material Usinq Tunqsten Carbide as AX, Dimolybdenum Carbide as the Source of B and Trichromium Dicarbide as the Source of C.
The process of Example 1 was duplicated, save for lowering the preheat temperature to 1400C and using a powdered admixture containing 94.7 percent of the same WO 94t21574 ~ 8 2 8 PCT~S93/02~3 tungsten carbide as in Example 1, 3.1 percent dimolybdenum carbide (MozC) (average particle size of 211m) and 2.2 percent chromium carbide (Cr3Cz) (average particle size of less than about 48 llm). Physical properties of recovered parts are shown in Table lll.
Examples 8-9 Preparation of Densified Material Usinq Tunclsten Carbide as AX, Titanium 5 Carbide as a Source of B and Tantalum Carbide as a Source of C.
The process of Example 7 was replicated, save for using the same attritor as in Example 2, varying the preheat temperature as shown in Table lll, for a powdered admixture containi ng 93.6 % of the same tungsten carbide as in Example 1, 1.6 %titani um carbide (TiC) (average particle size of 3.8 ~lm) and 4.8 % tantalum carbide (TaC) (average particle size of 2 10 ,um). Physical properties of recovered parts are shown in Table lll together with the physical properties measured for Example 7.
Table lll Physical Properties of Examples 7-9 and Comparative Example T
E l Preheat D 0 Hardness Vickers Palmqvist xNOP e Temper- TheenOsrty /al Rockwell Hardness Toughness ature C I A(kg/mm2) (kg/mm2) 7 1400 96.3 95.32420 22.6 8 1 650 97.7 95.52494 22.4 9 1800 97.7 94.5 2243 ------ not measured The data presented in Table lll support several observations. First, the preheattemperatures needed to attain high density varies with the composition as shown in Examples 25 7 and 8. Second, an increase in preheat temperature may not provide any substantial gain in physical prope, lies. See Examples 8 and 9. Similar results are expected with other combinations of A, B, C and X, all of which are disclosed herein. The addition of one or other materials from the list common to A, B and C should also produce acceptable results. The densified materials, like others disclosed herein, are expected to provide satisfactory results in a 30 variety of high wear applications such as nozzles, metal-forming dies and cutting tools.
Examples 10-12 - PreParation of l:~ensified Material Usinq Tunqsten Carbide asAX, Cr~C~ asthe Source of B and Cobalt or Nickel as E
The process of Example l was replicated save for using the smaller attritor described in Example 2, modifying the attritor mixing schedule by adding E halfway through 35 the schedule rather than at its beginning and varying the preheat temperature for a variety of compositions, all of which are shown in Table IV together with relevant physical properties.

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_ _ - l 4-WO 94/21574 ~ .S ~ 8 PCT/US93/02443 The data presented in Table IV substantiate the utility of adding an amount of an iron group metal. The preheattemperature can be lowered significantlywithoutappreciable, if any, loss of physical properties. Similar results are expected with other variations of A, B, E
and X, all of which are disclosed herein.
The materials of the present invention are, as noted hereinabove, useful in a wide variety of end use applications where wear resistance or hardness or both are needed. The J materials are particularly useful in nozzles, such as sand blast nozzles and waterjet cutting nozzles, wear guides, bushings, powder compacting dies, valve parts, router bits, cutting tools, end mills, indexable inserts, wire drawing die parts and the like.

Claims

1. A material suitable for use in fabricating articles of manufacture requiring high degrees of hardness or wear resistance that comprises a substantially fully dense, complex, multi-phase, fine grained product of an incomplete reaction among components of a powdered admixture of AX, an optional amount of X and at least one other reactant that is selected from (a) BY, (b) a source of B and a source of C, or (c) a source of B and a densification promoting amount of E such that its presence as an unreacted material in the densified product is substantially precluded, AX and the other reactant(s) each having a melting point, the incomplete reaction taking place under pressure and at an elevated temperature that is less than about three fourths of the lowest of the melting points of AX and the other reactant(s), said product having minimal grain growth and containing at least one compound AX and at least one compound that is a product of varying stoichiometry selected from (A, B)XY, (A, B)X
and (A, B)Y when the selection of other reactant(s) is (a), (A, B, C)X, (A, B)X, (A, C)X and (B, C)X
when the selection of other reactant(s) is (b), and (A, B, E)X when the selection of other reactant(s) is (c), wherein A, B, C, X and Y are different materials; A is an element selected from titanium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten; B and C are an element or a material containing an element selected from vanadium, titanium, niobium, tantalum, chromium, molybdenum and tungsten with the proviso that titanium is not titanium carbonitride and molybdenum is not metallic molybdenum or an alloy thereof; X and Y are selected from boron, carbon, silicon, and nitrogen; E is selected from iron, cobalt and nickel.

2. A material as claimed in Claim 1 wherein the other reactant is a source of B
and a source of C, AX is tungsten carbide and the sources of B and C are, respectively, chromium carbide and molybdenum carbide or titanium carbide and tantalum carbide.

3. A material as claimed in Claim 1 wherein the other reactant is a source of B
and a densification promoting amount of E, A is tungsten, B is chromium or molybdenum and E
is cobalt.

4. A material as claimed in Claim 1 or Claim 3 having a Vickers hardness of at least about 2000 kg/mm2 measured using a 1 kg load, and an abrasion wear resistance (ASTM
G65) of at least about 400 cm-3.

5. A material as claimed in Claim 1 wherein the other reactant is BY, A is tungsten or titanium, B is titanium or tantalum, X is carbon and Y is nitrogen.

6. A material as claimed in Claim 5 wherein the reaction product also contains a residual amount of unreacted BY.

7. A material as claimed in Claim 5 or Claim 6 wherein BY is present in an amount of from 1 to 50 percent by weight based upon total weight of AX and BY.

8. A material as claimed in Claim 7 having a hardness of 1200°C of greater than about 5 gigapascals.

9. A method of preparing a material suitable for use in fabricating articles of manufacture requiring high degrees of hardness or wear resistance that comprises subjecting a powdered admixture of AX, an optional amount of X and at least one other reactant that is selected from (a) BY, (b) a source of B and a source of C, or (c) a source of B and a densification promoting amount of E such that its presence as an unreacted material in the densified product is substantially precluded, AX and the other reactant(s) each having a melting point, to a temperature that is less than about three fourths of the lowest of the melting points of AX and the other reactant(s) and a pressure sufficient to produce a substantially fully dense, consolidated product of an incomplete reaction between AX, the other reactant(s) and, optionally, X, said product having minimal grain growth and comprising at least one compound AX and at least one compound that is a product of varying stoichiometry selected from (A, B)XY, (A, B)X and (A, B)Y when the selection of other reactant(s) is (a), (A, B, C)X, (A, B)X, (A, C)X and (B, C)X when the selection of other reactant(s) is (b), and (A, B, E)X when the selection of other reactant(s) is (c), wherein A, B, C, X and Y are different materials; A is an element selected from titanium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten; B and C are an element or a material containing an element selected from vanadium, titanium, niobium, tantalum, chromium, molybdenum and tungsten with the proviso that titanium is not titanium carbonitride and molybdenum is not metallic molybdenum or an alloy thereof; X and Y are selected from boron, carbon, silicon, and nitrogen; E is selected from iron, cobalt and nickel.

10. A method as claimed in Claim 9 wherein the other reactant is a source of B
and a source of C, AX is tungsten carbide and the sources of B and C are, respectively, dimolybdenum carbide and trichromium dicarbide or titanium carbide and tantalum carbide.

11. A method as claimed in Claim 9 wherein the other reactant is (c) a source ofB and a densification promoting amount of E, A is tungsten, B is chromium or molybdenum and E is cobalt.

12. A method as claimed in Claim 11 wherein the admixture is heated to a temperature of less than about 1600°C prior to densification.

13. A method as claimed in Claim 11 or Claim 12 wherein the amount of E is from about 0.01 to about 2.0 percent by weight, based upon powdered admixture weight.

14. A method as claimed in Claim 9 wherein the other reactant is BY, A is tungsten or titanium, B is titanium or tantalum, X is carbon and Y is nitrogen.

15. A method as claimed in Claim 14 wherein the powdered admixture containing BY in an amount which is from about 1 to about 50 percent by weight based upon total weight of AX and BY.

16. A wear resistant article fabricated from the material of any of Claims 1-8.

17. A material suitable for use in fabricating articles of manufacture requiringhigh degrees of hardness or wear resistance that comprises a substantially fully dense, complex, multi-phase, fine grained product of an incomplete reaction among components of a powdered admixture of AX, an optional amount of X, a source of B and a source of C, AX and the other reactant(s) each having a melting point, the incomplete reaction taking place under pressure and at an elevated temperature that is less than about three fourths of the lowest of the melting points of AX and the other reactant(s), said product having minimal grain growth and containing at least one compound AX and at least one compound that is a product of varying stoichiometry selected from (A, B, C)X, (A, B)X, (A, C)X and (B, C)X wherein A, B, C, X are different materials ;A is an element selected from titanium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten; B and C are an element or a material containing an element selected from vanadium, titanium, niobium, tantalum, chromium, molybdenum and tungsten with the proviso that titanium is not titanium carbonitride and molybdenum is not metallic molybdenum or an alloy thereof; X is selected from boron, carbon, silicon, and nitrogen.

18. A material suitable for use in fabricating articles of manufacture requiringhigh degrees of hardness or wear resistance that comprises a substantially fully dense, complex, multi-phase, fine grained product of an incomplete reaction among components of a powdered admixture of AX, an optional amount of X, BY, AX and the other reactant(s) each having a melting point, the incomplete reaction taking place under pressure and at an elevated temperature that is less than about three fourths of the lowest of the melting points of AX and the other reactant(s), said product having minimal grain growth and containing at least one compound AX and at least one compound that is a product of varying stoichiometry selected from (A, B)XY, (A, B)X and (A, B)Y, wherein A, B, X and Y are different materials; A is an element selected from titanium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten; B is an element or a material containing an element selected from vanadium, titanium, niobium, tantalum, chromium, molybdenum and tungsten with the proviso that titanium is not titanium carbonitride; X and Y are selected from boron, silicon, and nitrogen.

19. A material suitable for use in fabricating articles of manufacture requiringhigh degrees of hardness or wear resistance that comprises a substantially fully dense, complex, multi-phase, fine grained product of an incomplete reaction among components of a powdered admixture of AX, an optional amount of X and at least one other reactant that is selected from a source of B and a densification promoting amount of E such that its presence as an unreacted material in the densified product is substantially precluded, AX and the other reactant(s) each having a melting point, the incomplete reaction taking place under pressure and at an elevated temperature that is less than about three fourths of the lowest of the melting points of AX and the other reactant(s), said product having minimal grain growth and containing at least one compound AX and at least one compound that is a product of varying stoichiometry selected from (A, B, E)X, wherein A, B, E and X are different materials; A is an element selected from titanium, zirconium, hafnium, vanadium, niobium, tantalum,chromium, molybdenum and tungsten; B is an element or a material containing an element selected from titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, with the proviso that molybdenum is not metallic molybdenum or an alioy thereof; X is selected from boron, carbon, silicon, and nitrogen; E is selected from iron, cobalt and nickel.