US3929424A

US3929424A - Infiltration of refractory metal base materials

Info

Publication number: US3929424A
Application number: US408606A
Authority: US
Inventors: Richard H Krock; Jerome J Pickett
Original assignee: PR Mallory and Co Inc
Current assignee: Duracell Inc USA
Priority date: 1973-10-23
Filing date: 1973-10-23
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30
Also published as: GB1449978A; DE2450361A1; JPS5083210A

Abstract

This invention relates to a heavy metal body of a refractory metal containing material with a matrix of refractory metal containing alloy and to a method of making the same. The refractory metal containing material is preferably tungsten. The refractory metal containing alloy preferably includes molybdenum and a metal selected from the group consisting of iron, nickel, copper, cobalt, chromium, and mixtures thereof. The method of making the body includes the step of filling voids of a sintered refractory metal containing material skeleton, such as tungsten, with a molten alloy, such as a molybdenum-iron-nickel molten alloy. The resultant body has a fine grain particle size of refractory metal containing material of approximately the same particle size as the refractory metal containing material had before formation of the body, good ductility, negligible interaction between the alloy matrix and refractory metal containing material, and the skeleton experiences no harmful shrinkage during processing.

Description

iinited States Patent Krock et a1.

[451 Dec. 30, 1975 [54] INFILTRATION 0F REFRACTORY METAL BASE MATERIALS [75] Inventors: Richard H. Krock, Weston; Jerome J. Pickett, Bedford, both of Mass.

[73] Assignee: P. R. Mallory & (30., Inc.,

Indianapolis, Ind.

[22] Filed: Oct. 23, 1973 [21] Appl. No.: 408,606

[52] US. Cl. 29/182.1; 75/200 [51] Int. CL 1322!? 1/00 [58] Field of Search 29/1821; 75/200 [56] References Cited UNITED STATES PATENTS 3,305,324 2/1967 Krock et al. 29/182.l 3,338,687 8/1967 29/1821 3,340,022 9/1967 Zdanuk 29/182.1 3,353,933 11/1967 Zdanuk et a1... 29/182.1 3,368,879 2/1968 Krock et al. 29/182.l 3,384,464 5/1968 Krock et al.. 29/182.1 3,407,048 10/1968 Krock et a1. 29/1821 3,440,043 4/1969 Zdanuk et a1... 29/182.1 3,505,065 4/1970 Gwyn.... 29/l82.l

Primary ExaminerRichard D. Lovering Assistant Examiner--B. Hunt Attorney, Agent, or FirmCharles W. Hoffmann; Robert F. Meyer; Donald W. Hanson [57] ABSTRACT This invention relates to a heavy metal body of a refractory metal containing material with a matrix of refractory metal containing alloy and to a method of making the same. The refractory metal containing material is preferably tungsten. The refractory metal containing alloy preferably includes molybdenum and a metal selected from the group consisting of iron, nickel, copper, cobalt, chromium, and mixtures thereof. The method of making the body includes the step of filling voids of a sintered refractory metal con taining material skeleton, such as tungsten, with a molten alloy, such as a molybdenum-iron-nickel molten alloy. The resultant body has a fine grain particle size of refractory metal containing material of approximately the same particle size as the refractory metal containing material had before formation of the body, good ductility, negligible interaction between the alloy matrix and refractory metal containing material, and the skeleton experiences no harmful shrinkage during processing.

US. Patent Dec. 30, 1975 INFILTRATION OF REFRACTORY METAL BASE MATERIALS The present invention relates to metallurgy and more particularly to improved refractory metal containing materials and to a method for making the same.

Heavy refractory metal containing bodies have usefulness in operations where high density or high temperature resistant materials are required. These bodies also have good mechanical properties such as high tensile strength, impact value, resistance to fracture under the application of a bending stress and low thermal coefficients of expansion. The bodies are used, for example, in aircraft counterbalances, radiation shielding, gyroscope inertia members, and high temperatures tooling components such as die casting dies. When used in tooling operations, these bodies tend to minimize the problems normally associated with hot worked sheets such as problems of thermal fatigue, heat checking, low hot hardness, soldering and oxidation.

Refractory metal containing bodies have a good combination of thermal and mechanical properties when produced by a liquid phase sintering process as compared with production by conventional melting and casting techniques. Liquid phase sintering (such as described in US. Pat. No. 2,793,95 l) is a method utilizing powder metallurgy techniques wherein powders such as refractory metal powders with lower melting point metal powders which form an alloy, are formed into the desired body shape. During the heating step in liquid phase sintering, the molten alloy dissolves an appreciable quantity of the refractory metal particles. It is believed that the portion of the refractory metal thus dissolved is reprecipitated on undissolved refractory metal particles. This results in growth of grains of the main constituent (the refractory metal) and the reduction or substantial elimination of voids in the skeleton by the formation of a matrix in the interstices between the grains of the refractory metal.

However, a drawback of the liquid phase sintering process is the harmful shrinkage which tends to occur as a result of sintering of some shapes or bodies. Although simple shapes, such as square or round shapes, can be made relatively easily, complex shapes such as die cavities can only be produced by extensive machining of the shapes. The problem of shrinkage, recognized in U.S. Pat. Nos. 2,916,809 and 2,922,721, results in the need for complex calculations to compensate for shrinkage and for good control of processing parameters to produce bodies within design tolerances, and, therefore, results in greater processing costs to yield the desired product.

It is, therefore, a primary feature of the present invention to provide heavy refractory metal containing bodies exhibiting a finer grain structure than heavy refractory metal containing bodies typically produced by a liquid phase sintering process. Another feature of the invention is to provide heavy refractory metal containing bodies with a ductility of about the same order of magnitude as heavy refractory metal containing bodies produced by a liquid phase sintering process. Another feature of the present invention is to utilize infiltration techniques in a method for the production of heavy refractory metal containing bodies. It is also a feature of the invention to hold shrinkage of the body to a minimum during production processing of heavy refractory metal containing bodies and to hold to a minimum the amount of machining required to produce the finished heavy refractory metal containing body. It is another feature of the present invention to produce refractory metal containing bodies experiencing negligible interaction between the refractory metal containing material and the alloy matrix. Other features will be apparent from the following description and the appended claims. In the drawings:

FIG. 1 is a 4l0X photomicrograph of a tungsten base body with an alloy matrix of molybdenum, iron and nickel produced by a liquid phase sintering process; and

FIG. 2 is a 4l0X photomicrograph ofa tungsten base body with an alloy matrix of molybdenum, iron and nickel produced by the process of this invention.

The bodies of the present invention are composed of a refractory metal containing material as the major constituent, and an alloy matrix of a refractory metal and a metal or metals selected from the group of iron, nickel, copper, cobalt, and chromium. To be effective for high temperature use, the body should include at least wt.% of the refractory metal containing material. The refractory metal containing material of the invention need not be a pure elemental metal but can be in association with another element or elements or contain amounts of impurities which do not significantly affect properties of the heavy metal body. Carbides of the refractory metals are an example of refractory metal containing materials which are not pure metals that can be used in providing the metal body.

Generally, the method of making the heavy metal body comprises the steps of forming a porous sintered skeleton of refractory metal containing material, filling voids of the skeleton with a molten alloy containing a refractory metal, and then solidifying the molten alloy to provide the desired body. In the process, the refractory metal containing alloy matrix does not dissolve significant amounts of the refractory metal containing skeleton as might normally be expected, and, therefore, the resultant body has a finer grain structure than that of bodies produced by a liquid phase sinter process. An important advantage is realized in that shrinkage is reduced significantly over liquid phase sintering thus allowing easier fabrication of complex body shapes. It is believed that the refractory metal present (such as molybdenum) in the infiltrant inhibits, to a significant degree, the dissolution of the refractory metal (such as tungsten) of the skeleton by the infiltrant. Although the mechanism by which such inhibition is accomplished is not understood, it is, perhaps, by saturation of the molten infiltrant alloy by the already present refractory metal (such as molybdenum).

More specifically, a compact of a refractory metal containing skeleton, such as tungsten, is formed by conventional powder metallurgy techniques so as to have a density range of about 55 to about 70 vol.% of theoretical density. A density of below about 55 vol.% of theoretical usually yields a tungsten compact of insufficent mechanical strength to support itself or to withstand handling. Compacts having densities above about 70 vol.% are difficult and costly to obtain in relation to their value. In forming the porous skeleton, a suitable mold is utilized to form the refractory metal containing particles into the desired shape. The size of the particles of refractory metal containing material of the compact may vary in accordance with the desired density of the finished body and with the desired pore size distribution in the skeleton. Choice of the particles size of the compact also affects the final grain size of the body as the size remains approximately the same throughout the processing steps. A usual average particle size for the particles of the compact is about 1 to about 10 microns. Compacting pressures or methods of compacting can also be varied to yield different compact densities. A typical compacting pressure for 10 micron tungsten powder is about 10 tsi.

The compact of refractory metal containing material is presintered from about l000 to about l900C to provide a skeleton. The skeleton and the refractory metal containing alloy, prepared by a separate melting operation, are placed in close proximity. The combination is preheated to about IOOO to about 1200C and then raised to normal sintering temperature, from about l350 to about l600C. At these temperatures, the refractory metal containing alloy melts and flows into the skeleton to fill void spaces of the skeleton yielding a body with an alloy matrix substantially surrounding the sintered particles of the refractory metal containing material. Temperatures associated with infiltration step are not critical and infiltration can be accomplished over a fairly wide temperature range. Presintering temperatures can also be used to control, to a degree, the porosity of the refractory metal skeleton. The infiltration step may take place in either a nonoxidizing atmosphere, such as hydrogen gas, or in a vacuum. After cooling, excess infiltrant, if any, is removed from the body.

The resultant body experiences negligible shrinkage from the initial dimensions of the porous skeleton and little, if any, distortion of the contour of the skeleton is observed. The finished body includes a refractory metal containing skeleton surrounded by the refractory metal containing alloy matrix with void spaces of the skeleton filled by the alloy matrix. Examination of the grain structure reveals that there is negligible interaction between the refractory metal containing particles of the skeleton and the alloy matrix since the grain size of the skeleton particles remains approximately the same as the refractory metal containing particles from which the skeleton is formed, much smaller than the grain size that is associated with liquid phase sintering of similar materials. Ductility and other properties of bodies formed by the method of the present invention and by liquid phase sintering remain approximately the same however.

Referring now to FIG. 1 of the drawing, a photomicrograph of 410 magnifications, a liquid phase sintered body of refractory metal containing material particles ll, tungsten particles, with an alloy matrix 12 of molybdenum-iron-nickel is shown. Note the large globule-like appearance of the tungsten particles 11. The globules of tungsten 1 1 are due to the interaction of the liquid phase (not shown) and refractory metal particles. The matrix alloy is in a weight ratio of 2 parts molybdenum to 1 part iron to 2 parts nickel. The tungsten is 90 wt.% of the total wt. of the body 10. In contrast, FIG. 2, a photomicrograph of4l0 magnifications, shows a body with a grain-like structure of tungsten particles 21 which experience little, if any, interaction between it and the infiltrant (an alloy 21 of molybdenum-iron-nickel in a 2:1:2 wt. ratio) during processing. The tungsten grains 21 of the body 20 are substantially surrounded by the matrix 22 of the refractory metal containing alloy infiltrant. The tungsten is about 75% by weight of the body 20. A comparison of the grain structures of body 10 of FIG. 1 and that of body 20 of FIG. 2 would seem to indicate that the body 10 would be significantly more ductile than body 20 as the grain structure is much more rounded in body 10. Surprisingly enough, such is not the case however, as the ductilities of the two bodies are of about the same order of magnitude.

The initial average tungsten particle size of the bodies shown in FIGS. 1 and 2 is substantially the same. The process used to make the body shown in FIG. 2 results in an average tungsten particle size substantially the same as the initial average tungsten particle size, whereas the process used to make the body shown in FIG. 1 results in an average tungsten particle size much greater than the initial tungsten average particle size.

Preferably the invention is utilized by employing tungsten particles as the material for the skeleton, as tungsten apparently functions better in the invention than other refractory metal containing materials. More preferably, tungsten is about to about 83 wt.% of the total wt. of the body, and the refractory metal contain ing matrix is molybdenum, iron and nickel preferably in a weight ratio of about 2:112, respectively. The weight percent of molybdenum and nickel in the resultant body is preferably about 6.8 wt.% to about 10 wt.% for each and for iron in the resultant body is about 3.4 wt.% to about 5 wt.%.

The following EXAMPLES are illustrative of the preparation of fine grained refractory metal containing bodies.

EXAMPLE I A sintered tungsten skeleton is infiltrated with an alloy of about 40 wt.% molybdenum, about 20 wt.% iron and about 40 wt.% nickel to provide a body consisting essentially of about 75 wt.% W, about 10 wt.% Mo, about 5 wt.% Fe, and about 10 wt.% Ni.

A porous tungsten mass is compacted at about 10 tsi from tungsten particles having an average particle size of about 3 to about 5 microns. The compact is presintered in hydrogen gas for about 4 hours at a temperature of about l460C to provide a skeleton. The density of the tungsten skeleton is about 58.5 vol.% theoretical. An infiltrant alloy of Mo-Fe-Ni in a wt. ratio of 221:2, respectively, is prepared by induction melting. The required quantity of infiltrant, plus 15% volume excess is placed on the porous tungsten skeleton. The combination of infiltrant and skeleton is preheated to about ll0OC for about 1 hour in hydrogen gas and then heated to about l460C for about one-half hour in hydrogen gas to complete filling of voids of the skeleton with infiltrant and then cooled. Excess infiltrant is removed. The body is sound and exhibits negligible shrinkage and distortion. The body exhibits the following properties.

Density 14.7 g/cm Hardness R 36 2% yield strength ll9 ksi Ultimate tensile strength ksi Elongation 2.4%

The body has a fine grain structure as illustrated in FIG. 2.

EXAMPLE 11 A sintered tungsten skeleton is infiltrated with an alloy of about 40 wt.% tungsten, about 20 wt.% iron, and about 40 wt.% nickel to provide a body consisting essentially of about 89.8 wt.% W, about 3.4 wt.% Fe and about 6.8 wt.% Ni.

A porous tungsten mass is compacted at about tsi from tungsten particles having an average particle size of about 3 to 5 microns. The compact is presintered in hydrogen for 4 hours at a temperature of about 1480C. The density of the porous skeleton is about 68% theoretical by volume. An infiltrant of W-Fe-Ni in a wt. ratio of about 2:1:2 respectively is prepared by melting and is placed on the top of the skeleton with a volume excess. The skeleton is infiltrated by the infiltrant by preheating to about 1100C for about 1 hour in hydrogen gas and then heating to about 1450C for about one-half hour in hydrogen gas. After the body is cooled, excess infiltrant is removed.

EXAMPLE III A sintered molybdenum skeleton is infiltrated with an alloy of about 40% molybdenum, about 40 wt.% nickel and about wt.% iron to provide a body consisting essentially of about 85 wt.% Mo, about 10 wt.% Ni and about 5 wt.% Fe.

A porous molybdenum mass is compacted at about 12 tsi from molybdenum particles having an average particle size of about 4 to 6 microns. The compact is presintered at about 1480C for about 4 hours. The infiltrant alloy of Mo-Ni-Fe in a wt. ratio of about 222:] respectively is prepared by induction melting and then placed on top of the porous skeleton. The infiltrant and the porous skeleton are preheated to about 1000C for about 1 hour in hydrogen gas and then heated to about 1450C for about a half hour in hydrogen gas to infiltrate the voids of the skeleton and then cooled. Excess infiltrant is then machined from the body.

EXAMPLE IV A sintered tungsten skeleton is infiltrated with an alloy of about 28.5 wt.% molybdenum, about 28.5 wt.% copper, about 28.5 wt.% nickel and about 14.5 wt.% iron to provide a body consisting essentially of 83 wt.% W, about 4.86 wt.% Mo, about 4.86 wt.% Cu, about 4.86 wt.% Ni and about 2.42 wt.% Fe.

The operational steps and parameters are the same as in Example 1 except the infiltrant alloy is of a different composition and the skeleton is of a different density.

EXAMPLE V A sintered tungsten skeleton is infiltrated with an alloy of about wt.% molybdenum, about 40 wt.%

- cobalt and about 20 wt.% iron to provide a body connsisting essentially of about 75 wt.% W, about 10 wt.% Mo, about 10 wt.% Co and about 5 wt.% Fe.

The operational steps and parameters are the same as in Example I except the infiltrant alloy is of a different composition.

Refractory metal is used here in the metallurgical sense to mean the group consisting of tantalum, molybdenum and tungsten.

Skeleton as used in this disclosure means a structure capable of supporting its own weight with interconnected void spaces throughout its volume.

Matrix is a substance or material in which another substance or material is embedded.

The presence of small amounts of impurity elements is not believed to play a critical role in the invention. It

should be understoodthat it is contemplated that minor amounts of other elements can be added to the skeleton material or to the matrix material or both and such practices are considered to be with the invention herein described.

The present invention is not intended to be limited to the disclosure herein, and changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention. Such modifications and variations are considered to be within the purview and the scope of the present invention and the appended claims.

We claim:

1. A body including refractory metal containing particles and a metal containing matrix, the refractory metal containing particles having an average particle size substantially equal to the average particle size of the refractory metal containing particles prior to the formation of the body, the body comprising as major weight constituent, refractory metal containing particles, the refractory metal selected from the group consisting of tantalum, molybdenum and tungsten and as the minor weight constituent, a metal containing matrix including a refractory metal selected from the group consisting of tantalum, molybdenum and tungsten and a metal selected from the group consisting of Ni, Fe, Co, Cu, Cr and combinations thereof.

2. A body according to claim 1, wherein the refractory metal containing particles are tungsten particles, preferably from -83 percent by weight.

3. A body according to claim 2, wherein the refractory metal of the metal containing matrix is molybdenum, preferably 40 wt.% of the matrix, and the other metals of the matrix are iron and nickel, preferably 20 wt.% and 40 wt.% of the matrix respectively.

4. A method of making a body as claimed in claim 1, the body including refractory metal containing particles in a metal containing matrix, the method comprising the steps of a. forming a porous shape of joined refractory metal containing particles,

b. filling voids of the shape with a molten metal containing matrix material in such a manner that the average particle size of the refractory metal containing particles after filling voids with the molten matrix material is substantially the same as the average size of the refractory metal containing material prior to filling voids with the molten matrix material, the molten metal containing matrix material including a refractory metal and a metal selected from the group consisting of Ni, Fe, Co, Cu, Cr or combinations thereof, and

c. solidifying the molten alloy to provide the body.

5. A method as claimed in claim 4, wherein the filling of the voids of the shape with the molten metal containing matrix material is done by infiltration.

6. A method as claimed in claim 4, wherein the step of forming the porous shape of joined refractory metal containing particles includes pressing of the particles.

7.'A method as claimed in claim 4, wherein the step of forming the porous shape of joined refractory metal containing particles includes sintering of the particles.

8. A method as claimed in claim 4, wherein the refractory metal containing particles are tungsten particles and the molten metal containing matrix is molybdenum, nickel and iron, preferably in the weight ratio of 2:2:1 respectively.

9. A body according to claim 3, wherein the tungsten particles are pressed and sintered, infiltrated with an alloy of molybdenum, iron and nickel and then cooled.

UNITE!) siieirEs Pr-kIEN-T OFFICE CERTIFECATE 0F (ZORRECTION PATENT NO. 929 424 DATED December 50, 1975 rNvENTOR(S) 1 Richard H. Krock and Jerome J. Pickett It is certified that error appears in the above-identified patent and that sard Letters Patent are hereby corrected as shown below.

Signed and Scaled this twenty-third Day of March 1976 sun A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofParenls and Trademarks UNHEE) 3%1' ETES PATENT OFFICE CETtFEQATE )F QURECTION PATENT NO. I 3 929 424 DATED December 50, 1975 iNVENTORt I Richard H. Krock and Jerome J. Pickett It is certified that error appears in the above-identified patent and that said Letters Patent 0 are hereby corrected as shown below.

- C01. 3, tine H insert "C" after 1000 0 ..Co]. 3, tine i5 insert "C" after 1000 C01. 3, tine i7 insert "C" after 1350 gigncd and Scaled this 6 twenty-third of March 1976 [SEAL] Arrest.

b RUTH c. MASON C. MARSHALL DANN Arresting Officer (ommixsinner ofParenls and Trademarks

Claims

2. A body according to claim 1, wherein the refractory metal containing particles are tungsten particles, preferably from 75-83 percent by weight.

4. A method of making a body as claimed in claim 1, the body including refractory metal containing particles in a metal containing matrix, the method comprising the steps of a. forming a porous shape of joined refractory metal containing particles, b. filling voids of the shape with a molten metal containing matrix material in such a manner that the average particle size of the refractory metal containing particles after filling voids with the molten matrix material is substantially the same as the average size of the refractory metal containing material prior to filling voids with the molten matrix material, the molten metal containing matrix material including a refractory metal and a metal selected from the group consisting of Ni, Fe, Co, Cu, Cr or combinations thereof, and c. solidifying the molten alloy to provide the body.

7. A method as claimed in claim 4, wherein the step of forming the porous shape of joined refractory metal containing particles includes sintering of the particles.