US2131994A - Refractory metal composition - Google Patents

Description

Patented Oct. 4, 1938 4 UNITED STATES REFRACTORY METAL COMPOSITION Franz R. Hensel, Indianapolis, Ind., assignor to P. R. Mallory & 00., Inc., Indianapolis, 11111., a corporation of Delaware No Drawing.

Application August 13, 1935,

Serial No. 35,985

Claims.

This invention relates to metal compositions and articles made therefrom and more particularly to metal compositions including refractory materials.

An object of the invention is to improve the manufacturing characteristics and final properties of a metal composition of the type disclosed.

Another object is to provide welding electrodes, welding dies, electric make-and-break contacts, and hard or refractory metal articles such as valve seats, machine tools, bearings and the like of improved characteristics.

Other objects of the invention will be apparent from the following description taken in connection with the appended claims.

The present invention comprises the combination of elements, methods of manufacture, and the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements without departing from the spirit of the invention.

The present invention comprises an improvement in the methods and products set forth in Nathan H. Adams patents, 1,477,797 issued Dec. 18, 1923 and 1,552,184 issued Sept. 1, 1925, and in Robert T. Gillette Patent 1,539,810 issued May 26, 1925, and contemplates the use of an age-hardening alloy instead of the unalloyed copper set forth in these patents as an impregnant for the refractory material. It is preferred to use a refractory material including a metal such as tungsten or a compound thereof, for instance, tungsten carbide. The age-hardening alloy preferably comprises one or more of the highly conductive metals, such as silver and copper combined with nickel and silicon, cobalt and silicon, or other suitable precipitation hardening ingredients. In addition an arc-extinguishing agent may be added if desired.

The refractory material for use in the composition, such as the tungsten or tungsten carbide, may preferably be prepared for combination with the other ingredients by forming into a sintered porous mass. The age-hardening alloy may then be added in such a manner that it will penetrate the sintered mass and fill up the pores in the refractory material. The proportion of refractory material in the resulting composition may be 50 to 95% depending in part upon the percentage of voids originally in the sintered mass before impregnation.

Age-hardening alloys which are suitable for impregnating the refractory material may be prepared by melting together or by compressing mixtures of ingredients having one of the ,'following compositions:

Per cent (a) Nickel plus silicon 1.2 to 7.5 Copper Remainder.

(b) Cobalt plus silicon 0.3 to 6.0 Copper Remainder.

(c) Nickel plus silicon 1.5 to 12.0 Silver Remainder.

(d) Cobalt plus silicon 0.3 to 6.0 Silver Remainder.

The limits given above for the nickel and cobalt plus silicon mark the range of proportions below which no substantial hardening takes place and above which little or no added hardening effect is obtained. Additions of these elements in greater proportions have little or no beneficial effect and tend to decrease the electrical conductivity.

In forming the alloys the preferred ratios of either nickel or cobalt to silicon is 4:1. This gives the preferred combination of high strength and high electrical conductivity after a proper heat treatment. Variations in the ratios between the limits 3:1 and 5:1, however, cause no great reduction in the desirable properties of the finished material.

In some instances it may be desirable to add from 0.03 to 10% silver to the copper alloys or from 0.03 to 10% copper to the silver alloys. The hardness may be increased somewhat by this expedient but the electrical conductivity will be lowered thereby.

Where it is desired to improve the arc extinguishing characteristics of the finished composition an arc-snufiing agent may be added. Cadmium and zinc are preferred for this purpose and may be added to any of the age-hardening alloys mentioned above in proportions up to 10%, preferably within the range 0.1 to 10%. It is obvious that mixtures of cadmium and zinc may also be used.

One age-hardening alloy which has been found to be very suitable for use as an impregnating material is the following:

Per cent Nickel 2.0 to 2.4 Silicon 0.5 to 0.6 Cadmium 0.35 to 0.75 Silver 0.1 to 0.25

Copper Remainder.

An increase in the combined percentage of nickel and silicon above 3% within the limits given causes little change in the hardness or conductivity. Hence it will ordinarily be suitable to use no more than 3% of these ingredients.

One method of producing the metal compositions of the present invention is as follows:

Tungsten or tungsten carbide powder and 1% paramn are mixed together and an ingot is formed by subjecting the same to pressure of such an amount as is necessary to obtain the preferred percentage of voids. The pressed density of the tungsten may be, for instance, 8.8, 10.0 or 13.0 grams per cubic centimeter. For tungsten carbide the density may be 5.8 grams per c. c. The bar may then be sintered in a hydrogen furnace at about 1250 C. The agehardening copper or silver alloy: in solid form, such as in bars or shot, is then placed on the top of, or surrounding, the sintered ingot. The whole is then further heated in a reducing atmosphere until the age-hardening alloy penetrates the refractory ingot, filling up the voids therein. l'he temperature during this operation may range from 1200 C. to 1300 C. If the resulting composition is reheated to the same temperature, it will be found that none of the metal will fiow from the base. By means of the present method, excellent compositions are obtained comprising a bonded unitary mass of interspersed particles or areas of refractory material and age-hardening alloy.

After preparing the composition in the above manner it is susceptible to age-hardening. This may preferably be produced by a double heat treatment. The material may first be heated to a temperature above 700 C. and rapidly cooled 01' quenched to room temperature. It is preferred to use 800900 C. as quenching temperatures but it has been found that the temperature may be as low as 700 C. and still obtain the desired results. The most suitable treatment comprises heating the completed composition, before machining, to 900 C. for 15 minutes and then removing from the furnace and immediately quenching and agitating n cold water.

The quenched ingots are then preferably reheated to an elevated temperature below 700 C. for a period ranging from a few minutes to many hours. The preferred ageing treatment comprises reheating the bars for about four to eight hours in a salt bath which is kept at a temperature of 450 to 500 C., for example, at 470 C.

It is possible, although not as satisfactory, to omit one of the steps by quenching the composition immediately after impregnation, following this with the low temperature precipitation treatment.

If the pieces are to be brazed the heat treatments may be combined with the brazing operations. This may be brought about by brazing the finished, but untreated composition, with a suitable brazing material, such as silver or silver solder at about 900 C. and then quenching in water as soon as the braze sets. This operation should be followed by an ageing treatment, preferably for four to eight hours at about 500 C.

The heat treatments described above bring about an age-hardened or precipitation hardened state in the finished composition. Not only is its hardness raised considerably by the heat treatment but the conductivity is considerably improved. With a composition consisting of 65% tungsten and 35% of a copper alloy which contains 5% of an intermetallic compound of nickel and silicon the hardness before quenching may be approximately 100 on the Rockwell B scale and the conductivity approximately 23.7%. After quenching the hardness may be about 90 Rockwell 3" and the conductivity 19%. After ageing four hours the hardness will be increased to such a value as 30 to 32 Rockwell C and the conductivity may be 31%.

A B W plus alloy W plus 011 Modulus of rupture (lbs. per sq. inch)..- 250, 000 110,000 Deformation (inches in 1% lengths) 04 .03 Density (gm. per 0. c. 13. 7 13. Electrical conductivity 0e 31 44 Brinell hardness 300 160 This comparison shows very clearly the great superiority of the composition of the present invention. The Brinell hardness and the modulus of rupture is increased more than while the electrical conductivity is not unduly decreased. Operating tests made with welding electrodes of this new composition have shown that it has a life more than double that of the compositions 'described in the Adams and Gillette patents, Patent 1,848,437 to G. N. Sieger et al. and others.

Similar superiority is shown if tungsten carbide is used as a refractory material. By combining tungsten carbide with pure copper, an electrical conductivity of 24% may be obtained, and a. Brinell hardness of 200. If an age-hardening copper alloy containing 5% of an intermetallic compound consisting of 4 parts nicked and 1 part silicon is used for impregnating, a Brinell hardness of 350 and electrical conductivity of 22% may be obtained.

Furthermore, it has been found that an agehardening copper alloy containing nickel and silicon in the form of an intermetallic compound of 4 parts of nickel and 1 part silicon will more readily penetrate the refractory material, and a more firmly bonded product may be obtained with the copper alloy more uniformly distributed throughout the mass of refractory material than when only pure copper is combined with the re-- fractory material. This advantage is particularly noticeable if large cross sections of tungsten or tungsten carbide must be impregnated.

A further advantage of the new composition resides in its characteristic property of age hardening or precipitation hardening in a temperature range of 400 to 600 C. In welding, such temperatures are frequently encountered, and the material is therefore used in a temperature range where it possesses the highest hardness and the highest wear resistance properties.

Since the new composition has a. more uniformly bonded texture than prior compositions it may be readily machined after quenching and before the ageing treatment. After ageing the alloy may be approximately 100 Brinell units harder than in the as quenched condition. It is quite possible, however, to machine the aged material. It will usually be satisfactory to rough machine the quenched composition and finish machining after ageing.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An age hardened metal body comprising a porous mass of refractory material chosen from the group consisting of tungsten and tungsten carbide impregnated with an alloy of a metal selected from the group consisting of copper and silver containing a precipitated intermetallic compound of silicon with a metal selected from the group consisting of nickel and cobalt, said intermetallic compound being present in the proportions in which said compound is efiective in producing hardening by precipitation in said alloy. f

2, An age hardened metal body composed of a sintered porous base of refractory material selected from the group; consisting of tungsten and tungsten carbide and forming 50 to 95% of the weight of said body, the remainder of said body comprising an alloy impregnating said base, said alloy consisting of a metal selected from the group consisting of copper and silver containing a precipitated intermetallic compound of silicon with a metal selected from the group consisting of nickel and cobalt, said intermetallic compound being present inthe proportions in which said compound is effective in producing hardening by precipitation in said alloy.

3. An age hardened metal body composed of a porous base of refractory material selected from the group consisting of tungsten and tungsten carbide and forming 50 to 95% of the weight of said body, an alloy impregnating said base and forming the remainder of said body, said alloy having a base of a metal selected from the group consisting oi copper and silver and ingredients adapted to form intermetallic hardening compounds in said alloy, said ingredients consisting of a metal selected from the group consisting of nickel and cobalt together with silicon, the weight ratio of either of said last named metals to silicon being within the range 3:1 to 5:1.

4. An age hardened metal body composed of a porous base of tungsten comprising 50 to 95% of the weight of said body, and an alloy impregnating said base and forming the remainder of the weight 6f said body, said alloy being composed of 1.2 to 7.5% of nickel and silicon taken together and. the remainder copper, the weight ratio of the nickel to the silicon being within the range 3:1 to 5:1.

5. An electric contacting member of the type comprising pressure exerting welding electrodes and electric make-and-break contacts, said member being composed of a sintered base of refractory material selected from the group consisting of tungsten and tungsten carbide 50 to 95%, and the remainder an alloy impregnating said base, said alloy being composed of an intermetallic compound of silicon and a metal selected from the group consisting of nickel and cobalt and a base of highly conductive metal selected from the group consisting of silver and copper, the weight ratio of said nickel or cobalt to silicon being within the range 3:1 to 5:1, and said intermetallic compound being present in the proportions in which said compound is effective in precipitation hardening said basev and not substantially in excess of said eflective proportions.

6. An age hardened metal body composed of a porous base of tungsten comprising 50 to 95% of the weight of said body, and an alloy impregnating said base and forming the remainder of the weight of said body, said alloy being composed of 0.3 to 6.0% of cobalt and silicon taken together and the remainder a metal selected from the group consisting of copper and silver, the weight ratio of the cobalt to the silicon being within the range 3:1 to 5:1.

7. An age hardened metal body composed of a porous base of tungsten comprising 50 to 95% of the weight of said body, and an alloy impregnating said base and forming the remainder of the weight of said body, said alloy being composed of 1.5 to 12.0% of nickel and silicon taken together and the remainder silver, the weight ratio of the nickel to the silicon being within the range 3:1 to 5:1.

8. An age hardened metal body comprising a porous mass of refractory material chosen from the group consisting of tungsten and tungsten carbide impregnated with an alloy of a metal selected from the group consisting of copper and silver containing a precipitated intermetallic compound of silicon with a metal selected from the group consisting of nickel and cobalt, said intermetallic compound being present in the proportions in which said compound is efiective in producing hardening by precipitation in said alloy, said alloy containing 0.1 to 10.0% of an arc snufling agent selected from the group consisting of cadmium and zinc.

9. An age hardened metal body composed of a sintered porous base of refractory material selected from the group consisting of tungsten and tungsten carbide and forming 50 to 95% of the weight of said body, the remainder of said body comprising an alloy impregnating said base, said alloy consisting of a metal selected from the group consisting of copper and silver containing a precipitated intermetallic compound of silicon with a metal selected from the group consisting of nickel and cobalt, said intermetallic compound being present in the proportions in which said compound is effective in producing hardening by precipitation in said alloy and not substantially in excess of said effective proportion, said alloy containing 0.1 to 10.0% of an arc snufilng agent selected from the group consisting of cadmium and zinc.

10. An age hardened metal body composed of a porous base of refractory material selected from the group consisting of tungsten and tungsten carbide forming 50 to 95% of the weight of said body, an alloy impregnating said base and forming the remainder of the weight of said body, said alloy having a base of a metal selected from the group consisting of copper and silver and ingredients adapted to form intermetallic hardening compounds in said alloy, said ingredients consisting of a metal selected from the group consisting of nickel and cobalt together with silicon, the weight ratio of said last named metals to silicon being within the range 3:1 to 5:1, said alloy containing 0.1 to 10.0% of an arc snufilng agent selected from the group consisting of cadmium and zinc.

FRANZ R. HENSEL.