US2370242A - Refractory metal composition - Google Patents

Description

Patented Feb. 27, 1945 2,370,242 Fl C E 2,370,242 REFRACTORY METAL COMPOSITION Franz R. Hensel and Ea R Mallory & dianapolis, Ind., a corporation of lnd., asslgnors to P.

rl I. Larsen, Indianapolis,

00., Inc., In- Delaware No Drawing. Application January 15, 1943,

Serial No. 472,482

V 4 Claims. (Cl. 75-22) This invention relates to metal compositions (b) Molybdenum particles coated with rhoand articles made therefrom. dium 60 An object is to improve metal powder'compo- Silver 40 sitions. r

Another object of the invention is to improve 5 g gfg particles mated with 65 powder metal bodies such as electric contacts,

Silver 35 welding electrodes, welding dies, current carrying hearings or bushings, valve seats and the like. ((1) u l sten pa s Coa ed w th rho- Other objects of the invention will be apparent d1l1m 50 from the description and claims. 10 S11v6! 50 The present invention contemplates a metal (e) Tungsten coated with rhodium 80 composition made from refractory metal powsilver 2o ders, particularly tungsten and molybdenum, which are individually coated with protective Molybdenum Particles coated with i layers of a palladium-platinum group metal such 15 and/Or panadhlm 50 as platinum, palladium or rhodium and are S11v9! bonded together in a metal composition with a (g) M l bd n articles coated with platimetal from the first group of the periodic table nu and or palladium 60 such as copper, silver or gold. silver 40 33 525,222 :32 53 3 525 232 (h) Tungsten particles coated with platinum coating and the coating of protective metal such palladium as platinum, palladium or rhodium may vary ver '7 in thickness from a fraction of a micron to sev- (i) Tungsten particles coated with platinum eral thousandths of an inch. Thus the relative and/or palladium 50 percentages of refractory metal or compound and Silver 50 protective metals in the coated powders used for producing the metal composition of the present (7) gg i gfi i with platinum and/or 3 invention may fall within the following range Silver 20 of proportions: so

p t; (0) Tungsten coated with platinum and/or I Refractory metal 99,99 t 10 palladium or rhodium 45 Palladium-platinum group metal 0,01 t 90 Gold 55 The coated powders are interspersed and w Tun sten co t d with pl inum bonded with the second group metal and th r palladmm or rhod1um 70 suiting compositions may fall within the follow- Copper 30 mg range: p t; (or) Tungsten coated with platinum and/or Coated tungsten or molybdenum powpalladium or rhodium 50 ders 51,0 99 4 Copper 50 Copper silver or Balance The protective coating of rhodium, platinum This range may be divid d t t genera] or palladium may be applied by any one of several classes of.materia1s, namely: methods such as electroplating, cathode sputtering; metal spraying, condensing evaporated g gf refractory compositlons contam' metal on the particle surfaces, chemical deposi- Percent tion. They may also be coated by first coating c t refracmr powders 5013399 the powders with a dispersible adhesive. then Copper silver or g ld Balance dust ng the adhesive Coated particles the P d 1 n i t t l protective metal in powder form and subseg 0m g me mg n me a compo quently heating the coated powders to'disperse 5 con a ng Percent the adhesive and diffusing the protective metal onto the surfaces of the refractory powders." It Coated refractory puwders 5 to is'also possible to use a metal paste as a'coating Copper, silver or gold Balance medium. a Following are several examples of suitable 55 The metal-compositions of thepresent invenmetal compositions: tion may be made from the coated particles in Percent several ways. The coated refractory particles, I (a) Molybedenum particles coated with rhoor a mixture of them, may be pressed to form a dium 50 powder compact and the compact then sintered Silver 50 6 at a suitable temperature such as 1200 C. to form the mixture.

a slnter-bonded metal body. This body is then impregnated with silver, copper or gold or any alloy of two or more Of these, by placing the first group metal in contact with the sintered compact and heating the assembly in a reducing atmosphere to a, temperature above the melting point of the lower melting metal so that it will flow into the pores of the sintered body and fill them.

The metal composition may also be produced by mixing the coated particles directly with powders of copper, silver or gold, or mixtures of these, pressing the mixed powders and then sintering the pressed mixture at a suitable temperature such as 950 C. to produce the finished composition. If desired, subsequent repressing or coining operations may be applied to further increase the density and improve the physical characteristics of, the composition.

A third method of manufacture comprises a combination of the above two methods. According to this method, a portion of the copper, silver or gold in the form of a powder is mixed with the coated refractory powders and the mixture pressed in a suitable die. The pressed body is then sintered at a temperature to cause binding, such as 1250 C. Additional amounts of copper, silver or gold are then placed in contact with the sintered body and the assembly heated to a temperature above the lower melting point metal to cause impregnation.

During the sintering operation, according to any of the above methods, the protective layers oi platinum, palladium or rhodium on the refractory metal particles difiuse into the refractory material to a greater or lesser extent, forming alloys or compositions at the surfaces of the particles. These surface layers are considerably more noble in character as far as oxidation is concerned than the refractory particles themselves. The degree of diffusion of the protective metal will depend upon the time and temperature of the sintering process. It is also contemplated that in some cases the coated powders .may be pre-sintered in the loose state to accomplish diffusion before the powders are used in manufacturing the metal composition.

An advantage of the present composition and process resides in the afilnity between the first group metals such as copper, silver and gold and the protective metals such as palladium, platinum or rhodium. Since the first group metals have a tendency to alloy with the protective layers they are readily drawn into any pores or spaces in the metal compact resulting in a denser and more nearly perfect and homogeneous metal structure. The alloying also produces a strong bond between the various metal phases present.

In some cases additions of small proportions of other ingredients may be made to the compositions. For instance, from a fraction of a per cent to of carbon or boron may be added to The carbon is preferably in the form oi graphite.

Such elements as nickel, cobalt, iron, manganese or silicon may be added in proportions ranging from a fraction of 1% to 30%. These have the efiect of increasing the hardness, wear resistance and tensile strength of the compositions.

One important use of the metal compositions of the present invention is in electric contacts. Electric contacts have heretofore been produced of compositions of refractory metals and compounds with silver and copper in various proportions. However, such compositions have developed relatively high contact resistances between the contacting surfaces and have exhibited a substantial temperature rise when subjected to continuous operation. The use of a protective metal coating from the palladium-platinum group on the refractory particles reduces the contact resistance considerably and produces a contact much less subject to overheating.

By using contacts formed of the compositions described on one or both sides of a contact pair, sticking and high contact resistance can be eliminated in most cases.

Refractory compositions of the present invention which are particularly suitable for cooperation with cadmium oxide contacts of the type described in l-lensel Patent 2,145,690 are coated molybdenum particles with silver, and coated tungsten with silver.

While specific embodiments of the invention have been described, it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. A metal composition formed of particles of refractory metal selected from the group consisting of tungsten and molybdenum, and a coating thereon of metal selected from the group consisting of palladium, platinum and rhodium and metal selected from the first group of the Periodic Table consisting of copper, silver and gold interspersed with and bonded to said coated particles.

2. A metal composition formed of particles of refractory metal selected from the group consisting of tungsten and molybdenum, and a coating thereon of metal selected from the group consisting of palladium, platinum and rhodium and metal selected from the first group of the Periodic Table consisting of copper, silver and gold interspersed with and bonded to. said coated particles, said coated particles being formed of 99.99% to 10% of said refractory metal and .01% to of said coating metal, the coated particles forming 5 to 99% of said composition and said first group metal forming the balance.

3. An electric contact formed of a metal composition composed of particles of refractory metal selected from the group consisting of tungsten and molybdenum, and a coating on said par ticles of metal selected from the group consisting of palladium, platinum and rhodium and metal selected from the first group of the Periodic Table consisting of copper, silver and gold interspersed with and bonded to said coated particles.

i. An electric contact formed of a metal com position composed of particles of refractory metal selected from the group consisting of tungsten and molybdenum, and a coating on said particles of metal selected from the group consisting of palladium, platinum and rhodium and metal selected from the first group of the Periodic Table consisting of copper, silver and gold interspersed with and bonded to said coated particles, said coated particles being formed of 99.99% to 10% of said refractory metal and .01 to 90% of said coating metal, the coated particles forming 5 to 99% of said composition and said first group metal forming the balance.

FRANZ R. HENSEL. EARL I. LARSEN.