US2358326A - Metal composition - Google Patents

Description

Patented Sept. 19, 1

2,358,826 METAL COMPOSITION Frans R. Hensel and Earl I. Larsen, Indianapolis, Ind., assignors to P. R. Mallory & Co., Inc., Indianapolis, Ind., a corporation Delaware No Drawing. Application December 31, 1942,

Serial No. 470,852

6 Claims. (Ci. 75-22) r This invention relates to powder metal com- Following are several examples of suitable positions and articles made therefrom. metal compositions! An object is to improve metal powder compositions. A B o D E Another object of the invention is to improve powder metal bodies such as electric contacts, Nickel or cobalt coated with rhodium to c0 15 a0 40 current carrying bearings or bushings, valve 511v" 85 seats and the like.

Other objects of the invention will be apparent from the description and claims. 10 r o H I J The present invention contemplates a metal composition made from iron group meta1 pow- Nickel or cobalt coated with platinum or ders, particularly nickel and cobalt, which are s fi 33 i3 individually coated with protective layers of a palladium-platinum group metal such as platinum, palladium or rhodium and are interspersed with and bonded to metal from the first group i K M N o the periodic table such as copper, silver or gold.

nickel and Powders m vary in 25 75 so 95 40 average diameter between 50 and 400 mesh prior Golda 75 4 5 60 to coating and the coating of protective metal h as p a inum, ladium r r dium ay The protective coating of rhodium, latinum vary in thickness from 8 fraction of a, micron or palladium may be applied by any one of sevto several microns. Thus the relative percenteral methods such as electroplating, cathode ages of nickel or cobalt and protective metals 25 tt metal spraying condensing evapon t e mated Powde s ed for producing the rated metal on the particle surfaces, chemical metal composition of the present invention may deposition They may also be coated by t fall Within t following range of Proportions: coating the powders with a dispersible adhesive,

p cent then dusting the adhesive coated particles with Nickel or cobalt 5 the protective metals in powder form and subp n d tm group metal t 5 sequently heating the coated powders to disperse the adhesive and diffusing the protective metal The coated powders are interspersed and bond onto the surface of the nickel or cobalt powders. ed with the first group mfatal and resulting It is also possible to use a metal paste as a coatcompositions may fall within the following range: 85 mg mediunL Per cent The metal compositions of the present inven- Coated nickel or cobalt powders 5to 99 tion may be made from the coated particles in Copper, silver or gold Balance several ways. The coated nickel or cobalt particles, or a mixture or them, may be pressed to For a more ductile material it will generally form a powder compact and the compact then be desirable in Pmduce containinfi sintered at a suitable temperature such as 10oo- Per cent C. to form a sinter-bonded metal body. This Coated nickel or cobalt powders 5m 50 body is then impregnated with silver, copper or Copper, silver or gold Balance s r an alloy of two or more of these, y placing the first group metal in contact with For a harder material the coated iron group the sintered compact and heating the assembly powders will predominate, for example: in a reducing atmosphere to a temperature above Per cent the melting point of the lower melting metal so Coated nickel or cobalt powders to 99 that it will flow into the pores of the sintered Copper, silver or gold Balance so body and fill them,

2 assaase 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 900 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 or 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 nickel or cobalt powders and described on at least one side of a contact pair,

sticking and high contact resistance can be elimdium and metal selected from the group consistthe mixture pressed in a suitable die. The

pressed body is then sintered at a temperature to cause bonding, such as 950' 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 of platinum, palladium or rhodium on the nickel or cobalt particles diffuse into the nickel or cobalt to a greater or lesser extent, forming alloys at the surfaces of the particles. These alloys are considerably more noble in character as far as oxidation is concerned than the nickel or cobalt particles themselves. The degree of diflusion 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 amnity between the first group metals such as copper, silver and gold and the protective metals such as palladium, platinum and 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.

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 10% of carbon or boron may be added to the mixture. The carbon is preferably in the form of graphite. Also from a fraction 01' 1% to 30% of such elements as iron, manganese, molybdenum, silicon and tungsten may .be added.

One important use of the metal compositions of the present invention is in electric contacts. Electric contacts have heretofore been produced of compositions of nickel or cobalt with silver 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 metalcoating from the palladium-platinum group on, the nickel or cobalt particles reduces the contact resistance considerably and produces a contact much less subject to overheating.

By using contacts formed of the compositions ing of copper, silver and gold interspersed with and bonded to said coated particles.

- 2. An electric contact formed of a metal composition composed of particles of metal selected from the group consisting of nickel and cobalt coated with metal selected from the group consisting of palladium, platinum and rhodium and metal selected from the group consisting of copper, silver and gold interspersed with and bonded to said coated particles.

3. A metal composition formed of particles of a first metal selected from the group consisting of nickel and cobalt coated with a second metal selected from the group consisting of palladium, platinum and rhodium, said second metal amounting to 0.1 to 5% of the weight of the coated particles, and a third metal selected from the group consisting of copper, silver and gold interspersed with and bonded to said coated particles, said coated particles amounting to 5 to 99% of said metal composition.

4. An electric contact formed of a metal composition composed of particles of a first metal selected from the group consisting of nickel and cobalt coated with'a second metal selected iron: the group consisting of palladium, platinum and rhodium, said second metal amounting to 0.1 to 5% oi the weight of the coated particles, and a third metal selected from the group consisting of copper, silver and gold interspersed with and bonded to said coated particles, said coated particles amounting to 5 to 99% of said metal composition.

5.A ductile metal composition formed of particles of a first metal selected from the group consisting of nickel and cobalt coated with a second metal selected from the group consisting oi palladium, platinum and rhodium, said second metal amounting to 0.1 to 5% of the weight of the coated particles, and a third metal selected from the group consisting of copper, silver and gold interspersed with and bonded to said coated particles, said coated particles amounting to 5 to 50% of said metal composition.

6. A relatively hard metal composition formed of particles of a first metal selected from the group consisting of nickel and cobalt coated with a second metal selected from the group consisting of palladium, platinum and rhodium, said second metal amounting to 0.1 to 5% of the weight of the coated particles, and a third metal selected from the group consisting of' copper,

silver and gold interspersed with and bonded to said coated particles, said coated particles amounting to 50 to 99% of said metal composition.

FRANZ R. HENSEL. EARL I. LARSEN.