US2166794A - Copper-cobalt-beryllium alloys - Google Patents

Description

Patented July 18, 1939 UNITED STATES COPPER-COBALT-BERYLLIUM ALLOYS Gerald R. Brophy, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York No Drawing. Application November 2'7, 1936, Serial No. 112,999

1 Claim.

The present invention relates to precipitation hardened alloys consisting of copper, cobalt and beryllium and particularly to alloys of this composition which are employed as springs.

Dahl Patent 1,847,929 and Horstkotte Patent 1,957,214 both disclose precipitation hardened copper-cobalt-beryliium alloys containing not more than 1% beryllium and preferably about .4% beryllium. I have found however that precipitation hardened alloys of the above composition develop a network of line cracks when subjected to bending or cold working. These cracks are due to oxygen which, during the heat treatment, penetrates the alloy along the grain boundaries yielding a weak brittle film aroundthe grains. This oxidation occurs at all temperatures above 500 C. and even in furnaces employing line or commercial hydrogen.

By employing, during the heat treatment, an atmosphere which is oxygen free, for example a pure dry hydrogen atmosphere such as employed in producing bright annealed surfaces on stainless steel, it is possible to avoid embrittlement of the alloy and subsequent cracking during cold working.- However, the use of an atmosphere entirely free from oxygen is expensive and not always feasible.

It is an object of the .present invention to provide a precipitation hardened copper-cobaltberyllium alloy which is free from cracks or embrittlement and which may be heat treated in any atmosphere commonly employed in annealing furnaces.

In carrying out my invention I preferably employ an alloy which contains not less than 1.5%

beryllium and about 2.6% cobalt with the remainder copper. About 0.4% of the beryllium combines with the cobalt leaving an excess of 1.1% beryllium. The alloy is precipitation hardened in the manner disclosed in the Horstkotte patent. For example, it is heated to about 900 C., quenched in water, and thereafter heated at about 500 to 600 C. for about one hour and then allowed to cool. The alloy thus produced may I be forged and rolled into thin sheets and formed 0 into springs such as Sylphon bellows and like devices which are'subject to cold working or use at elevated temperatures. Alloys of this composition are free from intergranular oxidation when heated in oxidizing atmospheres.

While I prefer to employ a minimum of 1.5% beryllium in the alloy, higher percentages may be employed if desired, also a portion of the beryllium in excess of that combined with the cobalt may be replaced by any protective metal such as aluminum, titanium, zirconium, silicon and calcium which protects the alloy against intergranular oxidation. A preferred composition contains 2.6% cobalt, 1.5% beryllium and the remainder copper. During heat treatment, 25 I employ air or hydrogen as the furnace atmosphere although nitrogen, carbon monoxide or any atmosphere commonly employed in the heat treatment of metals may be employed if desired.

What I claim as new and desire to secure by Letters Patent of the United States, is:

A precipitation hardened alloy containing 1.5%

- beryllium, 2.6% cobalt with the remainder copper.

GERALD a. BROPHY.