US2169189A - Copper base alloy - Google Patents

Description

Patented Aug. 8, 1939 UNITED STATES 2,169,189 PATENT oFFicF.

2,169,189 oorrnn BASE ALLOY James M. Kelly, Trafl'ord, Pa., assignor to Westinghouse Electric at Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application October 21, 1938, Serial No. 236,301

Claims.

No. 149,146, filed June 19, 1937, now Patent Certain metals have been alloyed with copper to produce an alloy having better mechanical properties, but generally such alloys have been inferior to copper as conductors of electricity and heat. In the copper base alloys which have been produced and which have the desired conductivity or mechanical strength, the characteristics are difficult to duplicate, since a hardener alloying element is usually employed and the oxidation of the elements must be closely controlled. Thelhardener is usually easily oxidized and, therefore, diflicult to get into liquid solution while the recovery of the alloying elements introduced into the copper melt is difficult.

An object of this invention is to produce a copper base alloy having high physical strength and good electrical and thermal conductivity.

Another object of this invention is to provide a copper base alloy which will have the characteristics of high physical strength and good electrical and thermal conductivity when precipitation hardened.

A further object of this invention is to utilize a copper base alloy formed to shape and precipitation hardened to give high physical strength and good electrical and thermal conductivity.

A more specific object of this invention is to produce a copper base alloy which may be precipitation hardened to give it high physical strength and conductivity, and will retain its strength and be resistant to creep when subjected to elevated temperatures.

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

In order to produce a copper base alloy which will have desired mechanical and electrical properties, metals which can be precipitated to effect a dispersion of fine particles throughout a copper base when suitably heat-treated are added to a copper melt. It has been found that a copper base alloy containing even small proportions of cobalt, iron and silver has excellent mechanical and electrical properties when heat-treated.

In preparing the alloys, the metals, cobalt, iron an dsilver may be added directly to the copper melt in any suitable form, such as powders or in lump form, since they are not easily oxidized as compared to copper. Where extremely small amounts of silver are desireu argentiferous copper may be employed in making the alloy. The alloying content may thus be maintained substantially constant during the hot forming operations, since the alloying elements will not be lost by oxidation Y of the alloy.

I In practice, the alloy may be prepared by heating a melt of copper such as commercial electrolytic copper under a covering of charcoal in a graphite crucible and adding the alloying elements in any suitable form to the copper melt. In order to permit complete oxidation of the melt, it may be held at a temperature of between 1150 C, and 1200 C. for a period of time suflicient for the completion of the reaction of the graphite crucible with the oxygen. Where desired, the alloy may also be prepared by heating the melt in a ceramic crucible with a cover of lump charcoal over the surface of the melt. Although not always necessary as in the making of other copper base alloys, where desired, small quantities of calcium or phosphorus or other suitable deoxidizers may be added to the melt of copper, cobalt, iron and silver to insure complete deoxidation of the melt. The alloying elements are readily soluble in copper and enter into solution providing an alloy in which the alloying elements are uniformly distributed throughout the structure.

The alloy may be cast in massive, intricate or fine form in any suitable type of mold such as a sand casting or chill cast mold. Where desired, the alloy may be cast directly into the predetermined shape of the article which is to be manufactured, after which it may be easily machined as required, or it may be cast to a pattern suitable for forging to the desired shape. In its cast condition without the heat treatment to be described hereinafter, the copper, cobalt, iron and silver alloy is comparatively ductile, being easily forged or drawn to shape.

Alloys comprising from small but effective amounts up to 5% by weight of each of cobalt and iron and from a small but effective amount up to 3% by weight of silver with the balance substantially all copper when heat-treated as hereinafter described to precipitation harden them, have been found to have high physical strength and good electrical and thermal conductivities.

In order to develop the mechanical strength and the electrical properties of the alloy, it is subjected to a precipitation hardening treatment comprising subjecting the alloy to a high temperature below the melting point of the alloy for obtaining a high solid solution of the alloy'ng metals in the copper, quenching the alloy from a high temperature to retain the alloying metals in the solid solution, and then reheating the alloy to a lower or ageing temperature and holding it at this temperature for a period of time sufiicient to precipitate the alloying elements from the solid solution state.

In practice, heating at a temperature of between 750 C. and 1075" C. is found to effecta high solid solution of the alloying metals in the copper, while a re-heat at a temperature of between 450 C. and 600 C. eifects an efllcient precipitation of the alloying'constituents.

Alloys comprising copper, cobalt, iron and silver within the ranges given hereinbefore, when heattreated as described, have a high hardness, high ultimate strength and good conductivity. The heat treatment is found to be of special benefit to alloys comprising between .5% and 3% of each of the elements cobalt and iron, and from a small but effective amount up to 3% of silver with the balance of substantially all copper.

In the alloy of this invention, it is desired to maintain the ratio of the cobalt to iron content between .5 and 1.25 to 1, since it is found that such ratios produce the best combination of properties in the alloy. Since the conductivity and hardness values of the alloy may be taken as a criterion of the alloy, it is evident that the best alloying properties which will give the highest value as a product of the hardness and the conductivity is to be preferred. In all cases, the highest product of the conductivity and hardness values for different combined cobalt and iron contents within the limits given is found to be obtained when the ratio of the cobalt to the iron content approximates l.

The silver additions to the alloy give it a high ultimate strength without detrimentally affecting its conductivity and hardness while rendering the alloy resistant to oxidation. Further, the silver additions in preferred amounts of from small but effective amounts up to 1.5% render the alloy resistant to softening when exposed to high temperatures of about 500 C. for long periods of time. This improvement in thermal endurance or the property of retaining hardness at high temperatures is of special value in certain applications of the alloy.

As representative of the benefits afforded the alloy by the addition of silver, the following table gives the results obtained with different silver additions to an alloy in which the cobalt and iron contents are maintained constant at a preferred ratio of 1. In the table, the copper content is omitted, it being understood that the balance of the alloy content comprises copper with possible incidental impurities occurring during the alloying process:

Composition Percent Alloy No. Per Per Per gardtless conducockaellB lbs. 11. cent cent cent uvlty 1 Fe Co Ag The alloys identified in the above given table were subjected to a heat treatment consisting of quenching them from a temperature of 1000 C. and reheating or ageing them at a temperature of 500 C. for a period of time of 16 hours. In some cases conductivity values of over 70% have been obtained by ageing the alloys for more than hours without the exposure to the ageing temperature of 500 C. softening the alloy.

As illustrative of the effect which the time of ageing the alloy has on the conductivity, the following values are given as found in an alloy conscribed hereinbefore with the ageing time varying as indicated:

Percent conductivity Hardness Ageing time in hours Rockwan B Although the alloys produced in accordance with this invention have an extremely high Rock well B hardness when heat-treated, as cast they are quite ductile and may be readilyworked into the shape or form desired. The alloys prepared from the different alloying elements and within the limits given hereinbefore are particularly useful in the manufacture of large castings, such as commutator segments. Other uses of the alloy are as welding electrode tips or welding wheels or other articles where a conductivity of 60% or greater is required, together with high physical I strength. These alloys may also be efficiently em-- played in applications such as cylinder heads for internal combustion engines where high thermal conductivity is desired combined with high physical strength. The alloys may be cast directly into the predetermined shape of the article of manufacture or into a pattern suitable for forging or drawing.

It is, of course, to be understood that this invention is described with reference to specific embodiments thereof, and that other and various modifications may be made without in any way departing from the spirit of the invention as set forth in the appended claims.

I claim as my invention:

1. An alloy comprising from a small but effective amount up to 5% of cobalt, from a small but effective amount up to 5% of iron, from a small but effective amount up to 3% of silver, with the balance substantially all copper.

2. An alloy comprising copper, cobalt, iron and silver, the silver ranging from a small but effective amount up to 3%, the cobalt ranging from a small but effective amount up to 3%, and the iron ranging from a small but effective amount up to 3%, with the balance substantially all copper, the

ratio of the cobalt to the iron being between .5

and 1.25 to 1.

3. An age hardened alloy comprising from about .5% to 3% of cobalt, from about .5% to 3% of iron, from a small but effective amount up to 3% of silver with the balance substantially all copper which has been quenched from a temperature of between 750 C. and 1075 C. and aged at a temperature of between 450 C. and 600 C.

4. As an article of manufacture, an alloy comprising from about .5% to 3% of cobalt, from about .5% to 3% of iron, from av small but effective amount up to 3% of silver with the balance substantially all copper, formed to a predetermined shape and precipitation hardened to give