CHAPTER XI 

 THE COPPER-BERYLLIUM ALLOYS 



The copper-beryllium alloys are of some interest in 

 spite of their high cost and certain difficulties experienced 

 in their production because they exhibit, subsequent to 

 heat-treatment, mechanical properties materially in 

 excess of those attainable with other commercial alloys 

 of copper. The particular property that in most 

 instances prompts the industrial application of these 

 alloys is their high endurance limit in fatigue. 



The constitutional diagram for binary copper beryl- 

 lium is shown in Fig. 1. As would be suggested by 

 the diagram, these alloys are susceptible to heat-treat- 

 ment or "age hardening" because of the limited solid 

 solubility of the alpha phase at room temperature. 



The commercial copper-berylHum alloys after a 2- or 

 3-hour heat-treatment at 1450 to 1500°F., followed by a 

 water quench for the purpose of retaining the alpha 



structure, are malleable and can be drawn, stamped, or 

 otherwise cold-worked. Subsequent to such forming 

 ' or cold working and in order to establish phase equilib- 

 rium with attendant high mechanical properties, parts 

 are subjected to an "aging" anneal at 525 to 575°F. for 

 varying periods of time, dependent upon the physical 

 dimensions of the part and the properties required. 



It is common practice to add a third constituent to the 

 binary alloys. In commercial practice cobalt is fre- 

 quently added to obtain high temperature stability and 

 nickel is introduced as a minor constituent for the pur- 

 pose of retarding grain growth. 



Physical constants of the more important copper- 

 beryllium alloys are given in Table 1. on page 292. 

 Charts 1 to 4 and Table 2 on pages 291 to 293 give in 

 greater detail mechanical properties attainable. 



h40 



■S30 



■O20 



10 



24 



0.4 0.8 t.2 1.6 2.0 



Percent, Beryllium by Weight 



Chart 1. — The effect of aging time at an aging temperature of 575°F. 

 on the electrical conductivity of copper-beryllium alloys according to 

 Beryllium Corporation of American, Publications. ''s) 



200 

 c 



to — 

 0«^ 



£ feieo 



c Ji 



oi-c 



(S.4- 



-W 

 c c _- 

 o (u 80 



c « 

 -S-5 



LU E 



in'i40 C 



30 



150 



60 90 120 



Minutes in Salt Bath 



Chart 2. — The relationship of time and temperature of the age- 

 hardening treatment to tensile strength, electrical conductivity, and 

 percentage elongation in 2 in. of 2.25 per cent copper-beryllium strip, 

 previously cold-worked 1 B. & S. No., hard, according to Riverside 

 Metal Company.'^'' 



291 



