Abstract
This work is one of the series of studies which are concerned with basic data for the effects of additions of small amounts of low-melting point elements on the age-hardening of Cu-Be alloys. Using samples of Cu-Be alloys containing 1 to 2% of beryllium added with 0 to 1% of indium, investigations have been made mainly on age-hardening curves within the range of 275° to 350°C, microstructures and mechanical properties in the aged state after solution treatment at 800°C. The results obtained are summarized as follows: (1) Attainable hardness and other mechanical properties of Cu-Be alloys after aging are improved by indium addition, and the most prominent improvement is obtained when about 0.3% (0.15 at%) of indium is contained. The discontinuous precipitation is also supressed most greatly at this quantity of indium. This optimum amount of indium does not vary regardless of whether the alloy is cold rolled before aging. Therefore, it seems that this optimum amount is not especially sensitive to dislocation density. In case the beryllium content is as high as 2%, the optimum amount of indium is broadened to a range of 0.2 to 0.5%. (2) The activation energy of precipitation obtained from age-hardening curves is 23 kcal/mol for 50% cold rolled Cu-1.5%Be binary alloy, but it decreases to 16 kcal/mol when the alloy contains 0.3% indium. It is considered that the added indium facilitates the nucleation of coherent precipitation and thus lowers the activation energy of nucleation. Improvement in mechanical properties of Cu-1.5%Be alloy by the addition of 0.3% indium is superior to the addition of 0.3% cobalt.
