Processing and mechanical behavior of Cu-Bi alloys with high volume fraction of Bi: Suitability for high temperature soldering application

This work evaluates potential of Cu-Bi alloys comprising high volume fraction of Bi for high temperature soldering application. Cu-Bi alloys with 20, 40 and 60 vol% Bi are processed using liquid phase sintering (LPS). Effects of various sintering parameters, such as sintering time, temperature and relative green density, are studied to establish experimental conditions for preparing Cu-Bi alloys with optimum microstructure. Compression tests at different temperatures, ranging from RT to 260 °C, and strain rates, ranging from 5×10−4 to 1×10−2 s−1, are conducted to assess effects of temperature, strain rate and Bi content on the overall mechanical response of the material. The sintered density increases with increase in the green density and, with some exception, also with the sintering period and the sintering temperature. On the other hand, overall densification decreases with green density. Yield strength and strain-hardening exponent of Cu-Bi alloys decrease with increase in both the mechanical testing temperature and the volume fraction of Bi in the alloy. In addition, a set value of strain rate sensitivity can also be attained by optimizing the Bi content in Cu-Bi alloy and the test temperature. Microstructurally aware finite element analysis is performed to gain insights into deformation processes. Finally, a rationale for using Cu-Bi alloys as high temperature solders is presented.