The influence of precipitation transformation on Young's modulus and strengthening mechanism of a Cu–Be binary alloy

Abstract

A quantitative investigation on the influence of precipitation process and kinetics on the Young's modulus evolution and strengthening mechanism of a Cu-1.95 wt % Be alloy is conducted to in this paper. It is proved by both experimental and theoretical analysis that continuous precipitation of Cu–Be alloy is initiated by the coexistence of ordering and decomposition. The Young's modulus of Cu–Be alloy is found increasing from 114 to 115 GPa to higher than 130 GPa when aged at 593 K. The highest modulus is obtained in specimens aged at 593 K for 1 h and 16 h, corresponding to the microstructures containing G.P. zones & γ″ precipitates, and γ΄ & γ precipitates, respectively. The Young's modulus increases very slowly or even remains steady with aging time in range of 2 h–12 h. The evolution of Young's modulus is attributed to the combing effect of the continuous precipitation and the composition variation of Be atoms in matrix simultaneously, according to the quantitative analysis by a mathematical model and a finite element model. The strain-field generated by precipitations is found to be another important factor on modulus. The precipitation strengthening mechanism is investigated by a comprehensive theoretical model, to reveal the probability and contributions of the two dislocation pinning mechanisms, i.e., dislocation by-shearing and by-passing effects. Dislocation by-shearing is considered as the leading strengthening mechanism during the initial stage of precipitation, yet it will be weakened as aging time increases.