Mechanical properties optimization of a Cu-Be-Co-Ni alloy by precipitation design

The mechanical performance of precipitation hardening alloy depends much on the nature of precipitates. For the sake of properties optimization, various precipitation states were designed to clarify the correlation between the precipitation and mechanical properties of a Cu-Be-Co-Ni alloy. The characters of each precipitation state were quantitatively characterized using TEM. Then both tensile and tension-compression (Bauschinger) tests were conducted to investigate the isotropic and kinematic contributions to the work hardening. Based on the quantitative analysis results of the precipitates, a flow stress model with the integration of yield stress, isotropic and kinematic work hardening behavior was established. The model indicates that the strength and ductility are determined by two contradictory factors: the dislocation dynamic recovery rate and dislocation storage rate. Optimization of strength and ductility relies on the balance of these two contradictory factors. Large non-shearable precipitates will increase both the dynamic recovery and the storage rate while fine shearable precipitates will make them decrease simultaneously. It is suggested that the alloy containing the mixture of above two kinds of precipitates will achieve the optimization. (C) 2016 Elsevier B.V. All rights reserved.