Precipitation of Cu particles during low temperature aging in an Fe-1.5 mass%Cu alloy

Abstract

The effects of prestraining on the Cu precipitation and hardening were studied in an Fe-1.5 mass%Cu alloy. The specimens showed considerable precipitation hardening only at temperatures higher than 500°C without prestraining, while the 10% prestrained specimens exhibited an appreciable amount of hardening at temperatures as low as 300°C. To investigate the mechanism for hardening due to prestraining, the precipitation of Cu particles in bcc Fe matrix is simulated using Langer-Schwartz theory (modified by Kampmann and Wagner). The Cahn-Hilliard non-classical theory was employed to calculate the nucleation activation energy of nucleation of bcc Cu particles or nano-clusters. The influence of excess vacancies and dislocations introduced during prestraining on the Cu precipitation was considered, and simulated results were compared with experimental observation by 3D-APFIM and TEM. The increase in hardness above 500°C with and without prestraining may be attributed to the Cu precipitation in the matrix. A small, but significant amount of increase in hardness of prestrained specimens aged at a temperature as low as 300°C is likely to be due to Cu precipitation on dislocations. It is also possible that excess vacancies accelerate the diffusion and thus, the kinetics of Cu precipitation both in the matrix and at dislocations.