Effect of vanadium on the microstructure and kinetics of discontinuous precipitation in Cu–3.2Ti–0.2Fe alloy

Abstract

The microstructure and kinetics of discontinuous precipitation in Cu–3.2Ti–0.2Fe–xV (x = 0, 0.1, 0.2 and 0.3 wt.%) alloys aged at 723, 773, 823 and 873 K were studied by using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS), with the help of CALculation of PHAse Diagram (CALPHAD) method and Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. The volume fraction of Laves_C14 was increased with raising V content, leading to the effective grain refinement during casting and the inhibiting grain growth in solution treatment process. The activation energies of Cu–3.2Ti–0.2Fe–xV (x = 0, 0.1, 0.2 and 0.3 wt.%) alloys were 196.4, 172.9, 147.4, 154.1 kJ mol−1, respectively. The discontinuous precipitation was promoted and controlled by grain boundary diffusion in the early stages at low temperature, while it was inhibited by bulk diffusion at high temperature or in the later stages at low temperature. In addition, the peak-aged hardness was improved with proper amount of V addition due to the strengthening of Laves_C14 and grain refinement, as well as the inhibition of discontinuous precipitation.

Keywords

• Cu–Ti alloys
• Microstructure
• Kinetics
• Discontinuous precipitation
• Grain refinement