Morphological evolution of Ti2Cu in Ti-13Cu-Al alloy after cooling from semi-solid state

Abstract

The mechanical performance of Ti-13Cu-Al alloy is highly determined by its microstructure, which is significantly affected by the cooling process from semi-solid state as it induces peritectic solidification and the subsequent eutectoid transformation of the alloy. This work investigated the effects of cooling rates on the morphology of Ti2Cu phase and mechanical properties of Ti-13Cu-Al alloy after cooling from semi-solid state (β+L phase). Different cooling mediums have been considered, including furnace cooling (0.5 °C/s), air cooling (50 °C/s) and water cooling (150 °C/s), corresponding to a slow, normal and rapid cooling process, respectively. It is found that α+Ti2Cu phases are uniformly distributed in the alloy after different cooling processes, and the morphology of Ti2Cu phase is controlled by the peritectic solidification and eutectoid transformation. Specifically, the thickness and the volume fraction of primary Ti2Cu phase are larger than the sample cooling from β phase field when the cooling rate is the same. The morphology of Ti2Cu phase varies from “laths + blocky + sheaves” to “short laths + blocky + rodlike” as the cooling rate gradually increases. It is further revealed that the β/L interface provides a fast channel for solute atom diffusion, and the peritectic Ti2Cu phase provides a favorable nucleation site for the precipitation of eutectoid Ti2Cu. Based on the tensile property and hardness examinations, the mechanical properties of the Ti-13Cu-Al alloy show a clear dependency with the precipitation of Ti2Cu phase after cooling from semi-solid state, indicating the importance of cooling mode from semi-solid state on the microstructure and mechanical properties of the alloy.