Microstructure and Mechanical Properties of Vacuum Centrifugal Casted Ti-6Al-4V Alloy by Casting and Heat Treatment

Abstract

The Ti-6Al-4V alloy has been widely used for structural materials due to high specific strength property, however it is difficult to cast because of high reactivity at high temperature. In this study casting characteristics and post-casting heat treatment were studied in the cast Ti alloy. The cast alloy was prepared using high-frequency induction heating and horizontal vacuum centrifugal casting to reduce reaction with crucible and mold by minimizing overheating of the molten metal and casting fast. In the thin casting with a thickness of 2 mm, α’ martensite was observed, and in the casting with a thickness of 4~8 mm, α+β Widmanstätten was observed. As the thickness of the casting increased, the grain size, α-lath width, and α-case thickness increased. Accordingly, as the thickness of the casting increased, the hardness of the matrix decreased and the hardness of the surface increased. In addition, when the casting was heat treated below the β-phase transformation temperature, the α-lath width increased, and when quenched after heat treatment in the β-phase transformation temperature region, an α’ martensite was formed. On the other hand, when the casting was heat treated in the atmosphere, it was confirmed that the elongation was very low because hydrogen and oxygen in the atmosphere were induced. In addition it was confirmed that casting defects can be removed through HIP.