Research on aluminum component change and phase transformation of TiAl-based alloy in electron beam selective melting process under multiple scan

Abstract With the developments and applications of additive manufacturing technologies, additive manufacturing of hard-workable TiAl-based alloys has been widely studied. Electron beam selective melting (EBSM) is regarded as a promising additive manufacturing process with the advantages of high energy efficiency and high vacuum environment to avoid the cracks and oxidation of the brittle TiAl-based alloys. However, element loss and phase change due to evaporation in vacuum would alters the microstructure and mechanical properties. In this paper, the influence of evaporation on microstructure is investigated with higher element evaporation than that in regular EBSM process in order to understanding the effect exhaustively. A multiple low energy scan coupled with multi-region scan strategy, instead of conventional single layer scan, is utilized to enhance the element evaporation without causing the curly surface in scan area, which could damage the powder spread rake and deposition quality of subsequent layers. The results show that the atomic ratio of aluminum decreases with increasing energy input and vacuum degree and varies little in overlap between two adjacent scan region. The new (α+β) phase was formed by high evaporation of aluminum and the (α+β+α2) phases alloy exhibited the tensile strength of 947 MPa and elongation of 2.2% at room temperature.