Electron beam powder bed fusion of Ti–6Al–2Sn–4Zr–2Mo alloy: microstructure evolution and high-temperature mechanical properties

Ti-6Al-2Sn-4Zr-2Mo (Ti6242) is a promising alloy for hot engine parts and gas turbine components, such as discs, impellers, and turbines, due to its excellent performance, particularly at high working temperatures. However, there has been limited research on its thermomechanical performance and microstructural evolution at high temperatures. This study aims to investigate the microstructural evolution and flow behaviour of this alloy produced via the electron beam powder bed fusion process. The plastic response in a temperature range of 25-620 degrees C was investigated using warm tensile tests under a constant strain rate. The outcomes showed that the plastic deformation capacity of the alloy extends significantly by increasing the temperature due to the annihilation of the dislocation density and activation of pyramidal slip systems. Microstructural observations revealed that with increasing temperature, even if the initial size of the beta-grains remained in the range of 30-60 mu m, the width of alpha lath enlarged. In addition, it was found that with higher test temperatures, the lattice strain diminished, while the crystallite size increased, which affected the tensile strength of the material. Analysis of the fracture surface revealed a mixed fracture mode of ductile and brittle nature at room temperature, while a completely ductile fracture was obtained at high temperatures. All in all, it can be concluded that among the materials produced by electron beam powder bed fusion, the mechanical performance of Ti6242 alloy can surpass that of Ti-6Al-4 V(Ti64) in the temperature range studied and is also superior to the same Ti6242 alloy produced by casting. This work paves the way for the replacement of the widely used Ti64 or heavier alloys, particularly for highly loaded parts at high temperatures.