Microstructure, texture and tensile property as a function of scanning speed of Ti-47Al-2Cr-2Nb alloy fabricated by selective electron beam melting

Abstract

The effect of scanning speed on microstructure, phase composition, texture and tensile property of Ti-47Al-2Cr-2Nb alloy fabricated by selective electron beam melting (SEBM) was investigated systematically in this paper. With the scanning speed increasing from 1500mm/s to 2400mm/s, the microstructure transformed from near γ microstructure with average grain size of 5.11µm into fine duplex microstructure with average grain size of 2.98µm and the content of α2 and B2 phase decreased from 5.0% to 1.5% and 11.6–1.2%, respectively, while the volume fraction of γ phase increased from 83.4% to 97.3%. The crystallographic texture showing an obvious α2 (0001) and γ (111) orientation weakened with enhancing the scanning speed. Additionally, the tensile property was tested and the result showed that the ultimate tensile strength (UTS) increased from 626.07MPa to 684.98MPa with scanning speed increasing from 1500mm/s to 2100mm/s, while when the scanning speed reached to 2400mm/s, the UTS decreased to 556.9MPa. The fracture strain (δ) had the same tendency as the tensile strength with increasing the scanning speed. The increasing porosity was responsible for the degradation of tensile property with the scanning velocity of 2400mm/s. Finally, the mechanisms of microstructure refinement and texture weakening with increasing scanning speed were discussed detailedly.