Effect of Heat Accumulation during Selective Laser Melting on the Microstructure of TA15 Titanium Alloy with Different Geometry Characteristics

Author of the article:WANG Qian1,2, QIN Xiangyang1,2, LIU Xiaoyu1,2, ZHOU Junfeng1,2, TAO Siyuan1,2, LIU Shuai1,2, WANG Me

Author's Workplace：1. MIIT Key Laboratory of High Performance Additive Manufacturing and Innovative Design of Metal Structure, Northwestern Polytechnical University, Xi'an 710072, China; 2. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China

Key Words：TA15 alloy; selective laser melting; heat accumulation; microstructure; in situ decomposition of martensite

Abstract：The plasticity of as-deposited TA15 titanium alloy prepared by selective laser melting (SLM) is often poor, and heat treatment is necessary to promote the decomposition of martensite into lamellar (α+β) laths so that the plasticity can be improved. During the SLM process, the unique thermal history can promote the in situ decomposition of martensite and adjust the as-deposited microstructure to a certain extent. In this study, TA15 alloy specimens with cylinder and inverted cone were prepared by selective laser melting. The heat accumulation of the specimens was analyzed based on temperature simulation results for the building process, and the effect of thermal accumulation on the microstructure of the specimens was analyzed with reference to the microstructure observations. The results show that the grain structure in the cylindrical specimen is β columnar grains composed of the martensite α′ phase. However, with the severe heat accumulation in the inverted cone specimen, transformation from β columnar to equiaxed β is observed, and in situ decomposition of the metastable martensite α′ occurs, leading to the formation of a lamella (α+β) structure. The extent, as well as the holding time of heat accumulation, are important factors for the in situ decomposition of the martensite α′ phase.