Influences of island size on the forming quality, microstructure, and tensile properties of laser powder bed fusion Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy

Abstract

Island scanning can reduce the residual stress in the process of laser powder bed fusion (LPBF), however, the role of island size has rarely been systematically investigated. Herein, the influences of island size on the forming quality, microstructure, and tensile properties of LPBF-processed Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy were experimentally investigated coupled with a finite element simulation. Moreover, the alloy composition and microstructure around pores were investigated in the overlapped zone of island scanning. It was found that the laser jumps and the deformation of island edges formed the gully morphologies in the overlapped zone, which resulted in poor forming quality. Meanwhile, the overlapped zone generated several peak temperatures in a short time, leading to the increase of α′ phase transformations and basketweave α′ phases. The fracture behavior of the alloy was affected by the presence of oxides and non-uniform microstructures around pores. The samples with small island sizes had a complex microstructure, poor forming quality, high tensile strength, and low elongation, respectively. Therefore, the ultimate tensile strength and elongation of the sample with an island size of 2 mm were 1310 MPa and 5.6 %, and the corresponding values for the sample with 7 mm were 1193 MPa and 10.4 %, respectively. The findings of this work can shed some light on the relationship between the mechanical properties of LPBF-fabricated alloys and island size.