Energy-based efficient residual stress prediction of titanium alloys with lack-of-fusion porosity in powder bed fusion

Abstract

Residual stress and porosity exert adverse effects on the mechanical properties of metal parts fabricated by powder bed fusion. However, the modeling of the correlation between process parameters, process-induced porosity, and residual stress remains challenging. In this paper, a thermo-mechanical model of titanium alloy with porosity is established, where the relation between process parameters, porosity, and effective material properties is identified. The porosity is first predicted based on the power conservation principle in the process. The effective material properties of as-built titanium alloy with porosity are estimated using a homogenization method. Subsequently, the stress and distortion resulting from temperature variation are predicted using the shear deformation theory. The predicted results exhibit excellent agreement with the predictions and experimental results in the literature. Furthermore, the effect of the main process parameters on the porosity, residual stress, and distortion is investigated. The results show that excessive laser power, small laser radii, and extensive scan tracks contribute to a significant lack-of-fusion porosity. Additionally, the normal stress along the scan direction and vertical deflection are the major residual stress and distortion of titanium alloy with porosity, respectively. The proposed model can serve as a guideline for the design and fabrication of PBF-built titanium alloys.