Effect of the prior-β grain boundaries on mechanical behavior of Ti6Al4V alloy processed by laser directed energy deposition

Abstract

Laser directed energy deposition (LDED) has a manufacturing advantage, however, the anisotropy of mechanical properties is a challenge. In this work, the tensile and fatigue properties of LDED-ed samples under different direction stresses were systematically investigated. The pore distribution and the microstructure of LDEDed samples were researched, moreover, the micro-hardness, grain orientation spread (GOS), and Schmidt factor of prior-β grain boundaries (αGB) were calculated by nanoindentation and electron backscatter diffraction analyses. It was found that the micro-hardness of αGB was much lower than that of prior-β grains, however, the GOS Value and Schmidt factor of αGB were higher than those of prior-β grains. Therefore, dislocation slip at αGB was easily initiated. The anisotropy of mechanical properties was dependent on the relationship between the prior-β grains and the stress direction. The crack initiation and propagation easily occurred in αGB during horizontal stress. Furthermore, the forming height greatly affected the pore distribution, and larger pores caused a deterioration of mechanical properties during vertical stress. The findings of this work can provide useful insights into the anisotropy of LDED-ed titanium alloys.