Impact properties of half stress-relieved and hot isostatic pressed Ti-6Al-4V components fabricated by laser powder bed fusion

This study focuses on the impact properties of Ti-6Al-4V produced by LPBF using un-notched Charpy impact testing. The effects of the build orientation, impact orientation, and half stress-relief and hot isostatic press (HIP) heat treatments on the impact resistance were investigated. The impact properties of HIPed samples were significantly greater than those of stress-relieved ones. Microstructural analysis and fractography revealed that process defects such as porosity, and columnar grain boundaries play an important role in crack initiation and propagation in the stress-relieved samples. In the HIPed samples the orientation of prior-beta grain boundaries with respect to the impact loading, and impact energy absorption by microstructural modification from the high strains promoting formation of globular alpha were the main contributors in the impact resistance of the samples. Consequently, the vertically-built HIPed samples demonstrated the greatest impact energy from the combination of the perpendicular prior-beta grain boundaries to the impact and highest observed alpha globularization.