Tailoring microstructure of additively manufactured Ti6Al4V titanium alloy using hybrid additive manufacturing technology

Abstract

An innovative hybrid additive manufacturing (HAM) technology combining laser shock peening without coating (LSPwC) and laser powder bed fusion (LPBF) has been proposed to tailor the microstructure of additively manufactured Ti6Al4V titanium alloys. Herein, we investigated the characteristics and evolution of interfacial microstructures between adjacent LPBF layers using electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). The experimental results demonstrated that the martensitic laths in the LSPwC-treated region changed to equiaxed ultrafine grains under alternating mechanical and thermal effects. Moreover, the LSPwC-induced shock wave caused a transformation in the interface bonding behavior at the interface between the adjacent LPBF layers from the transitivity mechanism to the impregnation mechanism. Based on these results, the LSPwC-induced microstructural evolution mechanism at the interface between adjacent LPBF layers is related to LSPwC pre-activated high-density dislocations and nano twins that promote recrystallization during LPBF new layers and the formation of ultrafine equiaxed grain interlayers. Consequently, compared with the LPBF specimen, the HAM specimen indicated a high ultimate tensile strength of ∼1303 MPa and an excellent elongation of ∼12.7 %.