Crystal growth mechanism and mechanical properties of Ti-6Al-4 V alloy during selective laser melting

Abstract

In this study, the microstructure evolution and mechanical properties of Ti-6Al-4 V alloy fabricated by SLM were investigated with various energy densities. Experimental results showed that the fast solidification induced by high-speed laser scanning resulted in a prior β columnar grain and multistage acicular α' phase within the final solidified microstructure, and that a high energy density could cause the size of β columnar crystals and α' phase to rise. During SLM solidification, different crystallization types were found of the molten pool due to different temperature gradients and heat flow directions. Furthermore, the results indicated that grain size and densification degree, both of which are affected by energy densities, could have a considerable impact on mechanical properties. Additionally, the anisotropy of the material's tensile characteristics was determined by the geometry of the molten pool boundary and the growth direction of the microstructure. As the energy density was selected at the optimal value of 74.07 J/mm3, the largest tensile strength of 1138 MPa with a strain of 5.1% was obtained.