Influence of processing parameters on beta grain morphology of laser solid forming of Ti-25V-15Cr burn-resistant titanium alloy

Abstract

A burn-resistant titanium alloy Ti-25V-15Cr was deposited by laser solid forming (LSF) from blended Ti, V, and Cr powders, resulting in as-deposited samples with uniformly distributed elements of V and Cr. It was found that the grain morphology of LSF Ti-25V-15Cr alloy differed quite significantly from conventional titanium alloy components obtained by LSF, which are usually characterized by large columnar grains. With increasing laser power from 1500 to 2400 W, laser solid formed Ti-25V-15Cr alloy exhibited similar morphological characteristics of prior-β grains, which are mainly composed of near-equiaxed grains with an aspect ratio that is a little higher than 1, or small bamboo-like columnar grains. Meanwhile, gas porosity was significantly reduced with increasing laser power. By decreasing the scanning speed from 10 to 2.5 mm s−1 under certain processing parameters, the morphology of the prior-β grains of laser solid formed Ti-25V-15Cr alloy turned from small near-equiaxed grains to large columnar grains that grow epitaxially. The grain size increased while the gas porosity significantly decreased. Finally, the formation mechanism of prior-β grains under different processing parameters was elucidated by combining the columnar to equiaxed transition (CET) model and the thermal behavior analysis during deposition.