Complete fine-equiaxed β-columnar grains in laser direct energy deposition of Ti–6Al–4V parts

Abstract

Coarse β-columnar grains are often present in Ti–6Al–4V laser-additive-manufactured samples, resulting in anisotropic and inferior fatigue performance under dynamic loading. Fine-equiaxed grains (FEGs) with a mean grain size of approximately 139 μm were successfully obtained by a novel deposition strategy through coordinated regulation of direct energy deposition technological parameters. Microstructures were transformed from α′ martensite to α'' martensite. As a result, the comprehensive performance was significantly improved. Without the use of an argon atmosphere glovebox and post heat treatment, the tensile strength and elongation in the horizontal direction of the FEGs were 1091 MPa and 4.09%, respectively. The corrosion resistance was 11.71-fold higher than that of the coarse columnar grains (CCGs). Improving the microstructure and performance by optimizing pulsed laser parameters is simple, effective, and conducive to online regulation of the quality of laser additive samples.

Keywords

• Ti–6Al–4V
• β-columnar grains
• Fine-equiaxed grains
• Direct energy deposition
• Mechanical properties