Near α titanium alloy Ti60 with equiaxed β grain fabricated by laser direct energy deposition assisted with ultrasound

Abstract

Laser direct energy deposition (LDED) offers unique advantages in the integrated forming of 3D complex-shape parts. However, the columnar grains that grow epitaxially along the building direction are prone to reduce the performance of the as-built parts. Herein, external ultrasonic field are introduced during the LDED of near-α titanium alloy Ti60 (Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C), resulting in equiaxed β grains with an average grain size of 62.82 μm. The single track morphology, molten pool, microstructure, and mechanical properties under different ultrasonic powers are characterized and investigated. The results indicate that the ultrasound can induce columnar to equiaxed transition (CET) of the prior-β grains and promote the precipitation of silicides, but the width of the α laths increases due to heating effect caused by ultrasound. Consequently, the sample prepared with the 6 μm ultrasonic vibration exhibits a increases of 67.18 % in elongation, and the mechanical properties reach the forge standard. Finally, the effects of prior-β grain and α lath on the final mechanical properties of the samples are discussed. This work provides a deep insight into the LDED process of near-α titanium alloy Ti60 assisted with ultrasound.