Achieving grain refinement and ultrahigh yield strength in laser aided additive manufacturing of Ti-6Al-4V alloy by trace Ni addition

Fabricating fine equiaxed grains without undesirable secondary phases is highly challenging for additively manufactured Ti-6Al-4V alloy. The reference amount of Ni addition, which can achieve grain refinement without secondary phase formation, is 0.9 wt. % based on Thermo-Calc calculation. The Ti-6Al-4V-0.9Ni alloy produced by laser-based directed energy deposition demonstrate refined microstructure and an ultrahigh yield strength (1309 MPa). A modified quantitative model is proposed to analyse the strengthening mechanism, and the results demonstrate that the yield strength increment is mainly ascribed to the refined a phase. This work can contribute to the development of customised titanium alloy using additive manufacturing.

Automated summary

Fabricating fine equiaxed grains without undesirable secondary phases in additively manufactured Ti-6Al-4V alloy is highly challenging. By adding 0.9 wt. % Ni, refined microstructure and ultrahigh yield strength (1309 MPa) were achieved. A modified quantitative model was proposed to analyze the strengthening mechanism, showing that the yield strength increment mainly came from the refined a phase.