Overcoming the limitation of in-situ microstructural control in laser additive manufactured Ti–6Al–4V alloy to enhanced mechanical performance by integration of synchronous induction heating

Although a variety of processing routes were developed to in-situ manipulate microstructure for fabricating high-performance Ti–6Al–4V alloy by directed energy deposition (DED), the in-situ microstructural control ability has been limited and lead to a narrowed mechanical property control range. This work proved the microstructural correlation between β-grains and α-laths resulting from the unique thermal characteristics of DED for the first time and solved such a dilemma through synchronous induction heating assisted laser deposition (SILD) technology. The results confirmed that the laser energy and inductive energy have a different effect on the solidification and solid phase transformation conditions. By adjusting the laser-induction parameters, the microstructural correlation can be tuned; the β-grains and α-laths can be controlled relatively separately, thereby significantly enhancing the ductility of as-deposited sample (elongation from 14.2% to 20.1%). Furthermore, the mechanical properties of the tuned microstructures are even comparable to that of DED Ti–6Al–4V with post heat treatment, which indicates that the potential of SILD to be a one-step manufacturing process to fabricate high performance components without post heat treatment. Furthermore, the tensile testing results of the tuned microstructures indicate that α-lath size is more influential on the mechanical properties than the β-grain size due to its stronger hindering effect on the slipping of dislocations. This work promotes the understanding of the microstructural formation mechanism in DED titanium alloy and proves that the combination of synchronous induction and laser can expand the ability to control the microstructure and properties of multi-layer deposition.