The hot deformation behavior and dynamic microstructure evolution of additive manufactured Ti6Al4V with different hydrogen addition

During the laser melting deposition (LMD) additive manufacturing process, titanium alloys undergo rapid solidification, which induce grain growth into coarse columnar grains, resulting in lower mechanical properties of the material than conventional forgings. This study proposes the incorporation of hydrogen into titanium alloys to refine columnar grains, reduce deformation resistance, and improve machinability. In this work, the hot deformation behavior of hydrogenated Ti6Al4V alloy was analyzed via high-temperature compression experiment. The experimental results revealed the nucleated grains generated by the intense deformation and the twins brought by the hydrogen element led to massive dynamic recrystallizations, which effectively improved the hot workability. When the alloys are deformed above phase transition temperature, the flow stress is positive related with H content. Meanwhile, when the alloys are deformed below the phase transition temperature, the flow stress initially experiences a decrease with an increase in hydrogen content. Adding only 0.27 wt% H can reduce the flow stress by 34.4%-54%, but when the H content continues to increase, the flow stress still increases subsequently. Moreover, when the strain rate is constant, the flow stress of Ti6Al4V alloy can decrease by about 80% with an increase in deformation temperature from 820 degrees C to 940 degrees C. When the deformation temperature is constant, the flow stress of Ti6Al4V alloy with different hydrogen contents can decrease by around 65% as the strain rate reduces from 10s-1 to 0.01 s-1.