High-temperature deformation microscopic mechanisms of selective laser melted Ti6Al4V alloy: Experimental study and crystal plasticity modeling

Selective laser melted Ti6Al4V alloy has garnered significant attention due to its exceptional strength-to-weight ratio. However, at 673 K where twin annihilation occurs, this material exhibits a transition in the relationship between yield strength and strain rate response, namely a strain rate sensitivity transition (SRST). Elucidating the correlation between twinning activity and mechanical behavior of selective laser melted materials is crucial for understanding their deformation mechanisms. In this work, the SRST is experimentally observed in selective laser melted Ti6Al4V alloy. The evolution of grain size, precipitate solute states, and twin volume fraction is analyzed using SEM and EBSD, and the micro-mechanisms linking twinning activity with SRSTs are elucidated. Both results further demonstrate that the rapid decline of twinning activity at critical temperatures triggers the SRST, while the temperature-insensitive nature of solute precipitation yields similar strain rate sensitivity at non-critical temperatures. The high initial twin volume fraction suppresses its further increase during subsequent deformation, leading to reduced ductility. A dislocation-twinning coupled crystal plasticity constitutive model incorporating twinning evolution and temperature-dependent solid solution strengthening is developed, and the SRST in SLM Ti6Al4V is effectively simulated. This work may enhance the understanding of plastic deformation mechanisms of SLM Ti6Al4V.