Heat treatment effect on the microstructure and elevated temperature tensile property of the Ti6242S alloy fabricated via laser powder bed fusion

Abstract

The microstructural evolution and its consequence on the room and elevated temperature (500 °C) tensile properties of the Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti6242S) alloy fabricated via the laser powder bed fusion were investigated after the following heat treatments: solution treatment followed by aging (STA), super-transus heat treatment, and water quenching (WQ) after annealing at a sub-transus temperature (885, 925, 954, and 982 °C) in the (α + β) regime. The super-transus heat treatment results in the removal of columnar prior β grains and formation of equiaxed grains that consist of α colonies. The WQ triggers the formation of a bimodal microstructure of α and α´ phases, and the volume fraction of α´ phase increases with increasing the WQ temperature. The STA process leads to a high yield strength (σy: ~658 MPa) and an elongation to fracture (εf: ~14.8%) when tested at 500 °C. The super-transus heat treatment results in a lower yield strength at both room and elevated temperatures due to coarsening of the α laths. The WQ process allows for the tailoring of the tensile property in a broad window, and the yield strength increased with increasing WQ temperatures. Particularly, the 885 and 925-WQ samples showed a remarkably enhanced strain hardening behavior during tensile tests. The 925-WQ samples exhibited a high σy of ~706 MPa and an εf of ~11.0% at elevated temperature. The samples that underwent STA processing and 925-WQ showed a higher σy while maintaining a decent ductility relative to the conventionally fabricated counterparts at 500 °C, indicating the potential elevated temperature applications for the Ti6242S alloy fabricated via laser powder bed fusion coupled with heat treatment.