Microstructure and mechanical properties of β-21S Ti alloy fabricated through laser powder bed fusion

Metastable beta-titanium alloys are attractive for their high strength-to-density ratio, good hardenability, excellent fatigue behavior, and corrosion resistance. Among these alloys, beta-21S, with a composition of Ti-15Mo-3Nb-3Al-0.2Si (wt%), is known to offer improved elevated temperature strength, creep resistance, thermal stability, and oxidation resistance. In this study, laser powder bed fusion (PBF-LB) of beta-21S and the effect of post-PBF-LB heat treatment were investigated to understand the relationship between the microstructure and the mechanical properties. The as-built (AB) alloy is primarily composed of beta-phase, with columnar grains oriented along the build direction. The alloy AB presented a microhardness of 278 HV, a yield strength (YS) of 917 MPa, an ultimate tensile strength (UTS) of 946 MPa, and a ductility of 25.3% at room temperature (RT). Such properties are comparable to beta-21S in solution treatment (ST) condition. Solution treatment and aging (STA) of the alloy precipitated the alpha-phase, increasing the microhardness to 380 HV, YS to 1281 MPa and UTS to 1348 MPa, while reducing the ductility to 6.5% at RT. The STA alloy presented a YS of 827 MPa, UTS of 923 MPa, and a ductility of 7.7%, at 450 degrees C. The thermal treatment applied to PBF-LB beta-21S had a similar effect compared to beta-21S fabricated by non-AM techniques. The properties obtained demonstrate that beta-21S is a potential candidate for AM.