The microstructure and mechanical hardness of cast Ti-30Nb-5Sn after solution treatment

This work reports the investigation on the development of microstructure and the resulting mechanical hardness of a metastable β Ti-30Nb-5Sn alloy as a result of solution treatment. The solution treatment was conducted at 1000°C for 5 h followed by water quenching. The microstructure was studied by a field emission-scanning electron microscope (FE-SEM) which equipped with EDX analysis for identifying the elemental composition. The phase change occurred in the alloy was analyzed by XRD while the mechanical hardness was measured by Vickers's hardness technique. The results showed that the solution treatment induced the nucleation of intragranular α-phase precipitation in the alloy which formerly composed of only single β-phase with dendritic structure in the as-cast condition. The α-phase exhibited a micro size plate-like morphology distributed randomly in the metallic grain and along grain boundaries of the solution-treated alloy. The α phase precipitate contained a significantly lower Nb concentration (25.07 wt%) than the surrounding matrix (33.78 wt.%). The presence of α-phase precipitate enhanced the mechanical hardness from 274.3 to 335.8 HV. The results implied that the microstructure and hardness of the Ti-30Nb-5Sn were significantly altered by the solution treatment.