Achieving high strength and ductility in Ti-6.8Mo-3.9Al-2.8Cr-2Nb-1.2V-1Zr-1Sn alloy by rapid optimizing microstructure through gradient heat treatment

Abstract

In this stuy, a new high-throughput heat treatment method was applied to rapidly optimize the microstructure of metastable β titanium alloy Ti-6.8Mo-3.9Al-2.8Cr-2Nb-1.2V-1Zr-1Sn to obtain high strength and ductility. Continuous temperature gradient solution treatment was created in a tubular furnace at 746–909 ° C (the β-transus temperature (845±5) °Q on a length rod. Then, the gradient soluted sample was cut into four identical ones, three of which were aged for 8 h at 450, 550 and 600 °C, respectively. The effect of solution temperature on age hardening was rapidly achieved, and the gradient microstructure was characterized in detail in one high-throughput sample. The results showed that, the width and spacing of secondary α phase (α_s) decreased with the increase of solution temperature, resulting in the increase of strength and the decrease of elongation, while with the increase of ageing temperature the opposite trend appeared. After solution treatment at 746 °C for 2 h and ageing at 600 °C for 8 h, the hierarchical microstructure composed of the primary α phase (α_p), sub-micro α-rods (α_r), and α_s formed, which contributed superior combination between strength and ductility with the yield strength of 1140 MPa and elongation of 15%, respectively.

Keywords

high-throughput heat treatment / metastable β titanium alloy / hierarchical microstructure / high strength and ductility

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