Achieving Ultra-High Strength in Tib/Metastable-Β Composites Via Short-Process Isothermal Forging

Abstract

Lightweight titanium alloys with ultra-high strength and reasonable ductility are desirable for aerospace applications. However, titanium alloys typically require cumbersome heat treatment to achieve excellent mechanical properties. Here, ultra-high strength Ti-55531-based composites were fabricated by introducing TiB whiskers using a short process, i.e. melting and isothermal forging. The microstructure evolution during isothermal forging was investigated in detail, and it was found that the main softening mechanism of the matrix alloy was dynamic recovery. TiB whiskers would promote the discontinuous dynamic recrystallization and impede abnormal grain growth, resulting in significant matrix β grain refinement, equiaxialization, and crystal orientation randomization. In addition, a uniformly distributed of nano-scaled αs lamellae were formed in the β grains during isothermal forging, and TiB promoted dynamic globularization of αs lamellae. Moderate addition of TiB simultaneously improved the strength and elongation of the isothermally forged composites, 2.5 vol.% TiB/Ti-55531 achieved a superior strength-plasticity synergy with the ultra-high strength of 1525±4 MPa and elongation of 6.4%±0.2%, which were 9.2% and 12.3% higher than that of Ti-55531, respectively. The strengthening mechanisms were thoroughly analysed, and the ultra-high strength was mainly attributed to αs precipitation strengthening, β grain refinement strengthening, and load-bearing strengthening of TiB whiskers. Our study demonstrates that isothermal forging can effective prepare ultra-high strength TMCs while achieving a synergistic improvement of strength-plasticity.

Keywords: Short-process, Titanium matrix composites (TMCs), Ultra-high strength, Dynamic recrystallization, Strengthening mechanisms.