Effect of multistage lamellar microstructure on mechanical properties of Tc18 alloy

In this study, a three-step heat treatment approach, which included annealing, solution treatment at 740-820 degrees C, and aging at 450-550 degrees C, was employed to control the precipitation behavior of the alpha phase in TC18(Ti-5Al-5Mo5 V-1Cr-1Fe) alloy. The multistage microstructure resulting was found to contain both the primary lamellar structure (alpha) and the secondary lamellar structure (alpha s), and the relationship between the spacing of multi-level lamellar microstructure and the mechanical properties of the alloy was effeciently determined. The study demonstrates that lowering the solid solution temperature reduces the interlayer spacing of the primary alpha phase, and increasing the aging temperature enlarges the interlayer spacing of the secondary alpha s phase, thereby enhancing the material's mechanical performance. Nevertheless, a substantial discrepancy in yield strength exists between these two interlayer spacings, which impacts the stress-strain coordination and reduces the plastic zone at the crack tip, and also increases the likelihood of formation of microvoids and microcracks at grain boundaries.