Effects of subtransus triplex heat treatments on the microstructure and mechanical behaviors of a Ti–5Al–5Mo–5V–1Cr–1Fe near β titanium alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2022-11, Vol.859, p.144207, Article 144207
• Main Authors: An, Xinglong, Jiang, Wenting, Ni, Song, Song, Min
• Format: Article
• Language: English
• Subjects: Air cooling; Casting alloys; Casting defects; Cooling; Ductile fracture; Ductile-brittle transition; Elongation; Heat treating; Heat treatment; Hot rolling; Lamellar structure; Mechanical behavior; Mechanical properties; Microstructure; Morphology; Precipitates; Recrystallization; Tensile deformation; Tensile tests; Ti-5Al–5Mo–5V–1Cr–1Fe alloy; Titanium alloys; Titanium base alloys; Yield stress
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2022.144207

The effects of subtransus triplex heat treatments on the microstructure and mechanical behaviors of a Ti–5Al–5Mo–5V–1Cr–1Fe (Ti-55511) near β titanium alloy were systematically investigated in this study. The tensile testing results indicated that the yield stress and total elongation can be optimized from ∼1040 MPa, 3% of the as-cast alloy to ∼1140 MPa, 16% and ∼1195 MPa,12% of the heat-treated samples, respectively. The as-cast alloy exhibited a basket-weave structure containing mostly lamellar α phase. After triplex heat treatment, the morphology of α phase changed to a rod shape, and some nano-sized secondary α phase precipitates formed. The effects of heat treatment on microstructures and mechanical properties were analyzed as follows: (i) The first step (hot rolling at 830 °C + heating to 830 °C, holding for 0.5 h and furnace cooling) was conducted for recrystallization and homogenization to reduce the casting defects; (ii) The second step (heating to 750 °C, holding for 2 h and air cooling) was performed to adjust the morphology of α phase to a rod shape to improve the ductility; (iii) The third step (heating to 450 °C, holding for 8 h/16 h and air cooling) was performed to promote precipitation of secondary α and growth of primary α, to further enhance the strength. Dislocation slip was in dominance in the soft β phase, while both dislocation slip and {101‾1} twinning occurred in the α phase, during tensile deformation. The fracture behavior changed from brittle to ductile after heat treatment. Our work provided a convenient and feasible way to optimize the mechanical properties of the Ti-55511 alloy.