Influence of multi-stage heat treatment on the microstructure and mechanical properties of TC21 titanium alloy
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Influence of multi-stage heat treatment on the microstructure and mechanical properties of TC21 titanium alloy Wei Long 1,2,3), Song Zhang 1,2,3), Yi-long Liang 1,2,3), and Mei-gui Ou 1,2,3) 1) College of Materials and Metallurgy, Guizhou University, Guiyang 550025, China 2) Key Laboratory for Materials Structure and Strength of Guizhou province, Guizhou University, Guiyang 550025, China 3) National Local Joint Engineering Laboratory for High Performance Metal Structure Materials and Manufacturing Technology, Guizhou University, Guiyang 550025, China (Received: 5 November 2019; revised: 19 January 2020; accepted: 1 February 2020)
Abstract: Duplex-structured TC21 alloy samples were first solution-treated at a higher temperature in the α + β region (940°C) with furnace cooling (FC), air cooling (AC), and water cooling (WC), followed by a second-stage solution treatment at a lower temperature in the α + β region (900°C), and then finally aged at 590°C. The effects of the morphology and quantity of α phases on the structure and properties of the TC21 alloy after the different heat treatments were analyzed. The in-situ tensile deformation process and crack propagation behavior were observed using scanning electron microscopy (SEM). The quantity of equiaxed α phases as well as the thickness of lamellar α phases reduced, the tensile strength increased firstly and then decreased, the elongation decreased with the increasing cooling rate after the first-stage solution treatment. The amount and size of lamellar α phases increased after the second-stage solution treatment because of sufficient diffusion of the alloying elements, thereby leading to increased tensile strength. The amount of dispersed α phases increased after the third-stage aging treatment owing to the increase in the nucleation rate, resulting in a noteworthy strengthening effect. After the third-stage aging treatment, the first-stage FC sample exhibited better mechanical properties because it contained more equiaxed α and βtrans phases than the first-stage AC and WC samples. Keywords: multi-stage heat treatment; titanium alloy; in-situ tension; microstructure; mechanical properties
1. Introduction Titanium alloys are widely used in the aviation, aerospace, and petrochemical industries owing to their low density, high specific strength, heat resistance, and superior corrosion resistance [1−3]. With developments in the damage-tolerance design of titanium alloys intended for long-life structural parts, the demand for a good matching of the strength and toughness is increasing urgent for the applications such as key structural materials of modern aircrafts. The TC21 alloy based on the Ti-62222S alloy (Ti–Al–Sn–Zr–Mo–Cr– Nb−Si) is a new type of α + β titanium alloy with high strength, modulus, and damage tolerance [4−5]. Heat treatment plays an important role in the production of titanium alloys. The microstructure of titanium alloys is crucial to their mechanical properties and can be contro
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