The effects of heat treatments on the microstructure and mechanical properties of the Ti–2.19Al–2.35Zr alloy

Ti–2.19Al–2.35Zr alloy is one of the candidate materials for the steam generator tubing of an integrated reactor, System Modular Integrated Advanced ReacTor (SMART) being developed in Korea. In this study, the effects of heat treatments on the mechanical properties of Ti–2.19Al–2.35Zr alloy were evaluated. Mechanical tests were implemented to examine the effects of an annealing, cooling rate and re-annealing temperature/time on the mechanical properties of the alloy. The annealing temperatures ranged from 600 to 1050 °C and the cooling rates were controlled by introducing a water-quenching (WQ), air-cooling (AC), and furnace-cooling (FC). As for the re-annealing heat treatment, after a β water quenching, the re-annealing temperature was selected as 800 °C for the α-phase heat treatment and 940 °C for the α + β-phase heat treatment with various time intervals (1, 10 and 24 h). The results showed that an increase of the annealing temperature to above the β-region temperature induced an increase of the tensile strength and a decrease of the elongation in the 25 and 300 °C tests. A decrease of the cooling rates from water-quenching to a furnace-cooling revealed a decrease of the tensile strength and an increase of the elongation. Also an increase of the re-annealing time with different phase regimes exhibited a decrease of the strength and an increase of the elongation. These tendencies were more dominant in the 300 °C test rather than the room temperature test from the characteristics of the microstructures which were affected by the heat treatments.