Effect of intercritical annealing temperature on microstructure and mechanical properties of duplex Zr-2.5Nb alloy

Duplex microstructure in Zr-Nb alloy possesses excellent mechanical properties. However, the effect of annealing temperature on the formation of duplex microstructure and its mechanical properties is not known. Determination of this effect is important for optimising the heat treatment process and expanding the knowledge of the microstructure. The detailed microstructure information and the relevant mechanical properties of the Zr-2.5Nb alloy annealed at 700 °C–900 °C have been studied. The amount of ω phase in alloy gradually increases and then decreases with increasing annealing temperature. The highest amount of ω phase is obtained in the specimen annealed at 750 °C, and no ω phase is formed when the specimen is annealed at 900 °C, which is mainly affected by the solution of Nb element in the β phase. The amount of primary α phase gradually decreases with increasing temperature, and its size remains stable at ∼3 μm. However, the size of transformed β phase gradually increases from 1.5 μm to 12.4 μm. Mechanical property results reveal that the alloy annealed at 750 °C exhibits the highest strength of 996 MPa for the highest amount of ω phase, and the alloy annealed at 850 °C possesses the best ductility of 31.3%. •Duplex microstructure can be obtained when the temperature is higher than 800 °C.•Except for the 900 °C specimen, the ω phase is formed in all annealing specimen.•The most ω particles formed in 750 °C specimen, resulting in the highest strength.•The 850 °C specimen has the best comprehensive properties for highest ductility.