Structural evolution and mechanical properties of Zr-45Ti-5Al-3V alloy by heat treatments

The structural evolution and mechanical properties of Zr-45Ti-5Al-3V alloy during heat treatment are investigated. X-ray diffraction (XRD) is used to analyze the alloy phase composition. The omega phase is detected after normalizing at 773 K and 873 K. The beta-phase content increases with increasing holding temperature from 773 K to 973 K. The transmission electron microscopy (TEM) images of the microstructure shows that the thickness of the secondary alpha(s) phase is remarkably dependent on the cooling rate. The phase transformation is controlled by nucleation rate during cooling from low temperature 773 K and by growth velocity when cooled from high temperatures 973 K and 1073 K. The growth of the alpha(s) phase is very slow or stops when the temperature is cooled to 939.6 K. The thickness b of the alpha(s) phase of the Zr-45Ti-5Al-3V alloy relies on the onset transition temperature during cooling T-0, and cooling rate v has been deduced as b(T-0, v) = 0.019 root(T-0 - 939.6)/v based on diffusion controlled growth mechanism. Tensile test results indicate that the strength of heat-treated Zr-45Ti-5Al-3V alloy is very sensitive to cooling rate. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.