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

Abstract

► The temperature interval of α + β two-phase region is from 930.7 K to 1062.6 K. ► ω phase was detected after normalizing at 773 K and 873 K. ► An approximated relationship b ( T 0 , υ ) = 0.019 ( T 0 − 939.6 ) / υ was deduced. ► Mechanical properties were sensitive to cooling rate. 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 ω phase is detected after normalizing at 773 K and 873 K. The β-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 α 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 α s phase is very slow or stops when the temperature is cooled to 939.6 K. The thickness b of the α s phase of the Zr–45Ti–5Al–3V alloy relies on the onset transition temperature during cooling T 0 , and cooling rate υ has been deduced as b ( T 0 , υ ) = 0.019 ( T 0 − 939.6 ) / υ 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.