Microstructure evolution and phase transformation kinetics of low cost Ti-35421 titanium alloy during continuous heating

Abstract The thermal expansion behavior, microstructure evolution and β → ωiso phase transformation kinetics of the low cost Ti–3Al–5Mo–4Cr–2Zr–1Fe (Ti-35421, wt.%) titanium alloy during continuous heating have been investigated by using dilatometric (DIL) method. The results revealed that corresponding transformation sequence can be verified as β → ωiso, β + ωiso → α + β, β → α and α → β using TEM and SEM analysis during the heating process. The microstructure and local composition distribution was detected by STEM mapping. The phase transition curve exhibited a typical S-type pattern, indicating the phase transformation was controlled by the nucleation and growth mechanism. It was found that the S-curve shifted to a higher temperature and the phase transition interval became shorter as the heating rate increased. Furthermore, the average activation energy required for the β → ωiso phase transition was calculated by Kissinger–Akahira–Sunose (KAS) equation is about 90.21 kJ/mol. The Avrami exponent n in the Kolmogorov–Johnson–Mehl–Avrami (KJMA) model was used to study the nucleation growth mechanism of the ω phase during continuous heating. The exponent n can be divided into three stages: the initial phase transition (0.02