Formation and reversion of metastable fcc phase in a Ti–5Ta–2Nb explosive clad

• Formation and reversion of metastable fcc Ti phase in an explosively cladded Ti–5Ta–2Nb alloy were studied.
• The α phase nucleated both homogeneously within the fcc phase and on the fcc/α interfaces during the reversion.
• The orientation relationship between fcc and hcp phases was obtained as 1−1−0fcc//011−0α, 021fcc~2∘01−11α.
• The maximum reversion of metastable fcc phase was observed at a temperature of 600 °C.

This paper presents the results of an electron microscopy study on the formation of metastable fcc Ti phase under shock loading conditions in an explosive clad of α + β Ti–5Ta–2Nb alloy and the mechanism and kinetics of its reversion during annealing. The fcc Ti phase with a volume fraction of over 0.6 formed in hcp Ti matrix with a characteristic needle shaped morphology. The biphasic fcc + α structure when heat treated in the temperature range of 100–1100 °C showed the gradual transformation of fcc to parent α phase and the maximum reversion was observed at temperatures > 600 °C. The α phase was nucleated within the fcc as well as on the fcc/α interfaces. Orientation relationship between fcc and hcp phases has been derived using standard 1−12fccand [0001]α stereographic projections. The kinetics of the reversion process followed diffusion controlled nucleation and growth process with an effective activation energy corresponding to the self diffusion of Ti in hcp matrix.