Athermal stabilization of Cu–Al–Be β1′ martensite due to plastic deformation and heat treatment

Effects of plastic prestrain and of different heat treatments on the stabilization of martensitic β1′ crystals of a Cu–Al–Be alloy have been studied. Directly quenched and plastically prestrained samples (subjected to preliminary heat treatments, suppressing the stabilization) undergo the reverse martensitic transformation in two distinct stages. The first stage is a partial bulk transformation which exhibits typical stabilization properties: shift and broadening of the reverse transformation range. The rest of the martensite is hyperstabilized both in prestrained and quenched samples and retransforms through renucleation of lamellar β-phase at temperatures approximately 300 K above the nominal reverse transformation. In prestrained samples, the magnitude of shift and broadening of the first stage of the reverse transformation depends on the degree of plastic prestrain, whereas the renucleation of β-phase occurs at nearly constant temperatures, independent of the amount of prestrain. Relative fractions of martensite retransformed to the β-phase through the normal mechanism of reverse motion of variant interfaces and through renucleation of β-phase depend on the degree of prestrain. Stabilization registered after different heat treatments is virtually instantaneous and it is not related to martensite aging. The conclusion is drawn that heat treatment-induced stabilization in Cu–Al–Be β1′ martensite is athermal, not related to diffusion-controlled processes during aging of martensite, but associated with jamming the motion of interfaces, similar to prestrain-induced stabilization. Plausible mechanisms of athermal stabilization registered after heat treatment are discussed.