Defect-assisted diffusion and kinetic stabilisation in Cu–Al–Be martensite

An acoustic technique operating at a frequency of about 100 kHz and strain amplitudes of 10−7 to 2 × 10−4 is employed to investigate diffusion mobility of point-like defects in the β ′ 1 martensitic phase of a Cu–10.4 wt.% Al–0.47 wt.% Be single crystal at temperatures down to 9 K. Diffusion of the quenched-in point-like defects in the Cu–Al–Be martensite is detected by amplitude-dependent anelasticity at much lower temperatures than for other Cu-based martensitic alloys (Cu–Al, Cu–Al–Ni, Cu–Zn–Al). Strain amplitude dependence of the internal friction and Youngʹs modulus defect indicates that the formation of pinning atmospheres at temperatures up to 200 K is restricted to the regions swept up by oscillating partial dislocations/interfaces and, therefore, should be attributed to the efficient dislocation/interface-assisted diffusion of point-like defects. Observation of the intense defect-assisted diffusion in the Cu–Al–Be martensite accounts for the extremely strong “kinetic” stabilisation of martensite in Cu–Al–Be, which is evident from calorimetry data and is much less intense in other Cu-based martensites.