Observations of vacancy-controlled decay of elastic strain caused by phase transformation of small Pb inclusions in Al

The evolution of elastic strain caused by melting and solidification of small inclusions in aluminum was investigated by in situ transmission electron microscopy (TEM). The appearance and subsequent decay of elastic deformation during phase transformation of inclusions around 100 nm in size was observed directly by TEM, and the decay rate was determined as a function of temperature. The activation energy of the process was determined by using alloy composition and inclusion size to control the transformation temperature. Experiments conducted at 150 kV showed that elastic strain was accommodated by vacancy diffusion with an activation energy of 1.20 eV, in good agreement with the established value of 1.19 eV for self-diffusion in high-purity Al. Different rates observed at higher operating voltages were analyzed quantitatively in terms of radiation effects. The self-diffusion coefficient DS = D0 exp(-Q/kT) (with D0 = 1.55 × 1012 nm2/s and Q = 1.20 eV) derived from our data is in good agreement with the accepted values available in the literature.