Nucleation, growth and coarsening of γ′-precipitates in a Ni-Cr-Al-based commercial superalloy during artificial aging

A study of the decomposition kinetics of the IN-X750 Ni-based superalloy using positron annihilation lifetime spectroscopy (PALS), microhardness and transmission electron microscopy (TEM) is presented. PALS results confirmed that nucleation and growth of γ′-precipitates are assisted by vacancies. Due to the high sensitivity of positrons for vacancy-like defects, information regarding vacancy-solute clusters formed during the very early stages of aging was obtained. The positron lifetime and TEM results were analyzed following classical precipitation models to interpret the kinetics of the γ′-precipitate formation. Finally, from TEM measurements a value of the γ′-precipitate coarsening rate for the alloy studied was obtained.