Thermal Analysis of Relaxation Processes of Supersaturated Vacancies in B2-Type Aluminides

Abstract

ABSTRACTRelaxation behavior of supersaturated vacancies in water-quenched and rapidly solidified B2 type CoAl and NiAl with the stoichiometric composition was studied by differential scanning calorimetry (DSC). In both CoAl and NiAl quenched from 1773 K, a single exothermic peak due mainly to the recovery of supersaturated vacancies appeared near 950 K. On the other hand, the exothermic peak was also observed in as-spun rapidly solidified CoAl and NiAl ribbons, and the temperature range of the peak was much broader than that of quenched-in bulks, suggesting that the peak in the rapidly solidified ribbons results from not only a single recovery process of vacancies but also those of some other lattice defects. TEM observation showed that a large amount of dislocations were introduced in the NiAl ribbon and that comparatively many voids as well as an amount of dislocations were introduced in the CoAl ribbon.