Structural Evolutions of Nanostructured CoAl Intermetallic Compound during Mechanical Alloying and Subsequent Heat Treatment

Abstract

Nanostructured B2-CoAl has been successfully synthesized directly by MA of nominal composition of Co50Al50. The CoAl phase was found to be formed in an ordered structure via a gradual reaction which completed in less than 10 h. However, further milling up to 45 h led to disordering of the CoAl with a relatively constant long-range order parameter of 0.82. Lattice parameter measurements showed that disordering of CoAl was caused by triple defect mechanism. The results of isothermal annealing showed that the grains grew after isothermal annealing up to 0.7 Tm but still remained below 100 nm. The grain growth behavior was well described by the parabolic kinetics equation. The grain growth exponent remained constant above 873 K offering that grain growth mechanism does not change at high temperatures. The grain growth exponents and activation energies offered the mechanism of diffusing Co and Al atoms in the two separate sublattices at high temperatures. The equation 4 4 13 D D0 6 10 exp 175 RT t was suggested to describe the grain-growth kinetics of nano-crystalline CoAl during isothermal annealing at temperatures above 0.5Tm (873 K). When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35113