Thermal stability of nano-RuAl produced by mechanical alloying

The thermal stability of as-milled nano-RuAl has been studied by isothermal annealing at high temperatures. All three kinds of structural evolutions i n as-milled powders upon high temperature exposure, namely reordering, stra in relaxation and grain growth, show signs of stagnation. The total quantit y of impurities, mainly 15 at.% Fe has been analyzed as being dissolved sub stitutionally in RuAl and also segregated to grain boundaries. Upon grain g rowth, lattice diffusion and segregation of impurity atoms in grain boundar ies have been verified by the lattice parameter variation. The incremental apparent activation energy for grain growth at different temperatures is re lated to the accumulation of impurities in grain boundaries. Reordering and strain relaxation processes that accompany grain growth could consume a ce rtain part of the driving force for grain growth. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.