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 in as-milled powders upon high temperature exposure, namely reordering, strain relaxation and grain growth, show signs of stagnation. The total quantity of impurities, mainly 15 at.% Fe has been analyzed as being dissolved substitutionally in RuAl and also segregated to grain boundaries. Upon grain growth, lattice diffusion and segregation of impurity atoms in grain boundaries have been verified by the lattice parameter variation. The incremental apparent activation energy for grain growth at different temperatures is related to the accumulation of impurities in grain boundaries. Reordering and strain relaxation processes that accompany grain growth could consume a certain part of the driving force for grain growth.