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Published online by Cambridge University Press: 15 February 2011
Microstructural studies were performed on an alloy of composition Fe45Cr5Al50 heat treated at 950°C and oil-quenched and then given isothermal annealing treatments for times up to 200 hours at either 400°C or 500°C. The observed microstructures were correlated with variations in hardness during isothermal annealing. It was deduced that the thermal vacancies retained following the initial heat treatment are removed relatively rapidly from the lattice, which leads to an initial drop in hardness. However, during prolonged annealing, the coarsening of bothFeAl2 particles and a disordered a(Fe,Cr) phase leads to further softening. It was also deduced that the chromium atoms, which remain in solution, are effective solute strengtheners. The a(Fe,Cr) phase, which is coherent with the B2 matrix, appears to coarsen by a ledge growth mechanism.