A study of thermal vacancies and dislocation structure in Fe–40 at.% Al

Abstract

The densities of thermal vacancies and residual dislocations in bulk specimens of Fe–40 at.% Al have been investigated using differential dilatometry and X-ray diffraction. A large quenched-in vacancy concentration at temperatures above about 873 K was apparent from the decrease in average lattice parameter. This was correlated to a lowering of the effective enthalpy of vacancy formation from about 91 to 42 kJ mol⁻¹, possibly caused by the presence of different types of point defect in lower- and higher- temperature regimes. The residual dislocations were found to have a major concentration on {100} planes at any given temperature. An increase in the dislocation density and a concurrent fall in the vacancy concentration was observed with a lowering of the quenching temperature from 1223 to 1073 K, indicating the possibility of vacancy annihilation at 1073 K.

Acknowledgements

This work was supported by Région Rhône-Alpes, France, through grants under the programmes thématique 2001–2003. The authors are grateful to Dr. F. Valdivieso (Ecole Nationale Supérieure des Mines, Saint Etienne) for his help and valuable suggestions regarding the dilatometric measurements.