Point Defect Behavior in the B2-Type Intermetallic Compounds

Abstract

The point defect behavior in B2-type intermetallic compounds, and its relating structural, physical and mechanical properties are surveyed, especially focusing on the investigations made in 1990's. It is recognized that there is a strong correlation between the point defects and various properties. For example, the mechanical properties (hardness) could be successfully related to retained vacancy concentration and further, the role of point defects including the antistructure atoms on hardening effect has been quantitatively discussed. They were based on thermodynamic treatments in which each compound belongs to either the triple defect (TRD) type group or the antistructure defect (ASD) type one. However, some experiments concerning with the structural properties have indicated that this classification is not satisfactory. Further, the hybrid type defect mechanism where both mechanisms of the TRD and ASD occurs simultaneously has been first proposed theoretically, particularly for B2 FeAl. Recent experimental studies, such as Mossbauer spectroscopy and X-ray and in-situ neutron diffraction, did not only support a certain hybrid type behavior in FeAl but also suggest a necessity for extending this hybrid type mechanism for better understanding of point defect behavior in B2 compounds including TRD type. A possibility of defect clustering, such as double vacancies, was also proposed from theoretical approaches, existence of which affects, e.g., the mechanical properties and atomic diffusion properties. This was supported by recent measurements of positron annihilation and perturbed angular correlation of γ rays.