Bonding and brittleness in B2 structure 3 d transition metal aluminides: Ionic, directional, or does it make a difference?

Abstract

Because of its many attractive physical properties, the B2 (CsCl) structure intermetallic NiAl is a promising material for high temperature applications, in particular for use in aircraft engines. It is relatively light, has a high melting temperature with strength retention at high temperatures, and good oxidation resistance and thermal conductivity. its most important feature from a technological perspective, however, is the intrinsic brittleness at room temperature that limits its use in structural applications. For the past few decades, a great deal of effort has been invested into understanding the bonding in NiASl and related aluminides, and recently has begun to focus on brittleness. Despite a great deal of effort, however, the microscopic nature of the bonding in the aluminides is poorly understood, much less the implications that that bonding has for physical properties. Given the confusion that currently exist regarding these issues, the authors thoughts it worthwhile to revisit this problem in this paper and it is the intent of this study to systemically investigate the correlation of these bonding factors with brittleness.