Mechanical properties of Ni3Al and FeAl:: Recent developments

Recent developments in our understanding of the ductility and fracture behavior of Ni3Al and FeAl are reviewed. Both intrinsic factors (e.g., alloy stoichiometry), and extrinsic factors (e.g., environment) have been shown to affect their mechanical properties. Of all the recent developments, perhaps the most significant is the realization that Ni3Al and FeAl are intrinsically ductile (at least on the Al-deficient side of stoichiometry); their brittleness when tested in ambient air is due mainly to environmental embrittlement. Another intriguing discovery is that boron embrittles Ni3Al in gaseous hydrogen (until recently, B was thought to have only beneficial, or at most neutral, effects). We review these and other recent discoveries and discuss, wherever possible, the underlying physical mechanisms giving rise to the observed mechanical behavior.