Tensile ductility of extrinsically toughened intermetallics

Abstract

A theoretical analysis based on crack instability is presented to elucidate factors effecting the tensile ductility of intermetallics that are toughened by extrinsic mechanisms and resistance-curve effects. The analytical results indicate that extrinsic-toughening mechanisms are ineffec-tive in imparting tensile ductility in brittle intermetallics. The plastic strain at the onset of un-stable fracture is generally controlled by the initiation toughness,KIc, except for materials with a high-tearing modulus,TR.The consequence is that tensile ductility increases with the initiation toughness,KIc, but is unrelated to theK value measured at the peak load or theTRvalue for materials with low- to intermediate-tearing resistance (e.g., TR <18 forKIc= 10 MPa√m). Application of the model to a two-phase TiAl alloy reveals good agreement between theory and experiment. This finding indicates that tensile ductility in brittle intermetallics can be imparted more effectively by intrinsic-toughening mechanisms than by extrinsic ones.