RELATIONSHIPS OF SLIP MORPHOLOGY, MICROCRACKING, AND FRACTURE-RESISTANCE IN A LAMELLAR TIAL-ALLOY

The fracture resistance of a lamellar TiAl-alloy was investigated by J-testing under various displacement rates at ambient temperature. Possible relationships between slip morphology, microcracking, and fracture toughness were studied via optical electron microscopy and scanning electron microscopy (SEM). The results indicated that the lamellar TiAl-alloy exhibited a resistance-curve fracture behavior that was relatively rate insensitive in air at ambient temperature. Both interlamellar and translamellar deformation lines were observed in the crack-tip region and in the crack-wake ligaments. Theoretical analyses suggested that the interlamellar deformation lines were likely due to {111}[110] easy slip, and the translamellar deformation lines were probably produced by both {111}[110] easy slip and {111}[112BAR] ordered microtwins. Redistribution of crack-tip normal stresses led to a diffuse process zone of aligned microcracks formed by decohesion of slipbands. Relaxation of plastic constraint and interface decohesion resulted in higher plastic deformation, crack deflection, and redundant fracture in the crack-wake ligaments that gave rise to the relatively high fracture resistance observed in the lamellar TiAl-alloy.