MECHANISTIC MODELING OF DEFORMATION AND FRACTURE-BEHAVIOR IN TIAL ANDTI3AL

Phase stability and bulk properties of TiAl and Ti3Al are investigated based on the first-principles local-density-functional approach, and deformation and fracture behavior of two-phase lamellar gamma-TiAl all oys are analyzed using the linear elasticity theory applied to interfa ces, dislocations, and cracks. in terms of the calculated elastic cons tants, Young's and shear moduli are higher in Ti3Al than in TiAl. The coupling effect due to elastic incompatibility reduces the misfit stra in at an interface when a tensile stress is applied normal to it. The mode mixity of stress concentration by a dislocation pile-up plays an important role in determining whether slip transfer or microcracking o ccurs at the interface. The fracture morphology reported in notched po lysynthetically twinned crystals is explained in terms of the elastic interaction of a (11 ($) over bar 2)[1 ($) over bar 10] crack with an alpha(2)-Ti3Al plate. Additional factors that are involved in the brit tle-to-ductile transition behavior of TiAl are discussed.