The interrelationship of fracture toughness and microstructure in a Ti-5.25Al-5.5V-0.9Fe-0.5Cu alloy

Fracture toughness of anα-Β titanium alloy heat treated to a constant yield strength has been found to depend upon the morphology of α produced or remaining after the initial solution treatment. In equiaxed α structures, fracture toughness depends linearly upon the grain boundary area per unit volume,S _v, and is independent of equiaxed α particle size or spacing. In a grain boundary α structure fracture toughness depends both onS _v and, within limits, linearly on the thickness of the α. Explanations are offered for the observed propagation of cracks at α-@#@ Β interfaces and for the observation that high fracture toughness can accompany low tensile ductility. This paper is based on a thesis to be submitted by M. A. Greenfield in partial fulfillment of the requirements for the Ph.D. degree in metallurgy at New York University.