Mechanical Behavior of Titanium Alloys

Abstract

Abstract : Conditions for the formation of the alpha-beta interface phase in Ti- 6Al-4V have been determined, and the influence of this phase on mechanical properties examined. In previously reported work, it was shown that tensile yield strength could be increased by increasing the interface phase width. In the current work, it was found that fatigue crack propagation (FCP) resistance can also be improved by heat treatments which increase interface phase width. The improved FCP resistance was associated with an increase in secondary cracking, which propagated predominantly along alpha-beta interfaces, especially at higher stress levels. Fracture toughness was found to be relatively insensitive to interface phase width, so that treatments which improve both tensile yield strength and FCP resistance do not degrade fracture toughness. An influence on fracture toughness found in this study was banding of primary alpha particles parallel to the rolling direction. This type of microstructure exhibited a high fracture toughness for cracks propagating normal to the bands, and such effects appear to be larger than effects due to interface phase or volume fraction alpha.