The Influence on Microstructure and Microtexture on Fatigue Crack Initiation and Growth in Alpha + Beta Titanium

The strain paths and thermal cycles utilized during thermomechanical processing of two-phase alloys have a pronounced influence on the resulting distribution of grain orientations present and their spatial distribution. For example, large regions of similarly oriented alpha grains, commonly referred to as microtextured regions or macrozones, may persist despite the imposition of large macroscopic strains. The detrimental effect of microtexture on dwell fatigue life of high temperature alloys is well established; however, considerably less attention has been given to the effects of microtexture on fatigue life during continuous cycling . In the present work, the effects of microstructure and microtexture on the low cycle fatigue (Nf smaller or equal to 104 cycles) behavior of Ti-6Al-4V have been characterized using electron microscopy. Microstructural parameters such as the volume fraction and size of the alpha phase were assessed by quantitative metallography while the contiguity of the alpha phase and the size and shape of the microtextured regions were investigated with electron backscatter diffraction. Prepared in collaboration with Sumikin Kansai Industries Ltd. Osaka, Japan; Sumitomo Metal Industries, Ltd, Osaka, Japan; Sumitomo Metal Industries, Ltd, Hyogo, Japan; and Ohio State University, Columbus, Ohio. Preprint journal article to be submitted to 12th International Conference on Titanium. This document contains color.