Analysis of subsurface fatigue crack generation in Ti-Fe-O alloy at low temperature

Abstract

Subsurface microcracks developed in the Ti-Fe-O cross-rolled material were characterized in order to clarify the subsurface fatigue crack initiation. A considerable amount of microcracks in β platelets were detected. The {0001} transgraular microcracks in β grains predominantly generated at the β grain boundary between recovered β grain and recrystallized β grain, and grew into the recrystallized β grain along the basal plane, although the microcracks at the twist boundary of β grains and at the β interface were occasionally detected. Stress concentration around the microcrack in platelets may assist the microcrack initiation on basal plane (transgranular facet) in neighboring grain due to a combination of the shear stress and tensile stress normal to the basal plane at boundary. The {0001} transgraular microcracks growth and/or coalescence occurred with the assistance of shear stress on prismatic plane such as {1010} steps.