Special Issue on Fracture Mechanics. Effect of Microstructure on Small Fatigue Crack Growth and The Crack Opening-Closing Behavior in Ti-6Al-4V Alloy. Study on Materials Heat-Treated in Beta Field.

Abstract

The effect of microstructure on the small fatigue crack growth behavior was studied in Ti-6Al-4V alloy, to which three kinds of heat treatments were conducted in beta field, in comparison with the long crack growth properties. The small crack opening-closing behavior relevant to microstructure was also investigated. The crack closing ratio exhibited a noteworthy behavior near crystallographic orientation boundaries: the ratio gradually increased as the crack tip approached to the grain boundary, and decreased after passing through. This experimental result indicates that the change of the crack closure is one of the important factors which lead to the characteristic behavior of small crack growth near grain boundaries. It was shown from these experimental evidences that the microstructural influence on the small crack growth rate and the difference in growth rate between small and long cracks were intrinsic and not compensated only by the crack closure phenomenon.