Crack initiation induced nanograins and facets of a titanium alloy with lamellar and equiaxed microstructure in very-high-cycle fatigue

Abstract

Fractographic and microstructure features in crack initiation region in very-high-cycle fatigue (VHCF) were characterized for an extruded titanium alloy VT3-1 under stress ratios R =–1 and 0.1. The material consists of lamellar and equiaxed microstructure. All specimens failed by internal crack initiation with rough area feature in VHCF. Within the rough area region, facets initiated from a big cluster of lamellar α at R = 0.1, and nanograin layers formed at some local areas underneath fracture surfaces due to insufficient contact of NCP (numerous cyclic pressing) process in the inhomogeneous microstructure at R = –1. Here, NCP mechanism still dominates the VHCF behavior of this titanium alloy under negative stress ratios, and facets dominate at R > 0.