Nanograin formation and cracking mechanism in Ti alloys under very high cycle fatigue loading

This paper shows that nanograins appear in a locally high-stress region for very high cycle fatigue of TC17 alloy, and twinning is a main contributor to nanograin formation. The locally high stress results in twinning or slip in preferentially oriented alpha grains. Then, the interaction between twin systems or dislocations induces the forma-tion of dislocation cells or walls, nucleation of microbands, and finally the nanograins. As a result, the nanograin regions and the boundaries between the nanograin and coarse grain regions become preferential sites for crack initiation and early growth. The finite element analysis demonstrates the nanograin-related fatigue cracking behavior.

Automated summary

This paper reveals that nanograins are present in locally high-stress areas during the very high cycle fatigue of TC17 alloy, and nanograin formation is mainly attributed to twinning. The locally high stress induces twinning or slip in preferentially oriented alpha grains. Subsequently, the interaction between twin systems or dislocations leads to the formation of dislocation cells or walls, initiation of microbands, and ultimately the formation of nanograins. As a result, the regions with nanograins and the boundaries between the nanograin and coarse grain regions become preferential sites for crack initiation and early growth. Finite element analysis demonstrates the fatigue cracking behavior related to nanograins.