A Subsurface Fatigue Crack Generation Model in near Alpha Titanium at Low Temperature

Abstract:

The subsurface fatigue crack generation processes in near α type titanium alloy were divided into four steps: (1) development of a saturated dislocation structure by cyclical micro-plastic strain accumulation, (2) generation of localized slip and/or microcracking to relax the stress concentration in the vicinity of a boundary, (3) microcrack growth and transition to main crack, and (4) crack propagation. The experimentals on transgranular facets formation in Ti-Fe-O alloy were reviewed and a subsurface fatigue crack generation model was discussed. The β platelets which were aligned between the recrystallized α grain and the recovered α grain were responsible for the microcrack generation to form (0001) tansgranular facet in the recrystallized α grains. A combination of the shear stress and tensile stress normal to the basal plane may give a trigger of the (0001) microcracking in the recrystallized α grain. The localized shear stress following slip off on the basal plane was activated at the microcrack tip in the recrystallizedαgrain, and the microcrack grew into the recrystallized α grain to form (0001) transgranular facet.

• Periodical: Materials Science Forum (Volume 941)
• Pages: 1336-1341
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.941.1336
• Online since: December 2018
• Authors: Osamu Umezawa*, Wei Bo Li
• Keywords: Critical Resolved Shear Stress, High-Cycle Fatigue, Microcrack, Microtexture, Strain Incompatibility, Taylor Factor, Titanium

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