Fatigue Microstructures in Titanium Cyclically Stressed in Inert Environment

摘要

To clarify the fatigue crack growth micromechanism in titanium from the crystallographic and microstructural points of view, microstructures developed around a fatigue crack in different atmospheres were examined by optical and electron microscopy. Annealed CP titanium thin plate specimens have been cyclically stressed in plane bending in vacuum (1.3 x 10~(-3) Pa) and in argon gas (purity 99.999 %). Fatigue properties of titanium was more improved in vacuum than in argon gas. Mechanical twinning frequently occurred for the specimens fatigued in argon gas, while in vacuum it has hardly been observed. Mode of fatigue deformation in vacuum was finer, homogeneous and uniform slip bands, which widely spread over neighboring grains on a main crack. TEM examinations disclosed that twinning on the {1012} planes was characteristic of fatigue microstructures in argon gas, in which dislocation band traces on {1120} planes have been involved. In vacuum, fatigue damage occurred with slipping on {1010} and (0001) planes. The results obtained are discussed in connection with the relative easiness of slipping at crack tips, compared with those in air.