Environmental effects on fatigue failure micromechanisms in titanium

Fatigue behavior of titanium in inert environments has been studied from the microstructural viewpoints on thin-plate specimens subjected to alternating plane bending in vacuum (1.3 × 10−3 Pa) and in argon gas (purity 99.999%). Microstructural examinations were carried out in the process zone wake of a fatigue crack. Fatigue properties of titanium were better in vacuum than in argon gas and fatigue damage was distinguished between the testing atmospheres: in vacuum, homogeneous slip bands were uniformly formed and cracks propagated in transgranular mode, but in argon gas, twin systems as well as slip ones were activated and cracks propagated partly in intergranular mode. It was demonstrated that slip-bands cracking occurred at the junction of the intersecting slip bands developed on the { 1   0   1 ¯   0 } planes during cyclic stressing in vacuum, and grain boundaries were subject to selective damage in argon gas.