Effect of an environment in stainless steel on the damage mechanisms under LCF conditions

摘要

The effect of an environment on the damage mechanism was addressed in this study. Super austenitic steel Sanicro 25 grade was subjected to isothermal elasto-plastic cyclic loading at 700°C. The material was exposed to different environmental conditions to assess the effect of laboratory air comparing to high vacuum. The mechanism of the crack nucleation was the matter of the inquiry by means of scanning electron microscope equipped with focused ion beam technique. Distinctive mechanism of the crack nucleation was observed for different loading conditions. The isothermal fatigue loading in the air resulted in the early initiation of the cracks from the oxidized grain boundaries arranged perpendicularly to the loading axis. The significant change was revealed for the specimens strained under high vacuum conditions. The crack was found to be nucleated due to cavity formation and their subsequent mutual coalescence during further loading. Moreover, the crack formation was observed in the interior of the material. The effect of the environmentally related damage mechanism is documented.