Fatigue strength of a radical nitrided Ni-base super alloy

摘要

Radical nitriding was applied to Ni-base super alloy, Alloy 718, which is difficult to nitride and the fatigue strength of the alloy was also investigated in comparison with the aged alloy under push-pull loading at room temperature and 500°C. By radical nitriding, compound layer of about 5 μm was formed and specimen surface was hardened over HV1300. Consequently, fatigue strength was increased in wide life region, especially beyond 10~6 cycles at room temperature. This was mainly caused by the suppression of crack initiation due to formation of hard compound layer. There was no or little difference in fatigue strengths between specimen removed nitrided layer by electro-polishing and aged specimen. That is, radical nitriding method is effective to improve the fatigue strength at room temperature without the damage of matrix.