A repair process for fatigue damage using plasma nitriding

The effect of plasma nitriding on the fatigue life of AISI 4140 steel having a certain fatigue loading has been investigated. Untreated and nitrided specimens were subjected to fatigue loading up to a certain level, and then nitrided for 0.5 h and subjected to fatigue testing again. It was observed that the process applied to untreated specimens improves the fatigue life of the specimens that were plasma nitrided for 0.5 h due to the subsurface crack nucleation. However, for already nitrided specimens, a significant improvement in the fatigue life has not been observed by applying the proposed process because the compound layer on the surface prevents the diffusion during the second nitriding.