An enhanced rapid plasma nitriding by laser shock peening

Abstract

Laser shock peening was primarily adopted as a pretreatment prior to plasma nitriding for 42CrMo steel. It was found that laser shock peening had obvious enhancement effect on plasma nitriding. The thickness of compound layer and effective hardening layer could be effectively improved under the same plasma nitriding condition, which was about twice thicker as that of conventional plasma nitriding. Meanwhile, laser shock peening could significantly increase the surface hardness and slow down the decreasing trend of cross-sectional hardness. The significant enhancement effect of laser shock peening on plasma nitriding was mainly attributed to the increase of surface roughness from 0.015 μm to 0.454 μm and the pronounced defects in the deformation layer with a thickness of about 200 μm, the former was beneficial to the adsorption of nitrogen atoms, and the latter could promote nitrogen atoms diffusing inwards, thus increasing the microhardness in the nitriding layer due to higher nitrogen concentration.