The Effect of Ammonia Water on the Microstructure and Performance of Plasma Electrolytic Saturation Nitriding Layer of 38CrMoAl Steel

38CrMoAl nitriding layer had been prepared by plasma electrolytic nitriding under different concentration of ammonia water. The layer structure, surface and phase composition had been analyzed by OM 、 SEM 、 XRD, respectively. Deeper analysis about element distribution in layer had been implemented by GDOES. The layer corrosion resistance had been measured by Parstat2273 Electrochemical workstation. microhardness and the wear properties of specimens were also evaluated. The experiment results show that: the nitriding layer consist mainly of Fe2N and Fe3N, the layer thickness is 85±5 to 165±15μm and the cross-section microhardness of the layer is 650- 1023HV after treated 10min at 220V. When the concentration of ammonia water drops to 40%, FeO is observed in outer-layer. The intensity of the maximum diffraction peak changed with the varying of nitrogen concentration. With the increasing of ammonia water concentration, the thickness of uniform and compact the white layers increases, the diffusion layers consist of needle nitrides and small carbides first increases then decreases, the distance for the biggest microhardness position to the surface increases obviously. After treated at 60% ammonia water, the layer thickness would get 165μm, the diffusion layer reach 114μm, microhardness of the layer reach 1023HV while the substrate hardness remain 310HV. Compared with the treated sample, the untreated wearing weight increase 4.5 times. The corrosion potential had been improved greatly from -523.4mV to -464.1mV. The white layer reaches 52μm while the ammonia water reaches 70. However the diffusion layer is thinner, so the layer thickness decrease gradually.