Plasticity characterization of the modified layer produced by plasma nitrocarburizing of nanocrystallized 18Ni maraging steel

Abstract: The plasma nitrocarburizing of nanocrystallized 18Ni maraging steel was performed at 460 °C for 4 h. The surface phase composition, cross-sectional microstructure and hardness profile of the nitrocarburized layer were investigated by the X-ray diffractometer (XRD), optical microscope (OM) and microhardness tester. Plasticity of the surface layer of original and nitrocarburized samples was analyzed by Taylor factor obtained by electron backscattering diffraction (EBSD) data and nanoindentation tests. The nitrocarburized surface is composed of α-Fe, Fe4N and a small fraction of low nitrogen compound FeN0.049. The surface and core hardness of nitrocarburized samples are 200% and 130% of that of the original one, respectively. The Taylor factors for different slip systems of α-Fe grains are all decreased after nitrocarburizing and Taylor factors for Fe4N grains are lower than those of basal slip system of α-Fe grains. Plasticity factor ηp , i.e. the ratio of plastic deformation work to total deformation work dissipated during loading-unloading process, of the surface layer is reduced about 20% after nitrocarburizing. This suggests that plasticity and wear resistance of the surface layer could be decreased and improved after nitrocarburizing, respectively. The surface layer of the nitrocarburized sample also possesses certain plasticity because its plasticity factor ηp is more than 60%. [Copyright &y& Elsevier]