Search

A Fe 3 O 4 /Diamond-like carbon (DLC) coated carburized layer on M50NiL steel surface was fabricated by one-step plasma-assisted method in gaseous acetone at 550 °C. The surface layer showed high hardness (13.94 ± 0.92 GPa) and elastic modulus (314.18 ± 9.25 GPa) due to synergistic effect of rigid DLC and mild Fe 3 O 4 . The carburized layer with gradual hardness distribution served as supporting layer. The Fe 3 O 4 /DLC-containing carburized layer showed lower friction coefficient (about 0.25) and 97.6% reduction in wear rate (1.53 × 10 − 6 mm 3 N − 1 m − 1 ) compared with untreated specimen due to the lubricating effect and gradient multilayer structure. The tribological properties demonstrated that the treatment in present work has great advantages over other surface treatment. Moreover, the formation mechanism of the functionally graded carburized layer was discussed. The results pointed out a simple way to greatly improve wear resistance for steels. [ABSTRACT FROM AUTHOR]

In this study, plasma nitrocarburizing at various temperatures in the range of 460–540 °C were carried out on M50NiL steel in order to improve wear properties. The nitrocarburizing temperature was optimized to obtain the best wear properties. The phase composition, microstucture and microhardness profiles of nitrocarburized layers of M50NiL steel were characterized by XRD, optical microscope and Vickers microhardness measurements, respectively. Pin-on-disc tribometer and SEM equipped with EDS were applied to measure friction and wear properties and analyze wear mechanisms involved. XRD results show that the amount of ɛ-Fe 2-3 (N,C) phase increased as the nitrocarburizing temperature rose form 460 °C to 500 °C and then decreased at 540 °C, while the amount of γ′-Fe 4 (N,C) phase increased as the treatment temperature rose. The hardness of the nitrocarburized layers showed an obvious improvement accompanied with the increasing nitrocarburizing temperature, and obtained the maximum surface hardness of 1287 HV at 540 °C. The results of wear tests carried out at various sliding speeds indicated that the wear mechanism depends on sliding speed rather than the nitrocarburizing temperature. With the increase of the sliding speed, the wear mechanism transfers from oxidation mode to abrasive mode. The gradually deceased wear rate of the specimen nitrocarburized at 500 °C with the increase of the sliding speed indicated the excellent wear resistance under high sliding speed condition. Therefore, 500 °C can be selected as an optimized nitrocarburizing temperature for M50NiL steel. [ABSTRACT FROM AUTHOR]

Highlights: [•] Depth-related microstructure of the modified layer of M50NiL steel is analyzed. [•] Depth-related wear mechanisms of RE treated layer of M50NiL steel is investigated. [•] The relationship between phase structure, hardness and wear mechanism is studied. [Copyright &y& Elsevier]

Abstract: 30CrMnSiA steel was plasma nitrided in an atmosphere of 50% N2 +50% H2 at 460°C for 4h with and without rare earths addition, and the effects of rare earth elements on the microstructure and properties were investigated. The specimens nitrided with and without rare earths addition were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, microhardness tests, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The results show that both nitrided layer with and without rare earths consist of a compound layer and a diffusion zone. The introduction of rare earths into the atmosphere can enhance the proportion of ε-Fe2-3N phase in the surface layer and increase the surface layer hardness by 100HV0.1. Both the wear and corrosion resistances of 30CrMnSiA steel were improved by plasma nitriding, i.e. the friction coefficient and the wear rate can be dramatically decreased. Moreover, the involvement of rare earths further decreases the average friction coefficient and the wear rate of specimens, and improves the corrosion resistance. [Copyright &y& Elsevier]

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]

Abstract: 17-4PH stainless steel was plasma nitrocarburized at 460°C for improving its mechanical properties without compromising its desirable corrosion resistance. The plasma nitrocarburized layers were studied by optical microscope, X-ray diffractometer, microhardness tester, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The experimental results show that the nitrocarburized layer depths increase with increasing duration time and the layers growth conform approximately to the parabolic law. The phases in the nitrocarburized layer are mainly of γ′-Fe4N and α′-Fe with traces of CrN phase. The surface hardness of the modified specimen is more than 1200HV, which is three times higher than that of untreated one. The friction coefficient and corrosion resistance of the specimen can be apparently improved by plasma nitrocarburizing. With the increase of duration time, the surface hardness slightly decreases whereas the friction coefficient and corrosion resistance of the modified specimen are first increase and then decrease. The 8h treated specimen has the lowest friction coefficient and the best corrosion resistance in the present test conditions. [Copyright &y& Elsevier]

Abstract: 17-4PH martensitic precipitation hardening stainless steel was plasma nitrocarburized at 430°C and 460°C for 8h. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, microhardness tests, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The results show that the microstructure of plasma nitrocarburized layer is characterized by a compound layer with no evident diffusion zone. The phases in the 430°C treated layer are mainly of γ′-Fe4N, nitrogen and carbon expanded martensite (α′N), and some incipient CrN phases. When the temperature increases up to 460°C, there is no evidence of α′N phase. The processes of bulk precipitation hardening and surface treatment by plasma nitrocarburizing can be successfully combined in a single-step process on this steel. The hardness of modified layer can reach up to 1186HV, which is 3 times higher than that of untreated steel. The wear and corrosion resistance of the specimens can be apparently improved by plasma nitrocarburizing. The 460°C/8h treated specimen has the best wear and corrosion resistance in the present test conditions. [Copyright &y& Elsevier]

Abstract: 17-4PH stainless steel was plasma nitrocarburized at low temperature for improving its mechanical properties. The results show that the modified layer thicknesses increase with increasing treatment time and the layers growth approximately conforms to the parabolic law. The phases in the modified layers are mainly of incipient γ′-Fe4N and α′-Fe with amorphous characterization, and then changed into γ′-Fe4N, α′N and traces of CrN with the treatment time increasing. The hardness of the nitrocarburized specimen is more than 1280HV, which is about 3.5 times as hard as the untreated one. Meanwhile, the wear resistance of the steel specimen can be dramatically improved by plasma nitrocarburizing. The surface hardness and the wear resistance of the nitrocarburized specimens slightly decrease with an increase in treatment time for the surface hardness as well as microstructure changing. [Copyright &y& Elsevier]