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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]

To improve the mechanical properties of C61900 copper–aluminum alloy, a multi-phases coating was fabricated by the combination of thermo-diffusing Ti film and plasma nitriding. The results showed that a smooth coating with fine and uniform grains could be achieved, and the 9 μm thick multi-phases coating, containing Ti–Cu–Al intermetallics (CuTi 2 , CuTi, AlCu 2 Ti) and titanium nitride (Ti 2 N) formed on the nitrided surfaces. The surface hardness of the coating was obviously improved to be 630 HV 0.01 , and the cross-sectional hardness decreased gradually to that of C61900 Cu–Al alloy. Moreover, the wear rate of the coated specimen decreased significantly, dropping 95.5% compared with the untreated Cu–Al alloy. [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]

Abstract: In this paper, martensite transformation induced by plasma nitrocarburizing in AISI304 austenitic stainless steel is investigated. The optical micrographs and XRD results indicate the dual-layer structure of the nitrocarburized layer: the outer martensite transformation layer and the inner C supersaturated austenite layer. The initial transformation microstructure presents as nanoscale qusai-pealite which is composed of α′-martensite and NaCl-type MX (M = Cr, Mn, Fe, Ni; X = C, N) phase. The martensite transformation layer possesses high hardness and good ductility. [Copyright &y& Elsevier]

Highlights: [•] PN+LQ treatment results in thicker layer depth than single PN or LQ treatment. [•] The increase of layer depth is caused by the eutectoid point reduction due to introduction of N. [•] LQ treatment cause the brittle phase decomposed and the hardness redistributed of PN specimen. [•] PN+LQ specimen shows better wear resistance than the PN counterpart. [Copyright &y& Elsevier]

Highlights: [•] We study the interaction between lanthanum and nitrogen during plasma nitriding. [•] The addition of pure lanthanum could reduce the nitrogen content in the surface layer. [•] There is an attractive function between lanthanum and nitrogen. [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: 17-4PH Martensitic stainless steel was plasma nitrocarburized at conventional temperature (560°C) with and without rare earths (RE) addition. The surface treated layers were characterized by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction and microhardness test. The wear and corrosion behavior of the modified specimens was studied respectively using pin-on-disc tribometer and anodic polarization tests. The results show that rare earths atoms can diffuse into the surface of the stainless steel. The microstructures of all modified layers are characterized by a compound layer containing three distinct zones but without an evident diffusion zone. The phases on all modified surface layers are mainly of θ-Fe3C and CrN. It is exciting that the hardness profile of the modified layer is decreased gradually, which is rarely found in plasma nitriding of the stainless steel. The friction coefficient of a specimen can be dramatically decreased by plasma RE nitrocarburizing, whereas the corrosion resistance is deteriorated. In contrast, the corrosion resistance of a plasma nitrocarburized specimen is enhanced but the friction coefficient is not improved as much as that of a plasma RE nitrocarburized one. [Copyright &y& Elsevier]

Abstract: 17-4PH stainless steel was plasma nitrocarburized at 430°C for different time with rare earths (RE) addition. Plasma RE nitrocarburized layers were studied by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction, microhardness tests, pin-on-disc tribometer and anodic polarization tests. The results show that rare earths atoms can diffuse into the surface of 17-4PH steel. The modified layer depths increase with increasing process time and the layer growth conforms approximately to the parabolic law. The phases in the modified layer are mainly of γ′-Fe4N, nitrogen and carbon expanded martensite (α′N) as well as some incipient CrN at short time (2h). With increasing of process time, the phases of CrN and γ′-Fe4N increase but α′N decomposes gradually. Interestingly, the peaks of γ′-Fe4N display a high (200) plane preferred orientation. The hardness of the modified specimen is more than 1340HV, which is about 3.7 times higher than that of untreated one. The friction coefficients and wear rates of specimens can be dramatically decreased by plasma RE nitrocarburizing. The surface hardness and the friction coefficients decrease gradually with increasing process time. The corrosion test shows that the 8h treated specimen has the best corrosion resistance with the characterization of lower corrosion current density, a higher corrosion potential and a large passive region as compared with those of untreated one. [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 500°C with and without rare earths (RE) addition. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction, hardness tests and pin-on-disc tribometer. The results show that rare earths atoms can diffuse into 17-4PH steel surface and change the microstructure of the nitrocarburized layer. The incorporation of RE elements increases the layer thickness and the hardness of the nitrocarburized layer up to 29% and 70–120HV, respectively. The friction coefficients and wear rates of the nitrocarburized specimens are apparently lower than that of un-nitrocarburized one. The wear mechanisms of steel specimen plasma nitrocarburized with and without RE addition are different mainly due to the differences in the microstructure, the phase proportion and the hardness of the modified layer. [Copyright &y& Elsevier]

Abstract: 18Ni-maraging steel has been entirely nanocrystallized by a series of processes including solution treatment, hot-rolling deformation, cold-drawn deformation and direct electric heating. The plasma nitriding of nanocrystallized 18Ni-maraging steel was carried out at 410°C for 3h and 6h in a mixture gas of 20% N2 +80% H2 with a pressure of 400Pa. The surface phase constructions and nitrogen concentration profile in surface layer were analyzed using an X-ray diffractometer (XRD) and the glow discharge spectrometry (GDS), respectively. The results show that an about 2μm thick compound layer (mono-phase γ′-Fe4N) can be produced on the top of the surface layer of nanocrystallized 18Ni-maraging steel plasma nitrided at 410°C for 6h. The measured hardness value of the nitrided surface is 11.6GPa. More importantly, the γ′-Fe4N phase has better plasticity, i.e., its plastic deformation energy calculated from the load-displacement curve obtained by nano-indentation tester is close to that of nanocrystallized 18Ni-maraging steel. Additionally, the mechanical properties of γ′-Fe4N phase were also characterized by first-principles calculations. The calculated results indicate that the hardness value and the ratio of bulk to shear modulus (B/G) of the γ′-Fe4N phase are 10.15GPa and 3.12 (>1.75), respectively. This demonstrates that the γ′-Fe4N phase has higher hardness and better ductility. [Copyright &y& Elsevier]

Highlights: [•] M50NiL steel is nitrocarburized with and without rare earth (RE) addition. [•] RE addition can increase the surface hardness and layer thickness. [•] RE can increase C, N contents and proportion of iron nitrides in treated layers. [•] Plasma nitrocarburizing can significantly improve the wear resistance of M50NiL steel. [•] RE addition could further improve the wear properties of the treated layers. [ABSTRACT FROM AUTHOR]