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Abstract The previous article reported a valuable finding of diamond-like carbon (DLC) in-situ formed on Fe 3 C-containing carburized layer by plasma carburizing. The formation mechanism of DLC film was revealed with aid of first-principles calculations. However, the tribological behaviors of the duplex layer combining DLC film and carburized layer were not presented. In the present paper, the microstructure of the duplex layer was systematically analyzed by means of optical microscope and atomic force microscopy. The DLC film was characterized by scanning electron microscopy and high-resolution transmission electron microscopy. DLC film gradually forms on the carburized layer of specimen treated at 400 °C and 450 °C with treatment duration increasing. The tribological tests demonstrate that the DLC film coated carburized layer has lower coefficient of friction (less than 0.3) and wear rate due to the self-lubricating property. The predominant wear mechanism of DLC film coated carburized layer is transformed into micro cutting wear compared with the slight adhesive wear and abrasive wear for traditional carburized layer. The excellent tribological properties of the DLC film coated carburized layer exhibits great potential to modify ferrous alloys by plasma carburizing. Graphical abstract Unlabelled Image Highlights • DLC film in situ forms on Fe 3 C-containing carburized layer by plasma carburizing. • In-situ formed DLC has the amorphous carbon structure with nano diamond embedded. • DLC coated carburized layer showed 96.07% reduction in wear rate compared to untreated. • The wear mechanism is transformed to micro cutting wear with DLC film deposition. [ABSTRACT FROM AUTHOR]

Dual magnetron sputtering and thermo plasma nitriding were performed to fabricate Cu-Ti-N coating on the surface of Cu substrate, and the microstructure formation and evolution mechanism were investigated. The results showed that the composition of the Cu-Ti coating could be tuned to be around Cu:Ti = 1:1.2 by the appropriate choice of sputtering power for the dual targets, and only amorphous Cu-Ti phases formed. During the thermo plasma nitriding process, crystalline CuTi and Cu 3 Ti occurred. Moreover, a nitride layer of about 0.3 μm containing nanocrystalline TiN formed on the surface, and the multi-phase coating developed to be about 4 μm, which could provide better support for the nitrided layer. [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]

Abstract: In order to improve the surface mechanical properties of GB-5083 aluminum alloy, titanium–aluminum–nitrogen thermo-reactive diffusion coatings were fabricated on the surface of Al substrate through deposition and nitriding process. The substrates were firstly deposited with pure Ti film by magnetron sputtering and then plasma nitrided in an atmosphere of 40% N2–60% H2 at 460°C. The as-obtained coatings under different nitriding time were characterized by using X-ray diffractometer (XRD), scanning electron microscopy (SEM), microhardness tester, scratch tester and pin-on-disc tribometer. Results showed that the multiphase coating comprising two sub-layers (i.e. the outside TiN0.3 layer, and the inside Al18Ti2Mg3 layer) can be obtained. The coating thickness increased slightly with increasing nitriding time. The hardness of the as-obtained coating has reached about 600HV, which is much higher than that of the GB-5083 Al substrate. The critical load of adhesive failure for the coating obtained by 16h nitriding reached 13N. Compared with the untreated Al alloy, the wear rate of the coated sample decreased 65% after 24h nitriding treatment. The analysis of worn surfaces indicated that the coated GB-5083 Al alloy exhibited predominant abrasive wear, whereas the uncoated one showed severe adhesive wear. [Copyright &y& Elsevier]

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: [•] A novel duplex surface treatment on 2024 Al alloy was proposed. [•] A multiphase layer composed of TiN0.3, Al3Ti and Al18Ti2Mg3 was prepared on the surface of 2024 Al alloy. [•] The microstructures of TiN0.3, Al3Ti and Al18Ti2Mg3 were characterized by SEM and TEM. [•] The surface hardness of the multiphase layer reached to 590 HV0.01, five times harder than 2024 Al alloy. [•] The wear resistance of 2024 Al alloy was improved significantly. [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: C and N atoms are the most frequent foreign interstitial atoms (FIAs), and often incorporated into the surface layers of steels to enhance their properties by thermochemical treatments. Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Nb and Mo are the most common alloying elements in steels, also can be called foreign substitutional atoms (FSAs). The FIA and FSA interactions play an important role in the diffusion of C and N atoms, and the microstructures and mechanical properties of surface modified layers. Ab initio calculations based on the density functional theory are carried out to investigate FIA interactions with FSA in ferromagnetic bcc iron. The FIA–FSA interactions are analyzed systematically from five aspects, including interaction energies, density of states (DOS), bond populations, electron density difference maps and local magnetic moments. [Copyright &y& Elsevier]

Abstract: In the present study, low temperature plasma nitriding of nanocrystallized 18Ni maraging steel has been carried out at 360°C from 1 to 24h in a mixed gas of 25%N2 +75%H2. The surface phase constitutions and microstructures of the nitrided layer have been investigated by X-ray diffraction analysis, transmission electron microscopy and optical microscopy. Nanoindentation and microhardness tests have been performed to determine the surface hardness and the hardness profile in the nitrided layer. The plasticity of the nitrided surface has been analyzed based on the nanoindentation results. The results show that at the initial stage of nitriding, the surface phase consists of a solid solution of nitrogen in α-Fe, and nanoscale nitrides and aging phase are formed with increasing of treatment time. The surfaces nitrided for 8 and 16h possess the highest hardness. The plasticity factor calculations suggest that the nitrided surfaces have a good wear resistance and possess excellent plasticity. [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 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]

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: The effect of rare earth addition in the carrier gas on plasma nitrocarburizing of 17-4PH steel was studied. The microstructure and crystallographically of the phases in the surface layer as well as surface morphology of the nitrocarburized specimens were characterized by optical microscope, X-ray diffraction and scanning tunneling microscope, respectively. The hardness of the surface layer was measured by using a Vickers hardness test. The results show that the incorporation of rare earth elements in the carrier gas can increase the nitrocarburized layer thickness up to 55%, change the phase proportion in the nitrocarburized layer, refine the nitrides in surface layer, and increase the layer hardness above 100HV. The higher surface hardening effect after rare earth addition is caused by improvement in microstructure and change in the phase proportion of the nitrocarburized layer. [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]