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Aluminum-Copper alloys are widely utilized in military, aerospace and aircraft industries for its light weight, excellent castability, superior corrosion resistance, as well as high specific strength after solution, quenching and age hardening treatments. However, the distortion occurring in the quenching process limits its application, especially for the large scale complicated workpieces. In this study, a novel duplex treatment combining the coating and nitriding is applied to the sections of the thin-wall barrel that easy to deform during quenching. The results show that a gradient multiphase layer, consisting of two different regions, is shaped on the thin-wall sections easy to deform. The phase compositions of the surface and subsurface layer are dominated by TiN 0.3 and Al 3 Ti, respectively. The Young's modulus of the TiN 0.3 and Al 3 Ti are 199 GPa and 196 GPa respectively. While, the microhardness for both the two phases are 6.19 GPa and 4.24 GPa respectively, which are much higher than that for the aged ZL205A alloy substrate. The finite element method (FEM) simulation results show that the maximum temperature difference, thermal stress, residual stress as well as deformation of the thin-wall barrel workpiece are reduced due to the multiphase layer. Consequently, the maximum radial deformation of the workpiece can be reduced 96% due to the superior strength and hardness as well as heat conduction of the gradient multiphase layer. • Quenching deformation occurs on the thin-wall sections of the barrel according to the FEM simulation. • The gradient multiphase layer is prepared on the thin-wall sections by deposition titanium film and nitriding. • The phase composition of the multiphase layer is dominated by TiN 0.3 and Al 3 Ti. • The much higher heat conductivity and superior strength and hardness of the multiphase layer results in 96% reduction of the workpiece. [ABSTRACT FROM AUTHOR]

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]

Microstructure and mechanical properties of a quenched M50 steel plasma nitrided for 8 h at temperatures ranging from 480 to 540 °C in a gas mixture of 25% N 2  + 75% H 2 were investigated in this paper. Results show that, compared with the original specimen, microhardness and wear resistance of M50 steel after nitriding treatment are remarkably improved at various temperatures, wherein the N500 specimen achieved the optimum combination of surface hardness (1186 HV), substrate hardness (643HV) and wear resistance (wear rate reduced by 90% more than original specimen). Such significantly improvement could mainly be attributed to the formation of nanophase FeN 0.076 , occurrence of further secondary hardening of substrate and generation of a nitrided surface layer of M50 steel during nitriding process. Two types of carbides, identified as MC and M 6 C, were found to be the stable precipitates present in substrate of N500 specimen. These results provide us with an attractive method of combining nitriding with secondary hardening to achieve a comprehensive performance from surface to substrate of M50 steel. [ABSTRACT FROM AUTHOR]

Diffusion behavior of carbon and its hardening effect on plasma carburized M50NiL steel were investigated systematically. The plasma carburizing was carried out in a mixture of gaseous acetone (30%) and hydrogen (70%) at temperatures of 400, 450, 500 and 550 °C for durations of 4, 8 and 12 h, respectively. Influences of treatment temperature and duration on properties of the carburized layer were investigated with optical microscope, atomic force microscope, X-ray diffractometer, micro- and nano-indenters, and pin-on-disc tribometer. Results of the tests indicate that cementite is the main phase in the surface layer of specimens carburized at 400 and 450 °C, while that in those carburized at 500 and 550 °C is mainly the carbon expanded martensite. The specimens with cementite in the surface layer show lower surface roughness, higher surface hardness and thus lower wear rate. The diffusion behavior of carbon and resultant microstructure evolution mechanism were studied, indicating that plasma carburizing is a diffusion-controlled process. Activation energies of carbon diffusion into martensite and cementite were calculated, which are 64.5 kJ·mol − 1 and 120.7 kJ·mol − 1 , respectively. The information on the activation energies provides basic data for tuning and predicting the surface properties of plasma carburized M50NiL steel. [ABSTRACT FROM AUTHOR]

This article reports a study on catalytic growth of diamond-like carbon (DLC) on the Fe 3 C-containing carburized surface layer of M50NiL steel through a single-step plasma-assisted carburizing process. The catalytic effect of Fe 3 C on DLC growth was investigated by means of X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical and tribological tests demonstrate that the DLC growth endows the treated specimens with higher hardness, lower coefficient of friction and increased wear resistance than traditional carburization layer. First-principles calculations were conducted to verify the experimental observations and elucidate the mechanism for the catalytic growth of DLC on Fe 3 C surface. This study demonstrates that DLC can simultaneously form during carburization of steel under suitable processing conditions, resulting in a combination of DLC and carburized layers through a single-step process with help of the catalytic effect of Fe 3 C. This finding shows a promising approach to maximize the benefits of carburization treatment, and provides new clues for facilitating DLC production and improving traditional surface treatments for steels. [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]

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]

Low temperature plasma carburizing was employed to fabricate a carburized layer containing an amorphous carbon/Fe 3 C composite coating on the M50NiL steel surface in gaseous acetone. The influence of gaseous acetone content on the carburized layer was investigated by optical microscope, scanning electron microscope equipped with energy dispersive X-ray analyzer, X-ray diffraction, Raman spectroscopy, microhardness tests, pin-on-disc tribometer and anodic polarization tests. A specific carburized layer mainly comprised of carbon expanded martensite (α′ C ) with good wear resistance and modest corrosion resistance was formed by plasma carburizing at 550 °C for 4 h. The amorphous carbon/Fe 3 C composite coating-containing carburized layer was obtained using gas mixture of acetone (0.3 L/min) and hydrogen (0.2 L/min). The coating showed lowest friction coefficient (about 0.3) and 99.0% reduction in wear rate compared with untreated specimen due to its lubricating effect. Moreover, it showed better corrosion resistance than untreated specimen owing to its chemical inertness. The promising results demonstrated that the improved wear and corrosion resistance could be realized simultaneously by introducing the composite coating with merits of self-lubricating and anti-corrosion. [ABSTRACT FROM AUTHOR]

To design a high-performance Cu–Ti intermetallic coating, first-principles calculation is conducted to systematically investigate the phase stability, mechanical and electronic properties of the Cu–Ti binary intermetallics. The phase stability and mechanical properties are studied by calculating the formation enthalpy and independent elastic constants, respectively. The calculated formation enthalpy indicates that β-Cu 4 Ti, CuTi and CuTi 2 are stable phases at 0 K, while α-Cu 4 Ti, Cu 3 Ti, Cu 3 Ti 2 , and Cu 4 Ti 3 are metastable phases. In addition, the mechanical properties of Cu–Ti intermetallics present a positive correlation with their formation enthalpy. The electronic structures of the Cu–Ti intermetallics are evaluated by analyzing the bonds character to reveal the bonding characteristics, which is crucial to the phase stability and mechanical properties. Among the Cu–Ti intermetallics studied, CuTi phase exhibits the highest stability, hardness and a higher brittleness among all Cu–Ti intermetallics, while other Cu–Ti intermetallics show good toughness. Based on the calculated results, a high strength Cu–Ti intermetallic coating consisting of hard CuTi particles on a ductile Cu 4 Ti 3 matrix is proposed. [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]

By using the first-principles calculations within virtual crystal approximation (VCA) framework, the alloying behavior of transition metals M (M = Cr, Ni, Mo, V, Co, Nb, Mn, Ti and Cu) has been investigated in ternary ε-(Fe 1 − x M x ) 3 N nitrides ( x = 0–0.15). The phase stability and elastic properties are studied by calculating the formation Gibbs energy, independent elastic constants and densities of states. The calculated results show that the stability of the ε-(Fe 1− x M x ) 3 N nitrides decrease with the increase of the substitution content, indicating the decomposition of ε phase to α or γ′ phases. The elastic properties of the ε-(Fe 1− x M x ) 3 N nitrides are sensitive to the transition element types except Co and Mn which show the weakest effect. Densities of states are given for all ε-(Fe 1− x M x ) 3 N nitrides to confirm the origins of the variations of phase stability and elastic properties. The calculated results show a reasonable agreement with available experimental values. [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 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: [•] 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: [•] The site preference of N in Cr2N is studied by a first principles method. [•] Theoretic elastic properties of Cr2N are obtained. [•] Mechanical characteristics of Cr2N are predicted. [•] Density of states reveals the origin of the stability and elastic properties. [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]

Abstract: By means of magnetron sputtering method, pure Ti film with thickness of 1.25 μm was deposited on the surface of 5083 Al alloy specimens. The specimens were heated by ion bombardment in a plasma nitriding unit employing a mixed gas of N2 and H2 at 460 °C for 16 h. The treated surface layers of specimens were characterized by using SEM equipped with EDS, TEM, XRD analysis and nanoindentation as well as potentiodynamic polarization tests. The results show that the Al18Ti2Mg3 layer with a thickness of 6.3 μm can be formed on the surface of the specimens during interdiffusing of Ti, Mg and Al across the interface between Ti film and the substrate alloy. The interdiffusion layer possesses much higher Young's modulus (131 GPa), the nanohardness (8.97 GPa) and corrosion potential (−0.75VSCE) than those of 5083 Al–Mg alloy. Additionally, the Al18Ti2Mg3 phase layer has an excellent plastic deformation ability resulting mainly from its plasticity deformation power dissipation ratio (η p) up to 87%. [Copyright &y& Elsevier]

Abstract: In this paper, the effect of N distribution on the elastic and electronic properties of hexagonal ε-Fe6N x (x=1, 2, and 3) phases is studied by first-principles calculations. The calculated formation energies of ε-Fe6N x phases decrease with the increasing distance between the N atoms, which demonstrates that the interaction between the interstitial N atoms is of repulsive nature. The theoretical elastic constants, bulk modulus (B), shear modulus (G), ratios of B to G, Young's modulus (E), Poisson's ratios (v) of ε-Fe6N x phases are obtained, which are important parameters for the crystal materials and surface coatings. The more stable interstitial conifiguration enables the ε-Fe6N x phases to possess higher B, G and E. Densities of states are given for all the configurations of ε-Fe6N x phases to discuss the origins of the variations of energetic stability and elastic properties. [Copyright &y& Elsevier]

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: By using first-principles calculations, the influence of interstitial distribution on the elastic and electronic properties of ( and ) phase is investigated. Formation energy calculations exhibit the increasing stability of phase with the increasing distance between the interstitial atoms, indicating a repulsive nature between the interstitial atoms. The theoretical elastic constants, bulk modulus (B), shear modulus (G), ratios of B to G, Youngʼs modulus (E), Poissonʼs ratio (v) of phase are obtained. Density of states calculations reveal the electronic structure variations induced by interstitial distribution, by which the origins of the variations of stability and elastic properties are discussed. [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: 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: The nanocrystallized 18Ni maraging steel was plasma nitrocarburized at 460°C for 4h in a mixture gas of N2, H2 and C2H5OH. The surface phase compositions of the specimens were analyzed using X-ray diffractometer. The grain shape and size, and grain boundaries in the subsurface layers of the samples were characterized by electron backscattering diffraction and transmission electron microscopy. The results show that the nitrocarburized layers are composed of α-Fe, γ′-Fe4N and FeN0.049 phases. Most α-Fe and γ′-Fe4N grains show in columnar shape. The major and minor axes of some α-Fe grains are elongated and shortened after nitrocarburizing, respectively. In the subsurface layers of the untreated and nitrocarburized specimens, the average areas of γ′-Fe4N and α-Fe grains both with a dimension of nanometer are 0.395μm2 and 0.397μm2, respectively. The γ′-Fe4N grain boundaries are mainly high angle boundaries with a very small fraction of low angle boundaries. Coincidence site lattice boundaries in the subsurface layer of the untreated specimen are composed mainly of Σ3, Σ11 and Σ13b, and their fraction decreases after nitrocarburizing. [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: Carbon and nitrogen are the most frequent foreign interstitial atoms in α-Fe. The presence of even a little amount of these impurities in interstitial positions has a drastic influence on the properties of steels. However, the physics of the C–N interaction remains unclear. Here we perform first-principles calculations based on the density functional theory to study the interactions of C–N and those with vacancy (□) in α-Fe. When C and N atoms are in neighbor octahedral sites, a hybridization around −8eV of C 2p states with the N 2p states is observed. C and N atoms lie as far away from one another as possible. When a vacancy is introduced, it can attract two C atoms and a N atom, and a C–C–N–□ complex is formed. When the C and N atoms are the first nearest neighbors of the vacancy and stay in two neighbor octahedral sites, a covalent C–N bond is formed. And the peak of 2p states of the C atom’s density of states shifts to around −8eV, where the peak of the N atom’s 2p states lies. [Copyright &y& Elsevier]

Abstract: The elastic and electronic properties of an ordered intermetallic phase Al18Ti2Mg3 with cubic structure are first investigated by an ab initio method based on density functional theory (DFT) implemented in the Cambridge Serial Total Energy Package (CASTEP) code. The elastic constants are calculated to characterize the elastic anisotropy, the direction-dependent Young’s modulus and the macroscopic elastic modulus. The calculated results show that compared with binary compound Al3Ti, Al18Ti2Mg3 exhibits lower stiffness, slighter elastic anisotropy and better ductility, and the bond of Al18Ti2Mg3 has both covalent and ionic properties. [Copyright &y& Elsevier]

N atom is one of the most frequent foreign interstitial atoms in α-iron along with C atoms. The Fe–C potential has been well-developed and can reproduce many significant interactions of C with point defects present in α-iron. However, there exists no satisfactory Fe–N potential to describe the interactions of N with point defects. Here, we develop a many-body potential for N in α-iron. The potential parameters are determined by fitting to ab initio data, which includes energetics, configurations, and relaxations of Fe atoms close to N atom. This potential successfully describes the interactions of Fe–N across a wide range of defect environments. The potential employs the embedded atom method form and hence is appropriate for large-scale molecular dynamics simulation. [ABSTRACT FROM AUTHOR]

Abstract: Electronic structure and properties of Fe6(N1−x C x )2 carbonitrides with 0≤x≤1, i.e. the concentrations of N and C elements are respectively in range of 0∼7.69wt% and 0∼6.67wt%, have been studied by first-principles calculations based on density functional theory (DFT) implemented in the Cambridge Serial Total Energy Package (CASTEP) code. The calculated results show that the Fe6(N1−x C x )2 carbonitrides are thermodynamically and mechanically stable. Lattice parameters and stability of the carbonitrides increase when C atoms replace N atoms in Fe6N2 unit cell. In Fe6(N1−x C x )2 unit cell, the hybridization effect between C-2p and Fe-3d states is stronger than that between N-2p and Fe-3d states. Elastic properties and melting points of the carbonitrides change slightly with the substitution of C atoms for N atoms in Fe6(N1−x C x )2 carbonitrides. [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 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: The electronic structure, magnetic moment, elastic and ductile properties of the nitride (Fe1−x Ni x )4N with x from 0.00 to 1.00 were investigated by first-principles calculations within generalized gradient approximation (GGA). The calculated results indicate that the substitution of Ni for Fe in the (Fe1−x Ni x )4N nitride leads to the shrinkage of the lattice parameters and the decrease of the stability of this nitride with increasing x value from 0.00 to 1.00. The alloying ability of Ni to the nitride decreases with Ni content. In comparison with N–Fe covalent bond, the N–Ni covalent bond is weaker and can be also strengthened with Ni content in the nitride. The interactions between Fe2 (at face-centered site) and Ni1 (at corner site) atoms, between Ni1 and Ni2 (at face-centered site) atoms are bonding effect. However, the interactions between Fe2 and Fe2 atoms, between Fe2 and Ni2 atoms, between Ni2 and Ni2 atoms are anti-bonding effect and their bonding strengths depend on the Ni content in the nitride. The magnetic moments (MM) of (Fe1−x Ni x )4N and Ni2 atom decrease with the increase of Ni content, and the MM change of Fe2 and Ni1 atoms is opposite to that of Ni2 atom. Generally, the substitution of Ni for Fe improves the elastic properties and reduces the ductility for the (Fe1−x Ni x )4N nitride. [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]

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]

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]

Abstract: In this paper, the alloy 3J33 has been nanocrystallized by a complex thermomechanical treatment process: solution treatment, hot-rolling deformation, cold-drawn deformation and direct electric heating. The nanocrystallization mechanism for the complex thermomechanical treatment of alloy 3J33 was investigated as well. For this alloy two times of solution treatment at 1100°C for 60min, its grain can be refined remarkably from 100μm to nano-scale based on applying firstly 66% continuous hot-rolling deformation from 1100°C to 900°C and secondly 70% cold working at room temperature and finally direct electric heating to 1100°C and quenching in water. The nanocrystallization of alloy 3J33 results mainly from the decreases of the cold working stored energy and the free energy of α′→γ transformation during quick electric heating. [Copyright &y& Elsevier]

In this paper, the friction and wear behaviors of filled PTFE/steel couples are studied. The stationary specimen was made of filled PTFE. The rotating specimen, made of steels, underwent various treatments. The experimental results showed that the frictional coefficient and wear rate were low when the surface of the steel specimen contained nitrogen. The structure of the transfer film was examined by X-ray photoelectron spectroscopy (XPS). The transfer film containing nitrogen on the steel surface was thick. The authors consider that the hypothesis of the adhesion of the n–p–n structure may explain the characteristics of the different sliding couples in this paper and might be an important way to improve the friction and wear properties of the filled PTFE/metal sliding couples. [Copyright &y& Elsevier]

Abstract: We investigated the hardness enhancement in titanium carbonitrides (TiC x N1−x ) by the population analysis method based on first-principles calculations. Populations for bonds TiC and TiN in TiC x N1−x (0.25

The Fe-Cr-Ni alloy (17-4PH steel) with metastable state was plasma thermochemical treated with and without rare earths (RE) addition. The experimental results show that after plasma thermochemical treatments, the initial coarse-grained structure with 20–40 μm grain size of 17-4PH steel could change into composition gradient nanoscale grains (as small as 5 nm) with random crystallographic orientations in plasma nitrocarburized layer. The hardness, modulus and wear resistance properties of nitrocarburized layer with nanoscale grains could be improved apparently. The present surface nanocrystallizaion method demonstrates the technological significance of metal alloy in improving traditional processing techniques and provides a new approach for surface nanocrystallizing of metal alloys. • Nanocrystalline structures are obtained by plasma treatment of metastable metal. • Grain size of 17-4PH steel is decreased from 20–40 μm to 5 nm by plasma treatment. • Grain nanocrystallization mechanism is mainly due to quasi-spinodal decomposition. [ABSTRACT FROM AUTHOR]

In this work, we studied the microstructure formation and mechanical properties of the Ti alloyed C17200 Cu surface produced by plasma nitriding at 750 °C. The results firstly show that the multiphase coating consists of amorphous and nano-crystalline phases, and various types of Cu-Ti intermetallics, including CuTi 2 , CuTi, Cu 3 Ti 2 , Be 3 Ti 2 Cu, Cu 2 Ti, Cu 3 Ti, formed after the plasma nitriding at 750 °C. The formation of the specific type of Cu-Ti intermetallic depends on the processing duration, where a longer duration contributes to the formation of intermetallics with a higher Cu/Ti ratio. The evolution of the phase compositions is responsible for the change in the mechanical properties. The surface hardness of the modified C17200 Cu alloy improves to be 400 HV 0.01 to a depth of 15 μm after plasma nitriding for 6 h, which contributes to a higher surface tribological resistance with a friction coefficient of 0.3 and a wear rate of 4.15 × 10 −9 g/(r·N) for the modified suface. [ABSTRACT FROM AUTHOR]

Theoretical and experimental methods are utilized to design and prepare the expanded martensite (α′ N ) on the steel 38CrMoAl by plasma nitriding. Lehrer diagram is firstly calculated by thermodynamic method, based on which the plasma nitriding experiments are conducted to prepare single-phase α′ N layer. Microstructure and mechanical properties for α′ N layer are further characterized by XRD, TEM and nanoindentation methods. Results show that an expected single-phase α′ N layer is obtained by nitriding at 590 °C in atmosphere with the nitrogen-hydrogen flow ratio of 0.05:0.4. Moreover, single-phase α′ N layer is also detected beneath the outermost compound layer about 20 μm thick in 460 °C nitrided layer. The maximal peak offset of 0.5° and broadening for α′ N (110) indicate that the supersaturated N dissolved in refined grains. Ultra-refined grains about ~ 10 nm of α′ N observed by TEM, elucidate the nano-crystalline layer can be obtained by one-step low-temperature plasma nitriding at 460 °C. However, no evident refinement for α′ N is observed in the 590 °C nitrided layer. More importantly, compare with the γ′-Fe 4 N and ε-Fe 2 − 3 N, significantly improved H and the ratios of H/E and H 3 /E 2 of α′ N layer demonstrate its superior hardness, strength and toughness. [ABSTRACT FROM AUTHOR]

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]

Highlights: [•] Ti/Cu diffusion coatings were prepared on the surface of the C17200 copper–beryllium alloy. [•] The hardness of the coating is much higher than that of the substrate. [•] The wear resistance of the C17200 copper–beryllium alloy was improved significantly. [ABSTRACT FROM AUTHOR]

In this study, C 3 N 4 coating was successfully fabricated on AISI 304 stainless steel by electrochemical deposition method using N-N dimethylformamide (DMF) and KCl as the electrolyte. The influences of DMF concentration on the microstructure, hardness, and wear resistance of the coatings were investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Vickers hardness tester, and pin-on-disk wear tester. The results indicate that a continue C 3 N 4 coating layer can be formed on the steel surface. Compared to the untreated sample, the surface hardness and wear resistance of the stainless steel can be improved apparently after depositing of C 3 N 4 coating. The hardness and wear resistance of the coatings increase firstly and then decrease with increase of DMF concentration. The coatings fabricated with 50 % DMF possess the highest hardness of 1329 HV 0.05 and the lowest friction coefficient of 0.35 at 5 N. The main wear mechanisms are fatigue wear, abrasive wear, and oxidative wear. Deposition of C 3 N 4 coating conforms to the polarization-adsorption-electrochemical reaction mechanism in the present investigation conditions. [Display omitted] • C 3 N 4 coating can be successfully prepared by electrochemical deposition on AISI 304 stainless steel • C 3 N 4 coatings exhibit the high hardness and wear resistance • Deposition of C 3 N 4 coating conforms to the polarization–adsorption–electrochemical reaction mechanism [ABSTRACT FROM AUTHOR]

Abstract: The microstructure, hardness and erosion behavior of High velocity oxy-fuel (HVOF) thermal sprayed and heat treated NiAl intermetallic coatings with three different ceria were studied through erosion tests, Vickers hardness tests and microstructural characterizations in this paper. Test results showed that heat treatment can obviously change the erosion behavior of the HVOF thermal sprayed NiAl intermetallic coatings. After heat treatment at high temperatures, Al2O3, CeAlO3 and NiAl2O3 are formed in the NiAl intermetallic coatings. Heat treated at high temperature (above 600°C), the NiAl intermetallic coatings were strongly softened and exhibited higher erosion rates. Work hardening occurred during the erosion test. The degree of work hardening in thermal sprayed coating is larger than that in heat-treated coatings. Erosion surface morphologies and cross sections showed that the erosion is a mixture mechanism of mainly ductile combined with partly brittle for the coatings containing ceria. [Copyright &y& Elsevier]