Search

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]

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]

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]

• The service life of the treated copper alloy synchronizer ring can up to more than 2 × 105 cycles. • Microstructure and mechanical properties of different nanocomposite coatings were studied. • Hardness and wear resistance are remarkably improved by adding appropriate amount of nano-TiN. • Added TiN nanoparticles did not visibly affect structure and phase transformation behavior. Ni-P-nano TiN composite coatings were successfully prepared and used on the TL084 copper alloy synchronizer ring by electroless plating. The bench test on copper alloy synchronizer rings with the optimal processing indicates a service life as high as 2 × 105 cycles with sufficient friction coefficient, far exceeding the engineering requirements. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) were employed to characterize morphology, composition, structure and phase transformation behavior of the nano-composite coatings. Variations in hardness and wear resistance induced by the addition of various amounts of nano TiN particles were also investigated and correlated with microstructural characteristics. Compared with conventional pure Ni-P coatings, remarkable increases in hardness and wear resistance were observed in the nano-composite coatings, which can be ascribed to the nano TiN particles uniformly distributed in the Ni-P matrix. The introduction of TiN nanoparticles into the electroless Ni-P coating does not significantly affect the structure before and after the heat treatment, but can enhance the hardness. [ABSTRACT FROM AUTHOR]

In the present investigation, carbon-expanded α (α C) phase layers were prepared by low-temperature carburizing of AISI 431 martensitic stainless steel. The microstructures of the layers were characterized by optical microscopy and X-ray diffractometry, the mechanical properties of the carburized layers were characterized by nanoindentation tester. Then, first-principles calculation method was used to characterize α C phase from atomistic level. Experimental results show that there are the uniform layers formed on stainless steels after plasma carburized at 703 K. The layer thicknesses for the steel carburized for 14,400 s, 28,800 s and 57,600 s are about 25 μm, 38 μm and 46 μm, respectively. The surface phases are mainly of α C phase with a small amount of Fe 3 C phase. The surface hardness of the carburized specimen can be higher than 15 GPa by nanoindentation tests, the carburized layers possess a good wear resistance based on the higher H / E and H 3 / E 2 ratio evaluation criterions. Crystal cell of α C phase were established and describing as the nominal molecular formula of Fe 13 Cr 3 C x (x = 0, 2, 4, 6). The calculation results indicate that with increasing of carbon content, the structural and mechanical stabilities of Fe 13 Cr 3 C x (x = 0, 2, 4, 6) system decrease gradually, the hardness increases first then decrease, and can reach up to about 25 GPa. The elastic moduli decrease from about 210 GPa to 66 GPa with increasing of carbon content, while the toughness increase gradually based on B/G values evaluation criterion. The calculated and the experimental results are consistent within a reasonable range, which shows the validity of the established model for α C phase. • Carbon-expanded α (αC) phase was prepared by low-temperature plasma carburizing. • αC phase was firstly characterized by first-principles calculation approach. • αC phase treated as the nominal molecular formula of Fe13Cr3Cx (x = 0, 2, 4, 6). • Calculated results are almost in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The heat treatment (consisting of solid solution and aging), is integrated with the nitriding process of titanium coated ZL205A aluminum alloy to improve the surface and matrix mechanical properties simultaneously. Two-step duplex treatment is adopted to prepare the gradient multiphase layer on a magnesium-free ZL205A aluminum-copper based alloy. Firstly, pure titanium film is deposited on the aluminum alloy substrate using magnetron sputtering. Secondly, the Ti-coated specimen is nitrided at the solid solution temperature of the substrate alloying elements in a gas mixture of N 2 and H 2 and aged at 175 °C. The microstructure evolution, microhardness as well as the wear resistance of obtained multiphase layers are investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS), microhardness tester and pin-on-disc tribometer. The multiphase layer, dominated by TiN 0.3 or Al3Ti, is prepared with significantly increased layer depth after duplex treatment. The surface hardness of multiphase layer is remarkably improved from 23.7HV to 457HV. The core matrix hardness is also increased to 65HV after aging. The wear rate of the multiphase layer decreases about 55.22% and 49.28% in comparison with the aged and Ti coated specimens, respectively. The predominant wear mechanism for the multiphase layer is abrasive and oxidation, but severe adhesive wear for the aged and Ti coated specimens. [ABSTRACT FROM AUTHOR]

The structures of carbon-expanded α phase (α C) phase were modeled with nominal molecular formula of Fe 13-x Cr 3 Ni x C y (x = 0, 1, y = 0,1,2,3,4) based on body-centered cubic α-Fe and calculated by first-principles calculation using density functional theory (DFT). The results show that Fe 13 Cr 3 C y (y = 0,1,2,3,4) structures with less than 11.11 at% carbon (y = 2) can be easily formed and exist stable. The Young's moduli of stable Fe 13 Cr 3 , Fe 13 Cr 3 C, and Fe 13 Cr 3 C 2 are 227.08 GPa, 209.71 GPa and 189.19 GPa, respectively. The theoretical hardness of stable Fe 13 Cr 3 C y (y = 1, 2) are obviously improved and can be up to 8.26 GPa. As for Fe 12 Cr 3 NiC y (y = 0,1,2), Young' s moduli of Fe 12 Cr 3 Ni, Fe 12 Cr 3 NiC, and Fe 12 Cr 3 NiC 2 are 155.82 GPa, 258.24 GPa and 207.44 GPa, respectively. The hardness of Fe 12 Cr 3 NiC y (y = 1,2) can be as high as 17.88 GPa. Ni element can stabilize the structures of Fe 13 Cr 3 C y (y = 1,2) and improve their theoretical hardnesses. The toughness of Fe 13 Cr 3 C y (y = 1,2) structures are shown in ductility based on Pugh's ratio criterion, while the Fe 12 Cr 3 NiC y (y = 1,2) structures are shown in brittleness. Electronic structure calculation shown that there are mixture bonding of metal bonding, covalent bonding, and ionic bonding in Fe 13-x Cr 3 Ni x C y (x = 0,1, y = 1,2) structures, which should account for the high hardness of the structure for α C phase. • Optimization position of Cr atom in α-Fe with BCC structure was obtained. • Hardness of stable Fe 13-x Cr 3 Ni x C y (x = 0, 1, y = 1,2) can be as high as 17.88 GPa. • Effects of Ni element on mechanical properties of α C phase were given. • New covalent bonding and ionic bonding account for high hardness of the structure for α C phase. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microstructures and properties of three coatings Ni-P, Ni-P-TiN and Ni-P-TiN-Re are studied. • Re addition can significantly increase the deposition rate of Ni-P-TiN. • Re addition leads to a remarkable increase in crystallization temperature of coating. • Re addition can further improve hardness and wear resistance of Ni-P-TiN coating. Three different types of coatings Ni-P, Ni-P-TiN and Ni-P-TiN-Re are successfully prepared on a copper substrate by electroless plating. The effects of TiN and TiN + Re addition on surface morphology, microstructure, phase composition, deposition rate, thermal stability and wear resistance are investigated. Results show that all coatings exhibit amorphous microstructures, and that Re addition can significantly increase the deposition rate based on the coating thickness. X-ray diffraction of the coating before and after annealing indicates that the addition of TiN nanoparticles to the Ni-P coating barely affects the microstructures and phase transformation behavior, while the addition of Re results in a remarkable increase in crystallization temperature. Regardless of whether it is annealed or not, the wear resistance of Ni-P coating can be significantly improved after the co-deposition of TiN or TiN + Re, and the synergy effect of Re and TiN can further enhance the improvement. These findings provide a pathway to efficiently produce Ni-P-nano TiN composite coatings with excellent performance and thus have great potential in large-scale industry applications. [ABSTRACT FROM AUTHOR]

In this work, quenched AerMet100 steel is plasma nitrided at 460 °C for 8 h in a gas mixture of 50% N 2 + 50% H 2. The microstructures and mechanical properties are investigated. Results show that the current nitriding conditions can effectively inhibit the formation of brittle white compound layer in the surface of AerMet100 steel. Further investigations on orientations of martensite laths and prior austenite confirm that all 24 variants of martensite laths produced by one prior austenite grain follow the K S orientation relationship and this relationship holds during nitriding. Besides, a memory phenomenon that the orientation of precipitated γ′-Fe 4 N is exactly the same as that of prior austenite is observed, due to the strong variant selection. Compared with the un-nitrided specimen, the microhardness of AerMet100 steel after nitriding treatment is remarkably improved, and volume wear rate is reduced by an order of magnitude. Such a large improvement is primarily attributed to a desirable combination of high surface hardness, considerable nano-grains and secondary hardening of the substrate. Unlabelled Image • Brittle layer is avoided, with hardened substrate and improved wear resistance achieved. • K S OR between lath martensite and prior austenite holds during nitriding. • There is an orientation memory phenomenon between γ′-Fe 4 N and prior austenite. [ABSTRACT FROM AUTHOR]