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In order to improve the poor comprehensive performance of aluminum bronze surface, a duplex surface modification technology consisting of laser cladding and followed by plasma nitriding was adopted to prepare the infiltration composite modified layer. The effects of different surface treatment techniques on the microstructure and properties of the modified layer were investigated. The results show that the laser cladding surface is mainly composed of Cu-rich intermetallic compounds, and the AlN layer appears on the surface after plasma nitriding treatment, which significantly improves the hardness and tribological properties. The surface modification treatment changes the surface morphology. The microhardness of the alloy surface after composite modification is much higher than that of untreated and single treatment. It is about six times that of the Cu-Al matrix. At the same time, the composite modified layer has a lower friction coefficient and wear volume, showing excellent tribological properties. These research results can provide a new way for the surface design and development of metal materials.

In order to improve the wear resistance of the cable bolt and increase its life-time during operation, plasma nitriding was employed to obtain a protective nitriding layer on its surface. The microstructure, phase constitution, microhardness and wear resistance of the nitriding layer were investigated. It was shown that continuous and dense nitriding layers were formed on the surface of the samples. The microhardness of the nitrided sample was enhanced by the formation of nitriding layer, which mainly consisted of Fe₄N and Fe₃N. The mass losses of the nitrided samples were much smaller and the wear rates were almost hundred times lesser than that of the substrate. Plasma nitriding treatment can effectively enhance the wear resistance of cable bolt.

In this study, a novel pre-magnetization process, which enables easy diffusion of nitrogen, was used to enhance plasma nitriding efficiency. Firstly, magnetic fields with intensities of 1500G and 2500G were applied to the untreated samples before nitriding. After the pre-magnetization, the untreated and pre-magnetized samples were plasma nitrided for 4h in a gas mixture of 50% N₂–50% H₂ at 500${}^{\circ }$C and 600${}^{\circ }$C. The structural, mechanical and morphological properties of samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness tester and surface tension meter. It was observed that pre-magnetization increased the surface energy of the samples. Therefore, both compound and diffusion layer thicknesses increased with pre-magnetization process before nitriding treatment. As modified layer thickness increased, higher surface hardness values were obtained.

A pretreatment of sand blasting with the duration of 15min was carried out prior to plasma nitriding for 1045 carbon steel in this study. The corrosion behavior was evaluated by means of electrochemical polarization, electrochemical impedance spectroscopy (EIS) and soaking test, and compared with that without pretreatment of sand blasting. The results show that the pretreatment of sand blasting can significantly enhance the corrosion resistance, the corrosion potential shift to the noble direction, with higher corrosion potential of $-1.067\times 10^3$mV and lower corrosion current of 0.0853$\mu$A/cm², and exhibit larger diameter, higher phase angle and wider frequency region, there exists no corrosion pit after soaking test, and the corrosion rate is decreased from 0.0387g/mm² to 0.01341g/mm², only 1/3 comparing with that of sample without pretreatment of sand blasting. The enhancement mechanism of corrosion behavior is mainly ascribed to the excellent protection from the thicker and denser compound layer with higher amount of $\epsilon$-Fe${}_{2-3}$N.

Plasma nitriding of AISI 5140 low alloy steel was carried at pressures ranging from 100Pa–500Pa for 4h with hollow cathode discharge assistance. The treated samples were characterized by optical microscope, microhardness tester, X-ray diffraction and electrochemical workstation. The results show that the compound layer is about 5$\mu$m in thickness and the depth of surface hardening layer is about 240$\mu$m for the sample nitrided at 100Pa for 4h. The hardness value of nitrided surface is about 830HV${}_{0.1}$, which is about 2.9 times higher than that (290HV${}_{0.1}$) of the substrate. There is no obvious difference in the thickness of compound and diffusion layers, surface microhardness and phase composition of nitrided layers in comparison with that of samples nitrided at pressure 300 and 500Pa used by conventional plasma nitriding. But plasma nitriding with low pressure can effectively reduce the assumption of nitriding gas and amount of exhausted emission.

The 31CrMoV9 steels were plasma nitrided under different gas mixture ratios to investigate an influence of nitrogen amount on wear behavior. The structure, mechanical and tribological behavior of untreated and nitrided 31CrMoV9 steels were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), microhardness device, 3D profilometer and pin-on-disk wear tester. The analysis outcomes displayed that the compound layer consists of nitride phases (Fe₂N, Fe₃N, Fe₄N and CrN). Additionally, the thickness of the compound layers, surface hardness and roughness increased with increasing nitrogen amount in the gas mixture. The highest friction coefficient value was obtained at nitrogen amount of 50%, but the lowest value was seen at nitrogen amount of 6%. It was observed that wear resistance of 31CrMoV9 steel improved after plasma nitriding, and the best wear resistance was also obtained from plasma nitrided sample at the gas mixture of 94% H${}_2+6$% N₂.

Refuse-derived fuel (RDF) is a kind of renewable energy source to produce energy for replacement of fossil fuels. Aggressive working conditions in RDF facilities cause the shredder blades to wear out quickly. So, the purpose of this paper was to study the effect of plasma-nitriding process on wear resistance of shredder blades made of AISI D2 tool steel in the service condition of RDF facility. Shredder blades were commercially available from two different suppliers (A and B suppliers). These hardened shredder blades were plasma-nitrided in the mixed nitrogen and hydrogen atmosphere at a volume ratio of 3:1 at 450^∘C for 12, 18 and 24h at a total pressure of 250 Pa. Characterisation of plasma-nitrided layers on the shredder blades was carried out by means of microstructure and microhardness measurements. Wear tests of plasma-nitrided shredder blades were performed under actual working conditions in the RDF facility. Wear analysis of these shredder blades was conducted using three-dimensional (3D) optical measuring instrument GOM ATOS II. The compositional difference of the shredder blades provided by A and B suppliers played an important role on the nitrided layer. The case depth of A-blades significantly increased with increasing plasma-nitriding time. However, the case depth of B-blades was fairly lower at the same nitriding time and only slightly increased with increasing plasma-nitriding time. Plasma-nitriding process significantly improved the surface hardness of the shredder blades. Maximum surface hardness values were achieved at nitriding time of 18 h for both blades. In this case, this increase in surface hardness values was above 100%. At nitriding time of 24h, the maximum surface hardness of A-blades significantly decreased, whereas this decrease in surface hardness of B-blades was the negligible value. The wear test results showed that plasma-nitriding process significatly decreased the wear of shredder blades; 18 h nitriding for A-blades and 24h nitriding for B-blades had better wear-reducing ability in the service condition of RDF facility. In these cases, the decreases in the total volume wear loss for A- and B-blades were 53% and 60%, respectively.

The aim of this work is to improve the surface properties of aluminum, using active screen plasma nitriding (ASPN) equipped with aluminum active screen (Al-AS). The samples are treated in fixed processing conditions, except 0–50% hydrogen is admixed in nitrogen gas, for the better removal of the native oxide layer. The samples are analyzed using the micro-hardness tester, X-ray diffraction, scanning electron microscope and dry ball-on-disc wear tester. The results show that using Al-AS (particularly at 40% hydrogen), excellent film quality with better uniformity, surface hardness and wear resistance can be attained with aluminum nitride (AlN) as a leading phase. Using Al-AS, the deposition of inappropriate material (such as iron in some reports) can be avoided with improved results even in short processing time (3h).

Combined plasma nitriding and surface texturing approach were conducted on 316 stainless steel to enhance the tribological performance. Five different surfaces (316 substrates, plasma-nitrided 316, surface-textured 316, plasma-nitrided surface-textured 316, and surface-textured plasma-nitrided 316) were investigated. The tribological behaviors were studied using a ball-on-disk rotary tribometer against counterparts of Si₃N₄ balls in the air and under oil lubrication conditions. The results were analyzed from the aspects of friction coefficient, mass loss, and surface morphology about the tested specimens. The results presented that the frictional properties of the surface of plasma-nitrided surface-textured 316 were optimal under both friction conditions. Under dry friction conditions, the influence of plasma nitriding on mass loss was greater than that of surface texturing. Under oil lubrication conditions, the influence of surface texturing on mass loss was greater than that of plasma nitriding, and the processing sequence of surface texturing and plasma nitriding had little effect on the mass loss. The better wear resistance of plasma-nitrided surface-textured 316 resulted from the following aspects: first, the nitriding layer improved the surface hardness of the material. Secondly, the surface texture can capture the debris under dry friction conditions and provide continuous lubrication under oil lubrication condition.

Tribology is the study of friction, wear and lubrication. This work aims to study the effect of coatings on the wear behavior of H13 tool steel. Liquid nitriding, plasma nitriding, PVD TiN coating and DLC were utilized on H13 tool steel for increasing the tool life, quality of drilled holes and to reduce the cost of tool material. The wear behavior of H13 was evaluated using pin on disc wear test. Microstructural and scanning electron microscope analysis of wear surface of tool was carried out to identify the best coating and wear mechanism. This study reveals that PVD-TiN-coated H13 tool exhibited the best wear response and least coefficient of friction hence can be selected for friction drilling process.

Quenched and tempered (QT) S45C steel was processed by plasma nitriding (a mixture of 40%N₂-60%H₂, 400 Pa, 773 K) with two different durations: 8 h and 48 h. The microhardness, surface residual stress and nitriding layer compound were separately detected and the effect was discussed with the fatigue test result. The rotating bending fatigue properties was test with QT, QT nitiding 8 h, QT nitriding 48 h specimens. Fish-eye type crack formation occurred and the two crack initiation modes, fish-eye crack initiation and surface crack initiation, were observed by the scanning electron microscope and discussed. The result showed that the fatigue strength of QT specimens were improved by 54% at least compared with the untreated specimens. But the QT and un-QT have the mainly same fatigue strength in the same plasma nitriding condition, especially no-improvement with the 48 h plasma nitriding specimens.