Characterization and tribological evaluation of duplex treatment by depositing carbon nitride films on plasma nitrided Ti-6Al-4V

Carbon nitride (CN_X) films (with N/C ratio of 0.5) were deposited on both untreated and plasma nitrided Ti-6Al-4V substrates by D.C. magnetron sputtering using a graphite target in nitrogen plasma. TEM and XPS analysis revealed the formation of both amorphous CN_X structure and crystalline -C₃N₄ phases in the deposited coatings. Nano-indentation tests showed that the film hardness was about 18.36 GPa. Both the scratch tests and indentation tests showed that compared with CN_X film deposited directly on Ti-6Al-4V, the load bearing capacity of CN_X film deposited on plasma nitrided Ti-6Al-4V was improved dramatically. Ball-on-disk wear tests under both dry sliding and lubricated conditions (with simulated body fluids) were performed to evaluate the friction and wear characteristics of the deposited coatings. Results showed that under both dry and lubricated conditions, the duplex treated system (i.e., with CN_X film deposited on plasma nitrided Ti-6Al-4V substrate) was more effective in maintaining a favorable low and stable coefficient of friction and improving wear resistance than both individual plasma nitriding and CN_X films on Ti-6Al-4V substrate. Under dry sliding conditions, the generated wear debris of spalled films were accumulated on the wear track, mechanically alloyed and graphitized, thus significantly reducing the coefficient of friction and preventing wear of the substrate. However, under lubricated conditions, due to the flowing of the fluids, the lubricating wear debris was taken away by the fluids, and therefore, the direct contact of two original surfaces resulted in high coefficient of friction and extensive abrasive wear of the substrate for CN_X films deposited on Ti-6Al-4V substrate. Also when there was some small-area spallation of CN_X films, the fluids could seep into the interface between the film and substrate, thus degrading the interfacial adhesion and resulting in a large area spallation.     

Analysis of plastic deformation in diamond like carbon films-steel substrate system with tribological tests

The influence of plastic deformation of the substrate on the tribological properties of diamond like carbon (DLC) films was investigated in DLC films-steel substrate system. The tribological properties of DLC films deposited on different hardness steel were evaluated by a ball on disk rotating-type friction tester at room temperature under different environments. In dry nitrogen, DLC films on soft steel exhibited excellent tribological properties, especially obvious under high load (such as 20 N and 50 N). However, DLC films on hard steel were worn out quickly at load of 20 N. Plastic deformation was observed on soft steel after tribological tests. The width and depth of plastic deformation track increased with increase of the experimental load. Super low friction and no measurable wear were kept in good condition even large plastic deformation under high load conditions in DLC films-soft steel system. In open air, DLC films on soft steel exhibited high coefficient of friction and DLC films on ball were worn out quickly. Plastic deformation was not observed on soft steel because the contact area increased and the thick hardened layer on contact surface were formed by DLC films and debris particles together on the steel substrate. The wear track on steel became deep and wide with increase of loads and DLC films were worn out. The experimental results showed that super low friction and high wear resistance of DLC films on soft steel can be attributed to the good adhesion and plastic deformation. Plastic deformation played an active role in the tribological properties of DLC films on soft steel in the present work.     

Friction and frictional tracks on thick silica films prepared by vacuum deposition

Friction and frictional tracks on 2 µm thick SiO₂ films evaporated on polymethylmethacrylate (PMMA) substrate were investigated. Diamond spherical sliders of radius 30 and 100 µm, respectively, were slid on these coatings under a load of 50 to 200g at a sliding speed of 15 cm min^–1. The static and dynamic friction coefficients for SiO₂ films were found to be 0.1 and 0.06, respectively, depending on the load and radius of the slider. For lower load and small slider radius the tracks on SiO₂ film were groove-like, and whisker-like cracks regularly grew from the edges of the tracks. For higher loads and larger slider radius, semicircular cracks in the film were regularly found behind the slider, but in thicker film (6 µm thick), circular cracks occurred. The origin of these cracks is discussed in terms of a tension zone produced around the contact area between the slider and the substrate under frictional force.     

Relative performance of hydrogenated, argon-incorporated and nitrogen-incorporated diamond-like carbon coated Ti-6Al-4V samples under fretting wear loading

Hydrogenated diamond-like carbon (DLC) (H-DLC), argon-incorporated DLC (Ar-DLC) and nitrogen-incorporated DLC (N-DLC) coatings were deposited on flat rectangular Ti-6Al-4V samples. The DLC coatings were characterised by Raman spectroscopy and nanoindentation. Fretting wear tests were conducted on uncoated and DLC coated samples with an alumina ball as the counterbody. As the Ar-DLC and N-DLC coatings had relatively more sp² network compared to the H-DLC coating, they exhibited lower values of hardness and elastic modulus. At both loads of 4.9 N and 14.7 N, all DLC coated specimens showed lower values of tangential force coefficient (TFC), wear volume and specific wear rate compared to the uncoated samples. While the Ar-DLC coated sample exhibited the lowest TFC, wear volume and specific wear rate at 4.9 N load, the N-DLC coated specimen exhibited the lowest TFC, wear volume and specific wear rate at 14.7 N load.     

Wear of ceramic particle-reinforced metal-matrix composites

Pin-on-disc dry sliding tests were carried out to study the wear mechanisms in a range of metal-matrix composites. 6061-aluminium alloys reinforced with 10 and 20 vol% SiC and Al₂O₃ particles were used as pin materials, and a mild steel disc was used as a counterface. A transition from mild wear to severe wear was found for the present composites; the wear rate increased by a factor of 10². The effects of the ceramic particles on the transition load and wear with varying normal pressure were thoroughly investigated. Three wear mechanisms were identified: abrasion in the running-in period, oxidation during steady wear at low load levels, and adhesion at high loads. A higher particle volume fraction raised the transition load but increased the wear rate in the abrasion and adhesion regimes. Increase of particle size was more effective than increase of volume fraction to prolong the transition from mild wear to adhesive wear. The reasons for different wear mechanisms were determined by analyses of the worn surfaces and wear debris.     

The influence of load and surface treatment on the corrosive wear of cast iron in oil-sulphuric acid environments

An investigation into the influence of load and surface finish on the reciprocating corrosive wear of grey cast iron in oil-10 vol % sulphuric acid mixtures has been undertaken with particular respect to the contact between cylinder-lining and piston-ring materials from marine diesel engines. In mixtures containing acid of 10 vol% concentration, under loads of 1.5 to 3.5 kg, the hard-phase phosphide eutectic/alloy carbide material in the cast irons was able to support the load and aid in the retention of an oil film during sliding. However, at a load of 4 kg the hard-phase material was able to penetrate the oil film more effectively and contact the countersurface for long periods, giving considerably increased wear rates. In mixtures containing acid of 40% concentration, the wear rates were less than those of 10% concentration, due to formation of adherent, wear-protective corrosion-product films. These were particularly effective at loads of 1.5 to 2.0 kg, while at 2.5 to 4.0 kg such films were unable to be sustained on the hard-phase regions and wear rates were increased to some extent, although were still much less than in the 10% acid concentration mixture. During sliding in mixtures containing acid of 40% concentration, development of a wear-protective film was influenced very markedly by the surface finish of the cast-iron specimens. Corrosion-product films were able to develop more easily on rough surfaces (120 grit) than on smooth surfaces (1 m), while hydrodynamic oil films could develop more easily on smooth surfaces. The overall result was that the wear rate increased with decreasing surface roughness from 120 grit to a maximum at an intermediate value (800 grit), and then decreased with further decrease in roughness to 1 m.     

Optimization of tribological parameters in abrasive wear mode of carbon-epoxy hybrid composites

Abrasive wear performance of fabric reinforced composites filled with functional fillers is influenced by the properties of the constituents. This work is focused on identifying the factors such as filler type, filler loading, grit size of SiC paper, normal applied load and sliding distance on two-body abrasive wear behaviour of the hybrid composites. Abrasive wear tests were carried on carbon fabric reinforced epoxy composite (C-E) filled with filler alumina (Al₂O₃) and molybdenum disulphide (MoS₂) separately in different proportions, using pin-on-disc apparatus. The experiments were planned according to Taguchi L18 orthogonal array by considering five factors, one at two levels and the remaining at three levels, affecting the abrasion process. Grey relational analysis (GRA) was employed to optimize the tribological parameters having multiple-response. Analysis of variance (ANOVA) was employed to determine the significance of factors influencing wear. Also, the comparative specific wear rates of all the composites under dry sliding and two-body abrasive wear were discussed. The analysis showed that the filler loading, grit size and filler type are the most significant factors in controlling the specific wear rate of the C-E composite. Optimal combination of the process parameters for multi performance characteristics of the composite under study is the set with filler type as MoS₂, filler loading of 10 wt.%, grit size 320, load of 15 N and sliding distance of 30 m. Further, the optimal parameter setting for minimum specific wear rate, coefficient of friction and maximum hardness were corroborated with the help of scanning electron micrographs.     

Growth, structure and friction behavior of titanium doped tungsten disulphide (Ti-WS2) nanocomposite thin films

This study describes the synthesis, structure and friction behavior of titanium doped tungsten disulphide (Ti-WS₂) nanocomposite solid lubricant thin films grown by cosputtering at room and 300 °C in situ substrate temperatures. The films were studied by focused ion beam (FIB) prepared cross-sectional scanning and transmission electron microscopies and X-ray diffraction (XRD) to determine the thin film structure and crystallinity as a function of varying titanium atomic percent and sputtering power. XRD confirmed that the pure WS₂ thin films grown at room temperature (RT) and 300 °C were crystalline with hexagonal texture. Basal planes with c-axis orientated parallel to the substrate surface [(100) and (101) texture] were predominantly observed in all thin films. Co-sputtering at RT with any amount of Ti induced a dramatic change in the microstructure, i.e., Ti prevented the formation of crystalline WS₂, making it amorphous with well-dispersed nanocrystalline (1-3 nm) precipitates. For RT friction tests, longer thin film lifetimes were exhibited when the thin films were doped with low amounts of Ti (∼ 5-14 at.%) in comparison to pure WS₂ but there was no change in friction coefficient (∼ 0.1). For high temperature (500 °C) friction tests, slightly higher friction coefficients (0.2) but longer lifetimes were observed for the low at.% Ti doped thin films. Mechanisms of solid lubrication were studied by FIB prepared cross-sectional specimens and Raman spectroscopy wear maps inside the wear tracks to determine the sub-surface deformation behavior and formation of tribochemical products, respectively. It was determined that WS₂ oxidized to form relatively low shear strength WO₃ during wear (tribo-oxidation) and heating at 500 °C (thermal oxidation) as determined by Raman spectroscopy in the wear track and transfer film (third body) on the counterface.     

Transfer of molybdenum sulphide coating material onto corundum balls in fretting wear tests

Transfer films on corundum balls from sulfur deficient molybdenum disulfide (MoS_x) coatings with different crystallographic orientations were investigated after fretting tests performed in ambient air of different humidity levels. The morphology of wear tracks on MoS_x coatings and of transfer films on corundum balls were investigated by light optical microscopy with Normarski contrast. The thickness of transfer films was measured by scanning white light and optical phase-shifting interferometry, and their composition was analyzed by X-ray photoelectron spectroscopy. The effect of relative humidity in fretting tests on the composition of the transfer films as well as the effect of the transfer film on the tribological performance of MoS_x coatings in fretting wear tests is discussed.     

Schwingungsverschleiß an TiB2-ZrO2 und TiC-ZrO2 oberflächenlegierter Al2O3-Keramik unter Variation der Luftfeuchte

Oscillating sliding wear of TiB₂-ZrO₂ and TiC-ZrO₂ surface alloyed Al₂O₃ ceramic at different humidity A commerical alumina ceramic was surface-alloyed by adding TiB₂ and TiC in addition to ZrO₂ using infrared CO₂ laser radiation. Aside from the type of hard particles their volume fraction was varied between 6 and 31%. The average thickness of the alloyed surface layer was about 150 ¨?m. Tribological tests were carried out unlubricated under oscillating sliding contact against alumina counterbodies at relative humidities of 3 and 50% as well as in distilled water. Ceramographic studies showed that multiphase structures containing hard particles of TiC or TiB₂ embedded in the Al₂O₃ matrix were obtained by alloying. In addition Al-Zr-Ti-O complex phases were analyzed by using X-ray diffraction technique. Compared to the commercially available alumina ceramic A123, laser alloying reduced the friction coefficient and improved substantially the wear resistance under the applied conditions of tribological testing. It was found that tribological behaviour was strongly influenced by environmental humidity in addition to the effect of the type and volume fraction of the phases produced by alloying. The unalloyed alumina ceramic depended more sensitively on humidity than the alloyed ceramic.     

Effect of annealing temperature on the tribological behavior of ZnO films prepared by sol-gel method

The tribological behavior of zinc oxide (ZnO) films grown on glass and silicon (100) substrates by sol-gel method was investigated. Particularly, the as-coated films were post-annealed at different temperatures in air to investigate the effect of annealing temperature. Crystal structural and surface morphology of the films were measured by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). XRD patterns and AFM images indicated that the crystallinity and grain size of the films were enhanced and increased, respectively, with temperature. The tribological behavior of films was evaluated by sliding the ZnO films against a Si₃N₄ ball under 0.5 gf normal load using a reciprocating pin-on-plate tribo-tester. The wear tracks of the films were measured by AFM to quantify the wear resistance of the films. The results showed that the wear resistance of the films could be improved by the annealing process. The wear resistance of the films generally increased with annealing temperature. Specifically, the wear resistance of the films was significantly improved when the annealing temperature was higher than 550° C. The increase in the wear resistance is attributed to the increase in hardness and modulus of the film with annealing temperature.     

Si3N4和52100钢对磨副材料对CrN薄膜干摩擦学行为的影响

利用阴极电弧离子镀技术在316L不锈钢基体上制备了CrN薄膜。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、纳米压痕仪对CrN薄膜的形貌、成分和力学性能进行了表征。为了研究Si_3N_4和52100钢对磨副材料对CrN薄膜和316L不锈钢干摩擦行为的影响,在2N、5N、8N三种载荷下,将CrN薄膜和316L不锈钢基体与Si_3N_4陶瓷球和52100钢球分别进行了往复式滑动干摩擦实验。采用扫描电子显微镜观察了磨痕的微观形貌,并对CrN薄膜和316L不锈钢基体的磨损机制进行了分析。结果表明:CrN薄膜表面平整,缺陷较少;CrN薄膜的纳米硬度约为28GPa,弹性模量约为350GPa;与Si_3N_4陶瓷球相比,CrN薄膜与52100钢球摩擦时摩擦因数相对较小(保持在0.7左右)且更加稳定;316L不锈钢的摩擦因数远大于CrN薄膜且波动较大;对磨球为Si_3N_4陶瓷球时,CrN薄膜的主要磨损机制为磨粒磨损,伴有少量的氧化和黏着磨损,316L不锈钢的磨损机制主要为磨粒磨损和塑性变形,伴有少量的氧化和黏着磨损;对磨球为52100钢球时,CrN薄膜的主要磨损机制为黏着磨损,伴有少量的氧化,316L不锈钢的磨损机制主要为黏着磨损,伴有少量的氧化和磨粒磨损。CrN薄膜与两种对磨球的磨损量均小于316L不锈钢基体的磨损量,说明CrN薄膜有效提高了基体的耐磨性。     

Formation of UHMWPE polymeric transfer films on sliding glass counterfaces: early and steady-state wear studied by transmission electron microscopy

At a temperature of 30°C polymeric transfer films were generated on glass counterfaces during small-amplitude oscillatory sliding contact with an ultra-high molecular weight polyethylene (UHMWPE) pin under a constant load of 6.5 MPa. Early discontinuous and continuous (steady-state) transfer films were studied with vertical platinum-carbon replication and transmission electron microscopy (TEM). Nanometre-scale UHMWPE deposits in these transfer films have been visualized for the first time. Nanometre-scale particles averaging 20.6 ±6.3nm (5–40nm) were deposited on glass in the early stages of UHMWPE film transfer. After formation of a continuous transfer film, UHMWPE particles of slightly smaller dimensions, 13.5±6.1 nm (2–41 nm), were deposited on the transfer film surface. In addition, micrometre-scale particles (0.1–6.4 m) were found at the ends of the wear track. At high magnification, a fraction of the UHMWPE polymer chains observed in particle surfaces and in the transfer film surface nearby were not oriented in the sliding direction. Some crystal- or plate-like particles of UHMWPE were seen in the transfer film. Plate-like and micrometre-scale spherulitic inclusions were also identified on the mostly amorphous UHMWPE pin surface fractured at liquid nitrogen temperatures. The high frequency of nanometre-scale UHMWPE particles in contrast to the less numerous micrometre-scale deposits near the ends of the wear track suggests that the nanometre-scale deposits contribute significantly to transfer film formation and to the wear characteristics of UHMWPE.To whom correspondence should be addressed.     

Effect of heat treatment on microstructure and wear behavior of Al–Si alloys with various iron contents

Effect of T6 heat treatment on microstructure and wear behavior of hypoeutectic Al–Si alloys with iron contents of 0.15, 0.7 and 1.2 wt% was studied. Dry sliding wear tests were performed on a pin-on-disk tribometer under normal loads of 20, 30 and 40 N. The alloy with 0.7 wt% iron showed the highest wear resistance before the heat treatment under the loads tested. T6 heat treatment improved the wear resistance of the alloys with different iron contents compared to the non-heat treated 0.7 wt% iron alloy under all applied loads. The improvements in the wear can be attributed to the decrease of length and volume fraction of hard and brittle β-Al₅FeSi iron-rich intermetallics and spherodization of the coarse eutectic silicon particles by diffusion of iron and silicon into the matrix upon solution heat treatment. The change in the morphology of the phase particles reduced the probability of nucleation and propagation of subsurface cracks and increased the wear resistance in the samples.     

低碳钢的复合微动磨损特性研究

在球/面接触条件下,以恒定加载速度(6 mm/min),研究了20号钢在两种倾斜角(45°和60°)、三种载荷(F max=200,400,800N)下的复合微动磨损行为.在分析复合微动的动力学特性的同时,结合激光共焦扫描显微镜(LCSM)和扫描电子显微镜(SEM)对磨痕进行分析.结果表明随着倾斜角度和载荷的增加,表面磨损明显增加,并可根据F-D曲线的三种形状,将20号钢的复合微动运行过程划分为三个阶段.第I阶段的磨损主要表现为滑动磨损的特征,第II,III阶段的磨损机制主要为剥层,但氧化程度明显不同.     

Abrasive wear in filled elastomers

The abrasive wear of rubbers is strongly affected by the filler particles dispersed in the elastomer matrix. The fillers are incorporated usually for the purposes of mechanical reinforcement and improving the conductivity of the neat resins. It is found that the wear rates of the filled silicone rubbers increase slowly with filler concentration until a critical volume fraction,v _c, is reached, at which point they increase very rapidly with increasing filler concentration. This behaviour appeared to be universal in all the filled silicones we studied, regardless of the type of filler and silicone rubber used. However the magnitude of the critical filler fraction,v _c, can be changed significantly with the filler shape, resin cross-linking density and filler surface treatments. No reasonable relationship could be found between this wear behaviour and the mechanical properties measured in a macroscopic manner. Experimental evidence suggests that the incipient cracks that lead to wear losses may start within the thin layers of highly stressed material, the damage zones, surrounding the rigid particles. A simple model taking into account the stress concentration induced by the rigid fillers shows excellent correlation between the wear rate and the damage zones volume. With this new model, the observed wear behaviours can be explained satisfactorily.     

Abrasive wear of dental composite resins

Abrasive wear is a major problem in the application of dental composite resins. In this study the friction and wear behaviours of two types of dental composites: one containing relatively coarse filler particles and some microfillers (Estilux) and another containing only microfiller particles (Durafill), have been investigated by using a scratch testing machine. Experimental results show that the coefficients of friction in both composites are essentially constant for applied loads up to 20 N. The wear resistance of Durafill is better than Estilux. Under the same testing conditions, the size, shape and distribution of the filler particles are more important variables than applied load and sliding speed in controlling the wear mechanism. It is shown that for Estilux, plastic ploughing by the diamond indenter is the predominant mechanism. For Durafill, however, the formation and propagation of tensile cracks on the worn surface is the main wear mechanism. The effects of two different indenters, diamond and enamel, on the basic wear mechanisms are also discussed.     

SiC 和Gr 颗粒混杂增强Al 基复合材料的摩擦磨损特性的研究

比较了SiC 和Gr 颗粒混杂增强Al 基复合材料的干摩擦磨损行为, 并与单一SiC_P 和单一G_rP 增强Al 基复合材料的相应行为进行了比较。结果表明, 在低载荷(< 30 N ) 时, SiC_P 和G_rP 能协调作用, 使混杂复合材料的摩擦系数和磨损率均比单一SiC_P 和G_rP 增强复合材料低。在较高载荷(30～ 120 N ) 时, 混杂复合材料磨损以剥层磨损机制为主, 摩擦系数比单一SiC_P 增强复合材料低, 磨损率比单一G_rP 增强复合材料低得多, 比单一SiC_P 增强复合材料高。混杂复合材料对偶件的磨损比单一SiC_P 增强复合材料低得多。      

A study on sliding and erosive wear behaviour of atmospheric plasma sprayed conventional and nanostructured alumina coatings

Alumina coatings on stainless steel substrate (SS304) were deposited by using atmospheric plasma spray technique with a feed stock of manually granulated and sieved nano Al₂O₃ powder. The hardness, sliding, and erosive wear of the nanostructured alumina coatings (NC) were investigated and compared with that of conventional alumina coatings (CC). Pin-on disc type sliding wear test on the alumina coatings (NC and CC) was performed with load varying from 30 N to 80 N at a sliding speed of 0.5 m/s. Pot type slurry erosion test of the coatings was conducted for different concentrations of Al₂O₃ and a mixture of Al₂O₃ and SiO₂ slurry. The microstructural features of both NC and CC of alumina were characterized by using FE-SEM/EDS and SEM analysis to substantiate the failure of coatings due to wear. Wear and erosion resistance of nano alumina coating is better than the conventional alumina coating as observed in the present work. The bimodal structure of NC contributes for the enhanced wear resistance. The high fracture toughness of NC is due to suppression of cracks by partially melted particles in the coatings.     

Study of Abrasive Wear Volume Map for PTFE and PTFE Composites

The potential of this work is based on consideration of wear volume map for the evaluation of abrasive wear performance of polytetrafluoroethylene (PTFE) and PTFE composites. The fillers used in the composite are 25% bronze, 35% graphite and 17% glass fibre glass (GFR). The influence of filler materials, abrasion surface roughness and applied load values on abrasive wear performance of PTFE and PTFE composites were studied and evaluated. Experimental abrasive wear tests were carried out at atmospheric condition on pin-on-disc wear tribometer. Tests were performed under 4, 6, 8 and 10 N load values, travelling speed of 1 m/sec and abrasion surface roughness values of 5, 20 and 45 μm. Wear volume maps were obtained and the results showed that the lowest wear volume rate for PTFE is reached using GFR filler. Furthermore, the results also showed that the higher is the applied load and the roughness of the abrasion surface, the higher is the wear rate. Finally it is also concluded that abrasive wear process mechanism include ploughing and cutting mechanisms.