An investigation of sliding wear behaviour of WC-Co coating

Dry sliding wear tests on specimens of mild steel (MS) and WC coated mild steel (MSC) specimens were performed against a hardened EN32 steel (EN32) and a WC coated EN32 steel (EN32C) discs. Four different combinations of specimen and counter surface were tested under dry sliding conditions. Results suggest that wear mechanisms differ depending on the combination of materials under sliding contact. Expectedly the MS specimen suffered high wear loss, but the MSC specimen showed interesting results. When slid against EN32, MSC specimens showed negative wear results whereas positive wear results occurred against EN32C. Steady wear rate was attained after a critical sliding distance.     

载荷与滑动速度对铜合金磨损的影响

对热型连续定向凝固工艺生产的Cu-0．1Ag合金进行干滑动摩擦磨损实验并将该材料与耐磨性较好的单晶铜进行对比实验。分析讨论载荷、滑动速度等因素对该材料磨损率及磨损表面的影响。实验结果表明：滑动距离、滑动速度对铜合金的磨损有较大影响,而且铜合金的抗磨性能明显优于耐磨性较好的单晶铜。     

Correlation between adhesion and wear behaviour of commercial carbon based coating

Adhesion and wear behaviour of hard coatings are two important properties that concern researchers. We need to use different tests to obtain these two values and the correlation between adhesion and wear is not always obvious. The purpose of this paper is to find the relationship between the wear rate and the critical load for commercial hard coatings.Commercial carbon based coatings were deposited on M42 high speed steel by magnetron sputtering. Different lengths of pre-sputtering time were used to change the properties of the coatings. Single pass scratch tests and multi-pass bidirectional wear tests were used to obtain the critical load and wear rate values, respectively. Results showed that there was a correlation between wear and adhesion. It was found that adhesion increases, and wear rate decreases when the pre-sputtering time increases. It was also observed that adhesion strength varies with pre-sputtering time in a step function manner. To a large extent, the adhesion behaviour is related to the wear behaviour as far as the commercial carbon based coating is concerned. However, as different coatings have different microstructure and properties, further work should be done to decide whether a similar relationship can be applied in other cases.     

Friction and wear behaviour of pyramidal nanoscaled surface features

This study reports on the friction and wear behaviour of nanoscaled pyramidal surface features of chromium nitride thin films in relation to the dimensions of those features. The pyramidal features were created, and their size controlled, by PVD based in-process structuring. Microtribological tests analysed both the evolution of wear-induced surface alterations and the correlated evolution in the coefficient of friction as functions of normal load and duration of the loading. Results indicate that the severity of wear diminishes tremendously with increasing feature size when tested at the same normal load. So, wear-induced damage similar to that seen on surfaces with small-sized features was observed for the largest surface features tested only after a 100 times longer test duration. The less severe wear of the largest pyramids leads also to friction up to 75% lower compared to surfaces with the smallest features.     

Sliding wear behaviour of some Fe-, Co- and Ni-based metallic glasses during rubbing against bearing steel

The sliding wear behaviour of several compositions of Fe-, Co- and Ni-based metallic glasses have been studied while rubbing against AISI 52100 bearing steel under reciprocating-sliding conditions. The wear resistances of Fe-based metallic glasses and Ni-based metallic glass (MBF 50) have been found to be superior to that of the mating AISI 52100 bearing steel. The examination of worn surfaces indicates that the superior wear resistance of metallic glasses is not merely owing to their high hardness but it is determined by phenomena of material transfer vis-à-vis the mating material and the formation of protective oxide layers on the metallic-glass surface during sliding. This revised version was published online in August 2006 with corrections to the Cover Date.     

Friction and wear behaviors of nanocrystalline surface layer of pure copper

Surface mechanical attrition treatment (SMAT) was employed to fabricate a nanocrystalline surface layer on a pure copper plate. The grain size is about 10 nm in the top layer and increases with an increasing depth from the treated surface. The tribological behavior of the nanocrystalline surface layer was investigated under dry conditions. Experimental results show that the load-bearing ability is markedly enhanced with the nanocrystalline surface layer relative to the coarse-grained form. The friction coefficient of the nanocrystalline layer is lower than that of the coarse-grained copper when the applied load is below 20 N. With increase of the load, the difference in wear resistance between the SMAT and the conventional Cu decreases. When the load exceeds 40 N, for the SMAT Cu, there occurs a transition of wear regime from local damage to delamination of a mechanical mixed layer. There is an abrupt increase of the wear volume, which corresponds to the wearing away of the nanocrystalline layer. The enhanced wear properties of the nanocrystalline surface layer are correlated with the stability of the mechanical mixed layer and the high hardness of the nanocrystalline structure.     

Microstructure and oxidation behaviour investigation of rhodium modified aluminide coating deposited on CMSX 4 superalloy

The CMSX 4 superalloy was coated with rhodium 0.5‐μm thick layer and next aluminized by the CVD method. The coating consisted of two layers: the additive and the interdiffusion one. The outward diffusion of nickel from the substrate turned out to be a coating growth dominating factor. The additive layer consists of the β‐NiAl phase, whereas the interdiffusion layer consists of the β‐NiAl phase with precipitates of σ and μ phases. Rhodium has dissolved in the coating up to the same level in the matrix and in the precipitates. The oxidation test proved that the rhodium modified aluminide coating showed about twice better oxidation resistance than the nonmodified one.     

Microstructure and wear resistance of nickel–carbon nanotube composite coating from brush plating technique

This paper investigates the microstructure and wear resistance of nickel–carbon nanotube (CNT) composite coating deposited by brush plating technique. The Ni/CNT coating deposited with a pulse current source has less porosity, higher hardness and higher wear resistance than that with a DC source. CNTs greatly improve the coating performance. The wear mechanism is mainly the smearing of the Ni/CNTs coatings, instead of the fracture for the Ni coatings.     

Microstructure and sliding wear behaviour of Tribaloy T-800 coatings deposited by laser cladding

This work has focused on the obtainment of Tribaloy T-800 coatings by laser cladding on plane 18/8 stainless steel specimens (AISI 304). The appropriate selection of cladding parameters allowed defect-free coatings to be obtained with minimal dilution. In order to evaluate their microstructure, cross-sections of the coatings were examined by optical microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The elemental composition of the coatings was determined using an optical emission spectrometer with an excitation source (GDOES) and phase analysis was performed by X-ray diffraction (XRD). Several zones can be distinguished in the microstructure of the clad layer: a planar crystallization region at the interface with the substrate, followed by cellular and dendrite crystallization from the interface to the surface of the laser track and an overlap zone between tracks which is characterised by the coarsening of the structure and the formation of a lamellar eutectic phase. The mechanical properties were evaluated by hardness measurements and sliding wear tests (ball-on-disk and block-on-ring configurations) at room temperature and without lubrication. It was observed the great hardness (close to 850 HV_0.3) achieved for the Tribaloy 800 laser coatings, which presented a wear coefficient (k) between one and two orders of magnitude lower than the substrate. The analysis of the clad worn surfaces showed that there was a transition from an adhesive-oxidational mechanism to a more severe plastic deformation and crack formation wear process with increasing the applied load.     

耐磨涂料复合套代替高压泵上铜制内外导套

耐磨复合套以其良好的性能成功地替代铜导套，既降低了成本，又解决了生产急需，代表了未来的发展方向。     

Improving wear resistance of surface by depositing vibrational mechanochemical MoS2 coating

A solid-lubricating MoS₂-based coating formed on the surface of a part under conditions of vibrational treatment of freely moving indenters is studied. Peculiarities of the processes that occur at the metal-coating interface are shown, as well as their effect on the quality of the coating and on an increase in the wear resistance of the surface is considered.     

Sliding wear behaviour of an electrochemically modified austenitic high-nitrogen steel surface

Wear debris from artificial metallic implant joints is known to provoke detrimental foreign-body reactions in the surrounding human tissue. Although commonly used biotolerant metals generate only a little amount of particles, wear is still a major cause for concern. It is the aim of this work to evaluate the sliding wear resistance of a topologically modified high-nitrogen austenitic stainless steel. A disc-on-pin test in self-mating contact is performed in distilled water. Submicron particles are trapped by the structured topography and form together with the plastically deformed metal a hybrid surface which has the potential to significantly improve the tribological behaviour of the tested high-nitrogen steel.     

Friction and wear behavior of electroless Ni-based CNT composite coatings

Ni-based carbon nanotube (CNT) composite coatings with different volume fraction (from 5 to 12 vol.%) of CNTs were deposited on medium carbon steel substrates by electroless plating. The friction and wear behavior of the composite coatings were investigated using a pin-on-disk wear tester under unlubricated condition. Friction and wear tests were conducted at a sliding speed of 0.0623 m s⁻¹ and at an applied load of 20 N. The experimental results indicated that the friction coefficient of the composite coatings decreased with increasing the volume fraction of CNTs due to self-lubrication and unique topological structure of CNTs. Within the range of volume fraction of CNTs from 0 to 11.2%, the wear rate of the composite coatings showed a steadily decreasing trend with increasing volume fraction of CNTs. Because of the conglomeration of CNTs in the matrix, however, the wear rate of the composite coatings increased with further increasing the volume fraction of CNTs.     

Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior

An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior.

The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity and at room temperature. Clusters or crystallites with sizes up to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures up to 750°C. Contaminants can come from the bulk of the alloys to the surface on heating and impart to the surface oxides at 350°C and boron nitride above 500°C, The oxides increase friction while the boron nitride reduces friction drastically in vacuum.     

Multi-phase materials and their surface contact behaviour with reference to friction and wear

The recent advances in the development of composite surface coatings and the increasing tribological application of multi-phase materials in engineering require a more rigorous treatment of the problem of the contact of surfaces of such materials. This paper considers the surface contact behaviour of materials having contrasting physical properties and the results presented quantitatively identify the boundaries of three contact regimes, purely elastic, elastic/plastic and predominantly plastic. The treatment also offers a method for determining the real areas of contact and corresponding supported loads associated with the modes of deformation of each phase. This is particularly important for predicting the friction and wear characteristics of multi-phase materials.     

Experimental examination of the wear behaviour of the VAlN tool coating by strip drawing process

Resistance to wear, and therefore the lifetime of forming tools, can be increased by surface functionalisation using novel, multifunctional coatings. Thereby, the tribological requirements on the coating are an essential factor. Within the scope of the research work presented here, tribological examinations were carried out on a metastable vanadium aluminium nitride (VAlN) tool coating when drawing the high-strength sheet metal material DP 800. It was shown that the wear of the VAlN tool coating can already be determined at stable frictional behaviour (μ?<?0.085). The wear analysis was carried out considering the topography and change in hardness of the tool surface during the drawing path of 110,000?mm under a contact stress of 150?MPa.     

Fretting wear behavior of nanocrystalline surface layer of copper under dry condition

Unlubricated fretting tests were performed with a nanocrystalline surface layer of a 99.99 wt.% copper fabricated by means of surface mechanical attrition treatment (SMAT), in comparison with a coarse-grained (CG) copper. The measured friction and wear data show that the fretting wear resistance is markedly enhanced with the nanocrystalline surface layer relative to the CG counterpart. The friction coefficient and wear volume of the SMAT Cu are lower than that of the CG Cu. For both samples, the friction coefficients and wear volumes increase with an increasing applied load and fretting frequency. A rapid increase of the friction coefficient and wear volume under an applied load above a critical value (30 N for the SMAT Cu and 20 N for the CG Cu) is noticed, corresponding to the formation of a continuous oxide layer between two contact surfaces. Also two sharp increases of the friction coefficient and wear volume at fretting frequencies of 50 Hz and 175 Hz were observed for the SMAT and the CG Cu. The former is correlated with the formation of a continuous oxide layer, while the latter corresponds to wearing away of the oxide layer.     

The wear behaviour of copper alloy-steel and polyamide-steel sliding pairs for heavily loaded cardan joints

The wear behaviour of various copper alloy-steel and polyamide-steel sliding pairs for use in heavily loaded cardan joints was studied on two sliding surface test rigs that were constructed on the basis of practical considerations; the influence of numerous parameters such as surface pressure, lubrication and load oscillation was considered. For comparison with the metallic sliding pairs unfilled and filled or reinforced polyamides were used. Tests were carried out at high surface pressures under conditions of mixed friction using high additive lubricants (oils and greases) with and without contamination.     

Effects of substrate surface finish and substrate material on durability of thermally sprayed WC cermet coating in rolling with sliding contact

In this study, using a two-roller testing machine, the authors examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating in lubricated rolling with sliding contact conditions. The coating was formed onto the axially ground, blasted and circumferentially ground roller specimens made of a thermally refined carbon steel or an induction hardened carbon steel by means of the high energy type flame spraying (Hi-HVOF) method. The WC cermet coated roller finished to a mirror-like condition was mated with the carburized steel roller without coating having a surface roughness of Ry=3.05.0 μm. In the experiments, a maximum Hertzian stress of P_H=0.6 or 0.8 GPa was applied for the thermally refined carbon steel roller and P_H=1.4 GPa was applied for the induction hardened carbon steel roller in line contact condition. As a result, it was found that in the case of induction hardened steel substrate, the coated roller generally exhibits a long life without any serious damage and the surface durability is hardly affected by the substrate surface finish, while in the case of thermally refined steel substrate, the durability of coated roller is lowered and the life to flaking is very short particularly when the substrate surface is circumferentially ground and the mating surface is rough. The surface durability of coated roller was also compared with the durability of steel roller without coating. Finally, in order to discuss the durability of coated roller, the elastic-plastic behavior of the subsurface layer under repeated rolling with sliding contact was analyzed using a finite element method (FEM).