Wear study of Ni–WC composite coating modified with CeO2

In the present investigation, Ni–WC composite powder was modified with the addition of CeO₂ in order to form a new composition of Ni–WC–CeO₂. The Ni–WC and Ni–WC–CeO₂ compositions were used for coating deposition by high-velocity oxy-fuel (HVOF) spraying process so as to study the effect of CeO₂ addition on microstructure, distribution of various elements, hardness, formation of new phases, and abrasive wear behavior. Further, the effect of load, abrasive size, sliding distance, and temperature on abrasive wear behavior of these HVOF-sprayed coatings was investigated by response surface methodology. To investigate the abrasive wear behavior of HVOF-sprayed coatings four factors such as load, abrasive size (size in micrometers), sliding distance (meters), and temperature (°C) with three levels of each factor were investigated. Analysis of variance was carried out to determine the significant factors and interactions. Investigation showed that the load, abrasive size, and sliding distance were the main significant factors while load and abrasive size, load and sliding distance, abrasive size and sliding distance were the main significant interactions. Thus an abrasive wear model was developed in terms of main factors and their significant interactions. The validity of the model was evaluated by conducting experiments under different wear conditions. A comparison of modeled and experimental results showed 4–9% error. The abrasive wear resistance of coatings increases with the addition of CeO₂. This is due to increase in hardness with the addition of CeO₂ in Ni–WC coatings.     

Microstructure and performance of multi-dimensional WC-CoCr coating sprayed by HVOF

WC-based coatings deposited by high velocity oxy-fuel (HVOF) spraying have been widely used in many industrial fields, where mechanical components are subjected to severe abrasive wear. Much attention has been especially paid to nanostructured and multimodal WC-based coatings due to their excellent abrasive wear resistance. In this study, a new kind of multi-dimensional WC-10Co4Cr coating, composed of nano, submicron, micron WC particles and CoCr alloy, was developed by HVOF. The microstructure, porosity, microhardness, fracture toughness, and electrochemical properties of the coating were investigated in comparison with nanostructured WC-10Co4Cr coating deposited by HVOF. Abrasive wear resistance of both WC-10Co4Cr coatings was evaluated on wet sand rubber wheel abrasion tester. The results show that the multi-dimensional coating possesses low porosity (0.31 ± 0.09%), excellent microhardness (1126 ± 115 HV_0.3), fracture toughness (4.66 ± 0.51 MPa m^1/2), and outstanding electrochemical properties. Moreover, the multi-dimensional coating demonstrates approximately 36% wet abrasive resistance enhancement than the nanostructured coating. The superior abrasive wear resistance originates from the coating’s multi-dimensional structure and excellent mechanical and electrochemical properties.     

Performance of abrasive wear of WC-12Co coatings sprayed by HVOF

The performance of multimodal and conventional materials in the form of coatings deposited by high velocity oxy-fuel (HVOF) thermal spraying has been studied. WC-12Co coatings were deposited under same conditions using multimodal and conventional WC-12Co powder feedstocks. The phase composition of the feedstock powders and the coatings were analyzed by XRD. Abrasive wear resistances of coatings were carried out on wet sand rubber wheel abrasion tester. The characterizations of spraying feedstock powders, microstructure and surface micrographs of the prophase and anaphase attrition surfaces were performed by SEM. The results indicated the multimodal coating shows slight higher microhardness and better abrasive wear resistance than the conventional counterpart. Also, the thermally sprayed carbide-based coatings have excellent wear resistance with respect to the hard chrome coatings.     

Fine-particle slurry wear resistance of selected tungsten carbide thermal spray coatings

The surface degradation of tungsten carbide based thermal spray coatings when exposed to fine-particle slurry abrasion has been investigated. The coatings that were studied contain binder-phase constituents consisting of either nickel or cobalt. The coatings were deposited onto test cylinders using a detonation gun device. After applying approximately 0.15 mm thickness of thermal spray coating, the coatings were ground, then diamond polished to achieve surface roughnesses of 0.03 μm Ra or less. The coatings were exposed to a three-body abrasive wear test involving zirconia particles (less than 3 μm diameter) in a water-based slurry. Results show that preferential binder wear plays a significant role in the wear of these tungsten carbide coatings by fine abrasives. In the comparison presented here, the coating containing nickel-based binder with a dense packing of primary carbides was superior in terms of retaining its surface finish upon exposure to abrasion. The coating containing a cobalt binder showed severe surface degradation.     

Comparative Study of Thermally Sprayed Coatings Under Different Types of Wear Conditions for Hard Chromium Replacement

The tribological properties of part surfaces, namely their wear resistance and friction properties, are decisive in many cases for their proper function. To improve surface properties, it is possible to create hard, wear-resistant coatings by thermal spray technologies. With these versatile coating preparation technologies, part lifetime, reliability, and safety can be improved. In this study, the tribological properties of the HVOF-sprayed coatings WC–17%Co, WC–10%Co4%Cr, WC–15% NiMoCrFeCo, Cr₃C₂–25%NiCr, (Ti,Mo)(C,N)–37%NiCo, NiCrSiB, and AISI 316L and the plasma-sprayed Cr₂O₃ coating were compared with the properties of electrolytic hard chrome and surface-hardened steel. Four different wear behavior tests were performed; the abrasive wear performance of the coatings was assessed using a dry sand/rubber wheel test according to ASTM G-65 and a wet slurry abrasion test according to ASTM G-75, the sliding wear behavior was evaluated by pin-on-disk testing according to ASTM G-99, and the erosion wear resistance was measured for three impact angles. In all tests, the HVOF-sprayed hardmetal coatings exhibited superior properties and can be recommended as a replacement for traditional surface treatments. Due to its tendency to exhibit brittle cracking, the plasma-sprayed ceramic coating Cr₂O₃ can only be recommended for purely abrasive wear conditions. The tested HVOF-sprayed metallic coatings, NiCrSiB and AISI 316L, did not have sufficient wear resistance compared with that of traditional surface treatment and should not be used under more demanding conditions. Based on the obtained data, the application possibilities and limitations of the reported coatings were determined.     

Effect of heat treatment on wear behavior of HVOF thermally sprayed WC-Co coatings

A WC-17Co coating was deposited onto ST37 mild steel substrate using HVOF spray technique and then heat treated at different temperatures in a vacuum chamber. The coatings were then evaluated in the as sprayed and heat treated conditions. Inspections by SEM and phase analysis by XRD indicated that some brittle eta (η) phases were produced at high temperature heat treatments. Generation of these phases increased the coating's hardness and decreased fracture toughness of the coating. Tribological properties were studied under dry condition by using pin on disc machine and diamond metal matrix composite disc as counterface. Wear test results showed that as sprayed deposit had the best wear resistance and its wear mechanism was sharp cutting abrasion. The weight loss in heat treated samples increased by increasing heat treatment temperature and the wear mechanisms gradually changed from cutting to gouging abrasion.     

The friction properties of an ultrathin confined water film

A factorial design approach technique was adopted to understand the high stress abrasive behaviour of a diamond reinforced composite coating for various compositions at different loads and abrasive sizes. A linear regression equation was developed and used for understanding the influence of the diamond concentration, applied load, and abrasive sizes on the wear response. A negative value of the coefficient associated with diamond concentration, together with its interactions with the applied load; suggest that the wear rate decreases with increasing diamond concentration. By contrast, a positive coefficient suggests an increase in wear rate due to an increase in related factors such as the applied load and abrasive size. The coefficients associated with the interactions of the parameters are insignificant by comparison with the individual parameters, thereby demonstrating that the interaction effect of these parameters towards the wear rate is insignificant. The wear rate may be extracted in terms of the diamond concentration, the applied load and the abrasive grit size using the above linear regression equation.     

超音速火焰喷涂WC-Co涂层耐磨性研究

利用超音速火焰喷涂（HVOF）工艺制备了WC-Co涂层，测定了涂层孔隙率、显微硬度及干摩擦磨损过程中涂层材料失重，得出涂层干摩擦因数随时间的变化关系，分析了涂层摩擦磨损机制。结果表明，WC-Co涂层致密，平均孔隙率为1．29％，显微硬度达1140HV（测试载荷2．94N），干摩擦条件下材料失重低于电镀Cr镀层2个数量级；摩擦初期，干摩擦因数迅速增加，主要磨损特征是粘结相富Co区的犁沟切削，摩擦中后期，摩擦副间实际接触面积增大，摩擦因数变化较小，磨损趋于稳定。WC-Co涂层的主要磨损机制是疲劳磨损和犁沟切削。     

Micro-abrasion wear testing of triode plasma diffusion and duplex treated Ti–6Al–4V alloy

In this paper micro-abrasion wear testing is used to evaluate the wear resistance of triode plasma diffusion-treated, single-layered TiN-, CrAlN-, and WC/C-coated and duplex-diffusion and coated Ti–6Al–4V under uniform three-body rolling abrasion. Nanoindentation, Knoop microhardness, mechanical surface profilometry, optical microscopy, scanning electron microscopy and atomic force microscopy, were used to characterise the surfaces under investigation. Optimum testing conditions for rolling abrasion were established by varying the test parameters and resultant severity of contact. Very low normal loads and high volume fractions of particles in the abrasive slurry are necessary to obtain predictable and reproducible results. Relatively coarse SiC abrasive particles, having a mean diameter of around 3 μm, appear more suitable for micro-abrasion testing of the samples investigated, compared to finer Al₂O₃ particles. Problems associated with the measurement of the scar volume and subsequent calculation of the wear rate for hard coatings deposited on relatively soft metals like titanium are identified, and suitable testing and measurement techniques are suggested. Three-dimensional wear scar maps generated by mechanical stylus profilometry were used to measure the wear volumes. Under the test conditions used, wear coefficients can be determined from perforating and non-perforating tests, although perforating tests provide more consistent results. Triode plasma diffusion treatments, plasma-assisted (PA) PVD TiN and PAPVD CrAlN can reduce the specific wear rate of Ti–6Al–4V, while PACVD-based WC/C coatings do not provide suitable protection against abrasive wear. The combination of triode plasma oxynitriding diffusion treatments and PVD coatings to create duplex treatments can also lead to further reductions in the coating wear coefficient when compared to non-duplex coatings deposited on non-pretreated substrates.     

Abrasive Wear Analysis of Plasma-Sprayed LaCeYSZ Nanocomposite Coatings Using Experimental Design and ANN

The abrasive wear characteristics of plasma-sprayed nanostructured yttria-stabilized zirconia (YSZ) coatings on Inconel 718 substrates was evaluated using AFS 50/70-grade silica sand as abrasives. This article depicts the dependence of abrasive wear characteristics of plasma-sprayed nanocomposite LaCeYSZ coatings on abrading distance, keeping the applied load constant. The influence of four operating parameters—that is, load, wheel speed, time, and temperature with four different levels each—on the performance output (i.e., abrasion wear rate) is studied using Taguchi's L₁₆ orthogonal array design and analysis of variance (ANOVA). Out of the four parameters, load has been found to be most significant factor followed, by speed of the abrasive wheel and temperature influencing abrasion. The morphology of the worn-out surface also showed microcutting and small crater formation in the binder matrix caused by the repetitive impacts of abrasive particles. It was observed that coating with nano-LaCeYSZ grains exhibited higher wear resistance compared to conventional YSZ coating and the reason may be attributed to embedded crack-arresting nanozones, which toughen the coating. An artificial neural network (ANN) approach is then implemented taking into account training and test procedures to predict the triboperformance under different operating conditions. This technique helps in saving time and resources for a large number of experimental trials and successfully predicts the wear rate of the coatings both within and beyond the experimental domain.     

Improvements in the thread cutting torque for a 6082-T6 aluminum-based alloy with tapping tools utilizing diamond coating

The use of thin film diamond as a hard tool coating offers a significant wear protection in numerous machining operations and increases considerably tool's lifetime. The extreme hardness of the diamond is especially needed in machining highly abrasive materials such as aluminum-silicon alloys. Tapping is widely used for thread fabrication and it is often a time consuming process causing a delay on an automated production line. This study investigated diamond coatings in thread cutting and the aim was to gain knowledge about the performance of diamond-coated taps. PVD diamond coatings were deposited using ultra short pulsed laser deposition (USPLD) techniques. Another type of nanodiamond coating was a chrome-nanodiamond (CND) coating deposited by a two-phase electrochemical process to produce a metal matrix with embedded detonation nanodiamond (DND) particles. The main points were the analysis of tool torques of the thread machining data, sticking of aluminum alloy and wear behavior and mechanism of tested tapping tools. The tested tools were analyzed by Scanning Electron Microscopy (SEM) regarding tool wear and sticking of aluminum on tool surface caused by mechanical interaction. Coating approaches turned out to provide 13–30% improvements in cutting and 37–51% improvements in reversing for overall mean torques compared to uncoated reference tools.     

Abrasive wear behavior of sprayed hydroxyapitite coatings by gas tunnel type plasma spraying

Hydroxyapatite (HA) coatings were sprayed using gas tunnel type plasma spraying at different arc currents. Abrasive wear test was carried out for the coatings sprayed at different arc currents under unlubricated conditions in air atmosphere. The abrasive wear rate was measured at different coatings thickness to study the effect of coating thickness on the anti-abrasion resistance of HA coatings. The results showed that the abrasive wear resistance of HA coatings increases as the operating arc current of the plasma torch increases. On the other hand, the abrasive wear rate reaches a minimum value near the substrate with coating thickness less than 50 μm. The results showed that the coating hardness increases in the region near the substrate and increases as the arc current increases. The experimental results indicated that there is a relation between the abrasion resistance and hardness properties of HA coatings.     

Influence of CrC addition in Ni-Cr-Si-B flame sprayed coatings on microstructure, microhardness and wear behaviour

In the present paper the influence of the addition of chromium carbide (CrC) particles on the microstructure, microhardness and abrasive wear behaviour of flame sprayed Ni-Cr-Si-B coatings deposited on low carbon steel substrate has been reported. Wear behaviour of the coatings was evaluated with a pin-on-block wear system against SiC abrasive medium (120 & 600 grades) over a range of normal load (5–20 N). It was observed that the wear behaviour is governed by the material related parameters (microstructure, microhardness of coating) and test parameters (abrasive grit size and normal load). The addition of CrC reduces the wear rate three to eightfold. Wear resistance was greater against coarse abrasives at high loads than against fine abrasives. Heat treatment of both unmodified (1004) and modified powder (1004-10%CrC, 1004-20%CrC) coatings deteriorated the abrasive wear resistance. SEM study of wear surfaces showed that wear of the coatings largely takes place by groove formation, plowing and scoring. Electron probe micro analysis (EPMA) of the coating was carried out for composition and phase analysis.     

Structure and wear resistance of electron-beam nitrous coatings

The paper deals with the study of the tribological properties of nitrogen-containing austenite coatings deposited by electron-beam facing during abrasive wear and the sliding friction of a VK6 hard alloy indentor. The abrasive wear resistance of the nitrous coatings deposited by the electron-beam facing of steel 60Kh24AG16 powder in quartz sand is lower than that of the steel 65G coatings after hardening; it increases with increasing mass share of the filler. At contents of nitrided ferrovanadium of 10?C30 wt % the abrasive wear rate increases by 30?C50%, respectively. It is found that under a certain load applied to the VK6 ball indentor the friction coefficient and the shear resistance of the surface layer diminish. It is shown that under heavy specific loads applied to the ball indentor the nitrous coating faced from steel 60Kh24AG16 powder and composite nitrous coatings have wear resistance exceeding that of steels 110G13 and Kh18N10 by more than two and seven times, respectively. Based on the results of structural studies an explanation of the observed behavior of the nitrous coatings is proposed.     

超音速火焰喷涂碳化钨钴合金涂层对橡胶密封件的磨损研究

通过磨合试验,比较了超音速火焰(HVOF)喷涂碳化钨钴合金涂层与传统的含氰镀铬镀层与橡胶密封件对磨时的磨损情况.结果表明:HVOF喷涂碳化钨钴合金涂层具有良好的耐磨性和致密性,始终保持较良好的表面状况,对非金属密封件具有良好的适应性.     

纳米和微米La2O3颗粒增强镍基复合镀层的摩擦磨损性能

用复合电沉积工艺制备了纳米和微米La2O3颗粒增强镍基复合镀层，在销盘式滑动磨损试验机上考察了复合镀层在干摩擦条件下的摩擦磨损性能，用扫描电子显微镜分析了其磨损机理。结果表明：在干摩擦条件下，纳米La2O3颗粒增强复合镀层的摩擦磨损性能明显优于微米La2O3颗粒增强复合镀层；纳米La2O3增强镍基复合镀层的磨损主要表现为轻微磨粒磨损特征，而微米La2O3增强镍基复合镀层的磨损机制为剥层磨损和磨粒磨损。     

Effect of Operating Temperature on Tribological Behavior of As-Plated Ni-B Coating Deposited by Electroless Method

The present work investigates the tribological behavior of electroless Ni-B coating in its as-plated condition at elevated operating temperatures. Ni-B coating is deposited using an electroless method on AISI 1040 steel specimens. Coating characterization is done using scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction techniques. Vicker's microhardness and surface roughness are measured. Friction and wear tests are carried out on a pin-on-disc tribological test setup at room and elevated temperatures of 100, 300, and 500°C. The tribological behavior deteriorates at 100°C compared to room temperature. Electroless Ni-B coating shows excellent wear resistance at 300°C, which again degrades at 500°C due to severe oxidation and softening of the deposits. The worn surface of the coatings is analyzed using optical microscopy and scanning electron microscopy. Within the temperature range considered, the wear mechanism changes from adhesion to a combination of adhesion and abrasion as the temperature rises from ambient condition to 100°C, following which the wear mechanism is predominantly abrasive. The formation of a tribochemical oxide film also affects the tribological behavior of the coatings at high temperature.     

Properties and applications of composite diamond coatings

A wear resistant coating consisting of micron size particles of shock-synthesized diamond uniformly dispersed in a plated metal matrix has been developed. The composite coating process is described and the controlling parameters are discussed. Laboratory and field tests have demonstrated that the coatings have excellent wear resistance and are suitable for many industrial applications as a replacement for conventional wear resistant materials particularly for combating low to medium pressure abrasive and adhesive wear.     

Tribological evaluation of oil pump relief valve coatings compatible with an aluminum oil pump body

Wear can cause automotive relief valves to jam. In order to evaluate and screen candidate coatings for oil pump relief valves for reduction of aluminum pump cylinder bore wear and wear-related sticking, a laboratory reciprocating wear test using production parts has been developed. The coatings on valves include impinged and physical vapor deposited (PVD)-coated molybdenum disulfides, electroplated nickel–phosphorous with polytetrafluoroethylene (Ni–PTFE), electroplated bronze, and electroplated nickel–phosphorous–boron nitride (Ni–P–BN).

The test results showed that the electroplated bronze coating demonstrated the best wear resistance against 380 aluminum pump bores while Ni–PTFE ranked second, PVD-coated MoS₂ third, and Ni–P–BN ranked last. It was observed that the electroplated bronze coating showed only mild oxidative or abrasive wear after 20 h wear test. The Ni–P–BN coating gave the worst wear resistance due to severe abrasive wear, surface scoring, and coating abrasion during the wear test. The major wear mechanisms for valve bore/relief valve can be classified at different levels from mild wear (oxidative wear or surface delamination) to abrasive wear (scoring, scuffing, and ploughing). This paper also reviewed the rooted wear mechanisms of production pump relief valves against aluminum bores based on metallographic observations of worn surfaces after field tests. This tribological investigation of valve coatings has provided insights into the fundamental wear mechanisms which depend on the compatibility of two sliding materials, protective coating composition, hard particle content, and surface interaction. The information will be useful in preventing oil pump relief valves from jamming.     

Abrasive wear behaviour of B4C particle reinforced Al2024 MMCs

In this study, the effects of volume fraction and particle size of boron carbide on the abrasive wear properties of B₄C particle reinforced aluminium alloy composites have been studied. For this purpose, a block-on-disc abrasion test apparatus was utilized where the samples slid against the abrasive suspension mixture at room conditions. The volume loss, specific wear rate and roughness of the samples have been evaluated. The effects of sliding time, particle content and particle size of B₄C particles on the abrasive wear properties of the composites have been investigated. The dominant wear mechanisms were identified using scanning electron microscopy. The results showed that the specific wear rate of composites decreased with increasing particle volume fraction. Furthermore, the specific wear rate decreased with increasing the size of particle for the composites containing the same amount of B₄C. Hence, it is deduced that aluminium alloy composites reinforced with larger B₄C particles are more effective against the abrasive suspension mixture than those reinforced with smaller B₄C particles.