High-temperature oxidation and wear resistance of WC-Co based coatings with WB addition

A new type of WC-based coating with high oxidation- and wear-resistance at elevated temperature was fabricated by thermal spraying the pre-treated WC-Co powder doped with WB. Addition of WB led to in situ formation of WCoB, which acted as a substitute for Co in the powders and the resultant coatings. It was shown by thermal analysis that WCoB has obviously higher oxidation resistance at high temperatures than that of WC and Co. Thus, the oxidation of the WC-WCoB coating was mainly initiated from WC, rather than from Co in the conventional WC-Co coatings. Most of WCoB was preserved in the coating after high-temperature wear tests. Particularly, with an addition of 40 wt.% WB, the wear rates of the WC-Co coating were dramatically decreased by 90% and 77% at the room and elevated temperatures, respectively.     

Effects of hBN and Y2O3 Addition on Mechanical and Tribological Behavior of SiC Ceramic Matrix Composites Prepared by Spark Plasma Sintering

Silicon - The objective of the present work is to study the mechanical and tribological properties of SiC-hBN such as hardness, density, fracture toughness, friction and wear behavior with and...     

载重汽车销轴表面改性及其摩擦磨损性能的研究

在载重汽车销轴基材40Cr钢表面制备Ni-WC纳米复合镀层,实现表面改性,以期提高销轴表面的摩擦磨损性能。观察并分析了纳米复合镀层的表面形貌和微观结构,检测了纳米复合镀层的结合强度、硬度及摩擦磨损性能。结果表明:纳米复合镀层表面较平整、结构致密,与基材结合牢固,其硬度平均值为6 081MPa,约为基材的1.3倍;其平均摩擦因数约为0.35,磨损失重约为1.83mg,均比基材的低。低孔隙率、致密结构和高硬度,使纳米复合镀层具有良好的摩擦磨损性能。     

Mechanical and tribological properties of TiB2-SiC and TiB2-SiC-GNPs ceramic composites

TiB₂-SiC and TiB₂-SiC-graphene nanoplatelets (GNPs) composites were prepared using field-assisted sintering technology at 2100 °C in argon atmosphere, and the influence of the SiC and different GNPs addition on microstructure development, mechanical and tribological properties has been investigated. Instrumented hardness, bending strength, chevron-notched fracture toughness and ball-on-flat tribological tests were used for the testing and characterization of the composites. The addition of SiC significantly improved the bending strength and elastic modulus with values of 601 MPa and 474 GPa, respectively, but decreased the fracture toughness with a value of 4.8 MPa.m^1/2. The addition of GNPs has a positive effect on fracture toughness and flexural strength but a negative one on the hardness. The increasing amount of both GNPs has a positive influence on wear characteristics of the composites thanks to the described wear mechanisms.     

Investigation of SiC-AlN: Part II, Mechanical Properties

SiC/AIN composites with controlled interfacial solid solution were employed in the present work for investigating the effects of interfacial bonding and A1N polytypes on the mechanical properties. Platelike A1N polytypes and interfacial bonding were found to have substantial effects on the flexural strength, hardness, and fracture toughness.     

Synthesis and microstructure evolution of WCoB based cermets during spark plasma sintering

WCoB based cermets were prepared by spark plasma sintering at sintering temperature among 600°C-1200 °C. The phase evolution was investigated by detecting density behavior, phase composition, microstructure and mechanical properties during sintering process. The sintering process can be divided into three stages: powder densification, solid phase reaction and liquid phase sintering. WCoB hard phase forms at 1000 °C during solid phase sintering, showing better mechanical properties than Co₂B, especially on Vicker's hardness. WCoB hard phase forms on the basis of Co₂B binary boride and its content increases in liquid phase sintering stage with high density. The Vicker's hardness and transverse rupture strength (TRS) reach the maximum value of 1262 Hv and 1212 MPa at 1200 °C and 1170 °C, respectively. The fracture toughness reaches the maximum value of 21.8 MPa m^1/2 at 1050 °C, and the inter-granular fracture is the main fracture mechanism.     

Tribological behavior of nanostructured high velocity oxy-fuel (HVOF) thermal sprayed WC-17NiCr coatings

In this research, the nanostructured WC-17NiCr cermet coatings were developed using the high velocity oxy-fuel (HVOF) thermal spraying processes on ACI CD4MCu cast duplex stainless steel substrates, widely used in pump industry for abrasive wear protection of surfaces. The coatings, sprayed by both robotic and manual methods, had two different fuel (methane) to oxygen ratios (FTOR), namely 0.68 and 0.62. Using different analytical and microstructural techniques, the microstructural characteristics of the powder particles and mechanical, microstructural, and tribological properties of the coatings were determined. Different morphologies were assigned to sprayable particles, namely spherical, apple, donut, irregular, and mixed. It was revealed that the rate of WC decarburization had increased with increasing the FTOR. In contrast, the scanning electron microscopy and image analyses showed that the lowest porosity percentage was obtained for the robotically-sprayed coating with 0.68 FTOR. The Vickers microhardness increased along with fracture toughness, which can be attributed to the effect of the ‘duplex structure’ associated with the particle outer coating of Co and is a novelty in the research. The pin-on-disk reciprocal sliding wear tests at various loadings had shown different wear rates in the coatings. It was inferred that the wear performance was improved with the microstructural homogeneity, hardness, and the fracture toughness in the coatings. In all coatings, lower coefficient of friction (COF) was observed at higher loads. Finally, the wear mechanisms involved in the wear processes were identified as deformation and removal of the binder, fracture and pullout of the carbide particles, and delamination and spallation of the splats.     

Tribological behavior of graphene reinforced chemically bonded ceramic coatings

To investigate tribological behavior of graphene reinforced chemically bonded ceramic coatings at different temperatures, tribological tests at room temperature, 200 °C and 500 °C were carried out. Results show that the fracture toughness and the hardness of the coating are improved with the introduction of graphene. Besides, the friction coefficient of the coating decreases with the addition of graphene at the room temperature and 200 °C. The coating without graphene achieves the similar friction coefficient at all temperatures. However, the coating with graphene achieves the lowest friction coefficient at 200 °C, and achieves the highest at 500 °C. In addition, the wear rate of the coating decreases with the increase of graphene. Besides, the wear rate at 200 °C is almost similar with that at room temperature. In contrast, the wear rate at 500 °C is much larger than those at room temperature and 200 °C. The mechanisms for graphene to decrease the friction coefficient and improve the wear resistance of chemically bonded ceramic coatings at evaluated temperatures are clarified.     

Effect of hBN addition on the fabrication,mechanical and tribological properties of Sialon materials

This work aims to investigate the effect of hBN on the friction and wear resistance of Sialon composite. Sialon and its composite with 10 wt% hBN were fabricated by SPS sintering. The effect of hBN additive on the phase composition, microstructure, densification behavior, mechanical and dry sliding tribological properties of Sialon material was studied. Being sintered at 1600 °C for 10 min, compared to monolithic Sialon, Sialon-hBN composite has more refined β-Sialon grains with smaller aspect ratios and slightly declined relative density. The hardness of the Sialon-hBN composite was reduced due to the weak bonding between Sialon and hBN grains. Nevertheless, its fracture toughness increased ascribing to the toughening mechanisms, including crack deflection and crack bridging. hBN had an essential impact on the tribological performances of the composite due to its lower friction coefficient and good lubrication action. Under the same densification level (i.e., with a relative density of around 97.5%), the friction and wear resistance of Sialon-hBN composite were much better than monolithic Sialon. The main wear mechanisms were tribolayer formation, oxidized wear, and abrasive wear.     

Tribomechanical and microstructural properties of cathodic arc-deposited ternary nitride coatings

Sintered carbides are promising materials for surfaces that are exposed to extreme wear. Owing to their high service load, ceramic-based thin films are coated on carbides using different techniques. In this study, non-toxic and cobalt-free powder metallurgy-sintered carbide samples were coated with TiN, TiAlN, CrAlN, and TiSiN ceramic-based thin film coatings by cathodic arc physical vapor deposition. The microstructure (phase formation, coating thickness, surface roughness, and topography), mechanical properties (hardness, modulus of elasticity, and plasticity indices), and tribological properties (nanoscratch and wear behavior) of the thin film coatings were investigated. No cracks or defects were detected in these layers. The ceramic-based ternary nitride thin film coatings exhibited better mechanical performance than the TiN coating. The TiN thin film coating had the highest average surface roughness, which deteriorated its tribological performance. The ternary nitride thin film coatings exhibited high toughness, while the TiN thin film coating exhibited brittle behavior under applied loads when subjected to nanoscratch tests. The wear resistance of the ternary nitride coatings increased by nearly 9–17 times as compared to that of the TiN coating and substrate. Among all the samples investigated, the substrate showed the highest coefficient of friction (COF), while the TiSiN coating exhibited the lowest COF. The TiSiN thin film coating showed improved mechanical and tribological properties as compared to other binary and ternary nitride thin film coatings.     

Tribological and mechanical properties of amorphous and semi-crystalline PEEK/SiO2 nanocomposite coatings deposited on the plain carbon steel by electrostatic powder spray technique

One of the main practical limitations of polymer coatings is dependency of their mechanical and physical properties on the crystallinity of polymer matrix. In this research, the effect of the presence of silica nanoparticles on microhardness, interfacial adhesion strength and tribological behavior of amorphous and semi-crystalline polyether–ether–ketone (PEEK) coatings were examined. The coatings were prepared by a combination of ball milling and electrostatic powder spraying methods. The results showed that the semi-crystalline pure PEEK coating had higher hardness, lower adhesion strength, coefficient of friction (COF) and wear rate than the amorphous one. However, the incorporating of PEEK with surface modified silica nanoparticles led to an increase in the coatings microhardness and interfacial adherence. The wear rates of both the semi-crystalline and amorphous nanocomposite coatings were lower than the pure ones but their COF were slightly higher. It was also found that, compared with the pure coatings, the sensitivity of the mechanical and tribological properties of the nanocomposite coatings to the crystalline structure of the PEEK matrix are less pronounced.     

Effect of Grain Boundary Impurities on the Mechanical and Tribological Properties of Zirconia Surfaces

It is desirable to establish a relationship between the processing of ceramics, their mechanical properties that can be rapidly measured, for instance by indentation (hardness and toughness), their abrasion and scratch resistance, and their tribological performance. This paper examines such relationships for transformation-toughened zirconia. Experiments were performed on two zirconium oxides of similar doping with yttria (3%), one of high purity and one containing grain boundary impurities. The results are compared with those of previous work, in which the composition of the zirconium oxide was changed, but the processing and grain boundary purity were constant. It is found that the relationship between mechanical properties and triboiogical performance is complex but understandable in terms of the scale of the material responses (plastic deformation and fracture) with respect to its microstructure. The yttria content of the zirconia has a large influence on the wear resistance of the material (which increases with the fourth power of toughness). At constant yttria content, impurities produce relatively small changes in mechanical properties and wear behavior. The impurities weaken the grain boundaries with the following consequences: zirconia with pure grain boundaries behaves much like a brittle continuum, the material is hard, and macroscopic cracks develop at the corners of indentations and underneath wear tracks. Grain boundary impurities lower the hardness and increase the apparent (macroscopic) toughness by crack diffusion. At low bearing load, wear occurs by microchipping, and grain boundary phases have no effect. In water, wear is increased by intergranular fracture and the presence of grain boundary phases increases the wear rate. At high loads (44.5N), macroscopic cracks underneath the wear track develop early in the pure material; these cracks are retarded by intergranular fissuration in the material with grin boundary impurities.     

The influence of multilayer structure on mechanical behavior of TiN/TiAlSiN multilayer coating

Nitride coatings have been generally applied on light alloys like titanium and aluminium to promote their multiple performances, including hardness, thermal stability and wear resistance. In this work, TiAlSiN/TiN multilayered (ML) coating and TiAlSiN single-layer (SL) coating were deposited on TC18 (Ti5Al5Mo5V1CrFe) alloy by Multi-arc ion plating technique. The microstructure and chemical composition of the coatings were evaluated by SEM, XRD and XPS. Additionally, hardness, adhesion and wear resistance were measured through nanoindentation, scratch spectrometer and ball-on-disk tribometer. The results present that both ML and SL coating contain three main phases of TiN, Al₂O₃ and Si₃N₄. Nevertheless, the adhesion of ML coating is 62.4 N, compared to that of the SL coating is 51.8 N. The parameter H³/E² as an indication of plastic deformation to evaluate wear resistance shows that the ML coating has high hardness and high toughness concurrently. The tribological study indicated that the wear rate of the ML coated specimen was 1/7 of the SL coated counterpart.     

Improving the mechanical and tribological properties of amorphous carbon-based films by an a-C/Zr/ZrN multilayered interlayer

Amorphous carbon (a-C) films have been widely investigated to reduce the wear of medical implants due to their excellent tribological performance; however, the high internal stress of a-C films generated during the fabrication process remains an important scientific problem. Herein, we report novel a-C-based films with an a-C/Zr/ZrN multilayered interlayer. Our results reveal that, with increasing thickness of the multilayered interlayer, the hardness of the films decreased while their toughness and adhesion were improved. The Zr layers could act as a ductile phase, providing a toughening effect. A film with a 2:1 thickness ratio of multilayered interlayer to a-C top layer exhibited favorable tribological properties at various applied loads, especially at high applied load. The results indicated that by introducing a multilayered interlayer into a-C based films, the toughness and adhesion could be significantly improved without adversely sacrificing hardness. The tribological properties could be optimized by carefully tailoring the thickness ratio of multilayered interlayer to a-C top layer.     

Wear properties of Y–α/β composite sialon ceramics

The tribological properties of yttrium containing α/β composite sialon ceramics have been studied under non-lubricated conditions by means of block-on-ring and ball-on-disk type experiments against a commercial silicon nitride material. The sialon ceramics were produced by hot pressing powder mixtures of Si₃N₄, AlN, Al₂O₃ and Y₂O₃, resulting in composite ceramics containing different amounts of the α/β phases. The effects of microstructural differences on the mechanical properties of the ceramics, and their wear characteristics under a range of testing conditions have been assessed. It was found that Vickers hardness decreased whilst both fracture toughness and bending strength increased with increasing amount of β phase in the composite. Under mild testing conditions, material removal was considered to occur by polishing of the surface, and in this case the high α-sialon composites exhibited the highest wear resistance, reflecting their higher hardness. Under severe testing conditions, the wear behaviour was characterised as microcracking caused by the higher Hertzian stress levels, and resulted in grain removal or “dropping” from the surface of the materials. Under these conditions, the elongated microstructure and higher fracture toughness of the low α-sialon composites hinder the crack propagation and result in better wear characteristics when compared to the fine equiaxed α-sialon materials.     

Sliding Wear Behavior of ZTA with Different Yttria Stabilizer Content

In this study, tribological investigations were carried out on ZTA ceramics with 17 vol% Y‐TZP and different stabilizer contents (1, 1.5, and 2 mol% yttria) to analyze the influence of zirconia transformation on wear properties. Samples were tested in a linearly reciprocating ball on flat setup with different applied loads. Raising the fracture toughness by transformation toughening, microcracking, and residual stresses improves the wear resistance only at transition load but increases the wear at high loads. Higher yttria content of 2 mol% and lower zirconia grain size and thus low transformability, decreases fracture toughness but increases the wear resistance at high loads. Therefore the adjustment of stabilizer content on zirconia volume fraction in ZTA plays a decisive role in tribological applications.     

A comparative study on microstructure and tribological properties of Si3N4 and TiN thin films produced by IBED method

In this paper, the tribological properties of Si₃N₄ and TiN thin films produced by ion beam enhanced deposition (IBED) method were compared on an SRV friction and wear testing machine. In order to understand the reasons of their excellent properties the microstructure, microhardness and bonding strength with the substrate were analysed by SEM, X-ray diffraction, Knoop hardness test and scratching test methods separately. The results show that the TiN(1) film exhibits the best tribological properties, which are closely related with its higher hardness and bonding strength.     

Anisotropic mechanical and tribological properties of SiAlON matrix composites containing different types of GNPs

SiAlONs can have new application areas by increasing their lifetime and durability if their mechanical and tribological properties are improved. Even though the properties of the matrix improve with GNPs addition, the differences in GNPs properties lead to different property values. In this study, four different GNPs having different surface area, lateral dimension, thickness, and aspect ratio were added to SiAlON and composites were sintered by using SPS. The effects of these different properties on fracture toughness and friction coefficient of SiAlONs were investigated. GNPs, which have the high surface area, lateral dimension, aspect ratio and low thickness, provided the highest fracture toughness and best friction coefficient performance to SiAlON. The fracture toughness of composites were generally higher in the in-plane direction compared to through-plane direction due to GNPs orientation. Conversely, the friction coefficient and hardness values measured higher in the through-plane direction than in the in-plane direction.     

网络互穿型碳化硅陶瓷/铁基复合材料制备及其耐磨性能

通过酚醛树脂固化、碳化及原位硅化的技术制备复杂形状SiC陶瓷,并利用金属浇注工艺制备出了以高锰钢、高铬铸铁为基体的2种网络互穿型SiC陶瓷/金属复合材料。借助湿式橡胶轮摩擦磨损试验机和UMT-3多功能摩擦磨损试验机测试该2种复合材料及2种基体的摩擦学性能,并采用扫描电子显微镜分析了复合材料和基体磨损后的表面形貌。结果表明：由于SiC陶瓷体的强度、硬度比金属基体高,导致在磨损过程中2种基体材料的磨损量较大,且在复合材料表面形成微凸起,使得复合材料的耐磨性能明显提高;SiC陶瓷/高铬铸铁复合材料的耐磨性优于SiC陶瓷/高锰钢复合材料,但SiC陶瓷/高锰钢复合材料的界面结合更好。     

Characterization and tribological investigation of sol-gel Al2O3 and doped Al2O3 films

Thin films of Al₂O₃ and doped Al₂O₃ were prepared on a glass substrate by dip coating process from specially formulated ethanol sols. The morphologies of the unworn and worn surfaces of the films were observed with atomic force microscope (AFM) and scanning electron microscope (SEM). The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of obtained thin films sliding against Si₃N₄ ball were evaluated and compared with glass slide on a one-way reciprocating friction tester. XPS results confirm that the target films were obtained successfully. The doped elements distribute in the film evenly and exist in different kinds of forms, such as oxide and silicate. AFM results show that the addition of the doped elements changes the structure of the Al₂O₃ films, i.e., a rougher and smoother surface is obtained. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. As the results, the doped films exhibit better tribological properties due to the improved toughness. Sever brittle fracture is avoided in the doped films. The wear of glass is characteristic of brittle fracture and severe abrasion. The wear of Al₂O₃ is characteristic of brittle fracture and delamination. And the wear of doped Al₂O₃ is characteristic of micro-fracture, deformation and slight abrasive wear. The introduction of ZnO is recommended to improve the tribological property of Al₂O₃ film.