Instrumented indentation and scratch testing evaluation of tribological properties of tin-based bearing materials

This paper describes a study of some fundamental tribological behavior of two different tin-based bearing materials using scratch and Martens hardness techniques. The scratch test results obtained from the two different tin-based bearing materials were correlated with a function of scratch hardness and coefficient of friction. It is easily observed that the friction coefficients of WM5 are lower than those of WM2 under all scratch test conditions. Beside this, it is clearly distinguished that both materials give higher friction coefficients at higher normal loads and scratch velocities. Also it is found that scratch hardness values of the WM5 materials are higher than WM2 generally. Moreover, optical microscopy was used to determine the scratch hardness of two different tin-based bearing materials by examining the scratch widths. Scanning electron microscopic observations of two different tin-based bearing materials were performed in order to identify the scratch-deformation mechanisms and trace morphology. Beside scratch tests, Martens hardness tests were carried out to evaluate the indentation of materials by considering both the force and displacement during plastic and elastic deformation. By monitoring the complete cycle of increasing and removal of the test force, hardness values were determined.     

40Cr钢表面改性覆层的磨料磨损研究

采用新工艺在４０Ｃｒ钢表面制备了含ＴｉＢ２陶瓷相的覆层材料，覆层平均厚度为１００－１５０μｍ，表层硬度在１８００－２５００ＨＶ之间。研究成果可用于模具及耐磨蚀材料领域。     

Verbesserung des Verschleißverhaltens von Al-Werkstoffen

Improvement of Wear Resistance of Al-materials Wear behaviour of ductile materials can be improved by embedding suitable hard particles of appropriate size. With the Al materials tested here, embedding was achieved by extrusion of the powder mixtures. Wear resistance of the materials thus produced was determined using pin-disc and Klüber testers, commercially available fine grinding discs being used as abrasive partners. Thus, the effect of various parameters on wear behaviour and mechanical strength could be investigated. The mechanical properties are generally deteriorated by embedding hard particles, the amount of embedded material being of primary importance, but there is also a profound influence of the matrix-particle interface strength and, to a lesser degree, of particle size and shape. With regard to the wear resistance, the hard particles result in the desired improvement which is the more pronounced the higher the particle content and hardness. Even at low interface strength the particles are not torn of the matrix during wear stress. At lower matrix hardness (plain Al, Al alloys) better wear resistance is observed, as the abraded particles are more effectively rembedded and thus protect the matrix from wear. If suitable materials are used, excellent wear resistance combined with only insignificantly lowered mechanical strength is obtained.     

圆锥压头递增载荷对材料的划痕行为

用Rockwell C金刚石压头对16种材料(2种玻璃、2种聚合物、4种陶瓷、4种金属和4种金属玻璃)进行微米划痕测试。结果表明,这些材料都存在与弹性恢复相关的最大划痕保持率(残余深度与压入深度之比),可作为表观摩擦系数变化曲线的分段过渡点。划痕的表观摩擦系数由黏着摩擦系数和犁沟摩擦系数组成,使用三维力学接触模型可较为准确地表征除金属玻璃外的摩擦系数。材料的初始摩擦系数与泊松比有一定的关系。聚合物(PC和PMMA)因堆积和下沉效应出现独有的双划痕沟槽现象。16种材料的划痕硬度与压痕硬度的比值为0.33~2.5,划痕硬度与体积模量呈线性关系。使用线弹性断裂力学(LEFM)模型和微观能量尺寸效应(MESEL)模型计算了材料的断裂韧性。结果表明,LEFM模型、Akono's MESEL和Hubler's MESEL模型都能较为准确地表征断裂韧性较低材料(玻璃、陶瓷和高分子)的断裂韧性,而对断裂韧性较大的金属材料其表征结果偏差较大。用Liu's MESEL模型可表征断裂韧性较大材料(金属材料和部分金属玻璃)的断裂韧性。材料的断裂韧性,与泊松比呈分段线性相关。     

Modelling of the scratch resistance of particle filled sol-gel coatings on aluminium

Sol-gel derived coatings with 12 nm and 0.5-10 μm silica fillers were prepared on aluminium to evaluate the effect of particle size and filler content on coating properties The measured maximum crack-free thickness and hardness strongly depended on the type of particles used and the filler volume fraction. The scratch resistance primarily depended on coating thickness and much less on the mechanical properties of the coating. This finding was interpreted via modelling of the stresses under the scratching stylus. It was established that the initial yield occurred in the substrate for most of the coatings and the load needed for this initial yield had a relatively small dependence on the coating properties but it was strongly influenced by the coating thickness.     

Single-point scratching of 6061 Al alloy reinforced by different ceramic particles

Aluminium alloys reinforced by ceramic particles have been widely used in aerospace and automotive industries for their high stiffness and wear resistance. However, the machining of such materials is difficult and would usually cause excessive tool wear. The effect of ceramic particles on the cutting mechanisms is also unclear. The purpose of this study is to investigate the cutting mechanisms and the relationship between specific energy of scratching and depth of cut (size effect). The single-point scratch test was carried out on 6061 Al and its composites reinforced by Al₂O₃ and SiC ceramic particles using a pyramid indenter. The results indicated that the scratch process was composed of rubbing, ploughing, plastic cutting and reinforcement fracture. A simple model was proposed to interpret the apparent size effect. The effect of reinforcement on the specific energy was correlated to the ratio of volume fraction to particle radius. The paper found that for machining MMCs, a larger depth of cut should be used to maintain a lower machining energy, especially for those with a larger ratio of volume fraction to particle radius.     

二氧化硅纳米微粒对达克罗涂层性能的影响

将纳米SiO2微粒加入到达克罗涂层中制备出了复合涂层,利用SEM、EDS、XRD等分析方法对添加纳米微粒前后的涂层做了显微表征和分析.结果表明,复合涂层的硬度、抗划伤性、摩擦性能和耐腐蚀性都有不同程度的提高,且涂层保留了本身的优点,外观、耐水性、附着强度等都未受影响;从不同角度探讨了纳米微粒提高涂层性能的方法和原因.     

Micro/nanomechanical characterization of ceramic films for microdevices

Microelectromechanical systems (MEMS) are currently fabricated using single-crystal silicon, various polysilicon films and other ceramic materials. Silicon carbide (SiC) film has recently been pursued as a material for use in MEMS devices owing to its excellent mechanical properties and high-temperature capabilities. Since physical and chemical properties, friction and wear are important issues in such small-scale devices, it is essential that the materials used in MEMS have good micro/nanomechanical and tribological properties. Micro/nanomechanical characterization of single-crystal 3C-SiC (cubic or β-SiC) films, undoped and doped (n⁺-type) polysilicon films have been carried out. For comparision, measurements on undoped single-crystal Si(100) have also been made. Hardness, elastic modulus and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Fracture toughness was measured by microindentation using a microindenter. Friction and wear properties were measured using an accelerated ball-on-flat tribometer. It is found that the 3C-SiC film exhibits higher hardness, elastic modulus and scratch resistance as well as lower friction compared to other materials. These results show that the 3C-SiC film possesses desirable micro/nanomechanical properties that make it an ideal material for use in MEMS devices.     

山梨醇类成核剂对BOPP烟膜表面耐磨性能研究

目的研究自制山梨醇类成核剂对BOPP烟膜表面耐磨性能的影响。方法利用山梨醇类及其复配自制的成核剂,通过对比试验研究成核剂对烟膜力学性能的影响;对BOPP烟膜表面热封层进行耐磨性能改性,随后开展耐擦伤性能检测试验,通过平板上薄膜雾度变化来衡量耐磨性能。结果山梨醇类及其复配自制成核剂能明显改善烟膜的力学性能,尤其在硬度方面效果显著;与无添加成核剂的膜相比,当成核剂质量分数为0.2%时,烟膜热封层的邵氏硬度提高了近22.7%;经摩擦后,成核剂改性后烟膜的雾度提高了33.1%;此外,成核剂的加入对烟膜其他性能指标影响不大,也不需要对生产工艺做特别调整。结论研制的BOPP烟膜成核剂可以提高共聚PP薄膜的表面硬度,并在一定程度上改善了BOPP薄膜表面的耐擦伤性能。     

The role of particle size on the performance of pumice as a supplementary cementitious material

A critical area overlooked in previous research on pumice is understanding how its physical characteristics influence its behavior as a supplementary cementitious material (SCM). This study investigated three pumices with different particle size distributions to observe whether these porous materials exhibit enhanced nucleation and growth of hydration products, in the same way as non-porous materials, and whether the rate of pozzolanic reaction can be changed through particle size. The effect of particle size on compressive strength, rheology and resistance to alkali silica reaction (ASR) was also evaluated. Results showed that reducing particle size increased the rates of cement hydration, pozzolanic reaction, and compressive strength gain, while also increasing mixture viscosity. Interestingly, particle size did not impact the yield stress of the mixture or the resistance to ASR. These new findings give insight about how the particle size of pumice can be used to overcome drawbacks reported in previous literature.     

Influence of surface texturing on scratch/mar visibility for polymeric materials: a review

Surface texturing has long played a vital role in determining both the look and feel of modern consumer goods. Recently, texture patterns have also shown to be an effective method for enhancing the scratch resistance of polymeric surfaces, which are more sensitive to scratch damage due to their relatively low strengths and stiffness. This paper examines the emerging studies of scratch-resistant surface textures and analyses the key principles and challenges faced by texture design and the assessment of scratch resistance. The analysis of scratch resistance is broken into three key sections: (1) the influence of the base material on deformation characteristics, (2) the influence of surface texturing on scratch damage and visibility, and (3) the influence of human vision and the capacity of textures to obscure scratch damage. The complex interactions between these three facets highlight the wealth of opportunities for further study in this area, and the need for improved methods for quantifying scratch resistance for these materials. This paper also presents experimental results to demonstrate the variation in scratch damage and texture effects.     

电磁离心铸造SiCP/Al复合材料励磁电压对不同粒度颗粒分布的影响

采用电磁离心铸造( EMCC) 工艺制备SiCP/ Al 复合材料, 实验了两种不同粒度的SiCP 颗粒增强Al 基体, 测定了不同励磁电压下颗粒在基体中的分布, 测试了不同粒度增强基体均匀分布的材料的硬度和耐磨性。结果发现电磁搅拌更容易使小粒度的颗粒分布均匀。励磁电压为100 V 时的颗粒分布比励磁电压为50 V 时的颗粒分布更均匀。均匀分布的小颗粒增强基体的复合材料的硬度和耐磨性有很大提高。      

Modeling and simulation of hard-particle interaction in head/disk interfaces

A hard particle interacting with a slider and a disk in the head/disk interface of hard-disk drives can produce a scratch on the disk and result in data loss. Our work emphasizes modeling and simulation of slider, particle, and disk interactions, scratch generating mechanisms, and linking of scratch to interface design parameters. Two models are presented. The Monte Carlo method was used to calculate scratch probabilities and parametric studies were performed to determine the effect on scratch probability of various parameters, such as friction coefficients, particle mean size, slider wall angles, the ion-milling (IM) etch depth from the air-bearing surface (ABS) of the slider, and the efficacy of additional ABS structures acting as particle shields. Simulation results show that the friction coefficient is a dominant parameter. If the disk friction coefficient is smaller than the slider friction coefficient, scratches are not produced. Using shallow IM depths is an effective and practical way to reduce the scratch probability. Experimental results are very close to the simulation predictions.     

Effect of the particle size of nanosilica on the performance of epoxy/silica composite coatings

Four kinds of colloidal silica particles with different size (27, 58, 79 and 173 nm, respectively) were synthesized by sol-gel process and modified with 3-glycidoxypropyltrimethoxysilicane, then homogenously dispersed into the epoxy resin and cured with alicyclic amine on aluminum alloy substrates. The results showed that the Si-O-Al bond was formed at nanocomposite coat/substrate interface, introducing nanosilica significantly enhanced the adhesive strength, scratch resistance, abrasion resistance and corrosion resistance of coats, but different particle sizes of nanosilica had various impact on these properties, which seemed to be related to the structure of the silica surface.     

A study towards improving mechanical properties of sol-gel coatings for polycarbonate

Scratch-resistant coatings based on 3-glycidoxypropyltrimethoxysilane and tetraethylorthosilicate with a cross-linking agent and different amounts of colloidal silica are prepared on polycarbonate substrates by sol-gel technique. The failure mode of this type of coating on soft plastic substrate under pencil scratch test is studied. It is found that the pencil scratch failure contains a gouge failure under the static pressure and a film cracking failure under the sliding of the pencil tip. The gouge failure is due to the early plastic deformation in the substrate, while the film cracking is due to the tensile stress in the film induced by the sliding and friction of the pencil tip. Factors influencing the static gouge failure and sliding cracking failure are investigated. It is found that the cross-linking agent and colloidal silica filler increase the intrinsic cross-linking, hardness, elastic modulus and fracture toughness of the coating material, therefore, reduce the film cracking tendency; whereas the increased layer thickness and multi-layer coating improve the pencil scratch resistance significantly via delayed plastic deformation in the substrate. Based on these analyses, we conclude that the main factors towards improved pencil scratch resistance are: layer thickness, elastic modulus, fracture toughness and intrinsic hardness of the coating material. Pencil hardness is increased from grade 2B to 5H by adjusting these parameters.     

Preparation and properties of hollow glass bead filled silicone rubber foams with low thermal conductivity

Silicone rubber foams filled with various content and different particle size of hollow glass bead (HGB) were prepared by compression molding. It was revealed that compared with silica filled silicone rubber foams, HGB filled materials achieved higher foaming extent, lower thermal conductivity, and lower hardness, which can be significant for thermal insulation materials. For HGB filled materials, the morphology indicated the average cell size decreased with higher HGB content and larger particle size of HGB. The density, thermal conductivity, hardness and tensile strength increased with higher HGB content and larger particle size of HGB.     

Advanced polymer-inorganic hybrid hard coatings utilizing in situ polymerization method

Hard coatings are frequently used to give plastics high scratch resistance. Coating hardness and adhesion to the substrate are considered to be key factors influencing scratch resistance, but it is difficult to produce coatings that have both properties. Hybridization of polymers and inorganic materials is a promising approach for solving this problem. We prepared polymer-silica hybrid coatings by using in situ polymerization to carry out radical polymerization of vinyl monomers in a sol-gel solution of alkoxysilanes, and measured the abrasion resistance of the coatings. However, the expected properties were not obtained because the sol-gel reaction did not perfectly proceed on the surface of the coatings under the N2 conditions. We found that curing the hybrid coatings by UV irradiation in air promoted the sol-gel reaction on the surface, resulting in coatings having excellent abrasion resistance.     

Effect of fillers on the supermolecular structure and properties of polyformaldehyde

The authors studied the effect of fillers (silica and aluminum silicate) of various particle size and shape on the supermolecular structure, hardness, wear resistance, and compressive strength of polyformaldehyde (PFA). It was found that these properties are improved only by small filler additions; at higher filler concentrations the mechanical properties of PFA deteriorate and a change takes place in the character of wear of this material.     

Micromechanical properties of amorphous carbon coatings deposited by different deposition techniques

Amorphous carbon coatings about 20 nm thick are commonly used as an overcoat on magnetic thin-film rigid disks and tape and disk head surfaces to improve their wear performance. In this study, we deposited amorphous carbon coatings with thicknesses ranging from 20 to 400 nm on single-crystal silicon substrates by four deposition processes: cathodic arc, ion beam deposition, r.f.-plasma-enhanced chemical vapor deposition, and r.f. sputtering. R.f.-sputtered SiC coatings were also deposited for comparison. The hardness, elastic modulus, and scratch resistance of these coatings were measured by nanoindentation and microscratching using a nanoindenter. The cathodic arc carbon coatings followed by sputtered SiC coatings exhibited the highest hardness, elastic modulus, scratch resistance/adhesion, and residual compressive stresses. The critical load, a measure of the scratch resistance/adhesion of the coating, increases with thickness. The cathodic arc coatings of lower thicknesses (˜ 30 nm) exhibited instant damage when the normal load exceeded the critical load, whereas thick coatings (greater than or equal to 100 nm) exhibited gradual damage through the formation of tensile cracks. The sputtered carbon coatings exhibited damage to the coating at very low loads and ploughing of the tip into the coating occurred right from the beginning of the scratch.     

Fabrication of Graded, Spray, and Fused Coatings and Their High Temperature Erosion Performance

Thermally sprayed coatings are often used industrially to protect bulk metal structural and heat exchange surfaces against wear and corrosion at high temperature. Spray and fused coatings of Ni-based alloys are dense, with metallurgical coating adhesion and have provided excellent industrial corrosion resistance. This process allows the addition of hard particles to improve coating wear resistance in a functionally graded manner, and the first such coating is developed. There has been few wear studies of such functionally graded materials (FGMS), particularly as coatings. Because such materials provide a gradation in properties such as hardness and thermal expansion coefficient between the coating and the substrate, it is thought that they may have potential in aggressive environments such as high temperature energy conversion processes (resisting spallation and erosion).

In a low velocity fluidized bed erosion environment the effects of erodent particle size and bed temperature on the erosion rate through the section of a functionally graded spray and fused coating was studied. The coating consisted of a varying fraction of WC particles (0-42 vol.%) in a Ni-Cr-based, self-fluxing matrix. The erodent particle size varied from 200 to 600 μm, testing was between 25 and 600°C, with impact angles of 30° and 90°.