A study on surface polishing of SiC with a tribochemical reaction mechanism

This work investigates the surface polishing of silicon carbide SiC using the tribochemical reaction mechanism. Different metal discs – cast iron, AISI 304 stainless steel, S45C medium carbon steel plated chromium, brass and copper – are used to polish SiC in water and kerosene, respectively. The experimental results show that ferrous metal discs can effectively polish SiC in water. Also, no surface damage or scratches on the polished surface of SiC are observed by this method. The polishing debris was analyzed by electron spectroscopy for chemical analysis. The analyzed results indicate that the polishing surface of SiC is removed tribochemically with the aid of catalytic effect of iron oxide. Moreover, in this process the maximum material removal rate is about 0.06 m/h.     

Effect of counter materials on coefficients of friction of TiN coatings with preferred grain orientations

In order to investigate the effect of counter materials on the coefficients of friction of TiN coatings with preferred grain orientations, the coefficients of friction against six counter materials (ball) were measured. The ball materials were aluminum (A1050), stainless steel (SUS304, SUS440C), bearing steel (SUJ2), carburized steel (SWRM10), cemented tungsten carbide (WC-Co) and alumina (Al₂O₃). After tests, the worn flat surfaces of balls and the wear tracks of TiN coatings were analyzed by the electron probe micro analysis (EPMA) and the auger electron spectroscopy (AES) to observe the Ti oxide film on each ball material and the adhesion of ball materials to the TiN coatings. The Ti oxide film was observed on the worn flat surfaces of the ball materials and the ball materials did not adhere to the TiN coatings in case that the low coefficients of friction were obtained.     

Lubrication of nuclear reactor components Friction systems in liquid sodium and argon

Safe operation of liquid metal cooled nuclear reactors requires a knowledge of the tribological behaviour of contacting components at high temperatures with slow relative movement at high frictional loads in a chemically aggressive environment. Experiments have been performed on various material combinations in liquid sodium and argon. Due to the small sliding movements, hydrodynamic lubrication is not expected and thus surface finish is an important factor. Tests have been performed on brushed, ground and lapped surfaces. Among the material combinations tested, a CrC-coating on a 1.4961 stainless steel substrate performed well. Friction coefficients of 0.35–0.5 in argon and 0.1–1.2 in liquid sodium were recorded     

核主泵备用机械密封材料的摩擦性能研究

采用Falex-1506摩擦磨损试验机,研究了水润滑、室温条件下,载荷和速度对核主泵用机械密封材料:无压烧结碳化硅(WNV2)和碳化硅加碳(CHV1)、反应烧结碳化硅(R)和碳化硅加碳(R2)、石墨(MSMG)在不同配副条件下摩擦学特性的影响规律。使用扫描电镜(SEM),对磨损表面进行了观察和分析。研究结果表明,碳化硅和石墨材料自身的孔隙,在高载荷下容纳了更多的润滑流体,因此,不同配副条件下的摩擦系数均随载荷的增加而减小。另外,滑动速度引起的温度改变通过影响表面层性质影响摩擦力,而碳化硅和石墨在很宽的温度范围内机械性质保持不变,所以摩擦系数随速度的增加基本不变。     

不锈钢半固着磨具加工的工艺研究

为获得SUS440不锈钢的低／无损伤加工表面,实现高效加工,本文采用了一种半固着磨具。该磨具能够有效地阻止加工过程中大颗粒磨料对工件表面造成的异常深划痕,实现效率与加工质量平衡。本文使用了800。碳化硅磨料的半固着磨具对SUS440不锈钢进行研磨试验,研究了不同的加工参数对工件表面粗糙度和材料去除率的影响。试验结果显示在27kPa压力、60r／min转速下加工12min后,工件表面粗糙度Rn从250nm下降到50nm,材料去除率保持在1μm／min,实现了高精、高效的加工性能。     

Characterization of 4H-SiC (0001) surface processed by plasma-assisted polishing

For the finishing of some difficult-to-machine materials, such as silicon carbide, diamond, and so on, a novel polishing technique named plasma-assisted polishing (PAP) was proposed, which combined with the irradiation of atmospheric pressure water vapor plasma and polishing using soft abrasives. In this article, application of PAP to 4H-SiC (0001) substrate was conducted. We used helium-based water vapor plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was SiO₂. CeO₂ was used as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The scanning white light interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughness also decreased from 4.410 nm p-v, 0.621 nm root mean square (rms) to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy images, step and terrace structure was observed on the surface after PAP, which means an atomically flat surface was obtained. The PAP processed surface was observed using cross-sectional transmission electron microscope, which indicated that almost no crystallographical defects were introduced.     

Influence of abrasive hardness on the wear resistance of high chromium irons

The resistance to abrasive wear was determined for a series of alloyed white cast irons in a high stress abrasion test which utilizes a specimen in sliding contact with bonded abrasives. These were conducted on silicon carbide, alumina and two sizes of garnet abrasive.The results indicate that the hardness, or type, of abrasive used in the test significantly influenced the wear rate of white irons, i.e. the rate of wear increased with increasing hardness of the abrasive. Also, the results indicate that the type of abrasive used in the test was a significant factor in ranking white irons for resistance to high stress abrasion. When tested on silicon carbide or alumina abrasive, as-cast austenitic irons exhibited lower rates of wear than heat treated martensitic irons; when tested on garnet, an abrasive of lower hardness, those irons with martensitic matrix microstructures exhibited the same or less wear than irons with austenitic matrix microstructures. It was also evident that heat treated irons with martensitic matrix microstructures exhibited varying degrees of resistance to abrasive wear depending on cooling rates and alloy content.     

氧化剂含量对304不锈钢化学机械抛光的影响

为了探究氧化剂含量对304不锈钢化学机械抛光的影响及其作用机制,采用过氧化氢作为氧化剂,研究不同氧化剂质量分数下304不锈钢材料去除率及表面粗糙度值的变化规律,并基于接触角和电化学试验分析过氧化氢在抛光过程中的作用机制。结果表明：化学机械抛光过程中过氧化氢含量的增加有利于304不锈钢表面氧化膜的生成,从而有效提高304不锈钢的材料去除率及表面质量;但是过高的过氧化氢含量会导致304不锈钢表面氧化膜致密,使得化学作用与机械作用失衡从而造成304不锈钢表面质量下降;当过氧化氢质量分数为0.04%时,抛光后304不锈钢表面粗糙度值最低,仅有2.5 nm,材料去除率达到324.21 nm/min。     

Surface morphologies and erosion rates of metallic building materials after sandblasting

Erosion behaviors of AISI 430 and 304 stainless steels, ARC-TEN weathering steel, brass, and 6063 aluminum alloy were experimentally investigated using a sandblasting type test rig and silicon carbide erodent particles. Surface morphologies of eroded specimens were examined using scanning electron microscopy. The volume loss was measured for the evaluation of erosion rates. This paper stresses the relationship between erosion rate and surface hardness (before and after erosion). It was found that the erosion rate is proportional to (Hv)⁻ⁿ, where Hv is the microhardness number after erosion testing, and the exponent n is 1.4 or 3, depending on conditions.     

Effect of reinforcing submicron SiC particles on the wear process of electrolytic NiP coatings

The effect of submicron silicon carbide frictional strengthening admixtures and heat treatment on the wear process of nickel phosphide coatings obtained by electrolytic deposition is studied. Despite the heat treatment and admixtures of silicon carbides, the wear of the coatings is of abrasion-oxidizing nature; in the case of NiP-SiC composite coatings, the oxide films formed during the friction process do not exhibit the shield effect; these films show a considerable effect on the wear of silicon-free NiP coatings. The silicon carbide admixtures increase the hardness of the electrolytic coatings but prevent the oxide films formed in the frictional process from attaching to the contact surface. Annealing of the coating reduces the wear rate. In the process of heat treatment, the crystalline phase Ni₃P is formed in the NiP matrix, increasing the coating hardness. At the same time, in the process of annealing of NiP-SiC composite coatings, the NiP matrix cracks around the silicon carbides. As a result, silicon carbides are extracted in the frictional process and the wear rate of the NiP-SiC composite coating grows.     

碳化硼研磨后蓝宝石晶体的亚表面损伤

介绍了蓝宝石材料的亚表面损伤形成机制。考虑碳化硼磨料可产生较小亚表面损伤的优点,本文基于游离磨料研磨方式,研究了不同粒度碳化硼磨料研磨后蓝宝石晶体的亚表面损伤。利用KOH化学腐蚀处理技术,对研磨后的样品进行了刻蚀;通过特定的腐蚀坑图像间接反映了蓝宝石晶体的亚表面损伤形貌特征,获得了W20、W10和W5碳化硼磨料产生的亚表面损伤深度,得到了在不同刻蚀时间下蓝宝石亚表面损伤形貌、表面粗糙度和刻蚀速率。研究结果显示:游离碳化硼磨料研磨造成的蓝宝石晶体的亚表面损伤密度相当显著,但损伤深度并不大,其随磨料粒度的增大而增大,W20、W10和W5粒度的磨料研磨后产生的亚表面损伤深度分别为7.4,4.1和2.9μm,约为磨料粒度的1/2。得到的结果表明采用碳化硼磨料研磨有利于获得低亚表面损伤的蓝宝石晶片,而采用由大到小的磨料逐次研磨可以快速获得低亚表面损伤的蓝宝石晶片。     

基于不同磨料的氮化硅陶瓷球精研工艺研究

为探究磨料对氮化硅陶瓷球精研加工的影响,从而提高氮化硅陶瓷球的表面质量和材料去除率,以基液种类、磨料种类和研磨盘转速为主要影响因素设计正交试验,并分析各因素对表面粗糙度Ra的影响程度。以表面粗糙度Ra和材料去除率为评价指标,通过单因素试验优化研磨参数。根据正交试验结果,得到精研加工过程中各影响因素对于表面粗糙度Ra的影响程度,从大到小排列依次为:磨料种类>基液种类>研磨盘转速。综合考虑陶瓷球精研加工的要求,确定最佳的研磨参数组合为:煤油基液、碳化硅磨料以及150 r/min的研磨盘转速。在金刚石、碳化硅、氮化硼、氧化铬和氧化铁这5种磨料中,氧化铁磨料修复粗研过后的氮化硅陶瓷球表面缺陷的效果最好。     

Microstructure and abrasive wear resistance of cast Ni-Cr-C alloys

The abrasive wear behaviour of directionally solidified Ni-Cr-C alloys was investigated using a pin-type test. M₇C₃ carbide volume fractions (CVF) were varied from 0 to 40%. Two sets of alloys with different carbide and dendrite spacings were abraded with bonded SiC and corundum particles, varying the grit size and applied load. M₇C₃ carbides greatly improved the abrasive wear resistance against fine-grained SiC particles within the whole range of compositions. By refining the primary carbide structure in hypereutectic alloys, the wear resistance against coarse-grained SiC particles was also improved with increasing CVF although SiC is known to be much harder than M₇C₃. Coarse SiC abrasive particles had a detrimental effect on the wear resistance of all hypoeutectic alloys and, even more, of hypereutectic alloys if the primary carbides were coarse. In testing with corundum, the wear resistance always improved with increasing carbide volume fraction.Wear damage was arranged in three classes. First, SiC and corundum abrasives were partially broken from the substrate at the entrance edge of the specimen. The edges of SiC grains stayed sharp during the wear process whereas the edges of corundum particles were rounded or the corundum was crushed by M₇C₃ carbides. Secondly, damage in the wear surface occurred by fracturing of the edges of carbides facing the wear surface. In addition, SiC abrasives were able to groove carbides. Thirdly, coarse SiC grains transmitted shear stresses causing severe subsurface damage leading to microstructure disintegration and spalling of primary carbides. SiC transmitted larger shear stresses than corundum because the latter was separated by a thin layer of wear debris from the unworn material.The microstructural parameters influencing wear were CVF, size, morphology and distribution of carbides. Optimum wear resistance depended on the abrasive mineral. Alloys with high CVF and coarse primary carbides were best suited for wear with corundum whereas fine primary carbides were required to resist wear by SiC.     

Ceramic particulate composites in the system SiC–TiC–TiB2 sliding against SiC and Al2O3 under water

The tribological behaviour of SiC, SiC–TiC and SiC–TiC–TiB₂ was determined in oscillating sliding against SiC and α-Al₂O₃ in water at room temperature. The tribo-systems with the composite materials containing TiC and TiB₂ differ significantly from the systems with the single phase SiC: The wear is reduced and the friction is increased. The wear reduction up to a factor of 10 is mainly due to the formation of an oxide film containing titanium oxides which is soft, stable in water and well adhering to the bulk material. This oxide film is transferred to the alumina ball but not to the silicon carbide ball.     

基于车铣技术的刀具磨损和破损分析

在车铣加工中心上，分别采用硬质合金和TiN涂层硬质合金刀片，对铝合金和不锈钢工件进行了车铣加工的刀具磨损试验，研究分析了车铣刀具的磨损和破损特征。研究表明，车铣铝合金的刀具磨损机理主要以刀具表层材料的黏结磨损为主，而车铣不锈钢的刀具磨损机理主要以刀具表层材料的疲劳-剥落磨损为主。车铣不锈钢时，刀具的损坏形式常常以微崩刃、前刀面的剥落和碎断等破损形态为主。     

The Role of Ferric Oxide Nanoparticles in Improving Lubricity and Tribo-Electrochemical Performance During Chemical–Mechanical Polishing

The role of ferric oxide nanoparticles on the lubricating characteristics of passivating films formed on stainless steel (SS) was discussed in this study. The tribo-electrochemical behavior of mirror-like polished AISI 304 SS, used as an exemplary material, was evaluated in various electrolytes by means of a simulated chemical–mechanical polishing process in laboratory scale. It was clearly demonstrated that a suitable combination of abrasives (ferric oxide nanoparticles) and an oxidizer (nitric acid) can act as an effective lubricant that lowers the friction and wear of the AISI 304 SS surfaces. The excellent lubricating and anti-corrosion properties shown by a slurry containing a high content of ferric oxide nanoparticles at high nitric acid concentrations were attributed to the formation of a stable and robust passive film that was composed of chromium oxide and a mixture of iron oxides. The lack of ferric oxide nanoparticles in two solutions containing nitric acid of different concentrations led to pitting corrosion and abrasive wear. When low concentrations of both ferric oxide nanoparticles and nitric acid were used, wear-accelerated corrosion became the dominant mechanism that was caused by the presence of third-body wear particles in the contact zone.     

Fabrication of WC micro-shaft by using electrochemical etching

Tungsten carbide (WC) micro-shaft can be used as various micro-tools for MEMS because of its high rigidity and toughness. In this study, we performed fabrication experiments of the WC micro-shaft using electrochemical etching. H₂SO₄ solution was used as the electrolyte because it can dissolve tungsten and cobalt simultaneously. Optimal electrolyte concentration and applied voltage resulting in uniform shape, good surface quality, and high material removal rate (MRR) of a workpiece were experimentally selected. A straight micro-shaft with 5 μm diameter and 3 mm length was obtained by controlling the various machining parameters. Using the fabricated micro-shafts as tools, we machined a high quality micro-hole with 8 μm diameter and a micro-groove with 9 μm width in stainless steel 304 (304 SS).     

EDM of hybrid Al–SiCp–B4Cp and Al–SiCp–Glassp MMCs

Hybrid metal matrix composites are a class of material system, with two or more discrete particulate reinforcement. Notwithstanding their superior properties, their widespread application is constrained by the difficulty in machining them. Non-conventional processes such as electrical discharge machining can be applied to machine such composites. This work reports on the application of EDM to machine cast aluminum–silicon carbide–boron carbide and cast aluminum–silicon carbide–glass hybrid metal matrix composites and how the metal removal rate and surface finish vary in response to the various EDM parameters     

Influence of atmospheric humidity on abrasive wear — II. 2-body abrasion

Specimens of glass, steel, copper and an aluminium alloy were abraded on silicon carbide abrasive papers under controlled levels of atmospheric humidity. Under the testing conditions used, all materials show an increase in wear rate between 0 and 65% r.h. At higher humidity levels the softer materials show a decreasing wear rate, while the harder materials show a continuing increase. Atmospheric moisture decreases the fracture strength of the SiC abrasives. This results in improved cutting efficiency at low humidity and in grit deterioration at high humidity. The magnitude of the effect on wear rates is strongly dependent on experimental conditions, in particular load per abrasive, distance of contact with the specimen surface and supply of fresh abrasives.     

Study on the oxidation of stainless steels 304 and 304L in humid air and the friction during hot rolling

In rolling process, the contact friction is of crucial importance for accurate modeling, optimum design and control of industrial rolling processes. It is important to characterize the features of the oxide scale of stainless steel in hot strip rolling because the scale on the strip surface affects friction coefficient and thermal conductivity coefficient. To some extent, the rolling force and friction condition depend on the thickness and the microstructure of the oxide scale. Oxidation tests of stainless steels 304 and 304L were carried out in a high temperature electric resistance furnace. The humid air in which the water vapour content can be controlled was generated and remained to flow into the chamber of the furnace in 2.5 × 10⁻⁴ m³/s to study the effect of humidity on the oxidation of stainless steels. The microstructure and thickness of oxide scale layer of stainless steels were obtained and two or three oxide layers can be found. The humid air has a significant effect on the growth of oxide scale. Hot rolling tests were carried out on Hille 100 rolling mill. The friction condition at the roll–strip interface during hot rolling of stainless steel was determined and the transfer of surface roughness was discussed.