Friction and wear of self-mated SiC and Si3N4 sliding in water

The friction and wear of self-mated SiC and Si₃N₄ with different initial roughness sliding in water were investigated with pin-on-disk apparatus at normal load of 5 N and sliding speed of 120 mm/s in ambient condition. It was found that, for self-mated Si₃N₄, the wear mechanism for surface smoothening to obtain low friction was tribochemical wear, but for self-mated SiC, it changed from mechanical wear into tribochemical wear with increasing sliding cycles. After running-in in water, self-mated Si₃N₄ exhibited lower steady-state friction coefficient than self-mated SiC did. For these two ceramics, initial and steady-state friction coefficients were hardly dependent on initial roughness. Initial roughness mainly affected the running-in period. The larger the initial roughness, the longer the running-in period, but the running-in period was much shorter for self-mated Si₃N₄ at each initial roughness than that for self-mated SiC.     

Tribological behaviour of Si3N4 and Si3N4-%TiN based composites and multi-layer laminates

Si₃N₄-TiN based multi-layer laminates exhibit differences in residual stress between individual layers due to a variation of the thermal expansion coefficient between the layers. The residual stress distribution in these multi-layer laminates is known to improve the apparent macroscopic fracture toughness. In this work, the tribological behaviour of bulk, composites and multi-layers laminates are investigated. Si₃N₄ bulk, Si₃N₄ based composites with 10, 20 and 30 wt% TiN and different multi-layer laminates have been tested under dry conditions with reciprocal movement using a ball-on-block configuration. In particular, the influence of sliding directions with respect to the layer orientations has been investigated.The experimental results show that wear resistance increased with increasing TiN content in Si₃N₄-TiN composites. However, multi-layer laminates exhibit an up to three times higher apparent fracture toughness, but do not show an improvement of wear resistance compared to composites.     

The comparisons of sliding speed and normal load effect on friction coefficients of self-mated Si3N4 and SiC under water lubrication

The effects of sliding speed and normal load on friction coefficients of self-mated Si₃N₄ and SiC sliding in water after running-in in water were investigated with pin-on-disk apparatus at sliding speeds of 30 to 120 mm/s, normal loads of 1 to 14 N in ambient condition. The results showed that, after running-in in water, for two kinds of self-mated ceramics, friction coefficient increases with both decreasing sliding speed and increasing normal load when normal load is larger than a critical normal load. Friction coefficient was independent of normal load when normal load is smaller than the critical load. The lubrication film of Si₃N₄ under water lubrication exhibited larger load carrying capacity than that of SiC did. Stribeck curves indicated that, for self-mated Si₃N₄ ceramics, hydrodynamic lubrication will change into boundary lubrication abruptly when the sommerfeld number is less than a critical value; while for self-mated SiC ceramics, hydrodynamic lubrication will change into mixed lubrication and then into boundary lubrication gradually when the sommerfeld number is below critical value.     

Friction and wear properties of duplex MAO/CrN coatings sliding against Si3N4 ceramic balls in air, water and oil

It is evident that the micro-arc oxidation (MAO) ceramic coatings often exhibit relatively high friction coefficients as sliding against many mating materials. To reduce the friction coefficient for the MAO coatings, the duplex MAO/CrN coatings were deposited on 2024Al alloy using combined micro-arc oxidation and reactive radio frequency magnetron sputtering. The microstructure and phase of the duplex coatings were observed and determined using scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The friction and wear behaviors of the duplex coatings sliding against Si₃N₄ balls in air, water and oil were investigated using a ball-on-disk tribometer. The wear rate of the duplex coating was determined by non-contact optical profilometer and the wear tracks on the duplex coatings were observed by SEM. The results showed the CrN coatings mainly consisted of Cr, CrN and Cr₂N phases. The duplex coatings/Si₃N₄ tribopair exhibited the highest friction coefficient in air, while displayed the lowest friction coefficient in oil. When the normal load and the sliding speed increased, the friction coefficient in air increased from 0.65 to 0.72, whereas decreased from 0.58 to 0.36 in water and 0.20 to 0.08 in oil. The specific wear rates for the duplex coatings in air were higher than those in oil. In comparison to the MAO coatings, the duplex MAO/CrN coatings displayed excellent tribological properties under the same conditions.     

Sliding speed-temperature wear transition maps for Si3N4/iron alloy couples

The superior high temperature resistance of silicon nitride (Si₃N₄) based ceramics makes them suitable for tribological applications above room temperature or in high speed unlubricated sliding. There are some published works on the wear behaviour of Si₃N₄/metal alloys. However, experimental data are shown in a form that is not of direct use for engineers involved in materials selection. In the present work, Si₃N₄ pins were tested against tool steel and grey cast iron on a pin-on-disc tribometer. Ceramics were produced by hot-pressing and tested without lubrication at variable temperature and sliding speed. SEM/EDS and XRD analysis were used for chemical and microstructural characterisation of worn surfaces and wear debris. At low speeds (0.05–0.5 m s⁻¹) and room temperature, Si₃N₄ surfaces are polished-like due to a combination of humidity-assisted tribo-oxidation and abrasive action of very fine wear debris. At high sliding speeds (2–3.5 m s⁻¹), as well as for temperatures in the range 400–600°C, an extensive coherent tribolayer mainly composed by iron oxides spreads over the ceramic surfaces. Polishing and protection by adherent tribolayers are the mechanisms responsible for observed severe and mild wear regimes, respectively. Wear maps are constructed showing the transition of wear regimes in Si₃N₄/iron alloys contacts determined by constant flash temperature curves. Equations for calculation of bulk and flash contact temperatures in tribocontacts between dissimilar materials are deduced.     

Observation of delamination wear of lubricious tribofilm formed on Si3N4 during sliding against WC-Co in humidity air

Hot pressed silicon nitride that was exposed to high (90%) and low (32%) relative humidity was examined in ball-on-disc geometry against cemented carbide ball at various normal loads. The study indicated that Si₃N₄ tested at high R.H. gave less specific wear rate compared with Si₃N₄ at low R.H. The friction coefficient of Si₃N₄−WC-6% Co tribopairs was found in the range of 0.32–0.39 and 0.05–0.17 at low humidity and high humidity respectively. It is suggested that adsorbed moisture markedly affected the wear and friction properties of silicon nitride.Following the tests, SEM was used to elucidate the wear mechanism and particularly to delineate the effects of relative humidity on the wear and friction. SEM micrographs showed that the main wear mechanism at low relative humidity (32%) was caused by mechanical wear including abrasive grooves, large holes and polishing, whereas at high relative humidity (90%) the main mechanism was highly influenced by a tribochemical reaction related to the moisture adsorption from the environment. It is concluded that the removal of lubricious tribolayer was occurred by delamination induced crack propagation.     

Frictional deformation and fracture in polycrystalline SiC and Si3N4

Electron optical microscopy was employed to study the friction and wear of commercial polycrystalline varieties of SiC and Si₃N₄ in air at ambient temperature. Friction and wear tests were conducted in a reciprocating configuration with conical riders (both diamond and ceramic) sliding on a flat ceramic substrate. Worn surfaces were examined by both scanning electron microscopy and transmission electron microscopy. In general, friction and wear in the diamond-ceramic couples were severe. Friction with ceramic-ceramic couples was low, with friction coefficients between 0.1 and 0.4, wear being absent in single-pass tests.With ceramic-ceramic couple multipass systems, wear of Si₃N₄ occurs by plastic deformation which increases in severity with sliding distance accompanied by a corresponding increase in friction coefficient. With SiC, wear occurs by a mixture of intergranular fracture due to grain boundary weakness and plastic deformation.     

Dry and water-lubricated slip-rolling of Si3N4- and SiC-based ceramics

Tests on self-mated Si₃N₄- and SiC-based ceramics as well as ceramic-ceramic composites were performed in an Amsler-type wear tester under dry and water-lubricated rolling conditions with 10% slip. Under dry friction, wear coefficients of the materials varied by four decades. Unlubricated wear coefficients below 10⁻⁷ mm³/(N.m), defined as a practical limit for applicability, can be achieved with Si₃N₄-TiN below 775 MPa and with HIP-SiC below 750 MPa. HIPped Si₃N₄ and hot-pressed SiC-TiC under dry friction exhibit a small dependency of wear coefficient on Hertzian pressure, with wear coefficients below 10⁻⁶ mm³/(N.m). The lowest wear coefficient below 10⁻⁶ mm³/(N.m) with water lubrication was found for Si₃N₄-TiN and S-RBSi₃N₄; water reduces the variability in wear coefficient for Si₃N₄- and SiC-based ceramics.     

二步法制备Si3N4／MoSi2 合材料的研究

用Ｍｏ粉、Ｓｉ粉通过二步法反应制得Ｓｉ３Ｎ４／ＭｏＳｉ２复合材料,并用Ｘ射线衍射和扫描电镜、抗析仪等方法对材料进行了显微结构和机械性能的测定。研究表明,复合材料的机械性能,特别是高温机械性能比Ｓｉ３Ｎ４材料有显著的提高。     

Lubrication of Si3N4 and Al2O3 in water with and without addition of silane coupling agents in the range of 0.05–0.10 mol/l

To improve water lubrication of ceramics at a lower sliding velocity, the effect of the addition of silane coupling agents was investigated. Si₃N₄ and Al₂O₃ were slid against themselves in water with and without the addition of silane coupling agents in amounts ranging from 0.05 to 0.10 mol/l. Silane coupling agents containing one or more amino groups were effective in reducing the friction of Si₃N₄ and Al₂O₃ in water. Si₃N₄ also showed significant wear reduction but not Al₂O₃. However, the addition of a silane coupling agent containing an epoxy group increased both friction and wear of Si₃N₄. Improved lubricative characteristics of Si₃N₄ in water and in silane coupling agent solutions were obtained when Si₃N₄ contained smaller amounts of sintering additives. The adsorption behaviour of a silane coupling agent on ceramics was examined using both Fourier transform infrared spectroscopy and thin layer chromatography to clarify the interaction between the silane coupling agent and the ceramics. The role of polysiloxane film formation on ceramics is discussed to demonstrate the lubrication properties of ceramics.     

Surface initiated fatigue of pearlitic and bainitic steels under water lubricated rolling/sliding contact

The rolling contact fatigue behavior of steels that are, or could be, used for railroad rails is reviewed. Laboratory tests that reproduce the type of cracks observed in service rails have been employed to study the effects of maximum Hertzian contact pressure and slide/roll ratio on fatigue performance under water lubricated conditions. A comparison has been made of pearlitic and low/medium carbon, carbide free, bainitic steels. The development of ratchetting strains has been investigated and an empirical model produced.     

Comparison of the fretting wear of 100Cr6/100Cr6, Si3N4/Si3N4 and Si3N4/100Cr6 contacts in lubricated and dry conditions

The fretting wear behaviour of bearing steel against bearing steel, silicon nitride against silicon nitride, and silicon nitride against bearing steel, was investigated under lubricated and dry conditions. Amplitudes in the intermediate 5 to 50 μm range, and test durations from 10 to 360 min, were studied. Light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were employed to determine the detailed nature of the friction and wear processes. In the silicon nitride against silicon nitride contact, brittle fracture of Si₃N₄ grains, and tribochemical reaction creating an amorphous layer on the mechanically damaged surface, were found. The main mechanism of fretting wear in the case of bearing steel against bearing steel contact was delamination. In the silicon nitride against bearing steel contact, chemical reactions predominated.     

Friction and wear behavior of Ni-P coated Si3N4 reinforced Al6061 composites

Al6061 matrix composite reinforced with nickel coated silicon nitride particles were manufactured by liquid metallurgy route. Microstructure and tribological properties of both matrix alloy and developed composites have been evaluated. Dry sliding friction and wear tests were carried out using pin on disk type machine over a load range of 20-100 N and sliding velocities of range 0.31-1.57 m/s. Results revealed that, nickel coated silicon nitride particles are uniformly distributed through out the matrix alloy. Al6061-Ni-P-Si₃N₄ composite exhibited lower coefficient of friction and wear rate compared to matrix alloy. The coefficient of friction of both matrix alloy and developed composite decreased with increase in load up to 80 N. Beyond this, with further increase in the load, the coefficient of friction increased slightly. However, with increase in sliding velocity coefficient of friction of both matrix alloy and developed composite increases continuously. Wear rates of both matrix alloy and developed composites increased with increase in both load and sliding velocity. Worn surfaces and wear debris was examined using scanning electron microscopy (SEM) for possible wear mechanisms. Energy dispersive spectroscope (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) techniques were used to identify the oxides formed on the worn surfaces and wear debris.     

Si3N4-hBN陶瓷复合材料与Fe-B合金配副的摩擦学特性研究

利用MMU-5G销-盘式端面磨损试验机考察Si3N4-hBN陶瓷复合材料与Fe-B合金配副分别在干摩擦和水润滑条件下的摩擦磨损性能,分别采用扫描电子显微镜( SEM)、激光扫描显微镜(LSM)、X光电子能谱(XPS)、X射线能谱(EDS)和X射线衍射(XRD)分析摩擦面及磨屑的形貌与物质组成.结果表明,hBN的加入未能有效地改善Si3N4-hBN/Fe-B合金摩擦副的摩擦学性能,干摩擦条件下,Si3N4-hBN摩擦表面微凸体与Fe-B合金中的硬质相Fe2B发生碰撞而导致脆性断裂和剥落,发生磨粒磨损,摩擦因数均高于0.9,磨损率均高于10-5 mm3/ (N·m)数量级;水润滑条件下,由于水流带走了磨屑,避免磨粒磨损的发生,为Si3N4-hBN摩擦表面发生化学抛光提供条件,化学抛光使销、盘试样的摩擦表面变得光滑,从而获得较为优异的摩擦学性能.     

Probing the local temperature by in situ electron microscopy on a heated Si3N4 membrane

We present a method allowing us to obtain localized heating that is compatible with high-temperature operation and real time scanning and transmission electron microscopy. Localized heating is induced by flowing current through tungsten nanowires deposited by focused ion-beam-induced deposition on a 50-nm-thick Si₃N₄ membrane. Based on the heat transport between the nanowire and the substrate, we applied an analytical model to obtain the temperature profile as a function of electrical power. In this model, the key parameter is the thermal resistance between the nanowire and the substrate that we determined experimentally by measuring electrical power and local temperature. The local temperature is measured by observing the evaporation of gold nanoparticle by electron microscopy. These in situ heating and temperature-probing capabilities are used to study the crystallization of the Si₃N₄ membrane and the growth of silicon nanowires.     

Effect of shot peening on rolling contact fatigue and lubricant film thickness within mixed lubricated non-conformal rolling/sliding contacts

The effect of shot peening on rolling contact fatigue (RCF) and lubricant film thickness within non-conformal rolling/sliding contacts operated under mixed lubrication conditions was observed in this study. Rolling contact fatigue tests and film thickness measurements were carried out using specimens with modified surface topography by shot peening process using glass beads having diameter between 0.07 and 0.11 mm. It has been shown that the effect of shot peening on RCF has no positive effect even if shot peened surface of the roller exhibited somewhat higher hardness in contrast to the grounded surface. The reduction of RCF may be caused due to asperities interactions because after shot peening the surface roughness of the roller was increased. Film thickness measurements confirmed that the contact is realized actually only between asperity peaks of shot peened ball and smooth disc.Conversely, no negative effect on RCF was observed when the shot peened surface of the roller was polished. The polish of asperity peaks causes the creation of lands and micro-cavities, which may be employed as lubricant micro-reservoirs. From film thickness measurements it has been observed that lubricant emitted by shallow micro-cavities can provide the local increase in lubrication film thickness, which thereby reduces asperities interactions. Similar results were obtained for start-up conditions where the squeeze lubricant enlarges film thickness and reduces surface interactions.From the obtained results, it can be suggested that properly designed surface topography modification could help to increase the efficiency of lubrication films leading to the enhancement of contact fatigue life of non-conformal mixed lubricated rolling/sliding contacts.     

Si3N4陶瓷—白口铸铁在无润滑条件下的磨损性能分析

研究了无润滑条件下Si3N4陶瓷－白口铸铁磨擦副的磨损机理,通过对磨损表面的形貌分析和化学成分测试,发现粘附磨损和疲劳磨损是这一摩擦副磨损的主要形式,通过对试验数据进行回归分析,得知载荷对摩擦副磨损率的影响远大于速度对其的影响。     

水润滑超高压海水泵斜盘/滑靴副摩擦学特性仿真研究

超高压海水泵摩擦副在海水润滑条件工作,配合面的摩擦磨损严重。零件的表面形貌特征对配合副的摩擦与磨损有着重要影响,本文通过数值仿真计算,探索影响磨损的关键参数,较详细地研究在水润滑条件下表面形貌对斜盘/滑靴副摩擦与磨损的影响。计算结果表明:通过对表面凹坑的大小、形状与分布的控制可以减小配合面接触应力、限制磨粒运动及形成局部动压支承从而减轻配合副间摩擦与磨损。     

Effect of rubber on tribological behaviors of polyamide 66 under dry and water lubricated sliding

The friction and wear behaviors of polyamide 66 (PA 66) and rubber-filled PA 66 (PA 66/SEBS-g-MA) composites were investigated on a block-on-wheel model friction and wear tester under dry sliding and water lubricating conditions. In order to further understand the wear mechanisms, the worn surfaces and scraps of samples were analyzed by scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). The experimental results indicated that the wear mass loss and the friction coefficient of PA 66 decreased with the addition of rubber particles. The friction coefficients of PA 66 and PA 66/SEBS-g-MA composites under water lubricating condition are lower than those under dry sliding condition, but the wear mass losses are higher than those under dry sliding condition. The main wear mechanisms under dry sliding condition are the plastic deformation and mechanical microploughing. Whereas the main wear mechanisms under water lubricating condition are the mechanical microploughing and abrasive wear.