Effect of molybdenum disulphide upon the friction and wear in ceramic–steel pair

Friction and wear tests between a stationary block and a rotating ring under lubrication with molybdenum disulphide (MoS₂) were carried out at room temperature at a sliding distance of 500 m. Silicon nitride and cemented carbide blocks were pressed against a bearing steel ring, silicon nitride-bearing steel and cemented carbide-bearing steel pairs, by a load of 1600 N. The effect of molybdenum disulphide upon the coefficient of friction and the wear of the steel ring was discussed for both pairs in comparison with mineral oil lubricants. Molybdenum disulphide was more effective in reducing the coefficient of friction and the wear of the ring than the oil lubricants. Various mechanical pretreatment for forming MoS₂ film on the ring surface prior to the sliding tests were also considered. The mechanical pretreatment enabled the sliding test with the low friction coefficient even without lubrication over the sliding distance of 500 m. In general, the coefficient of friction and wear loss of the steel ring were smaller in the silicon nitride-bearing steel pair than in the cemented carbide-bearing steel pair.     

The lubricated wear of ceramics : Part II: The wear and friction of silicon nitride and steel in the presence of mineral oil or an ester based lubricant

The friction and wear characteristics of combinations of silicon nitride, alumina and AISI 52100 steel in the presence of mineral oil containing anti-wear, dispersant and detergent additives have been investigated in a tri-pin-on-disc machine. The tests were carried out at a nominal temperature of 100°C for a range of sliding speeds, loads and total sliding distances. In Part II of this two-part paper a comparison will be made between the tribological performance of these sliding pairs of materials in mineral oil and ester based lubricant environments. The results of the investigation showed that the alumina performed relatively poorly under these test conditions, whereas silicon nitride showed good potential as an improved wear resisting material compared with 52100 steel. Wear factors of the order of 10⁻¹⁰ mm³/Nm were deduced for the alumina, while values as low as 10⁻¹¹ mm³/Nm were typical of the silicon nitride sliding against 52100 steel discs. The alumina pins wore by a process of brittle fracture at the surface, whereas the silicon nitride pins wore primarily by a tribochemical polishing mechanism. The rate of tribo-chemical wear was found to be proportional to the nominal contact area.     

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.     

Frictional Behaviors of Some Nitrogen Ceramics in Conformal Contact with Tin Coated Al-Si Alloy,Steel and MMC

The frictional behavior of certain nitrogen-containing ceramics, such as silicon nitride, alpha sialons, and beta sialons as journal materials were studied in conformal contact with a tin-coated Al-Si alloy (Al-Si/Sn), forged 1141 steel and a cast aluminum matrix composite with silicon carbide reinforcement (cast MMC) as bearing materials while lubricated with SAE WW30. A case-hardened 1016 steel was also tested with the Al-Si/Sn and cast MMC bearings under the same conditions. The friction values of the ceramic and the steel journal wear pairs were compared and their frictional behaviors were evaluated.

Silicon nitride and one of the beta sialons exhibited higher load-supporting capacities than the others when they were in contact with the 1141 steel bearings. The journal surface roughness was found to be very important when the journals were in contact with the Al-Si/Sn bearings. The frictional behavior of the ceramics and cast MMC pairs and the steel and cast MMC pairs were controlled by different wear mechanisms, namely for the former, hard particle pull-out and matrix plowing, and for the latter, iron transfer from the journal to the cast MMC bearing surface.     

Tribological behaviour of alternate hypereutectic Al–Si alloys with different antiwear additives

Abstract

Two alternate hypereutectic Al–Si alloys, varying in composition and processing route, were investigated alongside their commercial equivalents, with two different lubricant antiwear chemistries. A reciprocating sliding wear test was used with a steel nitrided piston ring on substrate configuration. The conditions (average load and speed) replicated those seen in a fired gasoline engine. The oil containing zinc dialky dithiophosphate (ZDDP) antiwear gave the best antiwear protection, determined from the lower specific wear rate and friction coefficient with all alloy types. A zinc–phosphorus–sulphur based protective film was found in the wear track. The poor performance of a zinc free active phosphate ester (ashless antiwear additive) was thought to be due to no phosphorus based film forming. The presence of a calcium based film, originating from the detergent, suggests that it had a higher film forming affinity in the competitive surface interactions. The commercially termed Alusil (A390, Al–18·5Si alloy) is currently used as cylinder material in various gasoline engines. This reference material had a different microstructure to that produced by rheo-die casting. The high shear rate during the rheo-die casting process produced a finer microstructure with smaller but more numerous primary and secondary silicon particles. The increased surface area was envisaged to increase the wear resistance and evenly distribute the applied load. However, the reference Alusil gave considerably better wear performance with all oil types tested. The wear track microstructures showed material loss, void formation with fracture, fragmentation and sinking of the primary silicon particles into the aluminium matrix. The damage was controlled to an extent by use of the ZDDP oil with an organic friction modifier. An uneven wear pattern termed stick slip was occasionally observed. It was found not to be dependent on substrate alloy or oil type. The only differences were greater fluctuation in friction coefficient during the running-in period, higher overall wear track hardness and striated lines on a considerable number of fractured primary silicon particles.     

脉冲磁场处理改善硬质合金与钛合金摩擦行为研究

为了改善硬质合金刀具切削加工钛合金的摩擦磨损性能，从而减少钛合金加工中浓缩乳化切削液的用量，利用脉冲磁场对WC-6Co硬质合金进行强化处理，在不同配比切削液润滑下研究磁场处理对WC-6Co/钛合金的摩擦行为的影响。结果表明：磁场处理大幅提高了WC-6Co/钛合金的摩擦性能，且随着浓缩乳化切削液与水配比的降低，摩擦因数明显降低；脉冲磁场处理后，WC-6Co硬质合金/钛合金摩擦后的表面得到强化，黏结相Co的脱落减少。磁场处理后硬质合金磨损性能的改善，是脉冲磁场作用下Co相磁致伸缩对硬质合金的强化效果以及硬质合金剩磁对切削液中油滴吸附的耦合结果。     

Friction Reduction and Wear Resistance Enhancement of SiC and Si3N4 Ceramics under Dry Conditions

In this study, an effort was made to control the friction and wear behavior of silicon carbide (SiC) and silicon nitride (Si₃N₄) ceramics using an ultrasonic nanocrystalline surface modification (UNSM) technique. The friction and wear behavior of the ceramic specimens was investigated using a ball-on-disk tribotester under dry conditions against two different Si₃N₄ and bearing steel (SUJ2) balls. The experimental test results revealed the possibility of controlling the friction and wear behavior of ceramics, where the friction coefficient and wear resistance of the specimens were improved by the UNSM technique. The hardness of the specimens also increased after UNSM treatment, but it decreased abruptly with increasing depth from the very top surface. Microscratch tests showed that the critical load of the specimens was improved by the UNSM technique. In addition, Raman spectra results revealed that no additional phase was detected after UNSM treatment, but the intensity decreased after UNSM treatment. Hence, the UNSM technique ensures stronger ceramics and enables better friction and wear behavior than available conventional sintered ceramics.     

Organoamine and organophosphate molybdenum complexes as lubricant additives

The friction and wear characteristics of molybdenum complexes, from which sulphur is absent, were examined under reciprocating sliding conditions by adding them to a paraffinic base oil with, and without, sulphur and phosphorus compounds as additives. Two kinds of molybdenum complex were used, i.e. an alkylamine complex and an alkylphosphate complex. The complexes were capable of forming MoS₂ despite the absence of sulphur in their constituents when they were added to the base oil containing sulphur compounds. The friction was reduced by the formation of a surface film comprising MoS₂ but the wear performance was little improved by combining the alkylamine complex with a sulphur compound. Both the friction and the wear performance were improved markedly by the formation of FePO₄ besides MoS₂, i.e. it was effective for the alkylamine complex and the alkylphosphate complex to be used together with sulphur and phosphorus compounds and with sulphur compounds respectively.     

Self-assembled monolayer protective films for hybrid sliding contacts

Abstract

Silicon nitride as an energy efficient material is replacing conventional steels for new generation engineering components such as bearings, cutting tools, electronics and engine parts in automotive, aerospace and wind industries. Compared with steel bearings, silicon nitride bearings can be operated at much higher temperatures and speeds with >60% weight reduction and up to 80% friction reduction. These are all due to its unique material properties, including high wear and corrosion resistance, low density and heat generation. Current lubrication solutions for hybrid contacts, where silicon nitride balls and steel races are used, are mostly relying on the protection film formed on the metal surfaces. Self-assembled monolayers (SAMs) have been found very useful in modifying surfaces, especially for microelectromechanical system and nanoscale applications, e.g. atomic force microscopy tips, etc. This study aims to investigate the feasibility of forming a SAM protection film on industrial grade bearing material silicon nitride to reduce the friction for the oil lubricated hybrid contacts. Four silanes with different functional head groups, including octadecyltrichlorosilane (OTS), octyltrichlorosilane, chlorodimethyloctadecylsilane and octadecyltrimethoxysilane, were initially investigated to form SAMs on industrial grade silicon nitride surfaces. The effects of concentration and immersion time of the silanes on the formation of SAMs on the silicon nitride surface were evaluated using contact angle measurements. The preliminary results show that the wetting properties of the silicon nitride surface can be effectively modified by the formation of SAMs from the silane solutions. OTS can form an order and compact SAM on the silicon nitride surfaces within 2 min at the concentration of 2··5 mM in decane solution, while the other three alkylsilanes can also effectively modify silicon nitride surfaces given sufficient immersion time, e.g. over 1 h. Tribological tests were subsequently carried out on a ball on disc rig where a steel ball and a silicon nitride disc were used. The effect of the formation of alkylsilane SAMs on the friction between the sliding contacts has been evaluated in two different methods. The first method was to test preformed SAM films under dry conditions, and the second was to premix one of the surfactants with Shell Vitrea ISO 32 mineral base oil and then spray the mixture to the contacts during the ball on disc testing. The test results show that an average of over 40 and 30% friction reduction was achieved for the hybrid contact when lubricated with the base oil mixed with OTS (>2··5 mM) and octadecyltrimethoxysilane (5 mM) respectively compared with that of the sliding contact lubricated by the base oil only. Since OTS may produce corrosive byproducts during SAM formation, octadecyltrimethoxysilane may be a more suitable additive for the hybrid contacts.     

对偶材料对树脂基摩擦材料摩擦磨损性能的影响

分别以45#钢、铍青铜、碳化硅颗粒基体改性铍青铜、氧化铝涂层为对偶材料与同一种树脂基摩擦材料在MM1000-II型摩擦磨损试验机上进行干式摩擦磨损试验,研究对偶材料对树脂基摩擦材料摩擦磨损性能的影响;利用偏光显微镜观察材料磨损后的表面微观形貌。结果表明:氧化铝涂层对偶材料的磨损率最低,摩擦因数适中,但摩擦因数稳定性较差;对偶材料为45#钢时摩擦因数较低,但摩擦因数的稳定系最好;对偶材料为铍青铜时摩擦磨损性能最佳,摩擦因数较高且稳定性较好,铍青铜本身和与之匹配的摩擦材料的磨损率都很低,且摩擦表面均没有形成孔洞和犁沟;改性铍青铜在各方面都表现出较差的性能。     

Friction and wear behavior of AZ91D magnesium alloy against steel lubricated with N‐ and S‐containing organic borates

The friction reduction and antiwear properties of a range of nitrogen‐ and sulfur‐containing organic borates as oil additives in mineral oil were assessed using a Timken tester with a bearing steel ring against an AZ91D magnesium alloy block. X‐ray photoelectron spectrometry and scanning electron microscopy were employed to examine the boundary film formed on the surface of the magnesium alloy block. The results show that the borate additives were effective at reducing the wear of magnesium. The acting mechanism of borate, which acted as additive in the magnesium‐on‐steel tribological system, was proposed. Copyright © 2006 John Wiley & Sons, Ltd.     

WC-10Co-MoS2@Ni自润滑硬质合金与钛合金的摩擦学性能研究

为探究WC-10Co-MoS2@Ni自润滑硬质合金与TC4钛合金的摩擦学性能，通过热压烧结制备不同含量MoS2@Ni的硬质合金试样，采用扫描电子显微镜、三维轮廓仪、维氏硬度计等分析自润滑硬质合金的组织结构和力学性能，利用往复式摩擦试验机研究干摩擦、切削液环境和深冷环境下硬质合金与钛合金的摩擦学性能。结果表明：随着硬质合金中MoS2@Ni含量的增加，表面孔隙减少，力学性能缓慢下降；在干摩擦、切削液环境和深冷环境下，摩擦因数均随MoS2@Ni含量的增加而降低；钛合金和硬质合金在干摩擦时由于钛合金的黏附，阻碍了MoS2发挥润滑作用，磨损形式以黏着和氧化为主；在切削液环境中磨损形式以磨粒磨损和黏着磨损为主，而在深冷环境下减少了氧化和黏着，其磨损形式主要为磨粒磨损，并伴有分层磨损现象。     

硅化石墨的摩擦性能的试验研究

在 ＭＰＸ２００型环／环试验机上，对油和水介质润滑下的硅化石墨／硅化石墨、２０Ｃｒ钢／硅化石墨的摩 擦性能进行了实验评价。结果表明，水润滑下硅化石墨的摩擦系数为 ０．０１～０．０２左右，远小于油润滑下 的摩擦系数。对其摩擦化学作用机理进行了探讨。     

Influence of counterbody material on wear of ta-C coatings under fretting conditions at elevated temperatures

The high temperature tribological performance of tetrahedral amorphous carbon coatings has been analyzed at elevated temperatures up to 250 °C in air against three different counterbody materials—steel 100Cr6, α-alumina and silicon nitride. The results show that the counterbody material influences the friction and wear behavior and therefore coating life time strongly. This effect is well known for these coatings at room temperature under dry environmental conditions, equivalent to conditions above 100 °C when water molecules desorb from the surface. However, the sharp difference in tribological performance between silicon nitride on the one hand and alumina and steel on the other hand cannot be understood in this context. Analyzing the friction behavior during the running-in phase, it is evident that only alumina and steel form a stable interface with constant low friction and relatively low wear rates. Silicon nitride forms an unstable interface with fluctuating COF and relatively high wear rates due to its own inherent tendency to tribo-oxidation.     

Tribological behavior and topography of friction surfaces of diamond-like coatings in contact with steel,silicon nitride,and quartz glass

The paper presents the study results of the tribological behavior and surface topography formed at friction of diamond-like coatings against indenters made of silicon nitride, quartz glass, and steel. It is shown that the tribological behavior depends on the nature and hardness of the counterbody material whose wear causes changes in the surface topography of the diamond-like coating at the nanometer level. At friction of the diamond-like coating against the silicon nitride indenter surface asperities are deformed plastically and the deformation rate is governed by the coating structure.     

Effects of Microscale Particles as Antiwear Additives in Water-Based Slurries with Abrasives

Abrasive wear is the dominant cause of tool failure in the process of mining and petroleum/gas drilling. This research investigated the effects of two additives, polystyrene and silicon nitride, on the tribological properties of water-based slurries with silicon dioxide or alumina abrasives. A pin-on-disk configuration was utilized to evaluate the performance of the additives for a steel–steel contact. Experimental results showed that polystyrene particles were able to reduce wear but friction increased simultaneously. On the contrary, silicon nitride particles exhibited excellent performance on both wear resistance and friction reduction. Results in this study indicated that the addition of appropriate additives was able to improve the tribological properties of slurries with abrasives.     

多因素影响的格莱圈材料摩擦磨损试验研究*

格莱圈由聚四氟乙烯(PTFE)矩形滑环和丁腈橡胶(NBR)O形圈组成。为了研究不同因素对于格莱圈密封材料摩擦磨损性能的影响,利用UMT-3多功能摩擦磨损试验机,通过改变往复频率、粗糙度、润滑状态研究格莱圈材料与45钢配副时的摩擦磨损性能,利用SEM对试块试验前后表面形貌进行观测,并对摩擦磨损机制进行分析。试验结果表明:在干摩擦和滴油润滑条件下PTFE材料相比NBR材料具有更为优异的摩擦磨损性能;NBR材料表面粗糙度过高或过低都会导致摩擦因数升高,表面粗糙度对具有自润滑性能的PTFE材料的摩擦因数影响不大;高往复频率会使NBR材料摩擦因数降低,过高或过低的往复频率都会使PTFE材料摩擦因数降低;NBR材料的磨损形式以磨粒磨损和黏着磨损为主,PTFE材料以黏着磨损和疲劳磨损为主。     

Effect of lubricant fluid on plastic metal flow in sliding contact

Plastic metal flow in surface layers, especially “abnormal metal flow”, in which the direction of metal flow in the inner surface layer is different from that in the layer nearer the surface, in sliding contacts between a pin of cemented carbide and a ring of steel under lubrication is discussed in this paper. Low viscosity mineral oil is used as a base oil. Sulphide and chloride extreme pressure additives are also mixed with the base oil. Such a lubricant has a great influence on the plastic metal flow of a ring.While base oil produces severe plastic metal flow, the sulphide additive causes the plastic metal flow to be very mild. In contrast, a lubricant containing a chloride additive causes abnormal metal flow, where cracks can be seen. Conditions for and causes of abnormal metal flow are investigated.     

基于 STFT 的织构涂层硬质合金表面振动解析方法

针对织构涂层复合工艺对硬质合金表面改性时存在消极振动的问题,提出一种基于织构涂层表面摩擦振动行为的解析 方法来探索织构涂层复合工艺改性效果。 因此,搭建了微织构 AlSiTiN 涂层硬质合金-钛合金磨盘摩擦磨损试验平台,基于短 时傅里叶变换(STFT)与灰度算法对摩擦振动变化规律性映射和振动行为平稳时段进行了获取,进而分析了微织构 AlSiTiN 涂 层工艺参数对硬质合金的改性效果。 试验研究得出了微织构及 AlSiTiN 涂层对硬质合金表面耐磨改性效果最为积极的时间 段,即自接触摩擦起第 5~ 25 min 的稳定作用时期,得出微织构及 AlSiTiN 涂层参数对硬质合金表面改性的影响机理,优选该复 合改性方法抑制硬质合金表面消极摩擦振动的工艺参数,为提升硬质合金表面性能研究提供新思路。     

Dry sliding wear behavior of nano-sized SiC pins against SiC and Si3N4 discs

Micro- and nano-sized hot-pressed silicon carbide pins have been characterized by room-temperature unlubricated disk-on-pin tribological tests on hot-pressed silicon carbide and silicon nitride discs. The mean grain size was shown not to influence the steady state friction coefficient. The mean grain size clearly affected the disc wear rate: the finer was the grain size the lower was the disc wear rate. No impact of the grain size was observed on the pin wear rate. The basic wear mechanisms were grain fracture and fine abrasion. By depth-sensing indentation, it was shown that a possible explanation of the different wear behaviour between micro- and nano-sized silicon carbide are the values of mechanical properties, especially hardness, when they are measured on volumes scaling with the material microstructure.