An experimental study on radial fretting behaviour

A new test apparatus has been developed for radial fretting test. Main experimental conditions are as follows: the amplitude of normal load from 200 to 800N, the number of cycles from 1 to 3×10⁵ cycles. Three contact pairs (a 52100 ball against 52100, 1045, 1045 steel with TiN coating) were used for the test. Variations of normal load vs indentation depth between two contact surfaces have been analyzed as a function of cycles. Contact degradation was examined through metallographic expertise on the flat specimen and radial fretting behaviour was compared in the paper.     

Tribological behaviour of sintered 316L stainless steel impregnated with MoS2 plain bearing

The mechanical and tribological properties of sintered 316L stainless steel impregnated with molybdenum disulfide (MoS₂) were investigated. Tests were carried out at room temperature for two specific ranges of PV value (1.1 and 1.8 MPa m/s). The results prove that the friction coefficient and the wear are strongly influenced by the addition level of MoS₂.

In this paper, MoS₂ powder was mixed with 316L powder before being processed via compacting and sintering steps. The microstructure, hardness, tensile strength and elongation at breaking point of the sintered specimens were evaluated. The friction and wear properties of the materials were examined by a partial plain bearing wear test rig under dry conditions at room temperature and in air. Although some of mechanical properties of the composite decreased with increasing MoS₂ amount, the MoS₂ was very effective in reducing the friction and wear of the composites. Particularly, the sintered 316L–15% MoS₂ materials at 1.1 PV value showed a reduction of friction coefficient by approximately 20–25% when compared to the sintered 316L specimen without addition of MoS₂. In addition, wear of specimen with addition of MoS₂ was also reduced to some extent (5–10% weight loss reduction) at this specific PV value.     

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.     

物理气相沉积TiN薄膜疲劳磨损形貌的AFM观测

采用物理气相沉积工艺在高速钢表面沉积TiN薄膜,研究了TiN薄膜的疲劳磨损过程。采用原子力显微镜(AFM)观测分析了表面疲劳点蚀的形貌特征。试验结果表明:较厚TiN薄膜具有较低的疲劳磨损寿命,而较薄的TiN膜层具有较高的疲劳磨损寿命。在试验的初始阶段,磨损轨迹上都出现大量显微凹坑,AFM观测分析可知显微凹坑起源于薄膜表面,呈菱形状。随试验的进行,较薄的TiN薄膜出现典型的疲劳麻坑,而较厚的TiN薄膜在薄膜与基体的界面处形成疲劳裂纹,并出现严重的剥层和断裂。     

Study on rotational fretting wear of bonded MoS2 solid lubricant coating prepared on medium carbon steel

The rotational fretting wear behaviors of the bonded MoS₂ solid lubricant coating and its substrate steel were comparatively studied under varied angular displacement amplitudes, constant normal load, and rotational speed. Dynamic analysis in combination with microscopic examinations was performed through SEM, EDX, XPS, optical microscope, and surface profilometer. The experimental results showed MoS₂ changed the fretting running regimes of substrate. The friction coefficients of MoS₂ were lower than those of the substrate. For MoS₂, the damage in partial slip regime was very slight. The damage mechanism of the coating in slip regime was main abrasive wear, delamination, and tribo-oxidation.     

Fretting wear behavior of TiB2-based materials against bearing steel under water and oil lubrication

Lubricated fretting tests in water and paraffin oil were performed with a monolithic TiB₂, a TiB₂-based cermet with 16 vol.% Ni₃(Al, Ti) binder, a sialon–TiB₂ (60/40) composite and a ZrO₂–TiB₂ (70/30) composite against ball bearing grade steel. Based on the measured friction and wear data, the ranking of the investigated fretting couples was evaluated. Furthermore, the morphological investigations of the worn surfaces and transfer layers are carried out and the wear mechanisms for the investigated friction couples are elucidated. While fretting in water, experiments revealed that tribochemical reactions, coupled with mild abrasion, played a major role in the wear behavior of the studied material combinations. ZrO₂–TiB₂ (70/30)/steel wear couple has been found to have the highest fretting wear resistance among the different tribocouples under water lubrication. Under oil lubrication, extensive cracking of the paraffin oil at the fretting contacts, caused by tribodegradation, leads to the deposition of a carbon-rich lubricating layer, which significantly reduced friction and wear of all the investigated tribosystems.     

Fretting wear in seawater

Fretting tests of bearing steel (SUJ-2) and ceramics (Al₂O₃ and Si₃N₄) were carried out in the following environments: air, deionized water, 3.07% NaCl solution, synthetic seawater and natural seawater. Also, investigations to determine the optimum fretting wear resistant material for ships, marine equipment and offshore structures were conducted. The results showed that (1) the corrosion products formed in seawater behaved as a lubricant and reduced the fretting damage at large amplitudes, but the fretting damage was not greatly influenced by the different environments at very small amplitudes (such as 14 μm), (2) instead of natural seawater, synthetic seawater was adequate for the investigations of fretting wear, but 3.07% NaCl solution was found not to be and (3) the ceramic Al₂O₃ was a potentially useful material against fretting wear under light loads in seawater.     

Tribological Behavior of Patterned PVD TiN Coatings on M2 Steel

A series of lubricated pin-on-disk wear experiments were performed to investigate the tribological behaviors of in-line (IN) and staggered (ST) patterned PVD TiN coatings as well as a fully TiN-coated (FC) coating on M2 steel against ASSAB 17 tool steel mating pins. The influence of applied load on the tribological behavior of the individual types of coating was also investigated. The experimental results showed that the tribological behavior of the two patterns and the FC M2 steel sliding against tool steel was a function of applied load. The wear resistance for any PVD TiN coating pattern was relatively higher at the specific individual loadings of 394, 800, 900 and 1100 N for 4 h under wet lubrication. Wear loss of the two types of patterned discs and pins was lower than that of the full coating counterpart. Wear mechanisms are suggested.     

Friction and wear properties of Ni–Cr–W–Al–Ti–MoS2 at elevated temperatures and self-consumption phenomena

The composites of Ni–Cr–W–Al–Ti–MoS₂ with different adding amount of molybdenum disulfide (6–20 wt.%) were prepared by powder metallurgy (P/M) method. Their mechanical properties and tribological properties from room temperature to 600 °C were tested by a pin-on-disk tribometer. The effects of amounts of molybdenum disulfide, temperature, load, and speed on the friction and wear properties of composite were discussed. Besides, the tribological properties against different counterface materials, such as alumina, silicon nitride and nickel-iron-sulfide alloys were also investigated. Results indicated that the molybdenum disulfide was decomposed during the hot-press process and the eutectic sulfides of chromium were formed. The hardness and anti-bending strength can be improved by adding 6 wt.% molybdenum disulfide due to reinforcement of molybdenum. The friction coefficients and wear rates of composites decrease with the increase of adding amount of molybdenum disulfide until a critical value of 12 wt.%. The composite with 12% MoS₂ shows the optimum friction and wear properties over the temperature range of RT 600 °C. The friction coefficients of composite with 12% MoS₂ decrease with the increase of temperature, load, and sliding speed, while the wear rates increase with the increasing temperature and are insensitive to the sliding speed and load. The friction coefficients of less than 0.20 at 600 °C and mean wear rates of 10⁻⁵ mm³/N m are obtained when rubbing against alumina due to the lubrication of sulfide films and glaze layer formed on the friction surface at high temperature, while a relatively low wear rate of around 10⁻⁶ mm³/N m presents when rubbing against nickel-iron-sulfide alloys. At high temperature, wear rates of composite containing sulfide are inversely proportional to friction coefficients approximately.     

Fretting damage of TiN coated zircaloy-4 tube

Fretting has been reported and investigated for over 50 years. However, it is still one of the modern plagues for several industrial machineries. Especially, fretting of fuel rod cladding material, zircaloy-4 tube, in pressurized water reactor (PWR) must be reduced and avoided. Thin hard coatings are employed to improve the tribological properties such as friction and wear of conventional engineering materials. Among these coatings, physical vapor deposition (PVD) TiN coating is probably one of the most frequently and successfully used PVD coatings for the mitigation of fretting wear. Therefore, in this study a fretting wear experiment was performed using TiN coated zircaloy-4 tube as the fuel rod cladding material and uncoated zircaloy-4 tube as one of the grids. The fretting tester was designed and manufactured for this experiment. The number of cycles, slip amplitude and normal load were selected as main factors of fretting. The type of contact was cylinder-to-cylinder contact. The worn surface was observed by optical microscope, 3-D surface measuring instrument and scanning electron microscope (SEM). The results of this research showed that the wear volume of TiN coated zircaloy-4 tube decreased about 1.2–3 times more than uncoated tube and wear mechanisms were brittle fracture, fatigue fracture, adhesion, abrasion and oxidation.     

Mechanical and tribological properties of nanostructured TiN/TiBN multilayer films

Nanostructured multilayer films of TiN/TiBN with different bilayer thicknesses (Λ) were deposited onto Si(1 0 0) wafers (for mechanical analyses) and AISI M42 tool steels (for tribological measurements) at room temperature by reactive unbalanced magnetron sputtering in an Ar–N₂ gas mixture. The effects of different Λ values on mechanical and tribological properties were studied by atomic force microscope (AFM), scanning electron microscope (SEM), microindentation measurements, Rockwell-C tester, nano- and micro-scratch tester, impact tester, pin-on-disc tribometer, and Fourier-transform infrared spectroscopy (FTIR). It was found that the mechanical and tribological properties of multilayer films (typically 1.4 ± 0.1 μm in thickness) were closely related to Λ (varied from 1.4 to 9.7 nm). For the best multilayer film with Λ = 1.8 nm, a maximum hardness of 29.5 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of L_C1 (37 N), L_C2 (>80 N) and the highest adhesion strength (HF1). Moreover, by the dynamic impact testing this multilayer film could endure impact cycles up to 4 × 10⁵ without adhesive failure. It was also found that the nano-scratch test under single-pass and constant-load conditions showed that the frictional coefficients decreased with Λ and increased with normal load due to the ploughing effect. The enhanced hardness in the multilayer films with small Λ values improved the wear resistance and lowered the frictional coefficients. The frictional coefficients obtained at 5 N were kept at 0.5 and increased from 0.52 to 0.65 when Λ increased from 1.8 to 9.7 nm at 2 N. By FTIR analyses, the multilayer films with Λ = 1.8 and 2.2 nm showed the presence of h-BN which provided a lubricating function resulted in lower frictional coefficients and wear rates. The tribological properties of the TiN/TiBN multilayer films with different Λ values are also explained in terms of mechanical properties and wear mechanisms.     

聚四氟乙烯基粘结固体润滑涂层微动磨损性能研究

在不同位移幅值与载荷条件下研究了酚醛环氧粘结聚四氟乙烯(PTFE)基固体润滑涂层的微动磨损特性，并利用扫描电子显微镜、表面轮廓仪和傅里叶表面红外仪等对涂层磨斑进行分析。结果表明，粘结PTFE基涂层具有良好的抗微动损伤性能，随循环次数的变化只存在部分滑移区和滑移区，部分滑移区的损伤轻微，滑移区的损伤强烈依赖于栽荷，其损伤与PTFE分子链在往复交变载荷作用下的疲劳断裂相关。     

Wear behavior of Pb–Mo–S solid lubricating coatings

Amorphous Pb–Mo–S coatings 200 to 510 nm thick were deposited by dual ion-beam deposition (IBD) onto steel and Si substrates. Coating wear studies were performed using ball-on-flat reciprocating sliding with steel ball counterfaces in dry air. Tests were run between 1 and 100,000 sliding cycles, and wear depths measured by interference microscopy. Morphology and chemistry of the as-deposited coatings and worn surfaces were investigated with optical microscopy, micro-Raman spectroscopy and cross-section high resolution transmission electron microscopy (HRTEM). Pb–Mo–S coatings were found to be quite wear resistant; no more than 25% of the coating thickness was removed by 10,000 sliding cycles. Two wear mechanisms were identified. At the nanometer scale, wear proceeded in a two-part process: transformation of the coating surface to MoS₂, then layer-by-layer removal of MoS₂. At the micrometer scale, wear occurred by plowing. The long endurance of Pb–Mo–S coatings was attributed to slow wear of the coatings, with lubricant redistribution processes playing a minor role.     

粘结MoS2固体润滑涂层的转动微动磨损特性

采用粘结法在LZ50钢表面制备MoS2固体润滑涂层,研究MoS2涂层及LZ50钢基体在干态不同角位移幅值下的转动微动磨损行为。在分析转动微动动力学特性的同时,结合光学显微镜、扫描电子显微镜、电子能谱仪以及轮廓仪对磨痕形貌进行微观分析。结果表明:涂层和基体的转动微动运行区域仅呈现部分滑移区(Partial slip regime,PSR)和滑移区(Slip regime,SR),未观察到混合区。涂层改变基体的微动运行区域,使得PSR缩小,SR运行区域向小角位移幅值方向移动。由于MoS2涂层的固体润滑作用,涂层的摩擦因数在整个试验过程都明显低于基体。在PSR,涂层损伤轻微;在SR,涂层的转动微动磨损机制主要表现为剥层和摩擦氧化。研究表明粘结MoS2固体润滑涂层具有明显的防护作用,显著降低LZ50钢的转动微动磨损。     

WEAR PERFORMANCE OF MULTILAYER-COATED CARBIDE TOOLS

Three multilayer-coated carbides [two trigon-shaped inserts: Ti(C,N)/TiC/Al₂O₃ (T1), Ti(C,N)/ Al₂O₃/TiN (T2) and one 80°-rhomboid shaped insert: TiC/Al₂O₃/TiN (T3)] were used to machine a martensitic stainless steel at various combinations of cutting speed and feed rate without coolant to assess their wear performance. Significant nose wear and chipping/fracture of the cutting edge were the predominant failure modes affecting tool performance at higher speed conditions. Plucking of tool materials was the main rake face wear phenomenon observed on T1 grade insert with alumina as the top-layer coating when machining at the lower speed conditions. Attrition and plastic flow were the main wear mechanisms observed on the ceramic coating layers, with dissolution-diffusion being the probable wear mechanism of the tool grades where tungsten carbide substrate had direct contact with the flowing chip. The fitted statistical wear models revealed T3 grade insert with 80°-rhomboid shape as having the highest speed-feed capability, resulting in the highest material removal rate relative to T1 and T2 grade inserts with trigon shapes.     

An investigation of the fretting behaviour of low friction coatings on steel

Three different low friction coatings on steel (electrolytically deposited cadmium, PTFE solid lubricant in epoxy resin and PTFE solid lubricant in polyimide resin) were studied in order to relate their fretting behaviour with mechanical properties. Particular importance was given to adhesion which was measured using a scratch test. Fretting tests were carried out on the steel substrate and on the coatings under the same conditions. The major parameters of the tribological system were identified and then quantified. The values of the parameters obtained for each coating were compared with the corresponding values for uncoated steel. The mechanical characteristics of the coatings and their fretting parameters were plotted using a polar diagram in order to give an overview of the fretting behaviour of each coating. Differences were noted and the corresponding parameters were identified. The influence of the adherence of the coating and of the fretting test load on the lifetime of the coating was determined.     

The study of the adhesion of a TiN coating on steel and titanium alloy substrates using a multi-mode scratch tester

A titanium nitride (TiN) coating was deposited by magnetron sputter ion plating onto steel and titanium alloy polished substrates. The adhesion of the coating on each substrate material was investigated using a newly developed multimode scratch tester. Progressive loading scratch tests, constant load scratch tests, multiple scratch tests in the same track and indentation tests were all performed. It was shown that the modified scratch tester can be used to identify not only coating detachment during progressive load scratch tests, but also other failure events such as cracking and cohesive damage to the coatings. By using the additional modes of operation, it was possible to study the fracture mechanisms in more detail i.e. chipping in the scratch track was cohesive for the TiN coated steel and adhesive for the TiN coated Ti alloy.     

Adhesion, friction and wear of thin hard coatings

Chemically vapour-deposited and physically vapour-deposited coatings of hard and wear-resistant materials such as TiC, TiN, Ti(C, N), Cr₇C₃, Al₂O₃, SiO₂ and TiO₂ as well as other carbides, nitrides, borides, oxides and combinations thereof are increasingly used in industrial applications to protect metal, ceramic and in certain cases polymer parts against mechanical and chemical attack, sometimes with a decorative purpose also. Some relevant examples of coated products are cemented carbide throwaway cutting tips (TiC, TiN, Ti(C, N), Al₂O₃ etc.), high speed steel drills and milling cutters (TiN), hobs, deep drawing tools, ball-bearing elements, gears, machine elements, electrical contacts, body implants, surgical instruments and tools, cutlery, fuel pins and armatures especially for helium- and sodium-cooled nuclear reactors, low Z sputter-resistant protective coatings on parts (limiters, antennae etc.) and walls of the torus in fusion reactors (tokamak) and gold- or silver- or black-coloured watch cases and jewelry pieces. The life of such coated tools or machine elements as well as their performance are considerably increased, provided that the adhesive strength of the coating to the base material and the intrinsic cohesion of the coating are sufficient. Bad adhesion leads to flaking (adhesive failure) while poor cohesion causes chipping (cohesive failure).     

人体皮质骨/纯钛接触副径向微动损伤研究

对新鲜人股骨皮质骨对纯钛球(直径10mm)接触副,在12mm/min加载速度下,分别以最大法向载荷100,200,300,400N进行径向微动实验研究。在动力学特性分析的基础上,用激光共聚焦显微镜和扫描电镜观察皮质骨表面的磨痕形貌。结果显示:随着载荷的增加,股骨皮质骨表现出不同的界面变形行为,损伤随之加重,而且裂纹的产生存在一个临界载荷;裂纹在骨表面主要有4种生长方式,以沿粘合线生长最常见。讨论了减缓骨/种植体界面径向微动损伤的措施,表明降低界面应力和种植体表面改性有利于减缓骨/种植体界面径向微动损伤。