Friction and wear properties of Fe–Mo intermetallic compounds under oil lubrication

In this study several disc specimens of three different compositions of the Fe–Mo system were prepared by spark plasma sintering and annealing, and their friction and wear properties were investigated. It was found that, when ASTM 52100 steel balls were used as the paired materials, both the Fe–42 at% Mo and Mo disc specimens exhibited lower friction coefficients and lower wear rates than the Fe and cast iron disc specimens. It was also found that the spark plasma-sintered Fe–42 at% Mo disc specimens without any heat treatments exhibited lower friction coefficients than those annealed at 1323 K for 172.8 ks. According to the XPS analysis, iron oxides and iron sulfides were found on the worn surfaces of the Fe disc specimens that were slid against the ASTM 52100 steel balls, while molybdenum oxides such as MoO₂, but not MoS₂, were observed on the worn surfaces of the annealed Fe–42 at% Mo and Mo disc specimens that were slid against the steel balls.     

WC等离子喷涂涂层摩擦磨损特性研究

采用自制的销盘式摩擦磨损试验机、光学显微镜,研究了WC等离子喷涂涂层与GCr15钢配副的摩擦磨损特性.结果表明:WC涂层的耐磨性能比基体材料(HT250)提高了两个数量级,摩擦系数高于灰铸铁,对配副材料造成的磨损率基本相当.因此,WC涂层可显著提高钢铁制动摩擦副的使用性能和使用寿命.     

不锈钢与GFER及CFRPEEK在海水润滑下的摩擦磨损特性

为了寻找适合于低速大扭矩海水液压马达的各摩擦副之间的配对材料,分别以不锈钢(316L和9Cr18Mo)与玻纤环氧复合材料(GFER)及碳纤维增强聚醚醚酮(CFRPEEK)为摩擦副,利用MMU-5G屏显式高温材料端面摩擦磨损试验机对摩擦副在海水中接触表面的温度、摩擦因数和摩擦磨损状况进行了测试,并通过激光共聚焦显微镜对接触表面的磨损形貌进行分析。结果表明:不锈钢/GFER的摩擦因数随着时间的变化在0.3~0.4间波动且幅度较大,而不锈钢/CFRPEEK的摩擦因数随着时间的增加稳定在0.1左右;不锈钢/GFER所引起海水温升的幅度也远远高于不锈钢/CFRPEEK;不锈钢/GFER的接触表面出现了大面积的涂抹与擦伤,且磨损程度要大于不锈钢/CFRPEEK;不锈钢316L的耐腐蚀性优于9Cr18Mo。由此可知,316L/CFRPEEK较适合作为低速大扭矩海水液压马达的摩擦副材料。     

CrAISiN涂层与不同材料配副时的摩擦学特性

目的 研究CrAlSiN涂层分别与304不锈钢、TC4钛合金、Al2O3陶瓷和GCr15钢四种不同材料配副时的摩擦学特性.方法 采用阴极电弧离子镀技术在M35高速钢上制备了CrAlSiN涂层,采用扫描电镜(SEM)、显微硬度计、划痕仪、球-盘式摩擦磨损试验仪和3D轮廓仪分别测试了涂层的结构和性能.结果 CrAlSiN涂层与304不锈钢、TC4钛合金和GCr15钢配副时的磨损形式为粘着磨损和磨粒磨损,其中与亲和性高的304不锈钢、TC4钛合金粘着磨损严重.CrAlSiN涂层与不锈钢对磨时,摩擦系数最高,达到0.71;与GCr15钢对磨时,摩擦系数最低,但摩擦系数波动大;与钛合金对磨时,摩擦系数介于两者之间.CrAlSiN涂层与亲和性较差的Al2O3陶瓷之间的磨损形式为磨粒磨损,随着磨损的进行,摩擦系数逐渐降低.结论 CrAlSiN涂层与亲和性较高的材料对磨时,磨损形式为粘着磨损和磨粒磨损,与亲和性较差的Al2O3对磨时为磨粒磨损.     

Effect of Annealing Temperature on Tribological Properties and Material Transfer Phenomena of CrN and CrAlN Coatings

This study evaluates the effects of annealing temperature and of the oxides produced during annealing processes on the tribological properties and material transfer behavior between the PVD CrN and CrAlN coatings and various counterface materials, i.e., ceramic alumina, steel, and aluminum. CrAlN coating has better thermal stability than CrN coating in terms of hardness degradation and oxidation resistance. When sliding against ceramic Al₂O₃ counterface, both CrN and CrAlN coatings present excellent wear resistance, even after annealing at 800 °C. The Cr-O compounds on the coating surface could serve as a lubricious layer and decrease the coefficient of friction of annealed coatings. When sliding against steel balls, severe material transfer and adhesive wear occurred on the CrN and CrAlN coatings annealed at 500 and 700 °C. However, for the CrAlN coating annealed at 800 °C, much less material sticking and only small amount of adhesive wear occurred, which is possibly due to the formation of a continuous Al-O layer on the coating outer layer. The sliding tests against aluminum balls indicate that both coatings are not suitable as the tool coatings for dry machining of aluminum alloys.     

Friction and wear of Si3N4 ceramic/stainless steel sliding contacts in dry and lubricated conditions

Austenitic stainless steel AISI 321 is one of the most difficult-to-cut materials. In order to investigate the wear behavior of Si₃N₄ ceramic when cutting the stainless steel, wear tests are carried out on a pin-ondisk tribometer, which could simulate a realistic cutting process. Test results show that the wear of Si₃N₄ ceramic is mainly caused by adhesion between the rubbing surfaces and that the wear increases with load and speed. When oil is used for lubrication, the friction coefficient of the sliding pairs and the wear rate of the ceramic are reduced. A scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), and an energy dispersive x-ray analyzer (EDXA) are used to examine the worn surfaces. The wear mechanisms of Si₃N₄ ceramic sliding against the stainless steel are discussed in detail.     

Depassivation of some metals by sliding friction

Nickel, TA6V4 alloy and 316L stainless steel were passivated in aerated sulphuric acid solution (0.5 M), and submitted to sliding friction against a loaded alumina ball. The effects of sliding speed and normal applied load on tribological behaviour of the passivating films were analyzed. Friction coefficients were measured and the metal wear rates were deduced from 3D profilometry recordings on the wear tracks. Current variations were also measured during friction tests and the results are discussed in terms of depassivation-repassivation kinetics induced by the passivating film breakdown. The effects of sliding speed and applied load on the depassivation kinetics and thus current enhancement due to friction were particularly studied. The Passivating film formed on nickel surface shows the best resistance to friction and wear, whereas TA6V4 alloy shows the worst behaviour. The Passivating film on this alloy wears easily leading to a high material consumption. 316L stainless steel situates between the two other materials.     

WC-(W,Cr)_2C-Ni/Ag复合涂层的制备及摩擦学性能

针对众多运动部件存在严重的摩擦磨损问题,使用大气等离子喷涂(APS)设备在1Cr18Ni9Ti不锈钢金属基材上喷涂制备WC-(W,Cr)2C-Ni和WC-(W,Cr)2C-Ni/Ag两种防护涂层,使用CSM摩擦磨损试验机考察两种涂层在室温下与Si3N4球配副时的滑动摩擦磨损性能。结果表明:Ag相的添加可明显降低涂层在干摩擦条件下的摩擦因数,并能减轻涂层的磨损程度;APS制备的WC-(W,Cr)2C-Ni/Ag复合涂层不仅具有优良的自润滑性能,而且具有极佳的耐磨性能,有望作为一种新型耐磨自润滑涂层材料。     

Microstructure, Mechanical Properties and Wear Behaviourof Deep-Cryogenic-Treated HSS

In this paper we compare the wear behaviour of a vacuum-heat-treated ESR AISI M2 high-speed steel and the same steel that was vacuum heat treated in conjunction with a deep-cryogenic treatment at -196 ~C. Four different tempering temperatures for the specimens austenized at the same austenitizing temperature were carefully selected to obtain various in-advance-determined combinations of the microstructures, the fracture toughness, Kic and the Rockwell-C hardness. Each of the eight specimens was therefore characterised by these microstructures and resulting material properties.The wear study was performed using a reciprocating sliding device under well-controlled contact conditions. Relatively high loads were used to provide enough wear for a comparison of the selected samples. A much harder and dissimilar model counter-material, i.e. silicon nitride ceramic, was used in order to avoid excessive wear of the counter samples and adhesion,which could occur in contacts with similar materials (metals/steels) under such high loads and in non-lubricated conditions.The wear behaviours were then compared and discussed in terms of these microstructures and the related properties. The differences in the wear resistance obtained in our investigation were as high as an order of magnitude. However, the beneficial effects are not a direct result of the type of the treatment, but relate to a proper combination of the resulting fracture toughness and the hardness. The more uniform and moderate values, which, however, tend to be obtained with a deep-cryogenic treatment, are beneficial to the high wear resistance of the selected high-speed steel.     

Tribological behaviors of Zr-based bulk metallic glass versus Zr-based bulk metallic glass under relative heavy loads

As a novel engineering material, bulk metallic glass (BMG) has received much attention. However, the knowledge concerning the tribological behavior of BMG versus BMG under relatively heavy loads is still insufficient. In this study, Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 metallic glass pins and discs were prepared by copper-mold suction casting. The dry sliding friction and the wear characteristics of the as-cast Zr-based BMG versus Zr-based BMG were tested under loads of 100, 125 and 150 N, respectively, using a pin-on-disc tribological apparatus at room temperature. The worn surfaces were studied by scanning electron microscopy in order to identify the wear mechanisms. The results showed that both the coefficient of friction and the wear rate increased with both the normal load and the rotational sliding velocity. X-ray diffraction patterns recorded after the tribological experiments indicated that no sliding-induced crystallization occurred. Transmission electron microscopy was also used to confirm the amorphous of the BMGs after sliding tests. In addition, the wear mechanisms changed with the experimental conditions. For a normal load of 100 N, the main mechanisms were abrasive wear, slight grooves and micro-cracks. For higher loads, adhesive wear was predominant, accompanied by abrasive wear and deeper grooves and more micro-cracks. When the rotational sliding velocity was increased, the dominant wear changed from slight grooves to viscous flow and adhesive wear.     

TRIBOLOGICAL AND HIGH SPEED TURNING PERFORMANCE IN Ti1-xAlxN COATINGS PREPARED BY CLOSE-FIELD UNBALANCED MAGNETRON SPLTTERING

Titanium-aluminium-nitride (Ti1-xAlxN) coatings were deposited by close-field unbalanced magnetron sputtering on M42 steel substrates and WC-6wt%Co inserts at 450℃. The tribological behavior was analyzed by sliding against steel and WC-6wt%Co balls, while the turning performance was evaluated by a conventional turning machine at high cutting speeds without using coolants. In the tribological tests, the formation of transfer layer and the variations of hardness of the coatings played an important role for sliding against steel balls. For the coatings sliding against WC-6wt%Co balls, the Ti-Al-N coatings showed a similar friction coefficient, but the TiN coating exhibited a lower value. The difference could be explained by the tri-oxidation wear mechanism. In the turning tests, a superior cutting performance of the coating was found at x=0.45, which endured 38 minutes before the tool flank wear reached the maximum value of 0.3mm, whereas only 20 minutes were endured for the TiN coating. The excellent performance of the coatings in the turning tests could be explained by the enhanced mechanical properties and oxidation/diffusion resistance of the coatings.     

High-temperature tribological properties of CrAlN, CrAlSiN and AlCrSiN coatings

Cr-Al-Si-N coatings with high and low Cr/Al ratios (CrAlSiN and AlCrSiN, respectively) were deposited on WC substrates by cathodic arc and compared with a reference Cr-Al-N coating. The silicon content was close to 3 at.%. X-ray diffraction analysis showed that CrAlN and CrAlSiN coatings exhibited the cubic Cr(Al)N structure, whereas in AlCrSiN a mixture of cubic Cr(Al)N and wurtzite-type AlN was identified. All three coatings showed excellent thermal stability and oxidation resistance up to 800 °C. The tribological properties were evaluated by ball-on-disk tribometer in the temperature range 25-600 °C. Two materials were used as counterparts: alumina and 440C steel. Sliding against 440C steel balls led to the extensive wear of the balls and transfer of the ball material to the surface of the coatings. The coatings were not damaged. When sliding against alumina balls, the coating wear was low up to testing temperature 300 °C. At 400 °C, CrAlSiN coating was partially worn through. CrAlN and AlCrSiN coatings were almost immediately worn out at 600 °C. The analysis of the wear debris identified high-temperature adhesive failure of the coatings.     

Tribological studies of a Zr-based bulk metallic glass

In the present study, the tribological behavior of a Zr_52.5Cu_17.9Ni_14.6Ti₅Al₁₀ bulk metallic glass (BMG) was investigated using pin-on-disk sliding measurements under an argon atmosphere, rubbing against a type 303 stainless steel counterface. The tested pins and disk were examined using X-ray diffractometry, optical microscopy, profilometry, scanning electron microscopy and transmission electron microscopy. The results showed that the wear of the BMG pins was substantially larger compared with previous tests performed against a zirconia counterface. Strain softening was found in the near-surface region of the glassy pin due to the highly localized shearing. Frictional heating contributed to the occurrence of viscous flow and material transfer on the worn surface of the wear pin and the disk, respectively. Thus, the pin exhibited a severe adhesive-dominated sliding wear.     

Sliding behavior and wear mechanism of iron and cobalt-based high-temperature alloys against WC and SiC balls

The sliding behaviors of two typical high-temperature alloys of GH2132 and GH605 against WC and SiC balls were investigated at environments from room temperature to 800 °C with a sliding speed of 50 to 125 m/min under a load of 10 to 20 N. The wear performances of high-temperature alloys, WC and SiC balls were rated and their mechanisms were discussed. The four sliding pairs exhibited the markedly different sliding behaviours, in which the GH2132/WC sliding pair had the maximum friction coefficient with 125 m/min under 10 N at room temperature. The variation trends of ball wear rates with the ambient temperature were at odds with those of friction coefficient. The higher friction coefficient did not always lead balls to suffer from the higher wear rate. The maximum worn depth approximated to 250 μm for the GH2132/WC sliding pair with higher friction coefficient. The GH605/WC sliding pair exhibited the lower friction coefficient and lower worn depth of plate. Whether at room temperature or high temperature, the GH605/SiC sliding pair significantly exhibited good wear resistance with a minor damage of ball and plate despite of its higher friction coefficient.     

The correlation between the hardness and tribological behaviour of electroplated chromium coatings sliding against ceramic and steel counterparts

Electroplated chromium (Cr) coatings with different hardness were electrodeposited on steel substrate through adjusting the concentration of rare earth in a Sargent bath (CrO₃ 250 g/l, H₂SO₄ 2.5 g/l). The results show that with a Si₃N₄ ceramic counterpart, the wear rate of electroplated Cr coatings increases with the increase of the hardness owing to the delamination wear mechanism; while with a steel counterpart, the wear rate of electroplated Cr coatings decreases with increasing hardness thanks to the abrasion wear mechanism. The wear mechanism may be dictated by the adhesive force between the sliding pairs and the possibility of abrasive particles formation that weak adhesive force between the ceramic counterpart and electroplated Cr coatings can hardly result in the adhesion, transfer of material and formation of abrasive particles on the tribosurface of the electroplated Cr coating, and the frictional shear energy tends to transform to dislocation and deformation energy stored inside the material instead of friction heat; therefore, the delamination wear is more likely to occur on the tribosurface. Whereas, the strong adhesive force between the steel counterpart and electroplated Cr coatings will result in the adhesion, transfer of material and formation of the abrasive particles on the tribosurface, the frictional shear energy would be allowed to transform to cutting and plough energy; hence, the adhesive and abrasive wear may occur.     

滑动速度对团球共晶体增强奥氏体钢基自生复合材料摩擦学性能的影响

利用MPx-2000型主轴盘销式磨损实验机和扫描电子显微镜(SEM)研究了相对滑动速度对团球γ (Fe，Mn)3c共晶体增强奥氏体钢基自生复合材料(EAMc)摩擦学性能的影响．实验表明，在干摩擦磨损工况下，EAMc对G45钢摩擦系统的摩擦系数随相对滑动速度的增加呈递减趋势；而磨损率呈递增趋势，但始终远低于奥氏体中锰钢(单一奥氏体相)；并且，随着相对滑动速度的提高，EAMC与中锰钢磨损量的差值呈递增趋势．通过对磨损表面和磨屑形貌的分析，发现EAMC在低载下主要磨损机制是磨粒磨损与剥层磨损；高载下的磨损机制主要为剥层磨损与氧化磨损．对偶件之间的粘着作用随相对滑动速度的提高而增加．运用临界转变温度理论与Archard磨损理论分析了相对滑动速度对EAMC摩擦学性能影响的机制．     

Friction and Wear Behavior of Plasma-Sprayed Al2O3-13 wt.%TiO2 Coatings Under the Lubrication of Liquid Paraffin

Two types of ceramic composite coatings (denoted as N-AT13 coating and M-AT13 coating) were fabricated on 1Cr18Ni9Ti stainless steel substrate from ultra-fine and coarse Al₂O₃-13%TiO₂ feedstocks by air plasma spraying. The friction and wear behavior of as-prepared coatings sliding against Al₂O₃ and stainless steel balls under the lubrication of liquid paraffin was evaluated with an SRV friction and wear tester (Optimol, Germany). The fractured and worn surfaces of the coatings were observed using a scanning electron microscope and a field-emission scanning electron microscope; and the wear mechanisms of the coatings were discussed based on scanning electron microscopic analysis and energy dispersive spectrometric analysis. Results show that N-AT13 coating possesses a unique microstructure and strong inter-splat bonding, thereby showing increased microhardness and bonding strength as well as much better friction-reduction and wear resistance than M-AT13 coating. Moreover, there exist differences in the wear mechanisms of N-AT13 and M-AT13 coatings which slide against ceramic and stainless steel balls under the lubrication of liquid paraffin. Namely, with the increase of normal load, the burnishing of N-AT13 coating coupled with Al₂O₃ ball is gradually transformed to grain-abrasion and deformation, while M-AT13 coating is dominated by grain-pullout and brittle fracture in the whole range of tested normal load.     

Wear behavior of Al2O3-TiCN composite ceramic sliding on stainless steel

It is well known that austenitic stainless steel AISI302 is relatively difficult to cut. In order to investigate the wear behavior of Al₂O₃-TiCN composite ceramic when machining austenitic stainless steels, a blockon-ring tribometer was used to simulate a real machining process. The test results showed that the wear of both the ceramic and the stainless steel increased rapidly with increasing load and speed. The boundary lubrication actions of water and oil used in this test could not reduce the wear of the rubbing materials. Scanning electron microscopy and energy-dispersive x-ray spectroscopy analyses identified material transferred between the ceramic and the stainless steel surfaces in rubbing process. On the one hand, stainless steel transferred on the ceramic surface because of adhesion; on the other, some ceramic fragments caused by microfracture of the ceramic were found to be embedded in the worn stainless steel surface. The wear of Al₂O₃-TiCN ceramic sliding against stainless steel was caused primarily by adhesion between the rubbing surfaces and the microfracture of the ceramic.     

Friction and Wear Behavior of AlTiN-Coated Carbide Balls Against SKD11 Hardened Steel at Elevated Temperatures

In this study, AlTiN coatings were deposited on YT14 cemented carbide balls by arc ion plating technique. The friction and wear behavior of the AlTiN-coated balls against SKD11 hardened steel was investigated by sliding tests using a ball-ondisk tribometer at various temperatures from 25 to 700 °C in air. The results showed that the friction and wear behavior was significantly influenced by the testing temperature. Obvious fluctuations were observed in the friction curves at elevated temperatures, which could be attributed to the formation and rupture of unstable Fe and Cr oxide layers. As the temperature increased from 25 to 500 °C, the wear rate of the coated balls increased from the scale of 10~(-21)–10~(-20) m~3/N m, and then decreased to 10~(-22) m~3/N m as the temperature further increased to 700 °C. It was also found that the friction and wear behavior of the coated balls was directly dependent on the counterpart materials. As the temperature increased, the main wear mechanism of the coated balls changed from mild abrasive wear and adhesive wear to abrasive wear failure at 500 °C, and then transferred to adhesive wear and mild oxidation wear at 700 °C. For SKD11 hardened steel, the primary wear mechanism changed from delamination wear to abrasive wear and then transferred to plastic deformation and fatigue wear, accompanied by adhesive wear and tribo-oxidation wear.     

Wear and transfer characteristics of carbon fiber reinforced polymer composites under water lubrication

The tribological characteristics of carbon fiber reinforced polymer composites under distilled-water-lubricated-sliding and dry-sliding against stainless steel were comparatively investigated. Scanning electron microscopy (SEM) was utilized to examine composite microstructures and modes of failure. The typical chemical states of elements of the transfer film on the stainless steel were examined with X-ray photoelectron spectroscopy (XPS). Wear testing and SEM analysis show that all the composites hold the lowered friction coefficient and show much better wear resistance under water lubricated sliding against stainless steel than those under dry sliding. The wear of composites is characterized by plastic deformation, scuffing, micro cracking, and spalling under both dry-sliding and water lubricated conditions. Plastic deformation, scuffing, micro cracking, and spalling, however, are significantly abated under water-lubricated condition. XPS analysis conforms that none of the materials produces transfer films on the stainless steel counterface with the type familiar from dry sliding, and the transfer of composites onto the counterpart ring surface is significantly hindered while the oxidation of the stainless steel is speeded under water lubrication. The composites hinder transfer onto the steel surface and the boundary lubricating action of water accounts for the much smaller wear rate under water lubrication compared with that under dry sliding. The easier transfer of the composite onto the counterpart steel surface accounts for the larger wear rate of the polymer composite under dry sliding.