Friction and Wear Behavior of WS2/Zr Self-lubricating Soft Coatings in Dry Sliding Against 40Cr-Hardened Steel Balls

WS₂ and WS₂/Zr self-lubricating soft coatings were produced by medium-frequency magnetron sputtering, multi-arc ion plating and ion-beam-assisted deposition technique on the cemented carbide YT15 (WC + 15 % TiC + 6 % Co) substrates. Microstructural and fundamental properties of these coatings were examined. Sliding wear tests against 40Cr-hardened steel using a ball-on-disk tribometer method were carried out with these coated materials. The friction coefficient and wear rates were measured with various applied loads and sliding speeds. The wear surface features of the coatings were examined using SEM. The results showed that the WS-1 specimen (with WS₂/Zr composite coating) has higher hardness and coating/substrate critical load compared with that of the WS-2 specimen (only with WS₂ coating). The friction coefficient of WS-1 specimen increases with the increase in applied load and is quite insensitive to the sliding speed. The wear rate of the WS-1 specimen is almost constant under different applied loads and sliding speeds. The WS-1 specimen shows the smallest friction coefficient and wear rate among all the specimens tested under the same conditions. The WS-1 specimen exhibits improved friction behavior to that of the WS-2 specimen, and the antiwear lifetime of the WS₂ coatings can be prolonged through adding Zr additives. The self-lubricating and wear mechanism of the WS₂/Zr coating was also found from the sliding wear tests.     

Wear behavior of AISI D2 steel by enhanced ion nitriding with atomic attrition

An experimental study was performed to investigate the effect of atomic attrition on wear behavior of AISI D2 steel. Wear tests were conducted under three different loads (5, 10, and 20 N) and sliding speeds (100, 200, and 500 rpm), using ball-on-disk type tester and SiC ball. After wear test, the specimen nitrided with ion bombardment showed superior wear behavior. The enhanced hardness by ion bombardment could have a beneficial effect on increased wear resistance. In addition, a wider and more adhesive oxide layer formed on the worn surface of ion-bombarded specimen, because of the rougher structure on the surface by ion bombardment, could lead the surface to withstand wear for longer duration time, acting as a protective layer.     

Fe52Cr15Mo26C3B1Y3非晶金属含量对酚醛树脂基摩擦材料性能的影响

以Fe基非晶金属代替传统的润滑组元,采用热压成型法制备Fe₅₂Cr₁₅Mo₂₆C₃B₁Y₃/酚醛树脂摩擦材料,探究不同含量的非晶金属对摩擦材料性能的影响;利用SEM对摩擦材料磨损面进行观测,分析不同含量非晶金属对摩擦材料磨损机制的影响。结果表明:添加非晶金属后摩擦材料硬度得到提升,其中非晶金属质量分数为30%～40%的试样硬度在67.6HRB和73.6HRB之间,为摩擦材料合适的硬度范围;随非晶金属质量分数的增加,材料的体积磨损率逐渐降低,平均摩擦因数呈先减小后增加的趋势,当非晶金属质量分数40%时试样的摩擦因数最小;随着非晶金属含量的增加,材料的磨损机制由接触疲劳磨损逐渐转变为磨粒磨损为主,并伴随着轻微接触疲劳磨损的混合机制。     

Synergy Effect of Ultrasonic Nanocrystalline Surface Modification and Laser Surface Texturing on Friction and Wear Behavior of Graphite Cast Iron

Laser surface texturing (LST) followed by an ultrasonic nanocrystalline surface modification (UNSM) process was applied to graphite cast iron to improve the friction and wear behavior. The surface hardness of the UNSM-treated and UNSM + LST-treated specimens was increased significantly compared to the polished and LST-treated specimens. The friction and wear behavior of the specimens was assessed using a ball-on-disk friction tester at an applied load of 10 N and a speed of 5 cm/s in both dry and lubrication conditions. The friction coefficient of the UNSM-, LST-, and UNSM + LST-treated specimens reduced in both dry and lubrication conditions compared to the polished specimen by 64, 30, and 64% and 63, 67, and 75%, respectively. In lubrication condition, the friction coefficient of the UNSM- and LST-treated specimens was further reduced by about 30 and 25% by UNSM + LST processes. In dry condition, the UNSM + LST-treated specimen exhibited a reduction in the friction coefficient of 46% compared to the LST-treated specimen, whereas no reduction in friction coefficient was found compared to the UNSM-treated specimen. The wear resistance of the UNSM-, LST-, and the UNSM + LST-treated specimens was enhanced by 22, 11, and 37% in the dry condition, respectively, whereas minuscule wear was observed in the lubrication condition that was difficult to quantify in our experiment. UNSM and LST processes were effectively combined to improve the friction and wear behavior of graphite cast iron.     

A study on the tribological characteristics of duplex-treated Ti–6Al–4V alloy under oil-lubricated sliding conditions

The tribological characteristics of the polished, dimpled and over-coated dimpled specimens were investigated. Dimples were produced on a Ti–6Al–4V alloy specimen using a laser surface texturing (LST). A Cr-doped diamond-like carbon (DLC) film was deposited on a dimpled specimen using an unbalanced magnetron sputtering (UBMS). The effects of dimples and over-coated Cr-doped DLC film on the tribological characteristics were investigated by performing the friction tests against a Cr-plated steel pin. The test results showed that the over-coated dimpled specimen exhibited a lower friction coefficient and wear compared to those of the polished and dimpled specimens, which may be attributed to the storage of wear debris and high hardness. A model of the wear reduction mechanism of the specimens was discussed.     

The influence of surface oxidation on the wear resistance of cast iron

This paper reports a study of the influence of surface oxidation on the wear resistance of ductile iron, grey iron and vermicular iron during dry sliding friction. The mechanisms of wear are also reported. This study shows that the effect of surface oxidation (formed under normal atmospheric conditions) on the wear rate depends on the complex functions of graphite morphology and matrix structure. Generally the presence of surface oxidation decreases the wear rate of grey iron but increases the wear rate of ductile iron and vermicular iron when the cast iron has high hardness. This trend is reversed for low hardness cast iron.     

Effect of Cold Rolling on the Fretting Wear Behavior and Mechanism in Inconel 600 Alloy

The fretting test was carried out using an SRV IV fretting test rig in order to investigate the fretting wear behavior and mechanism in Inconel 600 alloy at room temperature. The materials were rolled to different reductions before the test. The effect of cold rolling on the friction coefficient and wear volume was subsequently investigated. The surface and cross-sectional morphologies of the wear scar were studied by scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM), and electron back-scattering diffraction (EBSD). The results indicated that the cold rolling had a different effect on wear behavior in different slip regimes. In the stick regime, cold rolling strongly decreased the wear volume, although it did not affect the friction coefficient. The 25% rolled specimen had the minimum wear volume. The mechanisms of as-received and 50% rolled specimens were delamination and oxidation wear, whereas for the 25% rolled specimen, cracking was the main wear mechanism. In the gross slip regime, cold rolling had little effect on the friction coefficient or wear volume. The fretting wear process gave rise to a decrease in the Σ3 grain boundary, an increase in local misorientation, and a change in the crystal orientation.     

Fretting wear behavior of nitrogen ion implanted titanium alloys in bovine serum lubrication

Nitrogen ion implantation was performed on biomedical titanium alloys by using of the PBII technology to improve the surface mechanical properties for the application of artificial joints. The titanium nitride phase was characterized with X-ray photoelectron spectroscopy (XPS). The nanohardness of the titanium alloys and implanted samples were measured by using of in-situ nano-mechanical testing system (TriboIndenter). Then, the fretting wear of nitrogen ion implanted titanium alloys was done on the universal multifunctional tester (UMT) with ball-on-flat fretting style in bovine serum lubrication. The fretting wear mechanism was investigated with scanning electron microscopy (SEM) and 3D surface profiler. The XPS analysis results indicate that nitrogen diffuses into the titanium alloy and forms a hard TiN layer on the Ti6Al4V alloys. The nanohardness increases from 6.40 to 7.7 GPa at the normal load of 2 mN, which reveals that nitrogen ion implantation is an effective way to enhance the surface hardness of Ti6Al4V. The coefficients of friction for Ti6Al4V alloy in bovine serum are obviously lower than that in dry friction, but the coefficients of friction for nitrogen ion implanted Ti6Al4V alloy in bovine serum are higher than that in dry friction. Fatigue wear controls the fretting failure mechanism of nitrogen ion implanted Ti6Al4V alloy fretting in bovine serum. The testing results in this paper prove that nitrogen ion implantation can effectively increase the fretting wear resistance for Ti6Al4V alloy in dry friction, and has a considerable improvement for Ti6Al4V alloy in bovine serum lubrication.     

A comparative study on the tribological behaviors of nitrided and sulfur-nitrided 35CrMo steel lubricated in PAO base oil with MoDTC additive

A nitrided layer on 35CrMo steel was prepared by the ion nitriding process, and then a sulfur-nitrided layer was obtained by low temperature ion sulfuration. The results showed that both the nitrided and sulfur-nitrided surfaces improved the wear resistance efficiently under PAO lubrication, and exhibited the best wear resistance and friction-reducing property under PAO with 0.75% MoDTC lubrication. Compared with the plain and nitrided surfaces, the sulfur-nitrided surface exhibited the best synergistic effect with MoDTC displaying the lowest friction coefficient and wear volume. The mechanism of the best effect was due to MoS₂ and FeS formed on the sulfur-nitrided surface.     

不同方法表面改性碳纤维增强热塑性聚酰亚胺复合材料的摩擦磨损性能

采用硝酸氧化改性和涂层复合改性法分别对碳纤维(CF)进行了表面处理,并制备了CF增强热塑性聚酰亚胺(TPI)复合材料;对CF的表面形貌进行了观察,研究了表面改性方法对复合材料摩擦磨损性能的影响,并利用扫描电子显微镜观察了磨损表面形貌。结果表明:硝酸氧化改性增大了CF的表面粗糙度,随处理时间的延长粗糙度增大;经涂层复合改性后,CF表面包覆了一层聚酰亚胺(PI),保护了CF并提高了其与基体界面的结合强度;经表面改性后的CF增强TPI复合材料的摩擦磨损性能均得到提高,以涂层复合改性的效果最好;硝酸氧化改性后的CF在摩擦过程中易断裂,复合材料的磨损形貌以磨粒磨损为主,而涂层复合改性后的CF断裂得到抑制,与基体结合更为牢固,磨损表面较为平整。     

矿用钛合金钻杆表面复合强化与摩擦性能研究*

为提高矿用钛合金钻杆的耐磨性能,以低成本粉末冶金Ti-Al-Fe-Mo合金为研究对象,采用表面机械碾磨与固相渗碳相结合的创新方式对其表面进行复合强化处理,研究不同表面碾磨道次加渗碳处理的钛合金表面的微观组织及其显微硬度。以氮化硅球为摩擦对偶,对表面复合强化钛合金样品进行往复式滑动摩擦试验,研究钛合金表面强化层对其磨损量、摩擦因数、表面磨痕微观组织的影响规律。结果表明：表面机械碾磨方法可以在粉末钛合金表面形成梯度纳米晶结构;钛合金经过表面机械碾磨处理后可显著提高表面渗碳的深度和均匀度;经表面机械碾磨与固相渗碳复合强化处理的钛合金,其磨损量相比于单一表面渗碳的钛合金降低了近58%。表面复合强化的钛合金摩擦磨损机制以疲劳磨损、黏着磨损、氧化磨损和少量的磨粒磨损为主。     

SLM成形表面织构对TC4钛合金干摩擦磨损性能的影响

基于一步法思路,采用金属3D打印机基于激光选区熔化（SLM）技术制备表面带有凹坑织构的TC4钛合金试样,采用光学相机、超景深显微镜和扫描电镜观察织构成形情况,利用激光共聚焦位移测试仪和显微维氏硬度计分别测试表面粗糙度和表面硬度,在干摩擦条件下采用摩擦磨损试验仪考察不同载荷下织构密度对TC4钛合金试样摩擦学性能的影响,并使用扫描电镜对摩擦实验前后的表面形貌进行分析。研究结果表明：一步法SLM成形能够在TC4钛合金表面获得成形良好的直径500 μm的织构;随着织构密度的提高,钛合金试样表面粗糙度增大,表面硬度有所降低;干摩擦条件下,提高TC4钛合金试样织构密度有利于磨屑的收集从而减少试样的三体磨损,提高载荷有利于改善摩擦副接触状态;5 N载荷下40%织构密度试样的平均摩擦因数和磨痕宽度均最小,与无织构试样相比,平均摩擦因数和磨痕宽度分别降低12%和16%;40%织构密度下,载荷提高会引起摩擦因数的降低和磨损量增大,磨损表面犁沟和片状剥落增多。在干摩擦条件下,3D打印一步法制备的表面织构可以显著改善TC4钛合金的磨粒磨损和黏着磨损。     

Effects of Contact Pressure and Sliding Speed on the Unlubricated Friction and Wear Properties of Zn-15Al-3Cu-1Si Alloy

The unlubricated friction and wear properties of Zn-15Al-3Cu-1Si alloy were studied over a range of contact pressure (1–5 MPa) and sliding speed (0.5–2.5 ms^?1) for a sliding distance of 2,500 m using a block-on-disc type test machine. It was observed that as the contact pressure increased, the friction coefficient of the alloy decreased but its working temperature, surface roughness, and wear volume increased. Sliding speed had no significant effect on the friction coefficient of the alloy but increased its working temperature, surface roughness, and wear volume. It was also observed that the formation of a hard and brittle surface layer had a great influence on the wear behavior of the experimental alloy. The hardness and thickness of this layer increased with increasing contact pressure and sliding speed. However, contact pressure was found to be much more effective on the hardness of the surface layer of this alloy. Both adhesion and abrasion were observed to be the dominant wear mechanisms for the alloy under the given sliding conditions. The results obtained from the friction and wear tests are discussed in terms of the test conditions and microstructural changes that take place during sliding.     

Method of implementation of the positive gradient of mechanical properties of triboengineering materials

Modern methods of implementation of the rule of positive gradient of mechanical properties are considered; this rule was formulated by I.V. Kragelskii and its application serves to minimize the friction and wear of solids. The given methods include the application of coatings with the method of finishing antifricton abrasion-free treatment; application of new metal-cladding lubricating materials; and creation of a nanostructural state of the surface iron nitride layer by nitriding steel with a positive gradient of hardness normal to the surface.     

Comparative study of the tribological properties of various modified mild steels under boundary lubrication condition

AISI1045 steel was modified by laser heat-treatment and conventional heat treatment. The friction and wear behaviors of the steel specimens after various surface modifications sliding against SAE52100 steel under the lubrication of liquid paraffin containing sulphurized olefin were comparatively investigated on an Optimol SRV oscillating friction and wear tester. The worn surface morphologies of the modified steel specimens were analyzed using a scanning electron microscope. The elemental compositions and chemical states of some typical elements on the worn surfaces of the modified steel specimens were analyzed with an energy dispersive X-ray analyzer and X-ray photoelectron spectroscope, respectively. It was found that the laser heat-treated specimen showed the highest hardness and best wear-resistance. The laser heat-treated and conventionally heat treated AISI1045 steel specimens sliding against SAE52100 steel under the lubrication of liquid paraffin containing sulphurized olefin registered smaller friction coefficients than under the lubrication of liquid paraffin alone. This was partly attributed to the increased hardness of the modified specimens. The tribochemical reaction between the steel and the active elements in the additive was involved in the sliding of the modified steel specimens against SAE52100 steel ball under the boundary lubricating condition, with the formation of a surface protective film composed of various tribochemical products. This also contributed to improve the friction and wear behavior of the modified steel specimens. The steel specimens subject to different surface modifications showed differences in the wear mechanisms under the boundary lubricating condition as well. Namely, the tempered steel specimen was mainly characterized by plastic deformation and pitting, the quenched specimen by grooves and delaminating, and the laser heat-treated one by polishing and mild adhesion.     

铜锡铅锌合金的摩擦磨损性能

利用MMU-200型摩擦磨损试验机研究了铜锡铅锌合金与GCr15钢对磨时的摩擦磨损特性,利用扫描电子显微镜对合金的磨损表面形貌进行了观察。结果表明:铜锡铅锌合金的磨损率随载荷和摩擦速度的增加而增大;其摩擦因数随摩擦速度的增加而减小,随载荷的增加先增大后减小;其磨损机制主要为磨粒磨损和粘着磨损;合金中的铅相起到了润滑作用,有利于提高合金的耐磨性能。     

Wear resistance of highly cross-linked and remelted polyethylenes after ion implantation and accelerated ageing

Ion implantation may provide medical polyethylenes with excellent mechanical and tribological properties, helping to lower the risk of long-term osteolysis. Highly crosslinked and remelted polyethylenes, materials currently used as soft components in artificial joints, were implanted with N+ and He+ ions at different ion fluences. The mechanical and tribological properties under distilled water lubrication at body temperature were assessed after ion implantation by means of microhardness and pin-on-disc tests respectively. Thus, the influences of the ionic species and implantation dose on surface hardness, friction coefficient, and wear factor were fully characterized. Furthermore, the tribological behaviour was evaluated after an accelerated ageing protocol (120 degrees C for 36h). Ion implantation increased the surface hardness, as well as friction coefficients, and decreased the wear factors especially at the highest doses. Also, even though all artificially aged materials showed a worse wear behaviour, polyethylenes implanted with either N+ or He+ at the highest doses maintained a relatively good wear factor in comparison with the aged non-implanted material. The origins of these modifications are discussed according to the effects of ion implantation on the microstructure of the polymer.     

Vacuum Tribological Properties of Titanium Enhanced via Ultrasonic Surface Rolling Processing Pretreatment and Plasma Nitriding

For the purpose of enhancing the vacuum friction-reducing and antiwear performance of UNS R50400 Ti, ultrasonic surface rolling processing (USRP) has been introduced as pretreatment of plasma nitriding (PN). Various nitriding temperatures from 650 to 950°C have been adopted to investigate the effects of USRP pretreatment on plasma nitriding of Ti. The results of experiments show that the friction-reducing and antiwear performance are enhanced by USRP pretreatment when the PN temperature is below 750°C, resulting from the formation of thicker and harder nitriding layer with a reasonable gradient structure. Nevertheless, USRP pretreatment results in a rough surface and a large-sized columnar crystal gradient structure when the PN temperature is above 750°C, leading to poor vacuum tribological performance. In aggregate, USRP pretreatment is an effective pretreatment to decrease the optimized plasma-nitriding temperature from 850 to 750°C.     

电沉积稀土改性陶瓷涂层磨损性能研究

探讨了在电火花加工机床上沉积碳化钛金属陶瓷涂层方法,利用TiC,WC,Mo,N i粉未添加不同比例稀土元素在高压下压制并烧结了试验电极,在45#钢表面沉积了不同稀土含量的TiC陶瓷涂层,并用扫描电镜(SEM)、X射线衍射仪(XRD)、显微硬度计、环块式磨损试验机对涂层组成、组织形态进行、硬度及摩擦学性能分别进行了研究,并结合试验结果进行了理论分析。试验结果表明:用电火花放电法可沉积TiC陶瓷涂层,涂层中加入质量分数为0.5%的氧化镧后,涂层的耐磨性能较未加稀土涂层提高了3倍,摩擦因数减少10%,而加入过多的稀土镧氧化物则不利于涂层组织性能及耐磨性能的改善。稀土氧化镧对涂层的组织有改善作用,加入适量的稀土元素使得涂层致密性提高,减少涂层中的缺陷,涂层表面呈多孔结构特性。     

FDM 3D打印聚醚醚酮零件摩擦磨损特性研究

为研究3D打印各向异性对摩擦性能的影响,通过熔融沉积成型(FDM)制备了0°、45°、90°3种打印角度的聚醚醚酮(PEEK)试样,研究3种不同打印角度及载荷变化对PEEK试样摩擦学性能及磨损机制的影响。利用MFT-5000摩擦磨损试验机对PEEK材料进行室温水润滑下的往复滑动摩擦试验,用超景深显微镜观察磨损后表面形貌。试验结果表明：不同载荷下3种打印角度试样的摩擦因数由大到小依次为0°试样、90°试样、45°试样,磨损率由大到小依次为90°试样、45°试样、0°试样;随着载荷的增大,3种不同打印角度试样的摩擦因数均呈现下降趋势,磨损率则呈现上升趋势;PEEK磨损机制是黏着磨损以及疲劳磨损引起的表层脱落。