40Cr超声表面滚压加工纳米化

采用超声表面滚压(Ultrasonic surface rolling extrusion,USRE)加工方法对调质态40Cr轴进行处理.通过对处理表层进行微观结构观察发现:该加工方法既可以使表层纳米晶粒细化至3～7nm,还可以使表面粗糙度水平降至0.05μm:USRE样品表面附近区域形成了厚度约为200μm的流变组织,且晶粒尺寸沿厚度方向呈现梯度分布.力学性能测试证明:USRE试件表面显微硬度提高了63%,表面残余应力最高为-846 MPa,压缩应力层深度可达1mm以上.摩擦磨损对比试验表明:USRE方法能够降低金属表面摩擦因数,提高其抗磨损性能.     

超声冲-滚处理工业纯钛焊接接头摩擦学性能研究

采用自行研制的超声冲-滚处理装置对工业纯钛焊接接头进行处理,分析不同工艺参数对工业纯钛焊接接头焊缝区域表面粗糙度、硬度的影响。结果表明:经超声冲-滚处理,材料表层晶粒尺寸均细化至纳米量级,变形层厚度可达320μm左右;试样表面的粗糙度略有增加;其硬度值由HV146.6提升至HV312.8,较未处理材料提高了113.4%。采用球盘式结构试验机对超声冲-滚处理试样进行干摩擦磨损实验,研究不同工艺参数对试样摩擦磨损性能的影响,用扫描电镜观察磨损后试样的表面形貌。结果表明:超声冲-滚处理试样摩擦因数与磨损量较未处理试样均有所减小,在冲击电流1 A、冲击时间9 min时达到最小值:超声冲-滚处理试样的磨痕更浅,磨损表面更平整,表明超声冲-滚处理明显改善了工业纯钛焊接接头摩擦磨损性能。     

超声表面滚压处理对45钢摩擦学性能的影响及机理

采用超声表面滚压处理(USRP)技术对45钢表面进行强化处理,通过表面形貌和表层显微组织观察、表面粗糙度和摩擦磨损性能测试,研究了USRP对该钢摩擦学性能的影响及机理。结果表明:USRP试样的表面粗糙度由未处理试样的3.2μm降低到0.23μm;显微组织得到了细化,晶粒取向趋于随机分布,有大角度晶界出现;表面显微硬度比未处理试样的提高约56%,强化层厚度达到400μm;USRP试样的摩擦因数小于未处理试样的,磨损量为未处理试样的1/4;未处理试样磨损过程中表面材料呈"片块状"脱落,磨损机制为黏着磨损,USRP试样磨损表面上存在犁皱形成的沟槽,磨损机制为磨粒磨损。     

GH4169 高能喷丸表面纳米化的研究

采用GH4169高温舍金进行高能喷丸表面纳米化试验,通过X射线衍射、透射电镜、扫描电镜、能谱及硬度测试等方法对不同时间喷丸后材料表面晶粒尺寸、形貌以及变形层硬度进行分析.结果表明:喷丸5 min实现表面纳米化,表面晶粒尺寸约为58.25 nm,随着喷丸时间的延长,晶粒逐渐细化,在喷丸30 min时,表层晶粒尺寸约为21.41 nm,强烈变形层深度达到8 μm,表面硬度约为HV480,继续延长时间,表层晶粒尺寸变化不大,在喷丸120 min时,表层晶粒尺寸约为20.27 nm,表面硬度约为HV600,强烈变形层深度达到40 μm.     

银固体润滑涂层低温下摩擦磨损性能

采用磁控溅射在镍基合金718基底上沉积了8μm银基自润滑涂层,用XRD对涂层相结构进行表征;在真空条件下对不同温度下涂层的摩擦磨损性能进行研究;用扫描电镜SEM及能谱仪EDS对磨痕形貌和成分进行观察测试。结果表明:所制备的银固体润滑涂层结晶良好,涂层表面均匀致密,与基底结合性能良好,晶粒尺寸约为200nm;银涂层具有良好的摩擦磨损性能,常温25℃下磨痕呈较深的犁沟状,磨损机制以磨粒磨损和黏着磨损为主; 0℃时,涂层表层内部局部地方出现裂纹和孔洞,发生了严重磨损;-50℃时,摩擦因数最低,磨损量最小,一层光滑且较软的银基润滑膜生成并粘附在硬质摩擦副表面,增加了润滑效果,磨损机制以轻微的黏着磨损为主;温度继续降低到-100℃时,磨痕表面重新出现犁沟状痕迹,磨损机制主要以脆性断裂的剥层磨损为主。     

超高强度钢热场-超声复合滚压表层微观组织强化机制

针对超高强度钢冷塑性变形能力弱、表面形变强化难度大的问题,提出热场-超声复合滚压强化方法。开展45CrNiMoVA钢表面热场-超声复合滚压试验,利用SEM、EBSD和TEM等检测手段,结合表面层残余应力分布结果,表征、分析表层微观组织的演变与强化机制。发现在声软化效应和热软化效应耦合作用下,热场-超声复合滚压后45CrNiMoVA钢表层材料的塑性变形程度加剧,塑性变形层深度增加,表层材料发生晶粒细化,形成沿深度方向晶粒尺寸呈梯度分布的微观组织结构,细晶强化和位错强化是主要的强化机制。证明了热场-超声复合滚压方法的有效性,对超高强度钢零件表面强化处理技术的发展具有重要意义。     

表面滚压处理对EA4T车轴钢疲劳性能的影响

表面强化可提高高速列车车轴疲劳性能，延长使用寿命。对广泛应用于高速列车的EA4T车轴钢表面进行滚压处理，使用激光共聚焦显微镜表征表面形貌和粗糙度；借助光学显微镜分析滚压处理前后试样的显微组织，并采用EBSD测试滚压试样表层晶粒尺寸；采用显微硬度计测试强化层显微硬度分布并与未处理试样进行对比，采用X射线衍射残余应力分析仪分析其残余应力分布；基于旋转弯曲疲劳试验和扫描电子显微镜下的断口观测分析试样的疲劳性能。研究结果显示：滚压强化后，试样表层发生塑性变形，表面质量得到改善，且形成厚度约为400μm的硬化层，表层产生纳米晶；显微硬度提高了29%,表面最大残余应力为-576MPa,试样显微硬度和残余应力变化趋势一致，均为从表面向心部减小；滚压试样疲劳强度增幅为28%。试验结果表明，滚压是车轴延长寿命的一种有效方式。     

表面纳米化是否生成纳米晶

喷丸或滚压和摩擦磨损的表面具有相同本质,都是冷加工导致组织细化.20世纪七八十年代从摩擦学角度对表面变形组织进行了系统研究,所得结论已成为材料学教材中的重要内容.21世纪初纳米风带动表面纳米化(SMAT)研究,忽视已有成果,认为变形细化的组织就是纳米晶.早期研究已经明确,变形后组织细化的尺度对性能影响不大,关键因素是其...     

表面纳米化预处理对1Cr18Ni9Ti不锈钢渗硫层摩擦学性能的影响

用超声速微粒轰击表面纳米化技术在1Cr18Ni9Ti不锈钢表面制备了晶粒尺寸约为30 nm的具有随机取向的等轴状纳米晶表层,后用低温离子渗硫技术在部分纳米化样品和原始样品表面分别制备了硫化物层.在YTи-1000型球盘式摩擦磨损试验机上对比研究了干摩擦条件下纳米化处理前后的1Cr18Ni9Ti不锈钢及两种渗硫试样的摩擦学性能.结果表明,纳米化处理明显提高了1Cr18Ni9Ti钢的摩擦学性能和低温离子渗硫的效果,纳米化表面的摩擦因数由0.65降低到0.45,而纳米化预处理后渗硫层厚度由1 μm增加到3.5μm.分析认为,这些性能的提升主要与纳米晶表面层具有较高的硬度、强度和化学活性有关.原始1Cr18Ni9Ti钢的主要磨损机制为磨料磨损和粘着磨损,而表面纳米化处理后转变为以疲劳磨损为主.     

填充纳米SiO2对超高分子量聚乙烯复合材料摩擦磨损性能的影响

用热压成型法制备了纳米SiO2填充超高分子量聚乙烯(UHMWPE)复合材料,采用销-盘式摩擦磨损试验机考察了纳米粒子对复合材料摩擦磨损性能的影响,采用扫描电子显微镜观察了复合材料磨损表面形貌,并借助X射线能谱仪对试样磨损表面进行了微区分析。结果表明:纯UHMWPE磨损表面局部存在着大量的粘着变形和疲劳裂纹的特征,填充15%(质量分数)的纳米SiO2能较好地改善UHMWPE/nano-SiO2复合材料的摩擦磨损性能,其磨损表面只存在粘着撕裂现象,看不到疲劳裂纹特征。当填充纳米SiO2质量分数达到20%时,其磨损表面存在贫Si区和富Si区,同时磨损表面呈现出热裂纹迹象,复合材料的耐磨性能改善程度明显下降,并且摩擦因数出现了增大趋势。     

Friction and wear behaviors of nanocrystalline surface layer of pure copper

Surface mechanical attrition treatment (SMAT) was employed to fabricate a nanocrystalline surface layer on a pure copper plate. The grain size is about 10 nm in the top layer and increases with an increasing depth from the treated surface. The tribological behavior of the nanocrystalline surface layer was investigated under dry conditions. Experimental results show that the load-bearing ability is markedly enhanced with the nanocrystalline surface layer relative to the coarse-grained form. The friction coefficient of the nanocrystalline layer is lower than that of the coarse-grained copper when the applied load is below 20 N. With increase of the load, the difference in wear resistance between the SMAT and the conventional Cu decreases. When the load exceeds 40 N, for the SMAT Cu, there occurs a transition of wear regime from local damage to delamination of a mechanical mixed layer. There is an abrupt increase of the wear volume, which corresponds to the wearing away of the nanocrystalline layer. The enhanced wear properties of the nanocrystalline surface layer are correlated with the stability of the mechanical mixed layer and the high hardness of the nanocrystalline structure.     

Formation of Friction Layers in Graphene-Reinforced TiAl Matrix Self-Lubricating Composites

The friction layer structure has been proved to be formed during severe plastic deformation and markedly improves the tribological properties of material. The dry friction and wear performance of graphene-reinforced TiAl matrix self-lubricating composites (GTMSC) at different sliding velocities are systematically researched. GTMSC show the best tribological properties and special friction layer structure containing a wear-induced layer and a grain refinement layer with a nanocrystalline (NC) structure under surface after sliding at a sliding speed of 1.1 m/s. Nanoindentation results show that the grain refinement layer has a higher hardness and elastic modulus than the wear-induced layer. This special microstructure of friction layers beneath the surface after sliding leads to a low coefficient of friction and high wear resistance of GTMSC. Moreover, it is deduced that the appearance of an NC structure results in hardening of the material. The formation mechanisms of friction layers are researched in detail. It can be concluded that the formation of a wear-induced layer results from frictional heat and fracture of the counterpart. The formation of a grain refinement layer is due to severe plastic deformation and dynamic recrystallization. Severe plastic deformation results in the formation of an NC structure and dynamic recrystallization leads to grain refinement.     

ENHANCEMENT OF SURFACE QUALITY AND TRIBOLOGICAL PROPERTIES USING BALL BURNISHING PROCESS

Surface treatment is an important aspect of all manufacturing processes to impart specific physical, mechanical and tribological properties. Burnishing process is a post-machining operation in which the surface of the workpiece is compressed by the application of a ball or roller to produce a smooth and work-hardened surface by plastic deformation of surface irregularities. In the present study, simple and inexpensive burnishing tools, with interchangeable adapter for ball and roller were designed and fabricated to meet the requirements of the present study. Then, ball burnishing processes were carried out on aluminium 6061 under different parameters and different burnishing orientations to investigate the role of burnishing speed, burnishing force and burnishing tool dimension on the surface qualities and tribological properties. The results showed that burnishing speed of 330 rpm and burnishing force of 160 N produce optimum results. Meanwhile, a decrease in the burnishing ball diameter leads to a considerable improvement in the surface roughness up to 75%. On the other hand, parallel burnishing orientation exhibits lower friction coefficient compared to cross burnishing orientation. Furthermore, ball burnishing process is capable of improving friction coefficient by 48% reduction and weight loss by 60–80% reduction of burnished surface of Aluminum 6061. These findings are further supplemented by the surface features as seen in SEM photomicrographs.     

四种牙科高分子修复材料摩擦学行为的对比研究

在往复滑动摩擦磨损试验台上以TA2纯钛为对摩材料,研究和比较了4种我国口腔临床常用牙科高分子修复材料在人工唾液介质中的摩擦磨损行为。结果表明在人工唾液介质中,3种成品树脂牙的摩擦因数、磨痕深度均较小,磨损表面主要呈现犁削效应;光固化树脂修补材料的摩擦因数大,耐磨性较差,磨损形貌以剥落为主,伴随犁削。     

Fretting wear behavior of nanocrystalline surface layer of copper under dry condition

Unlubricated fretting tests were performed with a nanocrystalline surface layer of a 99.99 wt.% copper fabricated by means of surface mechanical attrition treatment (SMAT), in comparison with a coarse-grained (CG) copper. The measured friction and wear data show that the fretting wear resistance is markedly enhanced with the nanocrystalline surface layer relative to the CG counterpart. The friction coefficient and wear volume of the SMAT Cu are lower than that of the CG Cu. For both samples, the friction coefficients and wear volumes increase with an increasing applied load and fretting frequency. A rapid increase of the friction coefficient and wear volume under an applied load above a critical value (30 N for the SMAT Cu and 20 N for the CG Cu) is noticed, corresponding to the formation of a continuous oxide layer between two contact surfaces. Also two sharp increases of the friction coefficient and wear volume at fretting frequencies of 50 Hz and 175 Hz were observed for the SMAT and the CG Cu. The former is correlated with the formation of a continuous oxide layer, while the latter corresponds to wearing away of the oxide layer.     

Optimum film thickness of thin metallic coatings on silicon substrates for low load sliding applications

The frictional behaviour of thin metallic films on silicon substrates sliding against 52100 steel balls is presented. The motivation of this work is to identify an optimum film thickness that will result in low friction under relatively low loads for various metallic films. Dry sliding friction experiments on silicon substrates with soft metallic coatings (silver, copper, tin and zinc) of various thickness (1–2000 nm) were conducted using a reciprocating pin-on-flat type apparatus under a controlled environment. A thermal vapour deposition technique was used to produce pure and smooth coatings. The morphology of the films was examined using an atomic force microscope, a non-contact optical profilometer and a scanning electron microscope. Following the sliding tests, the sliding tracks were examined by various surface characterization techniques and tools. The results indicate that the frictional characteristics of silicon are improved by coating the surface with a thin metallic film, and furthermore, an optimum film thickness can be identified for silver, copper and zinc coatings. In most cases ploughing marks could be found on the film which suggests that plastic deformation of the film is the dominant mode by which frictional energy dissipation occurred. Based on this observation, the frictional behaviour of thin metallic coatings under low loads is discussed and friction coefficients are correlated with an energy based friction model.     

双辉光离子渗铜对缸套-活塞环摩擦学性能的影响*

为研究铜元素对缸套-活塞环摩擦学性能的影响,通过双辉光离子渗透技术在缸套材料表面加工出不同厚度的渗铜改性层,使用RTEC多功能摩擦磨损试验机开展不同负载、不同润滑条件下的模拟试验,采集并分析试验过程中的摩擦因数以及试验后体积磨损量和磨损表面形貌,研究渗铜改性层对缸套材料摩擦学性能的影响规律及作用机制。结果表明：渗铜处理可有效降低缸套-活塞环摩擦副的摩擦因数,减少磨损量;高载荷和干摩擦条件下渗铜改性层的减摩抗磨作用效果尤为显著,最高可使摩擦因数分别降低13.15%和30.86%,磨损量分别降低30.70%和38.57%;渗铜后缸套-活塞环磨损表面形貌平整,摩擦表面形成了铜含量较高的润滑膜层,该表面膜起到了减摩、耐磨的作用。     

Effect of preliminary ball burnishing on wear resistance of the nitrided VT22 alloy

The effect of combined treatment on the tribotechnical properties of VT22 titanium alloy has been investigated. The combined treatment consisted of previous cold surface plastic deformation (ball burnishing) and subsequent thermodiffusion saturation of the surface by nitrogen. It was set that, in order to achieve high wear resistance of the VT22–BrAZhN 10-4-4 friction pair, it is necessary to carry out the ball burnishing at small loads, increasing the number of passes before nitriding.     

选择性激光熔化技术制备的Cu-10Sn合金的载流摩擦学性能

为提高Cu-10Sn合金接触线的力学及载流摩擦学性能,利用选择性激光熔化（SLM）技术制备Cu-10Sn合金,分析Cu-10Sn合金的组织结构及硬度等,研究不同载荷和电流对Cu-10Sn合金的载流摩擦学行为的影响;利用扫描电子显微镜对摩擦表面进行微观分析,揭示其磨损机制。试验结果表明：与载荷为10 N时相比,30 N时摩擦副的平均摩擦因数增大,接触电阻和电弧能量降低,磨损加剧;Cu-10Sn合金与GCr15球对摩,合金表面被氧化,铜元素被转移并粘附于对摩球上形成黏着磨损;与纯机械摩擦行为相比,载流条件下Cu-10Sn合金表面磨痕加深,黏着物、氧化物的数量明显增加,摩擦因数和磨损体积发生显著变化;小载荷小电流下磨痕表面出现电弧烧蚀现象;而电流为10 A时,磨损表面形成的氧化膜的润滑作用,减缓了材料的磨损。在无电流条件下磨损机制主要为疲劳磨损和黏着磨损;而在载流条件下,电化学氧化和黏着磨损显著增强。研究结论为SLM技术制备的铜锡合金应用于接触线等电传导接触材料提供参考。     

Improvement of surface conditions of 36 Cr Ni Mo 6 steel by ball burnishing process

Ball burnishing, a mechanical surface treatment, is becoming more popular as a finishing process. As results ball burnishing is noticed as a very simple way of surface mirror finishing and surface work-hardening. Applying the optimal input parameters, a pre-machined surface roughness Ra about of 3.01 μm can be finished to approximately 0.30 μm, whereas an initial hardness HRA about 66.35 can be increased to 71.33. A metallographic observation and some measurement of micro-hardness show that the depth of penetration strengthened by plastic surface deformation (PSD) reaches 100 μm. Results analysis show that burnishing force, burnishing ball radius and number of ball burnishing tool passes have the most significant effects on both surface responses (Ra and HRA). For the generating of high surface qualities and strengthening superficial layers, an alternative to chip-forming process and heat treatments can be given by ball PSD process.