Mechanical properties of tribologically modified nano‐layers

Wear in modern mechanical systems is characterised by ultra‐low wear rates in the range of a few nanometres per hour. Both the surfaces of the materials involved and their volumes undergo modification as regards morphology, crystalline arrangement, and chemical composition. The depth of tribological interactions for given conditions is in the order of a micrometre or less. Synchrotron‐based X‐ray diffraction and nano‐indentation were used to probe these thin modified zones. The specimens were taken from tribometric experiments employing the radionuclide technique as the ultimate tool to measure ultra‐low wear rates. To obtain different degrees of tribological interaction various loads and sliding velocities were applied. The specimens were classified according to the total power dissipated during the tribometric experiment.     

Interaction between friction surfaces and lubricating materials of the 2H-MoS2 type

The paper presents an analysis of investigations concerning the concept of the molecular-mechanical origin of the friction and fatigue mechanism as applied to solid lubricants having a structure of the 2H-MoS₂ type.     

Fluoropolymer composites of triboengineering purposes

The effect of polymer filler F-4MB on the properties of a composite based on polytetrafluoroethylene (PTFE) and magnesium nanospinel has been studied. The filler was found to exert a plasticizing effect on the polymer system. This promotes the formation of mobile interfacial layers, intensifies interfacial interaction between the composite components, and initiates a strong effect of nanospinel on strength and triboengineering characteristics of the composite. To provide adaptation of the polymer composite surface layer to frictional conditions, a plasticizing additive F-4MB is introduced during friction.     

Effect of a combined machining/burnishing tool on the roughness and mechanical properties

Burnishing is a cold working surface treatment process in which plastic deformation of surface irregularities occurs by exerting pressure through a very hard and a very smooth roller or ball on a surface to generate a uniform and work‐hardened surface. This treatment occurs generally after the machining process. In this study, a new combined machining/burnishing tool is designed and is fabricated. This tool allows for generating simultaneously the machining (turning) and the burnishing of the cylindrical surface using a turning machine. First, turned surfaces at different conditions, sketches, finishing and half finishing were performed using only the cutting tool. The evolutions of a surface roughness parameter and the technological time relative to every test condition have been investigated. Second, using the combined machining/burnishing tool at coarse conditions, the evolutions of the surface roughness and the technological time have been also investigated. A comparison among the parameters obtained under different machining conditions and those obtained using the combined machining/burnishing tool has been carried out. Moreover, the analyses of the layers obtained on the combined machined/burnished surface have shown that the burnishing process induces compressive residual stresses on the subsurface treated specimens. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of rare earths on mechanical and tribological properties of carbon fibers reinforced PTFE composite

The effect of a rare earth (RE) surface treatment on the mechanical and tribological properties of carbon fiber (CF) reinforced polytetrafluoroethylene (PTFE) composites was experimentally investigated. The tensile properties of the CF reinforced PTFE (CF/PTFE) composites treated with air oxidation and RE modifier were superior to those of untreated CF/PTFE composites, while RE treatment was most effective in promoting the tensile strength and strain at break of the CF/PTFE composite. The bending strength of the RE treated CF/PTFE composite was improved by about 16% compared with that of untreated composites, while 2% improvement was achieved by air oxidation. Under oil-lubricated conditions, RE treatment was more effective than air oxidation to reduce the friction coefficient and wear of PTFE composite. RE treatment effectively improved the interfacial adhesion between CF and PTFE. The strong interfacial coupling of the composite made CF not easy to detach from the PTFE matrix, and prevented the rubbing-off of PTFE, accordingly improved the friction and wear properties of the composite.     

Microstructure and mechanical properties of sheep horn

The sheep horn presents outstanding mechanical properties of impact resistance and energy absorption, which suits the need of the vehicle bumper design, but the mechanism behind this phenomenon is less investigated. The microstructure and mechanical properties of the sheep horn of Small Tailed Han Sheep (Ovis aries) living in northeast China were investigated in this article. The effect of sampling position and orientation of the sheep horn sheath on mechanical properties were researched by tensile and compression tests. Meanwhile, the surface morphology and microstructure of the sheep horn were observed using scanning electron microscopy (SEM). The formation mechanism of the mechanical properties of the sheep horn was investigated by biological coupling analysis. The analytical results indicated that the outstanding mechanical properties of the sheep horn are determined by configuration, structure, surface morphology and material coupling elements. These biological coupling elements make the sheep horn possess super characteristics of crashworthiness and energy absorption through the internal coupling mechanism. We suppose that these findings would make a difference in vehicle bumper design. Microsc. Res. Tech. 79:664–674, 2016. © 2016 Wiley Periodicals, Inc.     

Effect of copper content on the mechanical and sliding wear properties of monotectoid-based zinc-aluminium-copper alloys

One binary zinc-aluminium monotectoid and five ternary zinc-aluminium-copper alloys were produced by permanent mould casting. Their wear properties were examined using a block-on-ring test machine. Hardness, tensile strength and percentage elongation of the alloys were also determined and microhardness of aluminium-rich α phase was measured.It was observed that the hardness of the alloys increased continuously with increasing copper content up to 5%. Their tensile strength also increased with increasing copper content up to 2%, but above this level the strength decreased as the copper content increased further. Microhardness of the aluminium-rich α phase was also affected by the copper content in a manner similar to that of the tensile strength. It was found that the wear loss of the alloys decreased with increasing copper content and reached a minimum at 2% Cu for a sliding distance of 700 km. However, the coefficient of friction and temperature due to frictional heating were found to be generally less for the copper containing alloys than the one without the element. The effect of copper on the wear behaviour of the alloys was explained in terms of their microstructure, hardness, tensile strength, percentage elongation and microhardness of the α phase.     

Influence of ion bombardment on tribological properties of UHMWPE

Medical grade UHMWPE-s: GUR 1020 and 1050, were subjected to ion bombardment with H₂⁺, He⁺, Ar⁺ or Ag⁺ of different energy and various doses. The work presents changes to micromechanical profiles and surface morphology (AFM, SEM) of polyethylenes due to the treatment. Mechanisms behind the modification have been proposed owing to structural and chemical analyses by s-SIMS, FTIR-IRS, confocal Raman microscopy and “nuclear depth profiling”. Studies revealed that hardness of the surface layer increases due to radiolysis, probably leading to cross-polymerization of polyethylene. The depth of modification is limited to the penetration of ion beam, being dependent on a dose and a kind of ions applied. The treatment results additionally in oxidation, which together with a development of the surface geometry is responsible for its hydrofilization and, in some cases bacteriostatic character. Friction and wear of polyethylenes under a high load, adequate to extreme conditions of exploitation of hip joints, can be reduced even by three times, due to a proper ion beam treatment.     

青年与老年手指甲表面形貌、成分与力学性能的实验分析

应用红外光谱仪、场发射扫描电镜、差示扫描热量仪、原位纳米力学测试系统对青年(20~25岁)与老年(70~75岁)指甲的表面结构、形貌、水含量及力学性能进行了实验分析。结果表明:与青年组成员指甲相比,老年组成员指甲的PO 2、C-O、CH 2与CONH基团的峰位向高波数移动;老年组成员指甲表面比青年组成员指甲粗糙并表现出明显的纵向纹理;尽管其总含水量与青年组成员指甲相当,但老年组成员指甲结合水的含量比青年组成员指甲的低;老年组成员指甲的硬度与约化弹性模量均高于青年组成员指甲相应对比量,因此,老年组成员指甲在划痕实验中显示出更好的耐磨性,但在较大载荷时出现明显的裂纹。     

Influence of the processing route on microstructure and mechanical properties of the polycrystalline NiAl

The influence of grain refinement on the mechanical properties of differently processed NiAl was presented. Five NiAl near‐stoichiometric alloys were investigated, three conventionally cast and two sintered from powders (fine‐grained powder made by mechanical alloying and nanopowder made by gas condensation). The mechanically alloyed and cast materials were hot extruded at different conditions to obtain diverse grain sizes. The nanomaterial was synthesized in inert gas condensation and then compacted at 1.4 GPa at 300 °C. It was shown that the ductility and strength can be directly controlled by appropriate texture and grain refinement.     

热处理工艺对Ni36CrTiAl合金组织和力学性能的影响

为研究时效处理工艺对Ni36CrTiAl显微组织和力学性能的影响,对Ni36CrTiAl冷轧合金分别进行600℃、630℃、650℃、680℃、700℃时效处理,通过金相显微镜分析组织特征并测试力学性能指标。结果表明,650℃～680℃时效处理,析出的强化相细小均匀,强度和塑性都明显增加,而大于700℃时效后,强化相尺寸增大,强度和塑性随时效温度的升高而下降。确定680℃×3h时效处理后,具有适宜的强化及塑性的配合。     

变能量激光选区熔化IN718镍基超合金的成形工艺及高温机械性能

开展了基于激光选区熔化技术对IN718镍基超合金直接激光熔化成形的研究。将零件分为心部与轮廓区,通过改变激光线输入量进行选区熔化研究。首先,建立熔池内烧结的数值模型,改变激光线输入量,获得了激光线输入量对零件致密度的影响规律并观察了成形体中的组织生长。然后,增加轮廓部位扫描,改变激光线输入量与扫描顺序,获得其对零件表面质量的影响规律。最后,通过优化热处理工艺提高零件高温拉伸强度和高温持久性能。试验结果表明,在激光线输入量为300J/m时,成形体致密度最高,为98.9%,成形体沿层间方向组织为树枝晶加等轴晶,在层内方向组织为等轴晶。采用心部+后轮廓扫描的方式,轮廓激光线输入量为100J/m时表面质量最优,粗糙度为3.1μm。对成形体采用1 065℃固溶+双时效的热处理可以获得最佳高温性能组合,高温拉伸强度为1 356MPa,高温持久时间为34h。结果显示,通过激光选区熔化制作IN718镍基超合金可以满足航空结构件对致密度、表面质量和高温性能要求。     

The influence of added carbon nanotubes on the properties of the carbon‐fiber‐reinforced paper‐based wet clutch friction materials

Different carbon nanotubes (CNT) content was used to investigate the influence on physical properties, microstructure, tribological behaviour and thermal endurance properties of the materials. Experimental results show that the bulk density of the specimens increase with the increase of the CNT content, and the open porosity of the samples gradually reduced, whereas the CNT content increases. When comparing the tribological properties of the specimens with different CNT content, specimens that contain 4 wt.% carbon nanotubes show the highest dynamic friction coefficient and the lowest variation coefficient of the dynamic friction coefficient. Moreover, the specimens exhibit more thermal stability and lower weight loss after adding the CNT. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of temperature fields on wear of nonmetallic materials at abrasive machining

Wear characteristics of silicate glass and sapphire at abrasive machining have been studied. The data obtained and the analysis of images of worn surfaces have allowed the authors to conclude that two modes of material damage run simultaneously; these are the local melting of the glass followed by its squeezing towards the contact exit and periodical fatigue fracture (growth of microcracks). Under a short-term effect of high thermal stresses the glass was found to undergo thermal cracking even outside the contact site. The crystalline material (sapphire) demonstrated anisotropy of fatigue strength under abrasive wear, when its wear rate in two perpendicular directions differed almost by an order of magnitude. The possibility of sapphire damage outside the contact site is explained by the position of the maximal surface temperature region being some distance ahead of the zone of the abrasive tool-blank contact.     

同心连接器的力学性能测试技术和系统研究

为了能快速测量同心连接器插拔过程中的力学性能和准确评价机械寿命,研制了一种同心连接器的力学性能测试系统。该系统主要由运动模拟的机械装置和传感测量与电机控制的测控子系统组成,具有四路同步自动测试能力;根据连接器测试标准分析系统的性能指标,提出一种直线运动与旋转运动相结合的测试方法,使测试条件更加符合连接器真实使用情况;同时设计出具有自适应能力的柔性夹具,减少安装误差对测试结果的影响;对运动模拟机构进行建模分析研究,在极限速度条件下确定插拔循环周期内直线与旋转运动配合时序。对连接器样品进行单次和多次插拔测试,分析数据得到了连接器的力学性能并对机械寿命评估验证,实验结果表明该系统满足测试要求且能得到预期效果。     

假肢接受腔硅胶材料的力学性能研究

采用HY0580的压缩试验机,在反复压缩模式下模拟假肢接收腔/硅胶材料界面,研究了4种不同表面结构的硅胶内衬套材料的力学压缩性能。结果表明:4种不同表面结构的硅胶内衬套材料在载荷分别为0.5 N、3 N、7 N、10 N的试验工况下进行压缩试验时,都是在相同载荷(4.5 N)时出现平台期;在同等载荷的情况下,因1和4号硅胶材料正反两面均为光面,表面微凸体不高,粗糙度较小,2和3号材料与皮肤接触的反面上微凸体较高,粗糙度较大,故1号和4号材料的变形比2号和3号小,说明材料表面的各种纹路对缓解皮肤的压力有一定作用,硅胶材料反面上的粗大微凸体,增加了与皮肤的粘结性,有利于降低皮肤摩擦损伤的风险,提高残肢患者穿戴舒适性。     

激光处理对人牙釉质酸蚀和耐磨性能的影响

以人牙釉质为研究对象,对牙釉质表面进行激光处理,对激光处理前后牙釉质的表面形貌、力学性能和耐磨性能进行分析,旨在探索激光处理对牙齿酸蚀的抑制和修复作用,为激光在牙齿酸蚀抑制方面的临床应用提供理论指导。结果表明,原始牙釉质表面和酸蚀牙釉质表面经激光处理后,其表面硬度均显著提高、抗酸蚀能力增强;但是,激光处理会导致牙釉质表面变得粗糙,出现大量裂纹和孔洞,牙齿表面的弹性模量降低,表面脆性增大,从而使得牙齿耐磨性显著降低,造成的损伤重于酸蚀。     

改性聚四氟乙烯材料的力学性能实验研究

为了研究改性低密度聚四氟乙烯材料的力学性能,利用万能试验机进行了准静态拉伸和压缩试验,通过霍普金森杆实验研究其在冲击载荷作用下的动态力学特性.对不同长径比改性与非改性试样在不同载荷加载下的力学特性以及不同冲击速度下的动态响应特性进行了分析.结果表明,通过在聚四氟乙烯材料中添加铜粉可以提高其抗拉强度,改善伸长率,增强抗压缩强度;随应变率的增大,改性聚四氟乙烯的屈服强度得到提高.     

B4C颗粒对AZ61蠕变及磨损性能影响的研究

采用机械搅拌法制备B4C/AZ61镁基复合材料,并通过对比AZ61镁合金和B4C/AZ61镁基复合材料的蠕变和磨损试验,分析B4C颗粒对AZ61镁合金蠕变及磨损性能的影响.结果表明:在蠕变性能上,与AZ61镁合金相比,B4C/AZ61镁基复合材料具有较小的初始蠕变量和较小的总蠕变量,进入稳态蠕变阶段的时间和进入稳态蠕变状态时的蠕变速率与AZ61镁合金基本相同;在磨损性能上,B4C颗粒的添加使得AZ61镁合金的抗磨损性能得到明显提升.