Effect of Interfacial Microstructure on Mechanical and Tribological Properties of Cu/WS2 Self-lubricating Composites Sintered by Spark Plasma Sintering

In this study,Cu/WS2 self-lubricating composites are fabricated by spark plasma sintering.Interfacial microstructure and its effect on mechanical and tribological properties are investigated.High sintering temperature at 850 ℃ promotes decomposi-tion of WS2 and its following interfacial reaction with Cu to form Cu0.4W0.6 nanoparticles and Cu2S,enhancing mechanical properties as well as wear resistance of the composites.But the destruction of WS2 leads to a high friction coefficient.On the contrary,for the composites sintered at 750 ℃,a nanoscale diffusion zone forms at the Cu/WS2 interface.WS2 lubricant retains its lamellar structure.The composite shows excellent self-lubrication performance,with a low friction coefficient of 0.16.However,its mechanical properties are low,and the wear rate is one magnitude higher.     

Oxidation,Mechanical and Tribological Behaviors of the Ni/cBN Abrasive Coating-Coated Titanium Alloys

In order to improve the oxidation and wear resistance of blades tip of titanium alloys as well as the sealing performance of the gas turbine engine,a Ni/cBN abrasive coating was prepared on titanium alloys through composite electroplating.Oxidation,mechanical and tribological properties of the abrasive coating were investigated.Furthermore,the effect of the oxidation on the mechanical and tribological properties was also evaluated.Oxidation results revealed that the abrasive coating underwent slight oxidation within 700 ℃.Meanwhile,some intermetallic compounds,Ni_3Ti,NiTi and NiTi_2,were formed at the coating/substrate interface during oxidation.Due to the pinning effect of cBN particles and the different thermal expansion coefficients of the coating and substrate,the coating/substrate interface was cracked after oxidation at 700℃.Tensile results showed that the presence of coating reduced the strength of the alloy significantly at room temperature,while only marginal variations of the strength of the coated and uncoated specimens at elevated temperatures.Besides,the wear tests indicated that the coating had the excellent cutting ability and wear resistance,which can effectively protect the blades tip of titanium alloys.As the temperature increased,the wear resistance decreased due to the decrease in the mechanical properties of the Ni/cBN coating.     

Zr-4合金微弧氧化层的生物摩擦学性能

采用含Ca、P电解液,450V微弧氧化在Zr-4合金表面制备氧化膜层,在25%小牛血清润滑条件下做球盘往复式摩擦磨损试验,重点研究了氧化膜层的摩擦磨损特性。结果表明,微弧氧化膜层含Ca、P,主要由立方相氧化锆、四方相氧化锆和少量单斜相氧化锆构成,膜层表面粗糙多孔,有少量的微裂纹。Zr-4合金微弧氧化层与Si3N4球的摩擦因数低于Zr-4合金与Si3N4球的,氧化膜层硬度较高,摩擦副间的接触面积较小,膜层微孔储存小牛血清湿式润滑作用,均有利于摩擦因数降低。Zr-4合金微弧氧化层磨损量明显低于Zr-4合金,微弧氧化层硬度高是主要原因。Zr-4合金摩擦磨损以显微切削机制为主,微弧氧化层摩擦磨损则兼有疲劳剥落和显微切削两种机制。     

MoSi2及其复合材料的高温和低温抗氧化性能研究

采用热质量分析法(TGA)和X射线衍射(XRD)对MoSi2及其复合材料的高温氧化性能、低温氧化机理和影响因素进行了研究.结果表明,40vol%SiC/MoSi2复合材料在1300℃高温等温氧化条件下具有优异的高温抗氧化性;通过提高MoSi2的纯度、添加与氧有亲和力的元素及高温预氧化形成致密的SiO2保护膜都有利于改善和提高MoSi2材料的抗低温氧化性能.     

颗粒增强钛基复合材料的高温氧化行为研究进展

综述了近年来碳化物和硼化物两种颗粒增强钛基复合材料的高温氧化研究现状,包括氧化热力学和氧化机理的分析。氧化产物的热力学分析旨在为氧化机理的研究提供理论基础,并在此基础上指出了今后钛基复合材料氧化行为的研究重点和方向。     

High Temperature Properties of Discontinuously Reinforced Titanium Matrix Composites:A Review

Further improvement on high temperature durability is one of the most important aims except for high specific strength, high specific stiffness, and excellent wear resistance, to design and fabricate discontinuously reinforced titanium matrix composites （DRTMCs）. Their superior properties render them extensive application potential in aerospace and military industries due to the urgent demand for the materials with characteristics of lightweight, high strength, high stiffness and high temperature durability. With development on fabrication methods and room temperature properties, testing, characterizing, evaluating and further increasing high temperature properties of DRTMCs are becoming more and more important to promote their applications. This review provides insights and comprehensions on the high temperature tensile properties, superplastic tensile properties, creep behaviors, and high temperature oxidation behaviors of DRTMCs,     

Effect of C/SiC Volume Ratios on Mechanical and Oxidation Behaviors of Cf/C-SiC Composites Fabricated by Chemical Vapor Infiltration Technique

C/SiC volume ratios in carbon fiber-reinforced carbon-silicon carbide (C_f/C-SiC) composites may influence greatly mechanical and oxidation properties of the composites, but have not been well investigated yet. Herein, C_f/C-SiC composites with different C/SiC volume ratios were fabricated by chemical vapor infiltration (CVI) technique through alternating the thickness of a pyrocarbon (PyC) interlayer. The composites with C/SiC volume ratios of 0.37 and 0.84 exhibited the better comprehensive mechanical properties. The CS0.37 showed the highest flexural strength of 340.6 MPa, and CS0.84 had the maximum tensile strength of 139.1 MPa. The excellent mechanical properties were closely related to the relatively low C/SiC volume ratios and porosities, optimum interfacial bonding and reduced matrix micro-cracks. The composite with a low C/SiC volume ratio of 0.10 showed the best anti-oxidation performance due to its high SiC content. The oxidation mechanisms at 1100 °C and 1400 °C were discussed by considering the effect of the C/SiC volume ratios, pores and matrix micro-cracks, oxidation of carbon phase and SiC.     

陶瓷／石墨复合材料的制备及高温氧化性能

通过热压法制备了陶瓷／石墨复合材料。采用热分析仪考察了复合材料在1400℃～1600℃温度范围内的抗氧化行为；利用扫描电镜分析样品在1400℃和1600℃恒温氧化后的表面形貌。结果表明；陶瓷／石墨复合材料在1400℃氧化时有优良的自愈合抗氧化性能。在1600℃氧化时，对于粘度较高的样品来说，氧化新形成的玻璃膜可以弥补挥发形成的表面孔道，仍能形成均匀的、连续的玻璃膜覆盖在基体表面，从而有效地抑制氧气的进入。     

两种铸造镍基合金的高温氧化行为

利用热重分析法、XRD和SEM (EDS)对比研究了700℃超超临界发电机组用K317和K325铸造合金在900和1000℃大气环境下氧化行为。结果表明,K317的氧化性能要优于K325。在900℃氧化时,2种合金的氧化增重遵循抛物线规律,而在1000℃氧化时,氧化增重均分段遵循抛物线规律。K317的氧化膜分3层,外层是NiO、TiO_2和NiCr_2O_4,中间层是致密的Cr_2O_3,内层是内氧化产物Al_2O_3。而K325的氧化膜分2层,外层是NiO, NiCr_2O_4和Nb_2O_5,内层是致密的Cr_2O_3和嵌入的Nb_2O_5颗粒,没有内氧化现象发生。在1000℃氧化时,K325中的Mo严重被氧化形成挥发性MoO_3;同时氧化膜发生了局部剥落现象,氧化膜的附着性相对较差。     

Ti811合金的高温氧化行为

利用扫描电子显微镜(SEM)和光学显微镜,研究了Ti811合金在700～900℃的静止空气中的氧化行为,分析氧化时间、温度等因素对合金氧化动力学行为的影响.结果表明,合金的氧化动力学曲线主要为抛物线类型;低温短时氧化时,铝的热力学优势占主导,高温长时氧化时,钛的氧化动力学优势占主导;氧化皮与被氧化金属之间、氧化皮不同层次及复杂混合型氧化皮中不同相之间,由于结构上存在差异,将在界面上产生结构内应力,使氧化皮发生开裂或剥落.     

不同热处理下滑动速度对SiCp/Al复合材料摩擦学性能影响研究

SiCp/Al复合材料非匀质性微观结构使其摩损机制较传统匀质材料更为复杂,不同工况及热处理工艺下复合材料的摩擦学性能也存在差异。以SiCp/2024Al复合材料为研究对象,进行球-面接触干滑动摩擦磨损实验,探究它在不同热处理状态及滑动速率下的摩擦磨损性能及磨损机制。结果表明:热处理对复合材料力学性能和摩擦学性能有显著影响,固溶+人工时效态复合材料具有更高的强度、硬度及耐磨性;滑动速度影响复合材料的表面接触性质及磨损程度,摩擦因数和磨损量随滑动速度提高逐渐增大;随滑动速度增加,复合材料主要磨损机制由剥层磨损向磨粒磨损转变,而磨损机制的转变明显加快了复合材料的磨损,在实际应用中应尽量避免此现象发生。     

MoSi2基复合材料的摩擦学行为

采用热压烧结工艺,制备了TiC、TiCN和TiB2增强的MoSi2基复合材料.考察了MoSi2基复合材料的力学性能和摩擦学性能,采用扫描电子显微镜观察了复合材料的磨损表面形貌.结果表明MoSi2-TiB2显示出了良好的烧结性能;第2相陶瓷的加入明显地提高了MoSi2的力学性能和摩擦学性能,其中MoSi2-TiC尤为明显.MoSi2磨损表面粗糙,并伴有一些微裂纹;MoSi2-TiC和MoSi2-TiCN磨损表面存在微犁削现象及一些剥落坑;MoSi2-TiB2磨损机制为轻微的磨粒磨损.     

钢材热浸镀铝抗高温氧化的动力学研究

通过静态高温氧化试验,研究了纯铝、铝－3％硅、铝－7％硅和铝－9％硅4种镀层高温氧化的动力学特性,推导了动力学方程式的算法,计算了4种镀层的氧化激活能（Q）及其与镀液中硅含量的关系。结果表明：Q＝1029－3226kJ/kg,4种镀层在700-900℃时的氧化规律为非线性递增,纯铝镀的最高使用温度为900℃,对于铝－硅镀层,当镀液中含硅低于3％时的最高使用温度为800℃,高于3％时的最高使用温度为700℃。     

Oxidation and wear behaviors of Ti-based thin films

The degradation of Ti-based coatings is known to be due to the formation of titanium oxide (TiO₂) at their surfaces. In this study, wear and thermal oxidation behaviors of various magnetron sputtered Ti-based thin films were studied after static oxidation and sliding wear. The oxidized surfaces after the static oxidation and the wear debris generated from pin-on-disc wear tests with alumina ball were characterized to identify the compounds, particularly titanium oxides, to gain a better understanding of the tribochemical reactions. The coatings that were examined include TiN, TiCN (N rich), TiCN (C rich), TiAlN, AlTiN, TiSiN, and TiCNO thin films. These coatings were characterized using Raman spectroscopy, scanning electron microscopy, and X-Ray diffractometer. The results show that TiSiN and AlTiN have the highest oxidation resistance, comparing with other coatings. As for the analyses of wear debris, all of the Ti-based coatings are worn by the mechanism of forming TiO₂, except AlTiN. AlTiN is worn by ploughing wear.     

Relationship Between the Integrity of Lubricating Film and the Tribological Behavior on TiAl-Ag Self-Lubricating Composites

To explore the relationship between the integrity of the lubricating film and the tribological behavior of a metal matrix self-lubricating composite, the friction and wear experiments of TiAl-Ag self-lubricating composites were carried out with a ball-on-disk configuration. Besides, an approximate model was developed for analyzing the relationship based on Blau’s theory. The research results suggest that the friction and wear behavior of the TiAl-Ag self-lubricating composites changes in accordance with the formation conditions of the Ag-rich lubricating film. Specifically, the friction coefficients and wear rates of the TiAl-Ag self-lubricating composites decreased from high levels at full composite–counterface ball contact to low levels at full-film lubrication. Hence, the integrity of the lubricating film is a possible criterion for the self-lubricating property of the self-lubricating composites.     

不同方法制备的Cu-Si合金的高温氧化行为

采用电弧熔炼（CA）和机械合金化（MA）方法制备了不同显微组织的二元单相Cu-Si合金（CACu-0.15Si和MACu-0.15Si,CACu-1.3Si和MACu-1.3Si）,并研究了它们在700℃和800℃纯O2中的高温氧化行为。结果表明,两种方法制备的Cu-Si合金氧化后均形成了富SiO2的混合氧化区,但未形成连续的SiO2保护膜。两种成分的机械合金化Cu-Si合金的氧化速度均小于相同温度下同成分的熔炼Cu-Si合金,这是因为细晶材料及其氧化生成的氧化膜中包含了更多的晶界,为合金各元素及氧的扩散提供了更多的短路扩散通道,使它们扩散速度均有明显提高,SiO2富集区（Cu2O＋SiO2）的快速形成有效地限制了Cu的快速向外扩散。     

碳-铜基复合材料机械摩擦磨损性能研究

利用扫描电镜、金相显微镜等测试手段对面碳－铜复合材料几种组织状态下的机械摩擦磨损性能进行了研究。结果表明,复合材料具有合理的组织结构,可明显改善材料摩擦磨损性能,复合材料磨损性能随材料成形方向不同也有差异。     

石墨-AZ91镁基复合材料及其摩擦磨损性能的研究

研究了不同石墨颗粒含量对AZ91镁合金基复合材料摩擦磨损性能的影响。结果表明：在所研究的范围内，复合材料的摩擦磨损特性明显优于基体合金；随着石墨颗粒含量从5％增加到20％，镁合金基复合材料的耐磨性得到明显的改善，磨损质量损失与摩擦系数都降低到较低水平。在不同磨损阶段，对应着不同磨损机制。随着磨损过程的进行，在磨损试样表面逐渐形成一层连续黑色润滑膜，这层润滑膜有效隔离两摩擦副的直接接触，有效地延迟了镁合金基复合材料由轻微磨损向严重磨损的转变过程。     

改善钨渗铜喉衬的高温尺寸稳定性研究

某新型号固体火箭发动机的钨渗铜喉衬试车后发生了直径收缩，通过对钨渗铜材料的金相组织，断口形貌，工艺制度以及成分分析发现引起喉衬收缩的原因；一是钨渗铜材料的钨骨架在试车点火时产生的二次烧结收缩；二是材料的高温强度不足，点火试车过程的喉衬沿轴向伸长，相应以径向收缩来补偿体积变化，提出了改善钨－铜材料高温尺寸稳定性的途径并在后续发动机试车实验中获得了成功。     

Ni基高温自润滑涂层的显微结构及磨损性能

通过高能球磨、冷等静压及高频感应烧结在Ni基合金圆棒上成功制备HFIS304高温自润滑涂层。HFIS304成分(质量分数,下同)为NiCr(80/20)合金(60%),Cr2O3(20%),Ag(10%)和共晶BaF2/CaF2(10%)。HFIS304涂层组织致密,3种润滑相尺寸细小。研究表明,在室温到600℃的范围内,HFIS304涂层的耐磨性优于PS304涂层。