Abrasive wear of Al2O3-reinforced aluminium-based MMCs

The effects of volume fraction, Al₂O₃ particle size and effects of porosity in the composites on the abrasive wear resistance of compo-casting Al alloy MMCs have been studied for different abrasive conditions. It was seen that porosity in the composites is proportional to particle content. In addition, process variables like the stirring speed, and the position and diameter of the stirrer affect of the porosity content in a way similar to that observed for particle content. In addition, the abrasive wear rates of composites decreased more rapidly with increase in Al₂O₃ volume fraction in tests performed over 80 grade SiC abrasive paper than in tests conducted over 220 grade SiC abrasive paper. Furthermore, the wear rates decreased with increase in Al₂O₃ size for the composites containing the same amount of Al₂O₃. Hence, it is deduced that aluminium alloy composites reinforced with larger Al₂O₃ particles are more effective against abrasive wear than those reinforced with smaller Al₂O₃ particles. At the same time the results show that the beneficial effects of hard Al₂O₃ particles on wear resistance far surpassed that of the sintered porosity in the compocasting metal-matrix composites (MMCs). Nevertheless, the fabrication of composites containing soft particles such as graphite favors a reduction in the friction coefficient. For this reason graphite and copper were used in the matrix in different amounts to detect their effect on wear resistance. Finally, it was seen that wear rate of the composites decreased considerably with graphite additions.     

高Cu铸造铝合金的摩擦磨损性能EI北大核心CSCD

采用压铸工艺制备Cu含量为5%~20%(质量分数,下同)的Al-Cu合金试样。在布氏硬度计上测定试样的硬度,利用球盘往复式磨损试验机进行3种载荷(1~5 N)的磨损实验,通过SEM和EDS分析不同Cu含量试样的磨损机理。结果表明:随着Cu含量从5%增加至20%,Al-Cu合金中θ相的体积分数由2.00%增加到25.80%,且θ相的尺寸逐渐增大;硬度从59HB增加到170HB。摩擦因数在0.4~0.85范围内变化;Al-Cu合金试样的比磨损率随Cu含量增加先急剧降低后趋于平缓,Cu含量达到15%以上合金试样比磨损率变化不大,最低比磨损率在4.1×10^(-4)mm 3·N^(-1)·m^(-1)左右;较低Cu含量试样的比磨损率随载荷变化显著,随着Cu含量增加比磨损率差别减小。Al-Cu合金的主要磨损机制为黏着磨损和磨粒磨损,低Cu含量试样以黏着磨损为主,高Cu含量试样以磨粒磨损为主;随着载荷的增加,低Cu含量试样黏着磨损程度增加,高Cu含量试样磨粒磨损程度增加。     

铜合金压制凹坑织构表面的磨损性能

为了改善铜合金材料表面的摩擦磨损性能,采用压制加工方法,在CuSn6锡青铜试件表面制备出凹坑织构,分别进行压制凹坑织构试件和无织构试件的摩擦磨损试验,测量了摩擦系数和磨损量,观察了磨损表面及磨屑,分析了压制凹坑织构对试件磨损性能的影响。结果表明:与无织构试件相比,压制凹坑织构的磨损量减少。无织构试件的磨损机制为磨粒磨损与黏着磨损,压制凹坑织构的磨损机制为磨粒磨损和少量黏着磨损。压制凹坑边缘存在硬化区域,提高了试件表面平均硬度。凹坑容屑能力与边缘硬化区域有助于改善压制凹坑试件磨损性能。     

Tribology of metal coatings for electrical contacts

Noble metals are required for sliding low voltage low current electrical contacts such as those in electronic connectors, instrument slip rings and switches. This is to ensure that the contact resistance will be low and will remain stable. Gold, palladium and their alloys are the most commonly used materials and are employed primarily as electrodeposits and clad coatings.The major contact wear processes are adhesion, abrasion and fretting. Adhesive wear can operate in mild or severe regimes. Prow formation is the dominant wear process in the severe regime and is characterized by transfer from the member with the larger surface involved in sliding to that with the smaller surface, after which loose debris is formed. On repeat-pass movement, a transition to rider wear occurs in which the direction of metal transfer reverses. Unique gold electrodeposits have been developed that are relatively resistant to severe adhesive wear. These deposits are brittle, which lowers the tendency of adherent asperities at the mating surfaces to grow to large prows during sliding.Abrasive wear, in contrast, is accentuated when the coatings have low ductility, but as with other wear processes may be controlled if the contact materials are hard.Fretting wear of noble metal coatings leads to high contact resistance when they wear through to their base substrates. Frictional polymerization is the formation on the contact of insulating organic layers, which originate in organic air pollutants in the environment, and occurs during sliding and fretting of platinum group metals. Hard substrates and underplates are desirable because they reduce adhesive, abrasive and fretting wear. Smooth surfaces are superior to rough surfaces when adhesive and abrasive wear occur.     

掺杂纳米SnO_2-Al_2O_3/Cu新型电触头复合材料的制备及耐磨性能

为满足低压电器对于高品质电触头材料的迫切需求,同时保护稀缺资源、降低电触头成本,采用粉末冶金工艺制备了掺杂纳米SnO_2-Al_2O_3/Cu新型电触头复合材料,并对其电导率、硬度及耐磨性能进行了研究。结果表明:复烧与冷变形工艺均可显著提高复合材料的烧结质量、密度、电导率与硬度。随着纳米Al_2O_3及掺杂纳米SnO_2颗粒的总含量增加,掺杂纳米SnO_2-Al_2O_3/Cu电触头复合材料的硬度与耐磨性能表现出了相同的变化规律,即先升高后降低。当纳米Al_2O_3及掺杂纳米SnO_2颗粒的总含量为0.80wt%时,复合材料的硬度与耐磨性能均达到最优;而当纳米Al_2O_3及掺杂纳米SnO_2颗粒的总含量保持0.80wt%不变时,随纳米Al_2O_3颗粒的含量增加,掺杂纳米SnO_2-Al_2O_3/Cu电触头复合材料的硬度与耐磨性能改善;当掺杂纳米SnO_2颗粒的含量为0时,复合材料的耐磨性能达到了最优。因此较之掺杂纳米SnO_2颗粒,纳米Al_2O_3颗粒对掺杂纳米SnO_2-Al_2O_3/Cu电触头复合材料的耐磨性能有更显著的提高作用。     

热处理对炭/炭-铜复合材料载流磨损行为的影响

为探明炭/炭(C/C)多孔体热处理对炭/炭-铜(C/C-Cu)复合材料载流磨损行为的影响,采用化学气相渗透法(CVI)增密的C/C多孔体,再通过压力熔渗法制备C/C-Cu复合材料.采用载流动态磨损试验机测试C/C-Cu复合材料载流磨损行为,利用数字式三维视频显微镜和扫描电子显微镜观察复合材料磨损前后的表面形貌,研究了C/C多孔体经过2 000℃热处理对C/C-Cu复合材料载流磨损行为的影响.结果表明:C/C-Cu复合材料的质量磨损率和线磨损率比C/C多孔体未经热处理的复合材料分别降低了34.42%和17.84%;C/C多孔体经过2 000℃热处理,石墨化度提高,片层劈裂阻力减小,在载荷的作用下石墨片层易于劈裂形成细小的石墨微晶碎片,迅速填充修复表面缺陷,形成具有一定润滑作用、平整的摩擦膜,有效抑制了局部非均匀磨损的扩大,减弱了磨粒磨损和电弧放电引起的烧蚀、粘着、氧化磨损之间的循环交替磨损,载流磨损性能提高.     

Comparative investigation towards machinability improvement in hard turning using coated and uncoated carbide inserts: part I experimental investigation

The investigation of low cost uncoated and coated carbide insert in the hard turning of hardened AISI D2 steel (≥55 HRC) will definitely open up a new arena as an economical alternative suitable to industrial machining sectors. Thus, this paper reports the comparative machinability assessment for the hard turning of AISI D2 steel ((55 ±1) HRC) by coated and uncoated carbide insert in a dry environment. Micro hardness and abrasion tests were carried out to assess resistance capability against wear. The above test results confirmed the greater wear resistance ability of Al₂O₃ coated carbide insert over uncoated carbide. Based on the extensive investigation of comparative machinability, the coated carbide insert (TiN-TiCN-Al₂O₃) outperformed the uncoated carbide insert with regard to surface roughness, flank wear, chip-tool interface temperature, and chip morphology. Abrasion and diffusion were observed as the principal tool wear mechanisms in the investigated range. The uncoated carbide failed completely due to the severe chipping and quick dulling of the cutting edge, which led to its unsuitability for machining hardened steel. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0215-z     

Ti3SiC2/Cu复合材料的制备与摩擦磨损性能

以Ti₃SiC₂陶瓷粉和Cu粉作为原料,采用放电等离子烧结(SPS)工艺制备Ti₃SiC₂/Cu块体复合材料,研究不同Ti₃SiC₂添加含量及烧结温度对Ti₃SiC₂/Cu复合材料的组织、致密度和显微硬度的影响,研究SPS后Ti₃SiC₂/Cu复合材料的摩擦磨损性能。研究表明:采用SPS工艺制备的Ti₃SiC₂/Cu复合材料的Ti₃SiC₂在Cu中分布均匀,但随着Ti₃SiC₂含量的增加和烧结温度的升高,组织中出现团聚趋势,部分Ti₃SiC₂与Cu在界面处发生互溶现象,互溶增强了Ti₃SiC₂与基体的结合能力;Ti₃SiC₂含量和烧结温度对Ti₃SiC₂/Cu复合材料的致密度和显微硬度影响较大,当烧结温度为900℃时,Ti₃SiC₂/Cu复合材料的致密度达到99.7%,接近完全致密,Ti₃SiC₂/Cu复合材料的硬度较纯Cu提高了2倍左右;对于不同Ti₃SiC₂含量的Ti₃SiC₂/Cu复合材料的磨损机制也有所差异,当Ti₃SiC₂含量较低时(1vol%~5vol%),磨损机制为磨粒磨损和黏着磨损;随着Ti₃SiC₂含量的增加(10vol%~15vol%),Ti₃SiC₂发挥了本身的自润滑性,Ti₃SiC₂/Cu复合材料的摩擦磨损性能有所改善,磨损机制转为犁削磨损和轻微黏着磨损;当Ti₃SiC₂含量增加到20vol%时,Ti₃SiC₂/Cu复合材料的磨损表面变得均匀而平整,表明Ti₃SiC₂/Cu复合材料的耐磨性提高。      

Cu-Ag-Fe合金的电接触滑动磨损的研究

为改善接触线的耐磨性能,在Cu-Ag合金中添加微量Fe元素制备了Cu-Ag-Fe合金接触线,研究了电流强度、滑动速度和载荷对Cu-Ag-Fe合金的磨损形貌及磨损率的影响.实验结果表明：随电流强度、滑动速度和载荷的增加,合金的质量磨损率明显增加.磨损形貌表明,在受电滑动条件下,磨损形式以粘着磨损、磨粒磨损和电侵蚀磨损为主...     

无压熔渗制备TiC/Ti3SiC2复合材料高速载流摩擦磨损性能

采用无压熔渗反应烧结技术制备了TiC/Ti₃SiC₂复合材料,通过HST-100型载流摩擦磨损试验机,在60~90 m/s滑动速度范围内,对TiC/Ti₃SiC₂复合材料的高速载流摩擦磨损性能进行了研究。结果表明：当与HSLA80配副时,TiC/Ti₃SiC₂的摩擦磨损性能与摩擦速度和TiC含量呈现出一定的相关性。当摩擦速度小于80 m/s时,摩擦表面出现具有减磨作用的熔融状态的均匀分布氧化膜（FeTiO₃和Fe_2.35Ti_0.65O₄）,呈现山脊及犁沟状形貌,磨损机制以磨粒切削磨损、氧化磨损及粘着磨损为主;当摩擦速度超过80 m/s时,摩擦表面出现不均匀分布的氧化膜,呈现孤峰状形貌,磨损机制以氧化磨损及电弧烧蚀磨损为主。相同实验条件下,摩擦系数随着TiC含量的增加而增大,磨损率随之降低。     

Al_2O_3颗粒镀铜对铜基粉末冶金摩擦材料Al_2O_3-Fe-Sn-C/Cu摩擦磨损性能的影响

通过对陶瓷摩擦组元的表面进行化学镀铜来改善铜基粉末冶金摩擦材料中陶瓷相与基体间的结合效果,从而提高材料摩擦磨损性能。分别采用镀铜Al2O3颗粒和未镀铜Al2O3颗粒与铜粉和铁粉等经混合、压制、加压烧结制备Al2O3-Fe-Sn-C/Cu摩擦磨损试样。测试并分析了摩擦材料的微观结构、力学性能及摩擦磨损性能。结果表明:摩擦组元镀铜可使硬质颗粒与铜基体结合紧密;摩擦材料的布氏硬度增加了12%,弹性模量提高了约7%,摩擦系数提高了5%~10%,线磨损量降低了20%~50%;表面镀铜后的Al2O3颗粒不易脱落,摩擦系数稳定性提高了13%~23%。研究结果表明,摩擦组元表面镀铜可提高材料的综合性能。     

Al2O3-TiC/Al2O3-TiC-CaF2复合叠层陶瓷材料摩擦磨损性能

将Al₂O₃-TiC陶瓷材料与具有固体润滑特性的Al₂O₃-TiC-CaF₂陶瓷材料进行叠层, 通过真空热压烧结制备Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料。在环盘式摩擦磨损试验机上进行摩擦磨损实验, 研究该材料在不同载荷、 转速条件下的摩擦系数和磨损率, 分别用SEM及EDS观察材料磨损前后的微观形貌和分析其成分组成, 研究其磨损机制。结果表明: 在相同载荷条件下, Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料的摩擦系数和磨损率随着转速的升高而下降, 在相同转速条件下, 其摩擦系数和磨损率随着载荷的增加而下降; Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料的磨损机制主要是磨粒磨损和黏着磨损。     

放电等离子烧结Ni/TiB2-TiC复合材料微观组织及磨损性能

采用放电等离子烧结技术,以Ni、Ti、B₄C混合粉末为原料制备Ni/TiB₂-TiC复合材料,分析了Ni含量对复合材料的物相组成、组织结构、硬度和耐磨性的影响。结果表明：Ni/TiB₂-TiC复合材料主要物相为γ-Ni、TiB₂和TiC,其中TiB₂呈矩形条状和多边形状,TiC则呈现不规则块状;随着原始粉末中Ni含量的增加,TiB₂和TiC陶瓷相尺寸减小,其在Ni粘结相中的分布呈现出均匀化的趋势,复合材料更加致密。Ni含量显著影响Ni/TiB₂-TiC复合材料的耐磨性和磨损机制,Ni含量较低时（20wt%和30wt%）,复合材料摩擦系数（COF）较大且存在明显的波动,出现严重的疲劳磨损;随着Ni量的增加（40wt%）,材料的COF降低且趋于平稳,表现为微切削磨损;当Ni含量持续增加时（50wt%）,由于局部Ni的聚集导致粘着磨损产生,COF有所上升,耐磨性反而下降。     

TA15合金表面Ni-SiC复合镀层的摩擦磨损性能

采用共沉积法在TA15合金表面制备了Ni-SiC复合镀层, 分析了Ni-SiC复合镀层对基体合金硬度和磨擦磨损性能的影响, 并对其摩擦磨损机制进行了讨论。结果表明: 所制备的Ni-SiC复合镀层组织致密且与基体结合紧密, 硬度明显高于TA15合金基体。摩擦磨损实验结果表明, Ni-SiC复合镀层能为TA15合金提供良好的摩擦磨损抗力, 在相同的摩擦条件下, Ni-SiC复合镀层的磨损率明显低于TA15合金。TA15合金与GCr15球和Al₂O₃球对磨的磨损机制均主要为犁削磨损、粘着磨损, 同时伴随有氧化磨损和轻微的磨粒磨损; Ni-SiC复合镀层与GCr15磨球对磨的磨损机制主要为镀层组织的拔出及GCr15钢球在其表面上的涂抹, 与Al₂O₃磨球对磨时的磨损机制主要为疲劳磨损和削层磨损。     

Cu对粉末冶金Fe3Al基复合材料性能的影响

研究了Cu含量对粉末冶金Fe3Al基复合材料的烧结性能和力学性能的影响,分析了施加载荷和改变转速对加入不同量铜粉末冶金Fe3Al基复合材料的摩擦磨损性能的影响,并借助电子显微镜和能谱分析了不同铜含量Fe3Al基复合材料的磨损机理.结果表明:加入12%的Gu可使Fe3Al基复合材料具有良好的烧结性能和力学性能;载荷和转速对复合材料的磨损形式受铜的加入量的影响;铜的加入影响复合材料的磨损形式和磨损机理,当含铜量较少时,复合材料以磨粒磨损为主,随加入铜的量的增多,其磨损形式变为磨粒磨损和轻微的粘着磨损形式,加入大量铜时,则以粘着磨损为主.     

新型填料对高摩复合材料摩擦磨损性能影响及机制

采用干法热压成型工艺制备高摩复合材料,研究了基体材料腰果壳油改性酚醛树脂(CPR)与丁晴橡胶(NR)的质量比和新型高性能填料(主要成分为石墨粉Al2O3、MoS2、Fe粉)含量对高摩复合材料摩擦磨损性能的影响规律。在摩擦磨损试验机上测试了高摩复合材料的摩擦磨损性能,利用激光共聚焦显微镜、扫描电镜对摩擦表面形貌、磨屑进行观察和分析,借助EDS测定摩擦表面成分的变化。结果表明,随着CPR与NR质量比的增加,高摩复合材料的耐热性能、结合性能大幅提高,且具有较好的摩擦磨损性能。当高性能填料含量较低时,磨损表面出现大量连续的真实接触面,磨损机制为磨粒磨损和黏着磨损;当高性能填料含量较高时,真实接触面积减少,磨损表面剥落严重,并出现较多的裂纹,其主要磨损形式转变为磨粒磨损和疲劳磨损。随着高性能填料含量的增加,摩擦表面的元素从均匀分布逐渐转变为局部富集,磨粒的尺寸逐渐变大。     

多粒径TiB2颗粒增强铜基复合材料的制备与载流摩擦磨损性能

采用粉末冶金工艺分别制备了单一粒径TiB₂颗粒和多粒径TiB₂颗粒增强铜基复合材料,对比研究了非载流和载流条件下多粒径（2 μm+50 μm）TiB₂/Cu复合材料的摩擦磨损行为。微观组织观察表明:不同粒径的TiB₂颗粒在Cu基体中分布均匀。与单一粒径TiB₂/Cu复合材料相比,多粒径TiB₂/Cu复合材料具有更高的相对密度、硬度和导电率。摩擦磨损实验结果表明:多粒径TiB₂/Cu复合材料抗摩擦磨损性能明显高于单一粒径TiB₂/Cu复合材料,当2 μm与50 μmTiB₂颗粒配比为1:2时,多粒径TiB₂/Cu复合材料的抗摩擦磨损性能最佳。相对于2 μm单一粒径TiB₂/Cu复合材料,电流为0 A时,（2 μm+50 μm）TiB₂/Cu复合材料的摩擦系数和磨损率分别降低了17.3%和62.5%;电流为25 A时,（2 μm+50 μm）TiB₂/Cu复合材料的摩擦系数和磨损率分别降低了6%和45.8%,同时载流效率和载流稳定性得到明显提高,磨损表面更加平整。磨损机制分析表明:多粒径TiB₂颗粒合理配比有利于提高复合材料载流质量,同时摩擦过程中大粒径的TiB₂颗粒起到支撑作用,小粒径的TiB₂颗粒弥散强化Cu基体,二者的协同作用使TiB₂/Cu复合材料具有更好的抗载流摩擦磨损性能。      

Microstructural investigation on antifriction characteristics of self-lubricating copper hybrid composite

Abstract

Owing to good antifriction properties and high wear resistance, copper hybrid composites reinforced with hard ceramic particles and solid lubricant components are regarded as promising materials for applications in sliding electrical contacts. The present work investigates the antifriction mechanism of a (SiC+Gr)/Cu composite from a microstructural viewpoint, so as to assist the development and application of this material. A graphite rich tribolayer formed on the worn surface was responsible for good tribological properties of the composites. Testing results showed that nanoparticles of graphite were involved in a mechanically mixing process by adhering to both the other wear debris and the two contacting surfaces, thereby developing a solid lubricant tribolayer. The nanographite to nanographite contacting mode, formed between the composite and the counterface, significantly improved wear resistance and friction stability. The forming and failure process of the graphite rich tribolayer was studied. A mechanism has been developed based on the experimental results.     

Analysis of abnormal wear on a certain type of CRH380 high-speed railway grounding brush

This paper investigated the causes of premature wear of grounding brushes in high-speed train which was less than 40 % of design service life. The grounding brushes were analyzed from the material composition, microstructure and mechanical property under different wear conditions. The results indicated that their material composition and microstructure were basically identical, and the phase compositions of the four samples were mainly copper (Cu) and carbon (C). There were no obvious defects in the structure. The load differences will give rise to vibration of the friction pairs and lead to electrical erosion on the worn surface. The electrical erosion produced oxides and fused hard particles as well as caused abrasive wear. The test results also indicated that the spring-induced gap across the contact surfaces resulted in electrical erosion.     

马氏体基体含碳量对马氏体球铁磨损性能的影响

针对马氏体球铁,研究了马氏体基体不同含碳量(不同奥氏体化温度)对两体磨损和冲击磨料磨损耐磨性的影响。结果表明:在软磨料作用下的高应力两体磨损中,马氏体球铁以疲劳机制破坏,硬磨料作用下以切削机制破坏;在有较大冲击载荷作用的动载磨料磨损中,马氏体球铁存在有抗冲击疲劳剥落的最佳马氏体含碳量;石墨球的存在对耐磨性有害。