Controlled synthesis of microarc oxidation coating on Ti6Al4V alloy and its antifriction properties

Abstract

Ceramic coatings were fabricated on a Ti6Al4V alloy surface by microarc oxidation (MAO) in Na₂ SiO₃ – (NaPO₃)₆ aqueous solutions with and without NaAlO₂ additive using an AC power supply. The effect of NaAlO₂ on microstructure, composition, and homogeneity of ceramic coatings were characterised using SEM, XRD, and EPMA. The antifriction property of the coatings with optimised microstructure sliding against SAE 52 100 steel ball was investigated on a pin-on-disc friction and wear tester. The results show that the addition of NaAlO₂ into Na₂ SiO₃ – (NaPO₃)₆ solution assists the formation of more dense, uniform, and thicker coatings and increases rutile TiO₂ content in the coatings. The optimised coating sliding against the steel has a friction coefficient as low as 0.2 – 0.3 at an applied load of 0.5 N and sliding cycle below 2500, which is much smaller than that of uncoated Ti6Al4V against the same counterpart. The transferring of material from the softer steel ball onto the coating surface is the main wear event, while the microarc oxidation coating is characterised by slight abrasive wear and adhesive wear.     

Effectiveness of high-frequency ultrasonic peening treatment on the tribological characteristics of Cu-based sintered materials on steel substrate

The effects of high-frequency ultrasonic peening (HFUP) on the tribological characteristics of Cu-based materials sintered on low carbon steel by a powder metallurgy (P/M) technique were investigated. The friction and wear properties of the Cu-based materials were studied using a pin-on-disk reciprocating tribotester sliding against a hardened steel ball under dry and oil-lubricated conditions. Scanning electron microscopy (SEM) was utilized to analyze the worn surfaces and to assess the wear mechanisms. Experimental results showed that the HFUP process led to a reduction in friction and wear of the Cu-based materials in both dry and oil-lubricated conditions. This was attributed to the increase in hardness of the HFUP treated specimen. It was also found that the friction coefficient was independent of the normal load but decreased with increasing sliding speed. In addition, inclusion of Fe in the Cu-based material was helpful in reduction of friction and wear. SEM analyses showed that abrasive wear was the dominant wear mechanism of the specimens. The results of this work demonstrate the effectiveness of HFUP in improving the tribological properties of Cu-based materials.     

Ni-Cr-C复合耐磨涂层的研究

以Ni-Cr-C混合合金粉末为添加原料,采用等离子熔覆技术,在普通机械制造用钢Q235表面形成了以初生块状金属陶瓷Cr7C3为硬质耐磨增强相,以强韧性良好的γ/Cr7C3共晶为基体的复合材料冶金涂层,分析了涂层的显微组织和硬度,在室温干滑动磨损条件下测试了其耐磨性.结果表明:涂层组织致密,硬度较高,与基体之间为完全的冶金结合,在干滑动磨损条件下具有良好的耐磨性.同时,讨论了复合涂层耐磨损的4种原因.     

Q235低碳钢表面等离子熔覆TiB2-TiC/Fe复合涂层及耐磨性

采用等离子熔覆技术,以Fe55、Ti、B₄C混合粉末为原料,在Q235低碳钢表面获得了TiB₂-TiC/Fe复合涂层,并分析了涂层的物相组成、组织结构,测试了显微硬度和摩擦磨损性能,探讨了其磨损机制。TiB₂-TiC/Fe复合涂层的主要物相为TiB₂、TiC、α-Fe,其中TiB₂呈多边形和矩形,TiC则呈不规则块状;随着原始粉末中Ti、B₄C含量的增加,TiB₂、TiC尺寸逐渐增大,TiB₂-TiC/Fe涂层与基体之间结合紧密,呈冶金结合;随着TiB₂-TiC/Fe复合涂层陶瓷相含量的增加,涂层硬度和耐磨性显著提高,当陶瓷相含量增加到一定程度（35wt%）时,涂层耐磨性能有所降低,TiB₂-TiC/Fe复合涂层的磨损方式主要是磨粒磨损和剥层磨损。Ti+B₄C陶瓷相含量为30wt%的等离子熔覆涂层耐磨性能较好,约为Q235钢基体的7倍,当Ti+B₄C含量持续增加时,TiB₂、TiC尺寸增大、缺陷增多,最终使TiB₂-TiC/Fe复合涂层耐磨性降低。     

Ti6Al4V合金激光原位合成自润滑复合涂层高温摩擦学性能

为提高Ti6Al4V合金的高温摩擦学性能,采用激光熔覆技术在其表面原位合成多相混杂金属基高温自润滑耐磨复合涂层,熔覆粉末的成分为Ni60-16.8%TiC-23.2%WS_2(质量分数,下同),系统地研究复合涂层的显微组织、物相结构及其在20,300,600,800℃下的摩擦学性能和相关磨损机理。结果表明:复合涂层的显微硬度(701.88HV_0.5)约为基体(350 HV_0.5)的2倍;由于原位合成固体润滑相(Ti_2SC/TiS/NiS/TiO/TiO_2/NiCr_2O_4/Cr_2O_3)和硬质相(W,Ti)C_1-x/TiC/Cr_7C_3的协同作用,复合涂层的耐磨减摩性能明显优于基体。随着温度升高,涂层和基体的摩擦因数和磨损率均呈下降趋势,在800℃时复合涂层和基体的摩擦因数分别为0.32和0.43,磨损率分别为1.80×10^-4,2.92×10^-5mm/Nm。在800℃下塑性变形、分层和氧化磨损为基体主要磨损机理,复合涂层以氧化磨损和轻微的黏着磨损为主。     

聚四氟蜡/聚氨酯复合涂层的摩擦磨损性能

采用MHK-500型摩擦磨损试验机和日本协和株式会社产CA-A型接触角仪分别研究了聚四氟蜡、聚四氟乙烯(PTFE)/聚氨酯粘接固体润滑涂层的摩擦磨损性能和疏水性能;采用扫描电子显微镜、光学显微镜分析了涂层磨损表面、对偶表面的磨损情况。结果表明,聚四氟蜡和PTFE都能提高聚氨酯涂层的疏水性和耐磨性能,降低涂层的摩擦系数。聚四氟蜡/聚氨酯粘接润滑涂层的耐磨性明显优于PTFE/聚氨酯粘接润滑涂层的耐磨性。同时,速度与负荷对聚四氟蜡/聚氨酯粘接涂层的摩擦磨损性能有很大影响。在低负荷、中高速试验条件下,它具有良好的减摩耐磨性能。     

钛表面激光熔覆原位制备Ti5Si3涂层结构及摩擦学性能

利用激光熔覆技术在钛表面预置硅粉原位制备了Ti5Si3涂层.用XRD、SEM和TEM分析了涂层的组成和组织结构.在UMT摩擦磨损试验机上对Ti5Si3涂层在不同载荷和不同滑动速度下的摩擦磨损性能进行了测试.实验结果表明:涂层的物相主要是Ti5Si3相和基材Ti相,涂层的显微结构为球状和块状晶,Ti5Si3涂层具有较高的显微硬度,涂层截面的平均显微硬度约为840 HV0.2,是钛基材的4.4倍;Ti5Si3涂层可显著提高钛基材的耐磨性能;Ti5Si3涂层的磨损机理为磨粒磨损和粘着磨损.     

Sliding behaviour of nanophased AISI M2 tool steel obtained by mechanomaking and hot isostatic pressing

Abstract

The friction and wear behaviour of a nanophased AISI grade M2 tool steel was studied under dry sliding conditions and compared with that of a conventional AISI M2 steel. The nanocrystalline steel was produced by mechanosynthesis followed by cold and hot isostatic pressing. Slider-on-cylinder tests were performed against a ceramic coated countermaterial under loads of 10, 20, and 30 N and sliding speeds of 0.3 and 1.2 m s^-1 up to 10 km sliding distance. The nanocrystalline material underwent mild wear with low coefficient of friction under all testing conditions. The commercial M2 steel displayed distance dependent transitions from a regime of mild wear with low coefficient of friction, to a regime of severe wear with high coefficient of friction. The first tribological regime was due to the formation of a layer of iron oxides on the worn surfaces. In this regime, the wear resistance of both steels is mainly dominated by the mechanical properties of the carbides which have high load carrying capability. The second tribological regime, observed in the commercial steel, was due to the formation of cracks both on the mechanically mixed layer and at a depth beneath this layer, which also led to the detachment of carbides from the matrix. This abrasive ‘third body’ produced high wear damage of the commercial steel under high applied loads.     

Laser surface coating of Mo–WC metal matrix composite on Ti6Al4V alloy

Laser surface alloying of Mo, WC and Mo–WC powders on the surface of Ti6Al4V alloys using a 2 kW Nd-YAG laser was performed. The dilution effect upon the microstructure, microhardness and wear resistance of the surface metal matrix composite (MMC) coating was investigated. With a constant thickness of pre-placed powder, the dilution levels of the alloyed layers were found to increase with the incident laser power. The fabricated surface MMC layer was metallurgically bonded to the Ti6Al4V substrate. The microhardness of the fabricated surface layer was found to be inversely proportional to the dilution level. The EDAX and XRD spectra results show that new intermetallic compounds and alloy phases were formed in the MMC layer. With the existence of Mo content in the pre-placed powder, the β-phase of Ti in the MMC coating can be retained at the quenching process. With increasing weight percentage content of WC particles in the Mo–WC pre-pasted powder, the microhardness and sliding wear resistance of the laser surface coating were increased by 87% and 150 times, respectively, as compared with the Ti6Al4V alloy. The surface friction of the laser-fabricated MMC coatings was also decreased as compared with the worn Ti6Al4V substrate.     

304不锈钢激光原位合成自润滑涂层的宽温域摩擦学性能

由于304不锈钢在中、高温下摩擦学性能较差,制约了其在重要摩擦运动副零部件上的应用。为改善304不锈钢的摩擦学性能,以Ni60粉末为增韧相,WS2为合成润滑相的前驱化合物,TiC为高硬度耐磨相,采用高能激光束在其表面原位合成自润滑耐磨复合涂层。利用X射线衍射仪、扫描电子显微镜、显微硬度计、摩擦磨损试验机和探针式材料表面磨痕测量仪表征涂层和基体的物相、微观结构、显微硬度与表面形貌,并系统研究涂层和基体在20,300,600,800℃下的摩擦学性能及其磨损机理。结果表明:涂层主要由Cr0.19Fe0.7Ni0.11,Ti2SC,Fe2C,Cr7C3,CrS和WS2组成;涂层的平均显微硬度(302.0HV0.5)略高于基体(257.2HV0.5),但涂层上部区域的硬度(425.4HV0.5)约为基体的1.65倍;涂层在所有等温摩擦学实验中摩擦因数和磨损率均低于基体,300℃时涂层润滑效果最好,摩擦因数为0.3031,600℃时涂层耐磨效果最好,磨损率为9.699×10^-5 mm^3·N^-1·m^-1。     

Surface damage of unidirectional carbon fiber reinforced epoxy composites under reciprocating sliding in ambient air

For many technical applications friction and wear are critical issues. Reinforced polymer-matrix composites are widely used under vibrating contact condition in various automotive and aerospace applications as well as in structural engineering. In this paper, the friction and wear of bulk epoxy and unidirectional carbon fiber reinforced epoxy composite have been investigated under reciprocating sliding against either alumina or stainless steel balls in ambient air. The effect of sliding direction with respect to the long and unidirectional carbon fibers has been studied. We demonstrate that the carbon fiber reinforcement greatly improves the tribological properties of the thermoset epoxy: it reduces the coefficient of friction and the debris formation. It was found that on sliding in the anti-parallel direction a more significant degradation takes place than in the parallel direction. The coefficient of friction measured on bulk epoxy sliding against either stainless steel or alumina is around 0.65, whereas the coefficient of friction measured on epoxy reinforced with carbon fibers is significantly lower, namely down to 0.11. It was found that sliding with a stainless steel ball in a direction parallel to the fiber orientation results in a lower coefficient of friction than sliding in anti-parallel direction. The reduced coefficient of friction is largely influenced by the carbon fiber reinforcement due to the auto-protecting film formed as a paste in the contact area and along the wear track edges. The relationship between friction and degradation of the composite material including surface wear and debris formation are discussed based on an in-depth analysis of the worn surfaces by optical and scanning electron microscopy, micro-Raman spectroscopy, and white light interferometry.     

梯度自润滑复合材料在不同滑动摩擦下的摩擦学特性

梯度自润滑复合材料是一种新型润滑材料,利用粉末冶金工艺设计和制备了该材料,考察了其在不同摩擦条件下的摩擦学特性,并对其摩擦磨损机理进行了分析和研究.结果表明:梯度自润滑复合材料随着复合固体润滑剂含量的增多,摩擦学性能明显改善,但润滑剂含量过高将导致材料表面硬度过低;该材料适用于高载倚下的润滑部件;脂润滑条件下,复合固体润滑剂与润滑脂结合在摩擦面上形成的膏状润滑膜使梯度自润滑复合材料的摩擦学性能显著改善;在脂润滑高载荷条件下,梯度自润滑复合材料的磨损主要发生在磨损初期,之后磨损极小,摩擦系数也趋于减小.     

纤维及晶须增强PTFE复合材料的摩擦磨损性能研究

利用MHK－500型环－块磨损试验机,对炭纤维,玻璃纤维及钛酸钾（K2Ti6O13)晶须增强聚四氟乙烯（PTFE）复合材料在干摩擦条件下与GCr15轴承钢对磨时的摩擦学性能进行了较为系统的研究,并利用扫描电子显微镜（SEM）和光学显微镜对其磨屑和摩擦表面进行了观察。结果表明,炭纤维,玻璃纤维及K2Ti6O13晶须虽增大了PTFE的摩擦系数,但均可将PTFE的磨损量降低2个数量级,其中玻璃纤维的减磨效果最好,K2TiO13晶须的减磨效果最差,由于K2TiO13晶须的承载能力较差,致使K2Ti6O13晶须增强PTFE复合材料的磨损表面发生了明显的挤压变形,因而该复合材料具有较高的摩擦和磨损。     

等离子喷涂Cr_3C_2-NiCr及其表面化学镀Ni涂层的摩擦学特性

考察了等离子喷涂Ｃｒ３Ｃ２－ＮｉＣｒ涂层及其表面化学镀Ｎｉ镀层通过不同配副组成摩擦副的摩擦学特性,并应用ＳＥＭ、ＸＲＤ和ＸＰＳ对磨痕进行了分析．结果发现：等离子喷涂Ｃｒ３Ｃ２－ＮｉＣｒ涂层及其表面化学镀Ｎｉ镀层自配副组成摩擦副,均表现出较大的摩擦系数和磨损系数;但是,Ｃｒ３Ｃ２－ＮｉＣｒ涂层表面化学镀Ｎｉ镀层与Ｃｒ３Ｃ２－ＮｉＣｒ涂层配副组成摩擦副,在于摩擦条件下,能达到０．１２的摩擦系数和接近１０－６ｍｍ３（Ｎｍ）－１的磨损系数．上述结果是由于Ｃｒ３Ｃ２－ＮｉＣｒ涂层的磨损机理从强烈的层状颗粒剥落转变为沿气孔和微裂纹等处的颗粒断裂．     

纳米Fe2O3对聚氨酯/聚偏氟乙烯复合涂层摩擦学性能的影响

利用M-2000型摩擦磨损试验机考察了干滑动下纳米Fe2O3改性的聚氨酯/聚偏氟乙烯(PU/PVDF)复合涂层的摩擦磨损性能。采用扫描电子显微镜分析了纳米Fe2O3在复合涂层中的分布以及涂层的磨损表面。结果显示纳米Fe2O3在涂层中分布比较均匀,少量的纳米Fe2O3的加入不仅降低了聚氨酯/聚偏氟乙烯复合涂层的摩擦系数,而且还提高了聚氨酯/聚偏氟乙烯复合涂层的抗磨性。负载对复合涂层的摩擦磨损性能有较大的影响,随着负载的增加,涂层的磨损率升高。     

Tribological Behavior of Ti3SiC2—based Material

The wear and friction properties of Ti3SiC2-based materials were studied using the pin-on-disc method. The friction coefficient of Ti3SiC2-based material was not very sensitive to normal load, the steady state value, μ, increased from 0.4 to 0.5 when the normal load increased from 7.7 N to 14.7 N. The wear volume for Ti3SiC2 disc increased with increasing normal load or sliding distance in the tests. The average wear rate of Ti3SiC2-based material was 9.9×10-5 mm3/Nm. The debris on the Ti3SiC2 disc was essentially made up of Ti3SiC2 and steel pin materials, while the debris on the steel sliders was generally pin material. The wear mechanism was concluded as the fracture and delamination of Ti3SiC2-based materials followed by adhesive wear of steel sliders.     

Tribological properties of MoS<Subscript>2</Subscript> and carbon fiber reinforced polyimide composites

The tribological properties of carbon fiber reinforced polyimide (PI) composites with different MoS₂ containing sliding against GCr15 steel were comparatively evaluated on an M-2000 model ring-on-block test rig. The wear mechanisms were also comparatively discussed, based on scanning electron microscopic examination of the worn surface of the PI composites and the transfer film formed on the counterpart. It was found that small incorporation of MoS₂ was harmful to the improvement of friction and wear behaviors of carbon fiber reinforced PI composites. However, it was found that the increasing filler of MoS₂ significantly improved the wear resistance and decreased the friction coefficient of carbon fiber reinforced PI composites. It was also found that the tribological properties of MoS₂ and short carbon fiber reinforced PI composites were closely related with the sliding condition such as sliding rate and applied load.     

A Comparative Investigation of the Tribological Behavior of Short Fiber Reinforced Polyimide Composites Under Dry Sliding and Water-Lubricated Condition

The friction and wear behavior of high performance polyimide (PI) and its composites reinforced with short cut fibers such as carbon fiber, glass fiber and quartz fiber was comparatively evaluated under dry sliding and water-lubricated condition, aiming at selecting matching materials for the pumps of pure water power transmission. The wear mechanisms of the composites under the two different sliding conditions were also comparatively discussed, based on scanning electron microscopic examination of the worn composite and steel counterpart surfaces. As the results, the PI composites reinforced with carbon fiber have the best mechanical and tribological properties compared with glass fiber and quartz fiber. PI composites sliding against stainless steel register lower friction coefficients and wear rates under water-lubricated condition than under dry sliding though the transfer of PI and its composites was considerably hindered in this case. PI and its composites are characterized by plastic deformation, micro cracking, and spalling under both dry-and water-lubricated sliding. Such plastic deformation, micro cracking, and spalling is significantly abated under water-lubricated condition. The glass and quart2 fibers were easily abraded and broken when sliding against steel in water environment, the broken fibers transferred to the mating metal surface and increase the surface roughness of mating stainless steel. This is probably the cause of the increased wear rate of glass fiber and quartz fiber PI composites in this case.     

等离子熔覆ZrB_2-ZrC/Fe复合涂层组织及耐磨性

采用等离子熔覆技术,以Zr、Fe、B_4C混合粉末为原料,在Q235低碳钢表面原位反应合成了ZrB_2和ZrC增强的Fe基复合涂层,分析了ZrB_2-ZrC/Fe涂层的物相组成和组织结构,并进行了硬度、耐磨性对比试验,探讨了物相和组织结构的形成过程及磨损机制。结果表明:涂层主要物相为ZrB_2、α-Fe、ZrC、Fe_2B和Fe_3C,其中ZrB_2呈现针棒状、花瓣状,ZrC呈现规则的颗粒状;随着原始粉末中(Zr+B_4C)含量的增加,增强相ZrB_2和ZrC含量增多,尺寸变大,ZrB_2-ZrC/Fe涂层与Q235钢基体之间结合紧密,呈冶金结合;与Q235钢基体相比,ZrB_2-ZrC/Fe涂层耐磨性显著提高,最高可达基体的5.45倍,ZrB_2-ZrC/Fe涂层的磨损方式以磨粒磨损为主,断裂方式以穿晶断裂为主。     

SiC含量对激光熔覆SiC/Ni60A复合涂层显微组织和耐磨性能的影响

利用LDM2500-60半导体激光器在45#钢板上制备SiC颗粒增强Ni60A合金激光熔覆涂层,系统研究SiC含量对涂层的显微组织、稀释率、耐磨性、摩擦因数和显微硬度的作用规律。结果表明:随着SiC含量增加,熔覆表层的微观组织细化,稀释率、耐磨性、摩擦因数和硬度均先增加后降低;当SiC含量为20%(质量分数,下同)时,熔覆层的耐磨性能最佳,磨损量仅为0.0012g,为基体磨损量的1/36.3;摩擦因数最小为0.464,且磨损过程最为平稳;熔覆层平均硬度值最高,达到1039.9HV0.2,为基体的3.5倍;但当SiC含量达到25%时,熔覆层的显微硬度与耐磨性能反而下降。