两种离子液体的摩擦学行为研究

合成了1-丁基-3-甲基咪唑四氟硼酸盐([Bm im]BF4)及1-羟乙基-3-甲基咪唑四氟硼酸盐([C2OHm im]BF4)2种室温离子液体。在四球摩擦机上研究了这2种离子液体的摩擦学性能,用SEM和XPS对磨痕表面的形貌和元素组成进行了表征,并分析了2种离子液体不同的润滑机制。结果表明,由于[C2OHm im]BF4上的功能化基团容易吸附在摩擦副表面,其在中低载荷下有更好的减摩抗磨性能。     

水基混合纳米流体对内冷却磨削性能的影响

添加多壁碳纳米管(MWCNTs)、二硫化钼(MoS2)、离子液体(1-乙基-3-甲基咪唑四氟硼酸盐,[EMIm]BF4)和阿拉伯树胶(GA)制备成稳定分散的水基ILs-MWCNTs/MoS2混合纳米流体.研究了混合纳米流体的摩擦学性能和热物性,并与传统磨削液进行内冷却磨削对比试验,分析了两种磨削液条件下的磨削温度和表面...     

不同离子液体润滑条件下BCN薄膜摩擦学性能研究

利用中频磁控溅射技术,分别溅射硼靶和石墨靶,在单晶硅衬底上制备BCN薄膜;采用原子力显微镜(AFM)对薄膜的表面形貌进行分析;在1-正丁基-3-甲基咪唑四氟硼酸盐(L104)和1-正己基-3-乙基咪唑六氟磷酸盐(L-P206)离子液体润滑条件下,利用CSM摩擦磨损试验机考察BCN薄膜/钢球摩擦副的摩擦磨损性能;利用电化学腐蚀方法考察薄膜在离子液中的耐腐蚀性能.实验结果表明:所制备的BCN薄膜均匀、致密,表面粗糙度小;在离子液体润滑剂润滑下,BCN薄膜表现出良好的抗磨减摩性能和抗腐蚀性能;与L-P206离子液润滑剂相比,BCN薄膜在L104离子液体润滑剂润滑下的摩擦学性能更好,这可能与L104离子液体自身的分子结构及其腐蚀性弱有关.     

类金刚石碳基薄膜在1-乙基-3-甲基咪唑四氟硼酸盐中的摩擦学性能

利用射频等离子体增强化学气相沉积技术,以甲烷为气源,在单晶硅(P(001))衬底上制备类金刚石碳基薄膜(DLC);利用高速往复摩擦磨损试验机分别测试DLC薄膜/Al2O3球摩擦副在大气环境下和1-乙基-3-甲基咪唑四氟硼酸盐离子液润滑下的摩擦磨损性能;利用光学显微镜,X射线光电子能谱和三维轮廓仪分别对磨痕、磨痕表面元素和磨损率进行考察。实验结果表明:DLC薄膜在离子液润滑时,在低载荷下减摩作用明显,但在较高载荷下摩擦因数较无离子液润滑时高,且不随载荷增加而变化,推测是离子液形成了边界润滑膜;XPS分析表明这层边界润滑膜可能是由离子液物理吸附在摩擦接触面上形成的,并且对DLC薄膜有很强的抗磨作用。     

低温冷风微量润滑磨削钛合金换热机理与对流换热系数模型

钛合金磨削过程中工件表面热损伤已成为亟需解决的技术难题。微量润滑技术应用于钛合金磨削是实现可持续制造的发展方向,但存在热耗散和润滑减摩能力不足的技术缺陷。利用多能场辅助加工是解决以上技术难题的必然选择,低温冷风取代常温空气携带微量润滑剂,可显著提高磨削区液膜换热和润滑性能。但润滑剂物理特性演变规律及磨削区液膜换热机理等科学问题尚需揭示。基于此,研究了润滑剂低温物理特性演变规律,建立了冷风温度与润滑剂物理参数的量化映射关系。分析了低温冷风微量润滑砂轮工件界面流动液膜换热规律,建立了磨削区流动液膜换热量理论模型。进一步,建立了不同冷风条件下润滑剂对流换热系数模型。进行了流动液膜对流换热系数和低温冷风微量润滑磨削钛合金换热性能验证实验,结果显示,对流换热系数理论值与测量值吻合,冷风温度为-10℃时,误差为8.5%;工件表面温度实验值和理论值变化趋势吻合,磨削深度为30μm、冷风温度为-40℃时,误差为7.7%。研究结果为低温冷风微量润滑磨削钛合金提高工件表面完整性提供技术支持。     

纳米粒子射流微量润滑磨削表面粗糙度预测与实验验证

随着人们环保意识的增强,微量润滑技术已经开始应用于磨削加工中,但是它的冷却效果有限,不能满足高磨削区温度强化换热的要求。而纳米粒子射流微量润滑新工艺的提出,可以有效地解决磨削区换热问题,同时又增强了砂轮与工件界面的润滑特性。针对在纳米粒子射流微量润滑磨削条件下磨削工件表面粗糙度预测,提出一种用于测量砂轮表面形貌的装置以及对磨削工件表面形貌进行模拟仿真的方法。并以两种工件材料为研究对象进行表面形貌数值模拟和实验验证,结果表明该种预测方法能够较准确地对磨削加工工件表面粗糙度进行预测,对于磨削参数的选择具有一定的指导意义。     

磨削温度场建模及热传递分析与实验验证

以磨削原理为基础,分别建立了干磨削、湿磨削和纳米粒子射流微量润滑磨削的温度场理论模型,分别对各种冷却条件下的温度场进行热量的传递分析。借鉴强化换热理论,分析了纳米粒子射流的导热特性,并对纳米粒子射流微量润滑磨削温度场能量的分配进行分析,理论推导出由砂轮/工件界面传入工件的能量比例系数及工件平均表面温度,用4种冷却方式进行磨削实验,分别通过红外热像仪和测力仪测得工件的表面温度和切向磨削力,并计算出传入工件的能量比例系数,证实浇注式磨削能量比例系数最低,其次为纳米粒子射流微量润滑磨削,分别为40.06%和46.47%。     

基于静电微量润滑技术的磨削加工性能试验研究

在构建静电微量润滑(EMQL)磨削加工系统的基础上,分析了不同荷电电压下润滑液液滴的荷质比和润湿渗透性能,研究了正负荷电电压下静电微量润滑技术的磨削加工特性。通过分析工件表层的显微硬度和显微组织,揭示了静电微量润滑技术的磨削加工作用机理。结果表明：荷电液滴的表面张力与润湿角减小,液滴的渗透性和润湿性提高。与传统微量润滑（MQL）相比,荷电液滴更易在砂轮-工件接触面渗透铺展,提升了润滑与换热能力,在正荷电静电微量润滑条件下,工件表层显微组织中的铁素体相对含量增加,工件表层显微硬度降低,磨削加工性能更好。     

毛细管电泳法拆分二氧异丙嗪对映体的条件研究

采用毛细管区带电泳法,以咪唑类离子液体l-正乙基-3-甲基咪唑四氟硼酸盐[bmim]BF4)为手性分离添加剂,β-环糊精为手性选择剂,NaH2PO4为背景电解质,分离电压10kV,实现了二氧异丙嗪对映体的分离。考查了[bmim]BF4浓度、β-环糊精浓度、NaH2PO4浓度和分离电压对二氧异丙嗪对映体分离度的影响。当缓冲液中不含[bmim]BF4时,二氧异丙嗪对映体的分离度仅为0.28,当缓冲液中含[mim]BF4时,随着[bmim]BF4浓度的增大,二氧异丙嗪对映体的分离度增大,可达1.2。实验表明[bmim]BF4能够增强β-环糊精的手性拆分能力,对手性拆分有协同作用。     

磨削烧伤和磨削裂纹产生的原因及预防

磨削加工在机械加工中占有相当重要位置,淬火后工件表面的加工,及较高的尺寸精度和表面粗糙度,主要是靠磨削来保证。磨削加工所用的砂轮表面,是由无数磨粒组成的,每个磨粒相当一把刀具,所不同的是,大部分磨粒具有负前角和小后角。由于磨粒在砂轮表面的分布有高有低,很不规则,在磨削过程中,有些磨粒切削工件形成切屑,有些磨粒仅在工件表面上刻划出痕迹,还有一些磨粒即不切削也不刻划工件,而只是与工件表面产生滑擦,因为磨削速度很高(为车、铣床速度的20倍),这种刻划和滑擦将产生高达1000℃左右的温度,会引起被磨工件表层金相组织的变化。磨削所消耗的能量也是比较大的。因此,磨削过程比其他金属切削加工过程更为复杂。 1.磨削烧伤和磨削裂文产生的原因     

Tribological mechanism of carbon group nanofluids on grinding interface under minimum quantity lubrication based on molecular dynamic simulation

Carbon group nanofluids can further improve the friction-reducing and anti-wear properties of minimum quantity lubrication (MQL). However, the formation mechanism of lubrication films generated by carbon group nanofluids on MQL grinding interfaces is not fully revealed due to lack of sufficient evidence. Here, molecular dynamic simulations for the abrasive grain/workpiece interface were conducted under nanofluid MQL, MQL, and dry grinding conditions. Three kinds of carbon group nanoparticles, i.e., nanodiamond (ND), carbon nanotube (CNT), and graphene nanosheet (GN), were taken as representative specimens. The [BMIM]BF₄ ionic liquid was used as base fluid. The materials used as workpiece and abrasive grain were the single-crystal Ni–Fe–Cr series of Ni-based alloy and single-crystal cubic boron nitride (CBN), respectively. Tangential grinding force was used to evaluate the lubrication performance under the grinding conditions. The abrasive grain/workpiece contact states under the different grinding conditions were compared to reveal the formation mechanism of the lubrication film. Investigations showed the formation of a boundary lubrication film on the abrasive grain/workpiece interface under the MQL condition, with the ionic liquid molecules absorbing in the groove-like fractures on the grain wear’s flat face. The boundary lubrication film underwent a friction-reducing effect by reducing the abrasive grain/workpiece contact area. Under the nanofluid MQL condition, the carbon group nanoparticles further enhanced the tribological performance of the MQL technique that had benefited from their corresponding tribological behaviors on the abrasive grain/workpiece interface. The behaviors involved the rolling effect of ND, the rolling and sliding effects of CNT, and the interlayer shear effect of GN. Compared with the findings under the MQL condition, the tangential grinding forces could be further reduced by 8.5%, 12.0%, and 14.1% under the diamond, CNT, and graphene nanofluid MQL conditions, respectively.     

Effect of the Anion on the Tribological Properties of Ionic Liquid Nano-Films on Surface-Modified Silicon Wafers

The films of three kinds of 3-butyl-1-methylimidazolium base ionic liquids with thickness of 2 nm were prepared on hydroxyl-terminated and amino-terminated Si substrates by dip-coating method. As anions, tetrafluoroborate, hexafluorophosphate, and adipate, respectively, were chosen. The tribological performances of these thin films were examined by the determination of the film durability and friction coefficient by means of a UMT-2MT tribometer using a steel ball as counterpart. The morphologies of worn surfaces were investigated by a non-contact interferometric microscope. The findings showed that 3-butyl-1-methyl-imidazolium hexafluorophosphate having the poorest hydrophilicity of the ionic liquids exhibited the best tribological properties on aminated Si surface at 0.4 N and 4 Hz.     

An investigation on surface grinding of hardened stainless steel S34700 and aluminum alloy AA6061 using minimum quantity of lubrication (MQL) technique

In grinding process, the abrasives plunge and slide against the workpiece during material removal with high specific energy consumption and high grinding zone temperature. To improve process efficiency, lubrication becomes an important requirement of the grinding fluids, along with chip removal and cooling the grinding zone. Grinding fluids have negative influences on the working environment and machining cost in terms of the health of the machine operator, pollution, the possibility of explosion (for oil), filtering, and waste disposal. The use of minimum quantity of lubrication (MQL) with an extremely low consumption of lubricant has been reported as a technologically and environmentally feasible alternative to flood cooling. This paper deals with an investigation of the grindability of hardened stainless steel (UNS S34700) and aluminum alloy AA6061 using dry, MQL, and conventional fluid techniques. One type of SiC and five types of Al₂O₃ wheels (corundum) as well as vegetable and synthetic ester MQL oils have been tested. The influences of wheel and coolant–lubricant types have been studied on the basis of the grinding forces, surface topography, and surface temperature. Synthetic ester MQL oil was found to give better grinding performance than the vegetable MQL oils. It was argued that the improved performance of the ester oil is caused by the formation of tribo-films on the abrasives and the workpiece, which enhances lubrication by inhibiting metal–abrasive interaction. Also, the grindability of the machined specimens was found to increase substantially by using the MQL grinding process with soft and coarse wheels. In MQL grinding of AA6061 alloy, the use of vegetable oil resulted in the lowest surface roughness, whereas using synthetic ester additives lead to highest surface roughness because of higher chip loading on the grinding wheel and consequently more redeposited material on the workpiece surface.     

Tribological performances of two ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate) as nanolubricants on polyether-ether-ketone surface

This paper seeks to address the potential of using ionic liquids as nanolubricants on Polyether-ether-ketone (PEEK) surface. We characterize the tribological properties of two ionic liquids, namely1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate. The tribological data are compared with those of perfluoropolyether (PFPE) and Multiply Alkylated Cyclopentanes (MAC) data obtained from previous study. Ionic liquids at lower concentration of 0.4wt% (in solution prior to deposition) showed lower wear lives as compared to those for PFPE and MAC. However, at higher concentration of 4wt%, these ionic liquids have the same wear lives as those of PFPE and MAC, but show considerably lower coefficients of friction. Mechanisms of nanolubrication for ionic lubricants vis-a-vis those of PFPE and MAC are explained.     

Application of Nanofluids in Minimum Quantity Lubrication Grinding

This research investigated the wheel wear and tribological characteristics in wet, dry, and minimum quantity lubrication (MQL) grinding of cast iron. Water-based Al₂O₃ and diamond nanofluids were applied in the MQL grinding process and the grinding results were compared with those of pure water. During the nanofluid MQL grinding, a dense and hard slurry layer was formed on the wheel surface and could benefit the grinding performance. Experimental results showed that G-ratio, defined as the volume of material removed per unit volume of grinding wheel wear, could be improved with high-concentration nanofluids. Nanofluids showed the benefits of reducing grinding forces, improving surface roughness, and preventing workpiece burning. Compared to dry grinding, MQL grinding could significantly reduce the grinding temperature.     

Investigation into the performance of eco-friendly graphite nanofluid as lubricant in MQL grinding

In this study, the lubrication and cooling properties of eco-friendly graphite nanofluids in MQL grinding were investigated. Grinding forces, subsurface temperature of workpiece, surface roughness, micro-hardness and metallographic observations of ground surfaces were employed to evaluate the performance of synthesized nanofluids as lubricant under different grinding parameters. The results were also compared with grinding in dry, pure MQL and flood cooling conditions. The results showed that the tangential forces and force ratios in grinding using graphite nanofluid MQL are lower than that of other lubricating methods especially at extreme cutting parameters. Also, application of graphite nanofluid MQL reduced the grinding temperature at high velocities of workpiece. These reductions could be attributed to the formation of a tribofilm on the ground surface by the present of graphite nanoparticles in the wheel-workpiece interface. Additionally, the presence of this tribofilm in the contact area generated a smooth surface even at high depth of cut and velocity of workpiece. Furthermore, the micro-hardness of ground surfaces increased in graphite nanofluid MQL grinding because of infiltration of graphite nanoparticles in the grinding surface and the plastic deformation of subsurface of workpiece.     

Nanogrinding

Nanogrinding is an ultraprecision machining process well suited for surface machining of advanced ceramics. The machining kinematic is based on a lapping process, where the workpieces, forced by friction effects, revolve on a rotating plate. Lapping uses loose grain; however, for nanogrinding, the abrasive grain is completely embedded in a soft metallic plate, thus becoming the grinding tool. Therefore, nanogrinding is a two-step process. The first step is to create the grinding plate. In the second step, the workpiece is machined. Nanogrinding requires a significant grinding plate roughness, which is achieved by conditioning the plate with pumice. During this process, pumice is embedded in the grinding plate and remains there throughout the process. Between pumice particles, the basic soft metallic plate material forms plateus. Diamond grain is embedded here by a conditioning ring, with their summits aligned co-planar to the plate surface. This arrangement allows the performance of ductile machining, resulting in plastic material removal, minimal subsurface damage, and excellent surface finish.     

非一致曲率表面下的气压砂轮磨粒剪胀及加工试验研究#br#

针对软固结磨粒气压砂轮在加工异形曲面时,工件所受的切削力以及接触区内磨粒速度因工件曲率发生变化,导致工件不同曲率处材料去除量不均匀的问题, 基于修正的Rowe剪胀理论建立砂轮切削力模型,提出了非一致曲率表面下修正的气压砂轮材料去除模型。通过EDEM软件建立了软固结磨粒气压砂轮模型,分析了砂轮下压量为1.5 mm时工件曲率对接触力以及接触区内磨粒速度的影响。搭建气压砂轮加工试验平台,通过光整加工试验验证修正的材料去除模型。研究结果表明：修正的材料去除模型平均绝对值误差为0.095,而原始的材料去除模型平均绝对值误差为0.291,说明修正的材料去除模型可以用于气压砂轮抛光过程中的定量分析,且工件加工表面划痕明显减少。