Transfer film effects induced by 3D-printed polyether-ether-ketone with excellent tribological properties for joint prosthesis

Based on the building principle of additive manufacturing,printing orientation mainly determines the tribological properties of joint prostheses.In this study,we created a polyether-ether-ketone(PEEK)joint prosthesis using fused filament fabrication and investigated the effects of printing orientation on its tribological properties using a pin-on-plate tribometer in 25% newborn calf serum.An ultrahigh molecular weight polyethylene transfer film is formed on the surface of PEEK due to the mechanical capture of wear debris by the 3D-printed groove morphology,which is significantly impacted by the printing orientation of PEEK.When the printing orientation was parallel to the sliding direction of friction,the number and size of the transfer film increased due to higher steady stress.This transfer film protected the matrix and reduced the friction coefficient and wear rate of friction pairs by 39.13%and 74.33%,respectively.Furthermore,our findings provide a novel perspective regarding the role of printing orientation in designing knee prostheses,facilitating its practical applications.

Polymer transfer film formation from cryogenic to elevated temperatures

This study reports on the tribological performance of aromatic thermosetting co-polyester(ATSP)and polyether ether ketone(PEEK)-based polymer composite coatings mixed with PTFE filler.The coatings were tested across a wide temperature range from−180 to 110℃ to simulate the environmental temperatures on Titan,Moon,and Mars,which are of particular interest for NASA’s future exploratory missions.An experimental setup was developed to conduct the pin-on-disk experiments under dry sliding conditions and extreme temperature and contact pressure.Transfer film formation and its characteristics were found to play significant roles in the tribological performance,and the characteristics of the film were temperature-dependent.The XPS and SEM analysis indicated the increase of the PTFE content in the transfer film as the temperature decreased to cryogenic conditions.The coefficient of friction did not follow a linear trend with temperature and was minimum at 110℃ and maximum at−180℃.ATSP coating showed superior performance with lower friction and unmeasurable wear at all temperatures,whereas PEEK coating exhibited maximum wear at 25℃ followed by−180,and 110℃.

Filmwise Condensation Heat Transfer Enhancement with Dropwise and Filmwise Coexisting Condensation Surfaces

Six surfaces were prepared with defferent surface division patterns for the experimental investigationof steam condensation heat transfer characteristics for dropwise and filmwise coexisting(DFC)condensationsurfaces under atmospheric pressure Dropwise condensation(DWC)was promoted with an ultrathin polytetrafluoroethylene(PTFE)film,which was prepared by the dynamic ion-beam mixed implantation(DIMI)method.The results showed that the condensation phenomena at the intersection between the dropwise andfilmwise condensation regios were quite different for different relative positions of the dropwise and filmwisecondensation regions.The experimental results revealed that the condensation heat transfer characteristics werehighly influenced by the surface division number and the relative area ratio of the dropwise and filmwise conden-sation regions.The impact of thesc findings on heat transfer enhancement mechanism for condensation heattransfer is discussed in detail.

Interlayer Energy Transfer from Naphthalene to Anthracene Chromophores Organized in Langmuir-Blodgett Films

Interlayer energy transfer between 2, 3-naphtho-10-hexadecylaza-15-crown-5 (NC16) and N-[1-(9-methoxyanthryl)]decylaza-15-crown-5 (A10C) within multilayer Langmuir-Blodgett films has been studied by steady-state fluorescence spectra. The donor and acceptor could be separated precisely by inserting stearic acid (SA) spacers. The efficiency of the energy transfer increases with the decrease in the donor-acceptor distance by a quadratic manner, suggesting the donor excitations are delocalized in the layer.

Experimental study on microdeposition of the copper thin film by femtosecond laser-induced forward transfer

The morphologies of the deposited dots on the 40 nm-thick copper film by the femtosecond laser-induced forward transfer that depend on the irradiated laser fluence have been studied, and the variations of orderliness of the diameter of deposited dots on the quartz substrate and forward ablated dot on the donor substrate with increasing pulse fluence have been obtained experimentally. The experimental results show that a thinner copper film would generate larger-sized ablated dot and deposited dot at the threshold fluence for transfer. By x-ray diffraction measurement, it is demonstrated that the crystal form of the transferred copper films is unaltered and the size of the crystallites is diminished.

DETERMINATION OF DEGREE OF CHARGE TRANSFER IN CONDUCTING LANGMUIR-BLODGETT FILM OF BEDT-TTF-TCNQ

A mixed Langmuir-Blodgett film was built up by mixture 1:1 of bis (ethyldithio)tetrathiafulvalene-tetracyanoquinodimethane/stearie acid(BEDT-TTF- TCNQ/SA).A degree of charge transfer(CT)in complex of BEDT-TTF with TCNQ was estimated at 0.477～0,486 by Raman frequencies of central Vc=c and Vc-s,The existence of charge transfer in BEDT-TTF-TCNQ has been confirmed by FTIR and XPS spectroscopy.

Heat transfer characteristics of molten plastics in a vertical falling film reactor

The heat transfer efficiency during the pyrolysis process is a key factor to be considered in the design of pyrolysis reactors. In this study, the average apparent heat transfer characteristics of molten plastic pyrolysis in a vertical falling film reactor were explored by experiments and numerical simulation and the apparent heat transfer coefficients were determined. In addition, the temperature distribution and the thickness of the liquid film in the reactor were predicted and the influences of pyrolysis temperatures on the average apparent heat transfer coefficients were discussed.

EFFECTS OF MASS TRANSFER ON THE THINNING AND RUPTURE OF A PLANE PARALLEL LIQUID FILM

The effects of mass transfer and physical properties upon the thinning and rupture of adraining plane parallel film are investigated.An equation is derived in which the thinning rate is afunction of bulk properties.surface properties(surface tension,surface viscosities,and the variationof surface tension with surface concentration),intermolecular forces(London-van der Waals forcesand electrostatic double layer forces),adsorption and surface diffusion coefficients,bubble size andfilm thickness.An estimation for the critical thickness at which a film rupture is carried out and thecoalescence time is obtained by integration to the critical thickness,The coalescence time is predictedas a function of bulk and surface properties,London-van der forces,adsorption and surfacediffusion coefficients,and bubble size.

Fabrication of seeded substrates for layer transferrable silicon films

The layer transfer process is one of the most promising methods for low-cost and highly-efficient solar cells, in which transferrable mono-crystalline silicon thin wafers or films can be produced directly from gaseous feed-stocks. In this work, we show an approach to preparing seeded substrates for layer-transferrable silicon films. The commercial silicon wafers are used as mother substrates, on which periodically patterned silicon rod arrays are fabricated, and all of the surfaces of the wafers and rods are sheathed by thermal silicon oxide. Thermal evaporated aluminum film is used to fill the gaps between the rods and as the stiff mask, while polymethyl methacrylate （PMMA） and photoresist are used as the soft mask to seal the gap between the filled aluminum and the rods. Under the joint resist of the stiff and soft masks, the oxide on the rod head is selectively removed by wet etching and the seed site is formed on the rod head. The seeded substrate is obtained after the removal of the masks. This joint mask technique will promote the endeavor of the exploration of mechanically stable, unlimitedly reusable substrates for the kerfless technology.

Shadowgraphic Imaging of Fibre-Delivered Pulsed IR Laser-Induced Heat Transfer across Thin Aluminized Polymer Film

Shadowgraphic imaging was employed to investigate the mid-IR laser induced heat transfer through a double layer thin film. The effect of thin metal coat on the polymer film enhanced the transfer of heat and shock waves due to rapid thermal expansion and the explosive evaporation of the thin fluid layer. Sixty two percent of deposited heat expended for water enthalpy and 38% for other factors. A power of 8.8 kW was launched at the surface of aluminium. The thermal coupling of 45% further reduced the input energy to the film and the non-adiabatic heat diffusion (i.e., ) was transmitted instantaneously within the metal with very small loss. The temperature at the surface of the film was determined ≈301 K, well below the aluminium melting point. The Biot number showed that the metal as single layer and the whole film as double layer satisfies the thermally thin film (i.e., ). Considering the Newtons’s law of cooling, the overall film heat transfer coefficient was found 3 k W·m-2·K-1 equivalent of 3.3 × 10-3 W·m2·K-1 thermal resistance. The analysis of images indicated a reducing percentage of heat transfer as a function of delay time based on the comparison of volume ratios. A calculated power of ≈3 kW was transmitted from the rear side of the film sufficient to thermalize the surrounding water layer and form vapor bubble.

Heat transfer characteristics of thin power-law liquid films over horizontal stretching sheet with internal heating and variable thermal coefficient

The effect of internal heating source on the film momentum and thermal transport characteristic of thin finite power-law liquids over an accelerating unsteady horizontal stretched interface is studied. Unlike most classical works in this field, a general surface temperature distribution of the liquid film and the generalized Fourier＇s law for varying thermal conductivity are taken into consideration. Appropriate similarity transformations are used to convert the strongly nonlinear governing partial differential equations （PDEs） into a boundary value problem with a group of two-point ordinary differential equations （ODEs）. The correspondence between the liquid film thickness and the unsteadiness parameter is derived with the BVP4C program in MATLAB. Numerical solutions to the self-similarity ODEs are obtained using the shooting technique combined with a Runge-Kutta iteration program and Newton＇s scheme. The effects of the involved physical parameters on the fluid＇s horizontal velocity and temperature distribution are presented and discussed.

浸渍石墨在陶瓷摩擦副下的摩擦腐蚀行为研究

研究不同介质环境中浸渍石墨的摩擦腐蚀特性,采用扫描电子显微镜和激光共聚焦显微镜分别表征了表面磨痕形貌、磨痕轮廓和磨损体积,通过分析在纯水与海水中的开路电位、极化曲线与电化学阻抗图及其相关参数,对浸渍石墨与2种陶瓷对偶球的摩擦磨损情况与机理进行评估分析.结果表明:浸渍石墨与陶瓷球Si_(3)N_(4)相对摩擦时自腐蚀电流密度更低,容抗弧度与相位角较大,极化电阻值更高,具有更好的耐腐蚀性能和耐磨性.随着载荷的增大,开路电位负移耐腐蚀性增强.纯水中石墨磨损表面存在明显的犁沟现象,以摩擦磨损为主.海水中腐蚀产物与磨屑混合在接触表面形成转移膜,表现较为光滑.摩擦过程中磨损体积、摩擦耗散能与载荷呈正相关性,而磨损率与载荷呈负相关性.海水中黏着现象较为明显,伴有磨粒磨损和轻微的氧化磨损.纯水中接触区以磨粒磨损为主,伴有轻微的黏着磨损和疲劳磨损.

Preparation and Tribological Properties of Onion-like Carbon/Waterborne Polyurethane Coatings

Rice husk powder was used as a carbon source in a high-temperature carbonization reaction for the production of rice husk ash(RHA).Under the catalysis of ferric nitrate,onion-like carbon(OLC)nanomaterial with a particle size of approximately 200 nm was successfully prepared and incorporated into waterborne polyurethane(WPU).The tribological properties of the coatings were determined using a controlled-atmosphere tribometer(WMT-2E)under dry-friction conditions.Following the friction test,the friction mechanism was investigated by characterizing the abrasive spot surfaces of the test samples using 3D laser microscopy and scanning electron microscopy/energy dispersive spectrometer.The final results demonstrated that the thermal stability of WPU composite coatings containing various concentrations of OLC nanoparticles was significantly enhanced,binding forces between coatings and steel sheets increased,and hardness improved compared to pure WPU coatings.Tribological tests revealed a notable enhancement in the anti-wear properties of WPU coatings due to the presence of OLC particles.Specifically,the wear rate of the 1.5%OLC/WPU coating was reduced by 45.3%.The coating’s anti-wear mechanism was attributed to the improvement in the mechanical properties of WPU due to OLC,as well as OLC’s participation in the formation of a transfer film under induced friction,which protected the matrix.

双肩壁凹槽叶顶冷却传热性能的优化研究

为改善航空发动机透平第一级凹槽叶顶的冷却传热性能,利用自编程序搭建了凹槽叶顶的优化设计平台。采用三阶多项式响应面模型和Hooke-Jeeves模式搜索算法的组合优化策略,获得了一种具有优良气热性能的透平级双肩臂凹槽叶顶结构,并将优化结果与传统凹槽叶顶、4种典型双肩臂凹槽叶顶的传热和冷却性能进行了对比,分析了内肩臂的几何参数对凹槽叶顶流场结构和冷却传热性能的影响,评估了双肩臂凹槽叶顶冷却传热性能对设计变量的敏感性。结果表明:优化后的内肩臂分为上下两层;合理的内肩臂几何参数可有效降低泄漏流的冲击作用,有利于冷却流在内外凹槽区域形成良好的覆盖;与传统凹槽叶顶相比,优化后的双肩臂凹槽叶顶的平均传热系数下降了24.96%,平均气膜冷却效率上升了5.38%;叶顶平均传热系数对内肩臂下层的高度最为敏感,叶顶平均气膜冷却效率对内肩臂上层的起始位置更加敏感,而内肩臂上层的高度对双肩臂凹槽叶顶的冷却传热性能影响相对较小。

Light-Induced Charge Transfer at Interface Between Lipid-Free RhTSPc Film and p-Si(111)

The present paper covers the lipid-free rhodium tetrasulfonato-phthalocyanine (RhTSPc) films prepared on p-Si(111) by using Langmuir-Blodgett technique. Their surface photovoltage spectra were measured. It was found that there is a strong interaction at the interface between the RhTSPc film and p-Si (111) and that the surface photovoltaic effect of the film system is maximum when only one monolayer of RhTSPc molecules coats p-Si(111), which is similar to that of CuTSPc films on p-Si(111) reported previously. These results confirm that only the monolayer of dye molecules being adjacent to the semiconductor surface plays a key role in the light-induced interfacial charge transfer process.

水润滑轴承用聚合物复合材料的摩擦学研究进展

聚合物复合材料因其优异的自润滑、高化学稳定性和减振降噪等特性而备受关注。以水作为工作介质的水润滑轴承具有环境友好、维护成本低及结构设计简单等特点,已被广泛应用于船舶、水电和化工等领域。首先总结了水润滑轴承用聚合物复合材料特性,归纳了聚合物复合材料在水润滑条件下的摩擦学性能及磨损机制,介绍了提高聚合物复合材料摩擦学性能的常规方法,并进一步探讨了材料内部结构、摩擦界面微观结构与材料宏观摩擦学特性的内在关联。指出促进水润滑聚合物-金属配副摩擦界面原位生长固体润滑特性转移膜,可弥补水膜润滑能力不足、显著提高配副的摩擦学性能,深入研究水润滑状态下复合材料的微观摩擦磨损机制,对于理解水润滑配副的摩擦学机理有重要的意义。

宽温域环境环氧/聚氨酯复合材料摩擦学性能研究

目的考察环氧/聚氨酯(EP/PU)互穿网络复合材料在宽温域环境中的摩擦学性能,以及氧化石墨烯(GO)的添加对其摩擦学性能的影响。方法制备EP、EP/GO、EP/PU、EP/PU/GO等4种材料,其中EP和PU的质量配比为3︰1,GO的质量分数为1.0%。分别研究4种材料的热力学性能,并采用高低温摩擦试验机对比研究常温和–100、–50、50、100℃下GO对EP/PU互穿网络材料摩擦磨损的影响。结果热力学性能结果表明,PU的加入降低了起始分解温度,而加入GO,热分解起始温度有所提升,EP的拉伸强度最高约为90MPa。室温条件下,200r/min时,样品的摩擦因数和磨损率要优于400、500r/min,其中,EP/PU/GO在200 r/min时的摩擦因数最低,为0.03。同样地,在–50、50、100℃时,相对于EP、EP/GO和EP/PU,EP/PU/GO也表现出优异的润滑性和耐磨性。SEM及XPS结果表明,摩擦氧化和螯合反应促进了转移膜的生长,形成了均匀结构的转移膜,可避免摩擦副的直接接触,有利于润滑作用。结论添加GO可以有效改善材料的力学性能,提高EP/PU的摩擦学性能。

水平管降膜换热器性能规律研究进展

水平管降膜换热器具有热质传递效率高、阻力小、结构简单等优点,被广泛应用于化工等传统领域及能源利用的节能减排领域。降膜换热器内部发生复杂的流动及传热传质相互耦合过程。介绍了实验及模拟研究手段的进展,综述了不同操作参数(气体温度、流向及流量,溶液流量、温度及浓度,内部媒介流量及温度等)与结构参数(管径、管间距等)对水平管降膜管间流型、液膜厚度与润湿性等流动特性的影响规律,以及对蒸发传热特性、吸收传热传质特性等换热器性能的影响规律,包括整体性能和局部微细特征,为水平管降膜换热器的性能优化提供理论支撑。指出在不同气流特征以及多因素相互作用下多维度的局部流动与传热传质性能的耦合影响规律以及强化换热手段会是水平管降膜换热器未来研究的重点方向。

紫外辐照对自润滑关节轴承衬垫磨损性能的影响

PTFE/Kevlar织物材料具有优异自润滑性能,在航空关键部件中广泛应用,但紫外辐照对其影响规律尚不清晰。针对航空器飞行强紫外线暴露的特点,聚焦紫外辐照对航空常用PTFE/Kevlar编织关节轴承衬垫自润滑材料摩擦学性能的影响规律研究。对不同紫外辐照时长的PTFE/Kevlar织物衬垫材料进行往复摩擦试验,并采用多种表征手段对其宏观、微观损伤形貌以及化学状态进行分析。结果表明:PTFE/Kevlar织物衬垫材料的磨损程度随着紫外辐照时间的增加呈现出先降低后升高的趋势,短时辐照(T=100 h和200 h)的磨损最轻微,摩擦损失体积和磨痕最大深度仅为未辐照和长时辐照(T=300 h和500h)的2/3;紫外辐照后,衬垫材料与GCr15轴承钢球之间的磨损行为变化表现为PTFE纤维塑性变形和转移膜形成能力的下降,其主要原因是PTFE纤维结晶度的降低;衬垫材料的磨损机理随辐照时间的延长由疲劳磨损和粘着磨损向磨粒磨损为主转变。研究成果可为PTFE/Kevlar织物衬垫型自润滑材料在紫外辐照后的磨损性能跟踪和研制优化提供参考。

铜表面织构密度对铜/碳配副载流摩擦性能的影响

目的碳刷是大型水轮机组、风电、新能源汽车等装备中电机转子供电的唯一通道,在长期服役过程中其碳块磨耗过度,落粉现象严重,探索织构化对铜/碳配副载流性能和摩擦磨损性能的影响,提出改善碳刷服役性能的表面技术。方法在铜环表面制备不同织构密度的圆形微织构,与碳块构成滑动载流摩擦副,研究织构密度对铜/碳配副载流摩擦磨损性能的影响。采用光学显微镜、白光干涉三维形貌仪、扫描电子显微镜等表征手段分析试样的磨损形貌,并通过能谱仪分析铜环表面碳元素分布及含量,揭示织构化对铜/碳配副性能的影响机制。结果当织构密度从0%增至18%时,摩擦跑合时间下降了47.2%,碳块磨损量下降了31.8%,在同等名义接触面积下接触电阻增高了28.7%。结论铜表面织构化有利于收集和储存摩擦过程中产生的碳颗粒,促进碳转移膜的形成,织构密度的增加可有效缩短摩擦跑合时间、降低碳磨损率。由于织构化破坏了铜表面的连续性,且碳转移膜的导电性弱于铜,因此织构密度的增加导致接触电阻升高。铜表面织构化对于提高碳刷磨损寿命、减少落粉量有一定效果。