梯度结构对氧化铝陶瓷涂层结合强度及抗冲击性能影响的试验研究

理论分析表明梯度结构能有效减缓氧化铝陶瓷层与基体结合面上的应力突变,涂层内部最大Mises应力明显降低,合理的梯度结构能改善涂层内部Mises应力分布,改变应力分布特征。为验证理论分析结果的正确性,采用等离子喷涂制备具有不同幂指数分布特征的6层"三明治"式梯度结构涂层,对梯度涂层结构进行表征,并试验研究涂层的结合强度及抗冲击性能。结果表明,试验用梯度结构具备p=0.25,1.00,4.00次方幂指数梯度结构特征,不同结构梯度层结合强度均在14.0~18.0 MPa,幂指数p=1.00的涂层结合强度最好,而幂指数p=0.25涂层抗冲击性能最好,较线性结构梯度涂层提高了30%,较幂指数p=4.00结构的梯度涂层提高了45%,冲击失效后涂层截面分析证实p=0.25次方幂指数梯度结构减少了表面陶瓷层的应力,减缓了陶瓷层基体间应力突变梯度,涂层失效是从底层开始的,失效形式为梯度涂层层状结构间出现分层,而p=1.00、4.00次方幂指数梯度结构涂层冲击失效表现为表面陶瓷层脱落。     

梯度结构对氧化铝陶瓷涂层接触应力的影响

采用幂指数描述"三明治"式梯度结构形式,建立镍基氧化铝梯度陶瓷涂层在静态接触集中力载荷作用下有限元模型,分析静态接触集中力载荷作用下涂层的Mises应力分布,以及梯度层的厚度、中间层数及结构形式对涂层的Mises应力分布及最大Mises应力发生位置的影响。结果表明:梯度结构对接触区Mises应力大小及分布影响不大,但影响最大Mises应力发生位置;合理的梯度结构能避开最大Mises应力发生在表面强化区及梯度区中,防止陶瓷涂层在接触载荷作用下疲劳脱落。制备层状结构梯度陶瓷涂层时,采用氧化铝层厚度20μm、线性梯度层厚度80μm、8层中间层,可改善Mises应力,适当避开最大Mises应力发生在梯度区。     

梯度结构对氧化铝/镍梯度涂层抗热应力影响研究

采用“三明治”式梯度结构形式,建立镍基氧化铝梯度陶瓷涂层在热载荷作用下有限元模型,利用弹塑性有限元分析方法,分析梯度层的结构形式、厚度及中间层数等参数对涂层热应力分布的影响。模型采用轴对称结构形式,梯度是由系列理想中间层叠加而成,并假定各层结构材料性能存在微小差别,各中间层材料性能描述符合混合准则要求。结果表明：同无梯度结构陶瓷层相比,梯度结构能有效减缓涂层与基体结合面上的剪应力突变,涂层结合部最大剪应力明显降低;合理的梯度结构能改善涂层内部轴向热应力及剪应力分布,改变热应力分布特征,降低陶瓷层与基体结合面上的剪应力,减少塑性变形,从而防止陶瓷涂层在温度变化时过大剪应力作用下脱落。探讨制备层状结构梯度陶瓷涂层时梯度层结构的设计,并提出采用8层中间层、20 mm厚线性梯度结构就可有效减缓剪应力的突变的结论。     

梯度结构对氧化铝/镍梯度涂层抗热应力的影响

采用"三明治"式梯度结构形式,建立镍基氧化铝梯度陶瓷涂层在热载荷作用下有限元模型,利用弹塑性有限元分析方法,分析梯度层的结构形式、厚度及中间层数等参数对涂层热应力分布的影响。模型采用轴对称结构形式,梯度是由系列理想中间层叠加而成,并假定各层结构材料性能存在微小差别,各中间层材料性能描述符合混合准则要求。结果表明:同无梯度结构陶瓷层相比,梯度结构能有效减缓涂层与基体结合面上的剪应力突变,涂层结合部最大剪应力明显降低;合理的梯度结构能改善涂层内部轴向热应力及剪应力分布,改变热应力分布特征,降低陶瓷层与基体结合面上的剪应力,减少塑性变形,从而防止陶瓷涂层在温度变化时过大剪应力作用下脱落。探讨制备层状结构梯度陶瓷涂层时梯度层结构的设计,并提出采用8层中间层、2.0 mm厚线性梯度结构就可有效减缓剪应力的突变的结论。     

梯度复合结构对列车车轮力学性能的影响

基于列车车轮表面抗磨损的功能要求,划定列车车轮表面为抗磨损功能区,在功能区与车轮基体间设计合理的梯度复合结构,开展具有梯度复合结构的列车车轮设计方法研究。以Hertz接触理论为依据,采用ANSYS建立轮轨热-结构耦合模型,分析轮轨整体在温度载荷及静态接触作用下应力分布。分析梯度复合结构对列车车轮力学性能的影响。结果表明:与无梯度复合结构车轮相比,梯度复合结构能有效降低车轮表面抗磨区与基体间等效应力突变,改变列车车轮应力分布特征,从而防止抗磨区在热-结构耦合作用下脱落。基于文中特定工况下,提出当抗磨区厚度为1.0 mm时,列车车轮表面抗磨区与基体间采用厚度为2.0 mm,中间层为8层的线性梯度复合结构就可有效减缓结合面上等效应力突变的结论。     

渗氮钢粗糙表面的弹塑性接触研究

利用弹塑性有限元和单纯形法求解弹塑性接触模型，分别模拟了屈服强度呈梯度变化的渗氮钢、未经处理的匀质材料和硬涂层材料粗糙表面的弹塑性接触行为。与未经处理的匀质材料相比，渗氮钢可承受更大接触载荷。在相同载荷作用下，渗氮钢表面粗糙峰接触面积较小，平均间距较大，接触体内材料不易发生屈服，从而显著提高接触性能。和硬涂层材料相比，渗氮钢接触体内等效von Mises应力分布平缓，没有应力突变。最后讨论了渗氮层和硬涂层的厚度对粗糙表面接触特性的影响。     

动力蓄电池包冲击累积损伤数值模拟研究

分析了车用电池包(Pack)在多次冲击载荷作用下的累积损伤。应用Hypermesh建立了Pack的有限元模型,使用LS_DYNA显式求解器求解了冲击载荷作用下Pack结构的动态响应,得到冲击载荷作用下Pack结构的von Mises应力和塑性应变分布情况及最大值,然后采用LS_DYNA重起动技术实现损伤状态参量传递,进而实现考虑初始损伤结构在多次冲击载荷作用下的应力状态及塑性应变累积分析,最后采用Johnson-Cook失效模型评估了结构损伤,得到Pack结构损伤的分布。     

带热障涂层构件界面应力分析边界元法

提出带热障涂层构件二维应力分析边界元法。对薄体应力分析边界元中近奇异积分处理方法进行完善及改进，并将其推广应用于热应力及离心应力边界元分析，提出可以考虑温度及离心载荷的多层域结构应力分析边界公式，数值算例结果表明，采用本文方法可用少量单元得到梯度温度场，面力和／或离心载荷条件下涂层界面应力分布，三种载荷情况下界面切向拉伸应力的最大相对误差小于0．23％，本方法可作为带热障涂层构件设计及涂层剥落失效分析的有效工具。     

PVD TiCrAlN刀具涂层高频疲劳性能研究

通过超声辅助振动的方式,用金刚石压头对PVD TiCrAlN涂层进行不同振幅下的高频冲击试验。采用扫描电子显微镜(SEM)和3D轮廓仪等对冲击后涂层的表面破坏形式和压痕形状进行检测,得出TiCrAlN涂层的抗冲击能力,分析了涂层冲击失效机理。结果表明:TiCrAlN涂层在受到冲击时产生侧向裂纹等失效形式;涂层在冲击载荷下受到的最大拉应力靠近冲击中心接触区边界;TiCrAlN涂层在高频冲击载荷作用下容易发生破坏,但是没有发生剥落,原因可能是:TiCrAlN涂层与基体界面处的结合力较好,涂层与基体界面的结合力影响了刀具涂层的抗冲击强度。     

真空实型铸造钢基表面复合材料的耐磨冲击性能研究

测试了真空实型铸造工艺制备的碳化硅颗粒增强钢基表面复合材料的耐磨性能和冲击力学性能。结果表明钢基表面复合材料的耐磨性优于基体,磨损系数大于基体;在应变率为600 s-1时,冲击应力比基体高约70 MPa。微观组织分析表明,增强碳化硅颗粒在基体中粒形基本保持完整,分布均匀,且基体与复合层之间没有明显的边界,说明两者的结合强度较高,起到了传递载荷和减缓冲击的作用。     

硬质合金刀具高能离子源增强多弧镀AlCrTiSiN梯度涂层制备及性能研究

采用离子源增强的多弧离子镀新技术,在硬质合金刀具表面制备了不同含Si层梯度结构的AlCrTiSiN梯度涂层,并对涂层组织结构、残余应力、结合强度、摩擦磨损以及铣削和钻削加工灰铸铁性能进行了详细的研究。结果表明：不同含Si层梯度结构的AlCrTiSiN涂层主要由固溶的(Al,Cr) N、(Al,Ti) N相和非晶态Si₃N₄相组成。其中,含Si层梯度变化最缓和的G3(Gradient 3)涂层具有较高的结合强度,较低的残余压应力、摩擦因数和磨损率。铣削和钻削试验显示,涂层刀具的切削磨损机理主要表现为磨粒磨损和粘着磨损。G3涂层降低了磨粒磨损,其刀具的铣削和钻削寿命均最高,这主要得益于其含Si层的梯度设计、适当的压应力(-3.8 GPa)以及良好的膜基结合强度。研究结果表明,通过对含Si层进行梯度设计可显著提高涂层刀具的切削性能。     

梯度覆层体受粗糙面滑动作用时的弹塑性分析

运用大限元软件分别虽对单覆层体及梯度体受多微凸体粗糙面滑动使用时产生的应力在变进行了计算和研究，着重比较两种覆层体爱相同表面载荷作用下，在基体及表面出现部分塑性变形时，表面层、基体内及表面 基体界面处的应力、应变分北度层在防止其本产生塑性变形及改善界面应力等方面比单纯层体具有明显的优点。本文的研究结果表为表南 选一览表主加工提供参考。     

Sliding wear evaluation of hot isostatically pressed (HIPed) thermal spray cermet coatings

The aim of this study was to investigate the potential of applying hot isostatic pressing (HIPing) as a post-treatment to thermally sprayed wear resistant cermet coatings. The relative performance of the as-sprayed and hot isostatically pressed functionally graded WC-NiCrBSi coatings was investigated in sliding wear conditions. Coatings were deposited using a high velocity oxy-fuel (HVOF)—JP-5000 system, and HIPed without any encapsulation at temperatures of 850 and 1200 °C. The influence of post-treatment temperature on the coating's wear resistance was thus investigated. Sliding wear tests were carried out using a high frequency reciprocating ball on plate rig using steel and ceramic balls under two different loads. Results are discussed in terms of microstructural investigations, phase transformations, mechanical properties, and residual stress investigations. The results indicated significant alteration of the coating microstructure, brought about by the coating post-treatment, particularly when carried out at the higher temperature of 1200 °C. As a consequence, developments in the coating mechanical properties took place that led to higher wear resistance of the HIPed coatings.     

Gradient DLC-Based Nanocomposite Coatings as a Solution to Improve Tribological Performance of Aluminum Alloy

The low hardness and poor tribological performance of aluminum alloy as moving component greatly restricts their wide applications in automotive fields. In this letter, an attempt to deposit gradient Ti/TiN/Si/(TiC/a-C:H) multi-layer on aluminum alloy is thus effectively performed by a combined arc ion plating and magnetron sputtering process based on the concept of involving coatings with a functionally graded interface. Multi-layered structure within DLC-based coatings has shown to significantly improve the load-bearing capacity, anti-wear and self-lubricating ability of Al alloys. The friction coefficient of gradient DLC-based coatings decreased to 0.18 under dry sliding condition while kept at 0.05 under the oil-lubricated conditions. The wear rate of gradient DLC multilayers was lower by two and even three orders of magnitude when compared with Al alloys both under dry wear and oil-lubricated conditions. Such gradient DLC-based coatings with good adhesion strength, high hardness, and excellent tribological performance are considered as potential protective surfaces of Al alloys for engine parts.     

仿竹涂层的设计及其应力场

对竹的显微结构进行了分析，并建立了仿竹梯度涂层的数学力学模型，根据此模型设计了一种仿生梯度涂层，并进行了有限元接触力学分析，得到了Mises应力场与剪应力场，结果表明梯度涂层可应用于受弯曲载荷作用的场合，具有比其它涂层优越的特点。     

Stress Analysis on Layered Materials in Point Elastohydrodynamic-Lubricated Contacts

For multilayered or coated substrates in elastohydrodynamic-lubricated (EHL) contacts, the subsurface stress distributions under a normal load combined with shear traction have been analyzed in this article through computer simulations. The Papkovich-Neuber potentials and Fourier transform are adopted to deduce the pressure–displacement, pressure–stress, and shear traction–stress response functions in frequency domain for the coated substrates, and to calculate distributions of pressure and subsurface stress. The results from the analysis of EHL contacts on coated substrates are compared with those from dry contact model in which shear traction is assumed to obey Coulomb’s law. Effects of the Young’s modulus of coatings, the properties of lubricants, and the magnitude of traction are discussed. Similar to the results in dry contacts, hard coatings in lubricated cases tend to increase the von Mises stress, whereas soft coatings decrease the stress. Shear traction makes the max von Mises stress increasing and moving closer to surface. However, the changes in subsurface stress due to shear traction are less obvious in lubricated contacts. Comparison between EHL and dry contact models reveals that lubrication can reduce the von Mises stress in the coating layer due to smaller shear traction. The analyses show that pressure, film thickness, and subsurface stress distributions are influenced by surface coatings, sliding velocity, rheological models, and pressure–viscosity behaviors.     

功能梯度涂层热残余应力

涂层中的残余应力严重影响着涂层零件的机械完整性与操作可靠性。对于功能梯度涂层,由于各界面位移协调条件的限制,很难得到涂层内部残余应力的闭合解。基于传统的悬臂梁理论,获得了功能梯度涂层热残余应力的闭合解;这一分析模型的优点是残余应力的闭合解与涂层层数无关。讨论了采用传统的近似解所带来的误差, 针对含不同层数的ZrO2/NiCoCrAlY功能梯度涂层内部的残余应力进行了计算。另外,对应力诱导的涂层失效模型也进行了分析。     

Wear behaviour of iron boride coatings produced by VPS technique on carbon steels

The vacuum plasma spray (VPS) technique is a useful tool for designing the characteristics of the coatings and, thus, the tribological properties of coated components. In the present paper, the wear properties of iron boride coatings produced by means of VPS technique on AISI 1040 steel samples were evaluated as a function of their microstructural characteristics. One coating type was obtained by using Fe₂B pure powder, the other with differentiated FeB + α-Fe blends, with the FeB content increasing and α-Fe content decreasing from the matrix to the surface. Wear tests were performed by means of a tribometer in block-on-ring configuration, without lubricant and in air, by using 40- and 60-N coupling loads and 0.8- and 1.6-m s⁻¹ sliding velocities. On Fe₂B coated samples, wear is essentially oxidative until the failure of the coating, the fragments of which cause a third body abrasion. On the FeB + α-Fe coated samples the wear mechanism is mainly oxidative and the coating totally wears out without spalling as a consequence of its graded structure, which succeeds in both improving the adhesion of the coating to the substrate and reducing the residual stress at the coating–substrate interface.     

Achieving Low Tribological Moisture Sensitivity by a-C:Si:Al Carbon-based Coating

Owing to the requirements of the stable operation for mechanical components, the urgent challenges are to control tribological moisture sensitivity of protective coatings. In this letter, a-C:Si and a-C:Si:Al carbon-based coatings were successfully fabricated via magnetron sputtering Si, Al, and C. The microstructure, mechanical properties, and tribological moisture sensitivity of as-fabricated carbon-based coatings were comparatively investigated. Results showed that the as-fabricated a-C:Si and a-C:Si:Al coatings were dominated by typical amorphous structure. The co-introduction of Al could effectively relax internal stress and improve adhesive strength as well as maintain the moderately high hardness for the as-fabricated coating. The striking improvement in tribological moisture sensitivity of a-C:Si:Al carbon-based coating was mainly attributed to the superior mechanical properties and the formation of continuously compacted graphitized tribofilm under low relative humidity condition as well as low shear strength colloidal silica tribofilm under high relative humidity condition. The good balance between the hardness and toughness, low internal stress, and superior low tribological moisture sensitivity of a-C:Si:Al coating make it a good candidate for solid lubricating coating in engineering applications.     

Achieving High Tribological Performance of Graphite-like Carbon Coatings on Ti6Al4V in Aqueous Environments by Gradient Interface Design

A duplex treatment involving nitrogen ion pre-implantation and gradient interfacial transition was performed to obtain a high-performance graphite-like carbon (GLC) coating on a Ti6Al4V alloy. Characteristics of the as-deposited coating systems were systemically investigated by Raman spectrometry, scanning electron microscopy, atomic force microscopy, nano-indentation, and scratch tests. The friction and wear behaviors in distilled water and sea water environments were evaluated by a ball-on-disk tribometer. The results showed that the GLC multilayer coating on nitrogen ion-implanted Ti6Al4V possessed a greater hardness and adhesion strength than to that on un-implanted Ti6Al4V. The tribological performances of these duplex process systems showed a great improvement in both the distilled water and sea water environments. In particular, the Cr/CrN/GLC coatings on nitrogen ion-implanted substrates demonstrated the best friction and wear behaviors. These striking improvements were attributed to the greatly enhanced interface strength between substrate and coating by the nitrogen ion implantation process and improved adhesion strength between gradient layers by the appropriate gradient interlayers with a similar thermal expansion coefficient.