等离子喷涂铁—镍—钴—碳化钨涂层制动摩擦特性的研究

重载制动摩擦磨损特性制约着刹车装置的刹车性能及其使用寿命，在ＭＭ－１０００试验机上，对等离子涂Ｆｅ－Ｎｉ－Ｃｏ－ＷＣ涂层的重载制动摩擦特性进行了试验研究，结果表明，在相同的试验条件下，等离子喷涂涂层分别与石棉摩擦材料笠金属摩擦材料对摩时的摩擦系数均比与基体３５ＣｒＭｏ钢对摩时的高，制动时间短，劝 耐磨     

埋入式光纤传感器界面剪切强度实验

采用实验方法对光纤与基体间界面性能进行研究.用临界断裂长度法直接测定界面的剪切强度,由于光纤拉伸强度高于树脂基的拉伸强度,出现试验时基体破坏而光纤完整地从树脂基中拔脱的现象.用单丝拔出法测量光纤与基体之间界面剪切强度,试验结果表明,光纤单丝拔出时,总是出现光纤涂层在锚入端断裂,而纤芯从涂层中拔脱的现象,说明当光纤埋入复合材料中,涂层和基体材料结合为一体,光纤涂层与纤芯之间界面剪切强度最低.承载时,若光纤所受正应力超过σ_(max),会出现光纤涂层与纤芯之间界面脱离,产生裂纹,降低整体结构力学性能.     

等离子喷涂铁－镍－钴－碳化钨涂层制动摩擦特性的研究

重载制动摩擦磨损特性制约着刹车装置的刹车性能及其使用寿命．在ＭＭ－１０００试验机上，对等离子喷涂Ｆｅ－Ｎｉ－Ｃｏ－ＷＣ涂层的重载制动摩擦特性进行了试验研究．结果表明：在相同的试验条件下，等离子喷涂涂层分别与石棉摩擦材料和半金属摩擦材料对摩时的摩擦系数均比与基体３５ＣｒＭｏ钢对摩时的高，制动时间短，制动效率和耐磨性能都明显提高，制动力矩峰比小，刹车平稳，制动特性好；制动摩擦系数与制动压力、速度和转动惯量等参数密切相关，压力增大，摩擦系数减小，速度和转动惯量增大，石棉材料摩擦副的摩擦系数降低，半金属材料摩擦副的摩擦系数升高，而且半金属材料的摩擦系数的热稳定性比石棉摩擦材料的好     

埋入混凝土的光纤传感器包层力学特性研究

本文用解析解探索光纤传感器埋入混凝土中其包层的特性及重要性。针对外荷载平行与光纤方向施加于混凝土构件时，其包层的材料特性和厚度变化而引起其内部应力分布特性作了一些研究。从解的分析可以看出，在埋入光纤的附近横截面应力集中很大程度上取决于包层的厚度及材料性质。对于给定的混凝土材料存在包层材料和厚度相结合的优化问题，选择某一优化目标，可能减小或消除其应力集中，而这对于光纤传感器在整个运行期间是至关重要。     

类金刚石涂层在不同载荷和湿度下的摩擦特性

利用磁过滤阴极弧等离子体沉积装置在单晶硅基底上制备了类金刚石涂层，采用原子力显微镜和纳米压痕仪测定了其表面形貌及硬度，在DF－PM型动－静摩擦系数精密测定仪上考察了涂层在不同载荷及湿度下同GCr15钢对摩时的摩擦性能。结果表明，在不同环境湿度条件下DLC涂层的摩擦性能明显不同，这主要归因于转移膜形成机理的不同；在3N载荷下，DLC涂层同GCr15钢对摩时的摩擦系数相对较小，且较为稳定；当环境湿度增大至100％时，摩擦系数显著增大，并发生类似于含氢类金刚石涂层的灾难性磨损。     

POZD涂层方形钢筋混凝土板抗接触爆炸试验研究

为研究聚异氰氨酸酯噁唑烷聚合物高分子材料（polyisocyanate oxazodone，POZD）涂层方形钢筋混凝土板在接触爆炸作用下的破坏模式和抗爆性能，对POZD涂层方形钢筋混凝土板进行接触爆炸条件下试验研究。试验中采用建筑结构中楼面设计常用的钢筋混凝土板为研究对象，通过11次独立的爆炸试验，分析了不同POZD涂层厚度对抗爆性能的影响，观测了钢筋混凝土板在不同装药量和不同POZD涂层厚度条件下的破坏模式和破坏特征，研究结果表明:涂层POZD钢筋混凝土板的主要破坏模式为钢筋混凝土板正面爆炸成坑，背面POZD涂层的圆锥状鼓起。POZD涂层鼓起主要是在爆炸冲击波作用下POZD涂层从基体板脱离并出现较大塑性变形所致。当冲击波荷载强度超过POZD材料的极限抗拉强度时，在涂层锥尖处形成较小的圆孔装剪切破坏，涂层的其他区域保持完好，从而让钢筋混凝土板不会产生较大范围的震塌破坏。在强冲击波荷载作用下利用POZD涂层仍然能够保持大变形、高塑性特性，可以通过自身的大变形很好地延长爆炸荷载的作用时间和耗散时间，吸收较大冲击波能量，从而约束混凝土震塌碎片，提高钢混混凝土板的抗爆性能。随着POZD涂层厚度增加，板的抗接触爆炸作用下的抗爆能力越强，临界震塌破坏装药量越多。研究结果可为工程应用及毁伤评估提供参考。     

不同法向载荷下TiN涂层磨损寿命与失效机理研究

采用阴极弧等离子沉积技术在高速钢(HSS)和硬质合金钢(WC-Co)基体上制备TiN涂层,利用往复摩擦磨损试验机、轮廓仪、扫描电子显微镜和能谱仪等分析了不同法向载荷下TiN涂层的摩擦磨损特性和失效过程,建立了涂层磨损寿命图. 研究结果表明:TiN涂层/HSS试样摩擦系数随循环次数增加呈上升趋势;TiN涂层/WC-Co试样在30 N法向载荷下的摩擦系数随循环次数呈上升趋势,在60~120 N法向载荷下摩擦系数波动较大. 涂层试样的磨损深度随法向载荷与循环次数的增加而增加. TiN涂层/HSS试样在30 N法向载荷的主要失效形式是磨粒磨损、轻微黏着磨损和氧化磨损,在60~120 N法向载荷的主要失效形式是涂层断裂、磨粒磨损和剥层磨损. TiN涂层/WC-Co试样在30~50 N法向载荷下的主要失效形式是磨粒磨损,在60~120 N法向载荷下的主要失效形式是严重剥层. TiN涂层的磨损寿命图可以分为两部分:涂层工作区和涂层失效区. 接触应力越大,涂层磨损寿命越短. 基体材料抵抗变形的能力越强,涂层磨损寿命越长. TiN涂层/HSS基体具有良好的抵抗法向载荷的能力和较长的磨损寿命.      

火炮用PCrMo钢激光熔覆MoS_2润滑涂层摩擦学性能研究

PCr Mo钢是导致火炮系统故障的磨损失效零部件主要材料.为了提高零部件的寿命,将固体润滑技术引入火炮抗磨减磨设计中.选取8~10μm和3~5μm两种粒度下二硫化钼作为固体润滑材料,采用激光熔覆工艺在PCr Mo钢试样表面制备润滑涂层.通过对涂层宏观性能表征,发现粒度小的涂层熔覆厚度较好;采用扫描电镜和能谱仪分别对涂层表面、剖面微观形貌和化学成分进行分析,发现涂层表面有凹坑产生,且凹坑中氧的含量明显高于光滑表面;涂层剖面与基体结合处存在一定的缝隙,涂层元素与基体元素发生了熔渗.进一步开展的摩擦磨损试验表明:与PCr Mo钢裸基材试样相比,两种粒度下润滑涂层试样摩擦系数和磨损量皆降低,磨损量分别为14.84%和42.01%,其中大粒度下涂层摩擦性能较优.二硫化钼润滑涂层起到了很好的润滑效果,可以作为火炮磨损零部件减磨的有效手段.     

制备工艺对MoS2粘结固体润滑涂层微动磨损寿命的影响

在不同载荷和位移振幅条件下,考察了2种基体材料表面MoS2粘结固体润滑涂层的微动磨损性能,深入分析了基体表面预处理、涂层厚度及涂层固化温度等对涂层微动磨损寿命的影响.结果表明,通过提高基体材料硬度、增加涂层厚度、对基体表面进行喷砂预处理以及对涂层进行高温固化等均可不同程度地提高涂层的微动磨损寿命,其中高温固化对涂层磨损寿命的影响最显著;而基体表面喷砂处理对高温固化涂层磨损寿命的影响减弱.喷砂42CrMo基体表面涂覆的经高温固化的厚16±1μm的MoS2粘结固体润滑涂层的抗微动磨损性能最佳.     

含空心球涂层粒子复合材料界面的脱粘应力分析

在球对称拉伸载荷作用下针对空心球涂层复合材料分析了空心球涂层粒子增强复合材料的局部应力场，得到了界面临界脱粘应力的解析表达式．讨论了各相几何参数对非均匀涂层空心球粒子临界脱粘应力的影响，比较了均匀涂层和非均匀涂层的脱粘应力．结果表明：在球对称拉伸下界面脱粘更容易发生在涂层相与基体相界面间，空心球的壁厚和涂层厚度是影响界面临界脱粘应力的重要因素，因而选择适当的空心球、涂层厚度和提高界面粘结能将有利于提高界面的临界脱粘应力．     

The coatings optimization of embedded fiber optical sensors under thermal and mechanical load

This paper studies the influence of coatings on the overall performance of the fiber-coating-host structure under thermal and mechanical load. The results demonstrate that the stress concentration near an embedded optical fiber highly depends on the properties and thickness of coating. Subject to the thermal and mechaincal load simultaneously, there exists optimal coating properties and thicknesses for a given host and fiber optical material that can reduce the stress concentration in the host material surrounding the fiber, or in the coating, or in the fiber itself.This paper is supported by Chinese National Natural Science Foundation.     

Fracture-mode map of brittle coatings: Theoretical development and experimental verification

Brittle coatings, upon sufficiently high indentation load, tend to fracture through either ring cracking or radial cracking. In this paper, we systematically study the factors determining the fracture modes of bilayer material under indentation. By analyzing the stress field developed in a coating/substrate bilayer under indentation in combination with the application of the maximum-tensile-stress fracture criterion, we show that the fracture mode of brittle coatings due to indentation is determined synergistically by two dimensionless parameters being functions of the mechanical properties of coating and substrate, coating thickness and indenter tip radius. Such dependence can be graphically depicted by a diagram called ‘fracture-mode map’, whereby the fracture modes can be directly predicated based on these two dimensionless parameters. Experimental verification of the fracture-mode map is carried out by examining the fracture modes of fused quartz/cement bilayer materials under indentation. The experimental observation exhibits good agreement with the prediction by the fracture-mode map. Our finding in this paper may not only shed light on the mechanics accounting for the fracture modes of brittle coatings in bilayer structures but also pave a new avenue to combating catastrophic damage through fracture mode control.     

Residual Stress Analysis on Thick Film Systems by the Incremental Hole-Drilling Method – Simulation and Experimental Results

The residual stress state in thick film systems, as for example thermal spray coatings, is crucial for many of the component’s properties and for the evaluation of the integrity of the coating under thermal and/or mechanical loading. Therefore it is necessary to be able to determine the local residual stress distribution in the coating, at the interface and in the substrate. The incremental hole-drilling method is a widely used method for measuring residual stress depth profiles, which was already applied for thermally sprayed coatings. But so far no reliable hole-drilling evaluation method exists for layered materials having a stress gradient in depth. The objective was to investigate, how far existing evaluation methods of the incremental hole-drilling method that are only valid for residual stress analysis of homogenous material states can be applied to thick film systems with coating thicknesses between 50 μm and 1000 μm and to point out the application limits for these already existing methods. A systematic Finite Element (FE) study was carried out for coating systems with an axisymmetric residual stress state σ₁?=?σ₂. It is shown that conventional evaluation methods developed for homogeneous, non-layered material states can be successfully applied for a stress evaluation in the substrate and the coating for small and for sufficiently large coating thicknesses, respectively, regardless of the type of evaluation algorithm used i.e. the differential or the integral method. The same accounts for material combinations that have a Young’s modulus ratio close to one, between 0.8 and 1.2. The studies indicated that outside the given ranges case specific calibration must be applied to calculate reliable results. Further, calibration data were determined case specifically for a selected model coating system. The accuracy of a residual stress determination using these case specific calibration data was examined and the sensitivity of the evaluation with respect to an accurate knowledge of the boundary conditions of the coating system i.e. the coating thickness and the Young modulus was studied systematically. Finally, the calibration data were applied on a thermally sprayed aluminium coating on a steel substrate analysis and the results for using the incremental hole drilling method were compared to results from X-ray stress analysis.     

Elastic analysis of thick-walled pressurized spherical vessels coated with functionally graded materials

In recent years, functionally graded material (FGM) has been widely explored in coating technology amongst both academic and industry communities. FGM coatings are suitable substitutes for many typical conventional coatings which are susceptible to cracking, debonding and eventual functional failure due to the mismatch of material properties at the coating/substrate interface. In this study, a thick spherical pressure vessel with an inner FGM coating subjected to internal and external hydrostatic pressure is analyzed within the context of three-dimensional elasticity theory. Young’s modulus of the coating is assumed to vary linearly or exponentially through the thickness, while Poisson’s ratio is considered as constant. A comparative numerical study of FGM versus homogeneous coating is conducted for the case of vessel under internal pressure, and the dependence of stress and displacement fields on the type of coating is examined and discussed.     

On the driving force for crack growth during thermal actuation of shape memory alloys

The effect of thermomechanically induced phase transformation on the driving force for crack growth in polycrystalline shape memory alloys is analyzed in an infinite center-cracked plate subjected to a thermal actuation cycle under mechanical load in plain strain. Finite element calculations are carried out to determine the mechanical fields near the static crack and the crack-tip energy release rate using the virtual crack closure technique. A substantial increase of the energy release rate – an order of magnitude for some material systems – is observed during the thermal cycle due to the stress redistribution induced by large scale phase transformation. Thus, phase transformation occurring due to thermal variations under mechanical load may result in crack growth if the crack-tip energy release rate reaches a material specific critical value.     

多孔性镍基石墨复合电镀层的摩擦学特性研究

作者在对石墨粒子以表面活性剂进行润湿处理后,利用电镀的方法制取了多孔性Ni-石墨复合镀层。该镀层的孔隙率高且分布均匀,容易被油润湿,故其润滑性能良好。本文比较详细地研究了这种镀层的摩擦学特性,并以电感耦合等离子体发射光谱法研究了电解液中石墨粒子的吸附特性,且以X-射线透反射法证明了石墨粒子在镀层中具有择优取向性,同时讨论了镀层的表面及断面形貌。文章还对镀层的形成过程进行了理论分析与探讨。     

浸油碳化物衍生碳润滑涂层的承载机制研究

采用高温氯化处理工艺在碳化硅表面制备了具有多孔结构的碳化物衍生碳涂层(CDC),考察了浸油(聚a烯烃,PAO)对CDC涂层承载性能的影响.结果表明:在低载(5 N)下,浸油前后涂层的摩擦磨损性能相当,随着载荷的增加,尤其是在中等载荷(~10 N)下,浸油涂层的摩擦性能变差,表现为较大的摩擦系数与磨损.分析认为CDC涂层的孔洞被PAO填充,其孔壁在摩擦过程中受到载荷应力与液压的双重作用而破碎,是导致浸油CDC涂层磨损加剧,承载能力大大降低的主要原因.     

纳米和微米TiO2对聚四氟蜡/聚氨酯复合涂层摩擦磨损性能的影响

制备出纳米和微米TiO2改性聚四氟蜡/聚氨酯复合涂层,采用傅立叶红外光谱仪分析其结构,在MHK-500型摩擦磨损试验机上考察复合涂层的摩擦磨损性能,采用扫描电子显微镜和光学显微镜观察分析复合涂层的磨损表面和偶件转移膜的分布情况.结果表明:纳米和微米TiO2可以增加聚四氟蜡/聚氨酯复合涂层的摩擦系数;5%纳米TiO2提高了聚四氟蜡/聚氨酯复合涂层的耐磨性;而添加微米TiO2则降低了聚四氟蜡/聚氨酯复合涂层的耐磨性能;同时,载荷和速度对纳米TiO2改性聚四氟蜡/聚氨酯复合涂层的摩擦磨损性能有很大影响,在低载荷、中速条件下复合涂层具有较好的耐磨性能.     

Micromechanical analysis of failure in thin protective coatings

The integrity of protective coatings is the subject of this investigation. Specifically, we concentrate on the case of thermo-protective coatings, so-called thermal barrier coatings, aiming at development of methodology for service life estimation of the coated components under thermal loading. At the current phase of the development, we establish relationships between various thermal loading patterns and failure driving parameters at different failure stages by developing an analytical–computational model of the process. The analysis addresses a typical failure development pattern consisting of a system of multiple surface cracks leading to and branching along or near the interface between the coating and the base material. The process is driven by thermal stresses. The developed model is applicable to thin coatings and provides insight into the processes taking place during failure development and the effect of the details of the applied thermal loading.The methods developed in the course of this investigation may be applied to the analysis of environmental effects on protective coatings and to investigations of failure development in layered composite systems under general loading conditions.