界面形貌对残余应力的影响

以等离子喷涂热障涂层为研究对象,采用有限元分析软件ANSYS中热应力分析功能,对于不同的界面形貌模型,分析计算了其热障涂层中的残余应力的分布和极值,从而得出了不同的界面形貌对涂层中残余应力的一些影响规律。     

等离子喷涂熔滴沉积凝固后的残余应力分析

应用ANSYS软件中的热分析功能,对热喷涂过程中熔滴在基体表面沉积凝固后的残余应力进行有限元分析,此结果为等离子熔积成形技术的应用提供了理论支持,也为热障涂层界面的优化提供了指导依据。     

ZrTiAlN涂层的残余应力分析

采用有限元法分析Q235 A基ZrTiAlN涂层的残余应力,研究涂层厚度、过渡层对残余应力的影响。结果表明:层-基界面边缘处存在明显应力集中现象;涂层内的切向应力和轴向应力主要表现为拉应力,径向应力则表现为压应力。涂层厚度的变化对层-基界面应力的性质与分布影响很小;但随着涂层厚度的增加,界面处的切向应力增大,径向应力和轴向应力减小。加入过渡层后,涂层内残余应力明显减小,其中含有TiAl/Zr过渡层的涂层的切向应力、轴向应力和径向应力的最大值分别降低33%,25%和14%。     

TiC涂层梯度硬质合金残余热应力分析

采用有限元方法分析有无梯度2种TiC涂层硬质合金的残余热应力,研究了残余应力随涂层及梯度层厚度的变化。结果表明:增加梯度层后,涂层内残余热应力的减小超过10%,合金中残余应力减小30%以上,表面残余应力也明显下降;随着涂层厚度的增加,涂层内拉应力大幅减小,剪切应力与等效应力略微增加,涂层梯度硬质合金的等效应力呈下降趋势;随着梯度层厚度的增加,涂层内残余应力减小,当梯度层厚度较大时,残余应力不再改变。因此,选择合适的涂层和梯度层厚度,涂层厚度一般为5～8μm,梯度层厚度控制在20μm左右,可以有效缓和残余应力,提高材料的结合强度。     

残余应力对压头诱导的硬质薄膜断裂机制的影响

近年来,随着制备工艺的革新,硬质薄膜作为保护涂层已有了广泛的应用.在实际使用过程中,硬质涂层经常承受接触载荷作用.薄膜在接触载荷下易产生环形裂纹,从薄膜的表面起裂并扩展到界面,从而影响材料的可靠性和稳定性.同时,硬质薄膜中的残余应力的存在也将直接影响薄膜的服役周期.基于内聚力模型,采用有限元方法模拟来探究残余应力对压头诱导的硬质薄膜/韧性基底中薄膜本身断裂的影响规律.给出在不同残余应力下薄膜发生环形裂纹的起裂半径、裂纹间距、临界压入深度以及临界载荷,进而对运用压痕法测量薄膜的断裂韧性和工程应用提供指导.     

表面涂层裂纹的特性分析

采用有限元方法研究TiN涂层裂纹在弹性球循环挤压和滑动接触状态下的三维弹塑性特性,计算分析了涂层-基体的应力分布规律、涂层表面及界面裂纹的断裂强度。结果表明:在接触区边缘、涂层基体结合界面应力幅较大,容易萌生疲劳裂纹;裂纹强度J积分随载荷循环而呈周期性变化;涂层厚度、基体材料、裂纹形状、裂纹倾角等参数对涂层表面和界面裂纹的J积分有显著影响。     

基于Hertz接触理论的涂层界面应力分析

应用大型有限元分析软件ANSYS 8．1，对接触载荷条件下涂层材料的应力场进行了数值模拟．通过比较有限元解与经典Hertz解析解验证了有限元模型的可信度；分析了不同涂层厚度、不同涂层／基体弹性模量比情况下，接触应力分布情况及接触宽度随着载荷的变化情况．数值模拟结果表明：涂层／基体界面剪应力峰值出现在略偏离界面中心位置；涂层／基体界面正应力峰值出现在界面中心位置；涂层／基体的弹性模量比在1～2．5之间取值时，对涂层／基体结合效果较为有利；涂层过薄容易导致界面剪应力过大，致使材料失效．模拟结果能够为涂层材料的力学研究及设计提供参者．     

关于基体曲率的热障涂层残余应力分析

采用空心和实心四相同心圆模型,导出了轴对称温度应力状态下的位移公式,分析了基体曲率对热障涂层残余应力的影响。结果表明:热障涂层结构中各层内既有环向应力,又有径向应力,应力大小与温降成线性关系;当陶瓷层在外层时,在氧化层/陶瓷层和粘结层/氧化层界面上产生垂直界面的拉应力,且实心模型的拉应力远大于空心模型的拉应力;当陶瓷层在里层时,空心模型中相应界面上的应力为压应力。     

42CrMo钢超声喷丸强化模拟与实验研究

以42CrMo钢作为研究对象,利用超声喷丸工艺对42CrMo钢进行表面强化处理,并对超声喷丸过程进行有限元模拟,分析超声喷丸工艺与材料表面残余应力、显微硬度和表面形貌之间的关系。有限元模拟计算结果表明,超声喷丸冲击针头直径越小、冲击速度越大,喷丸后材料硬度越大,表面形貌越差;冲击针头直径对材料残余压应力场深度有显著影响;冲击速度对材料最大残余压应力值和残余压应力场深度有显著影响。     

陶瓷梯度耐磨涂层中残余热应力的有限元分析

运用ANSYS软件，对不同耐磨涂层试样中的残余热应力进行有限元分析，得出梯度过渡越多，涂层内的残余热应力越小。对实际工件耐磨涂层中的残余热应力进行分析，得出残余热应力主要集中在工件形状突变的地方，并对工件的设计生产提出合理建议。     

枪速对热障涂层组织性能及残余应力的影响

为了研究等离子喷涂制备热障涂层(TBCs)时不同枪速对陶瓷面层组织性能和残余应力的影响,在GH4169高温合金基体上采用超音速火焰喷涂(HVOF)Ni Co Cr Al Y粘结层(BC层)和大气等离子喷涂(APS)8YSZ陶瓷层(TC层).通过对比不同参数样品的微观组织以及显微硬度、残余应力和热震性能差异,研究了枪速对热障涂层的影响.结果表明:枪速过低或过高时,涂层表面残余应力较大,热震性能较低;随着枪速的增大,涂层表面粗糙度逐渐增大,而孔隙率和显微硬度逐渐减小;枪速过低时,涂层出现纵向裂纹,热震失效方式为整体剥落;而枪速较大时,涂层从边缘向中心不断剥落,涂层表面出现白点.     

Finite Element Analysis of Thermal Stresses in Ceramic/Metal Gradient Thermal Barrier Coatings

This paper studied the thermal stresses of ceramicl metal gradient thermal barrier coating which combines the conceptions of ceramic thermal barrier coating （TBC） and functionally gradient material （FGM）. Thermal stresses and residual thermal stresses were calculated by an ANSYS finite element analysis software. Negative thermal expansion coefficient method was proposed and element birth and death method was applied to analyze the residual thermal stresses which have non-uniform initial temperature field. The numerical results show a good agreement with the analytical results and the experimental results.     

Thermal residual stress analysis of diamond coating on graded cemented carbides

Finite element model was developed to analyze thermal residual stress distribution of diamond coating on graded and homogeneous substrates. Graded cemented carbides were formed by carburizing pretreatment to reduce the cobalt content in the surface layer and improve adhesion of diamond coating. The numerical calculation results show that the surface compressive stress of diamond coating is 950 MPa for graded substrate and l 250 MPa for homogenous substrate, the thermal residual stress decreases by around 24% due to diamond coating. Carburizing pretreatment is good for diamond nucleation rate, and can increase the interface strength between diamond coating and substrate.     

Effects of supersonic fine particle bombarding on thermal cyclic failure lifetime of thermal barrier coating

Thermal barrier coating ( TBC) consisting of a NiCoCrAlY bond coat ( BC) and a ZrO2-8 wt. % Y2O3 topcoat ( TC) was fabricated on the nickel-base superalloy by air plasma spray ( APS) . The BC was treated by supersonic fine particle bombarding ( SFPB) . Thermal cyclic failure and residual stress in thermally grown oxide ( TGO) scale were studied by SEM with EDS and ruby fluorescence spectroscopy ( RFS) . As shown in the results,after treated by SFPB,thickening of TGO was relatively slow,which reduced the level of growth stress. The TBC with SFPB treatment was still remained well undergoing 350 times of thermal cycle. However,after thermal cycle with the same times,the separation of TC was observed in TBC without SFPB treatment. The residual stress analysis by RFS showed that the residual stress of SFPB-treated TBC increased with the increasing number of thermal cycle. The residual stress of conventional TBC reached a value of 650 MPa at 350 times of cycle and that of SFPB-treated TBC only reached 532 MPa at 400 times of cycle. The BC with SFPB treatment after 400 times of cycle was analyzed by RFS,the high stress value was not observed in local thickened region of TGO. Thermal cycling resistance of TBC can be improved by the SFPB technology.     

纤维拔出时Coulomb摩擦界面应力传递

假设纤维/基体界面分离区域内的摩擦剪切应力遵循Coulomb摩擦律，包括泊松效应的影响，建立了纤维拔出时的摩擦界面应力传递模型，获得了包含摩擦滑移和由纤维/基体热失配引起的法向残余热应力效应的纤维轴向应力和界面剪切应力的表达式.对纤维增强复合材料SCS-6/Ti-6Al-4V作参数化的数值计算，且和有限元结果进行比较.结果表明，随纤维轴向位置的增加，纤维轴向应力和界面剪切应力均减小；法向残余热应力、高纤维体积分数和短纤维延缓纤维失效.     

Morphology and Mechanical Characteristics of Monolayer and Multilayer Ir Coating by Double Glow Plasma

Multilayer iridium coating was manufactured on tungsten carbide substrates by a double glow plasma process.As comparison,monolayer was also produced.The microstructure and morphology were observed using scanning electron microscopy.Grain orientation and phase were determined using X-ray diffraction.The residual stress of the coating was studied by glancing incidence X-ray diffraction.The adhesive force of the coating was measured by a scratch tester.The results showed that both monolayer and multilayer had a polycrystalline phase with a strong(110) reflection.The coating had an excellent adhesion with no evidence of delamination.The adhesive force of the monolayer and multilayer was about 50 and 43 N,respectively.The interfacial reaction between the substrate and the layer occurred and a new WIr phase was found due to the high-temperature deposition process.The residual stress in the monolayer and multilayer was-1.6 and-1.1 GPa,respectively.     

基体界面屈服强度和残余应力失配对界面裂纹扩展的影响

对基体界面屈服强度和残余应力失配情况下的界面裂纹扩展机制进行了力学理论分析,并通过位错与裂纹的关系理论计算了界面裂纹尖端塑性区尺寸。结果表明:当界面裂纹由低强度区向高强度区扩展时,高强度区的残余压应力和屈服强度减少了裂纹尖端的塑性区长度和裂纹尖端张开位移,从而起到了抑制界面裂纹扩展的作用。     

骨水泥假体柄与股骨界面应力传递简化模型

将股骨、骨水泥和假体柄看成为线弹性和各项同性材料结合的同心圆锥体,建立包含热效应时的轴对称界面应力传递简化模型.在骨水泥、假体柄承受压缩应力的状态下,应用弹性力学的基本方程,获得了假体柄、骨水泥、股骨轴向应力以及界面剪切应力随轴向位置的分布.界面失效是假体柄、骨水泥、骨结构承载的主要失效形式.热残余温差的存在,加速了假体柄、骨水泥和股骨界面的失效和假体柄的松动,加剧了股骨应力遮盖效应,这主要是骨水泥具有较高的热膨胀系数所致.由于Ti-6Al-4V（钛合金）材料的弹性模量和热膨胀系数比钴铬合金小,在一定程度上缓和了界面和股骨的失效,这和临床所见一致.     

Evaluation of properties and thermal stress field for thermal barrier coatings

In order to get thermal stress field of the hot section with thermal barrier coating (TBCs), the thermal conductivity and elastic modulus of top-coat are the physical key properties. The porosity of top-coat was tested and evaluated under different high temperatures. The relationship between the microstructure (porosity of top-coat) and properties of TBCs were analyzed to predict the thermal properties of ceramic top-coat, such as thermal conductivity and elastic modulus. The temperature and stress field of the vane with TBCs were simulated using two sets of thermal conductivity data and elastic modulus, which are from literatures and this work, respectively. The results show that the temperature and stress distributions change with thermal conductivity and elastic modulus. The differences of maximum temperatures and stress are 6.5% and 8.0%, respectively.     

Effect of cutting speed on residual stress of special coating during remanufacturing

To study the residual stress of the special coating at different cutting speeds, the cutting of FeAlCrBSiNb coating is analyzed with the finite element method (FEM) and experiment according to the coating characteristics. The CNC machine tool is used to cut the coating and the X-ray stress equipment is used to measure the residual stress of coating. The experimental and FEM results agree with each other. Also, the residual-stress coating depth is deeper and the residual stress of the coating surface is larger with increasing cutting speed. In addition, the residual stress of the coating surface is in the suppression state affected by axial residual stress and circumferential residual stress, and the residual stress of the deeper coating is in the tensile state based on the original state of arc spraying and cutting process.