梯度功能材料的研究现状与展望

回顾了梯度功能材料（ＦｕｎｃｔｉｏｎａｌｙＧｒａｄｉｅｎｔＭａｔｅｒｉａｌｓ，ＦＧＭ）的诞生背景，综述了ＦＧＭ的表征技术，制备方法和研究现状。ＦＧＭ的应用领域不再局限于结构材料，已扩展到其它功能材料，成为国际材料科学研究的前沿课题。本文重点介绍ＦＧＭ在电子材料和光学工程方面的应用，并对ＦＧＭ的未来进行了展望。     

Ni－ZrO_2精细功能梯度材料的设计、制备和分析

基于我们以前发表的精细复合Ｎｉ－ＺｒＯ２的热渗流现象；采用薄层迭层法，设计和制备了２８种不同成分分布曲线Ｙ［ｐ，Ｙ（１）］（Ｘ）的Ｎｉ－ＺｒＯ２ＦＦＧＭ；并用电子探针和扫描电子声显微镜分析了其成分分布、应力分布和组织结构；最后得到一种成分分布曲线为Ｙ［１，４０］（Ｘ）的Ｎｉ－ＺｒＯ２ＦＦＧＭ，它具有较显著的应力缓和效果、较高的结构完整性和致密度．本文为Ｎｉ－ＺｒＯ２ＦＦＧＭ的优化设计、制备和研究其成分分布及应力分布提供了一种崭新而有效的方法．     

NiO／NiFeCo／Cu／NiFeCo自旋阀结构的巨磁电阻效应及影响因素的研究

用电子蒸发的方法制备ＮｉＯ／ＮｉＦｅＣ／Ｃｕ／ＮｉＦｅＣｏ自旋阀多层膜,通过磁场中退火得到好的偏置型自旋阀ＧＭＲ效应。通过对制备态以及磁场退火后样品的ＭＲ曲线的研究,讨论了交换耦合作用,单层磁性能以及层间耦合作用对材料ＧＭＲ效应的大小和磁场灵敏度的影响,得出提高交换耦合作用,改善单层磁性能和尽可能减小层间耦合将有得于得到高性能的偏置型自旋阀ＧＭＲ材料的结论。     

HA-Ti生物功能梯度材料微观组织及热应力缓和特性

本文用粉末冶金法制备了ＨＡ－Ｔｉ系生物ＦＧＭ,并测定了ＨＡ－Ｔｉ复合体材料的弹性模量和热膨胀系数．应用经典叠层板理论和热弹性力学理论分析了ＨＡ－Ｔｉ系ＮＦＧＮ双层板和ＨＡ－Ｔｉ系ＦＧＭ的制备残余热应力和热应变．结果表明,ＨＡ－Ｔｉ系生物ＦＧＭ呈现出宏观不均匀性与微观连续性的组织特征．ＨＡ－Ｔｉ系复合体材料的弹性模量在Ｔｉ－ＨＡ８０达到谷值,并受到气孔率的影响．其热膨胀系数随着ＨＡ含量和测试温度的升高而增大．残余热应力和残余热应变强烈依赖于组成分布,ＦＧＭ由于组成梯度化减小了成分变化幅度,其最大残余拉应力只有ＨＡ／Ｔｉ直接叠合体（ＮＦＧＭ）的１／３,具有显著缓和热应力的功能.     

Al_2O_3-Ti系梯度功能材料残余热应力的有限元分析

采用有限元方法（ＦｉｎｉｔｅＥｌｅｍｅｎｔＭｅｔｈｏｄ）对Ａｌ２Ｏ３－Ｔｉ系梯度功能材料在制备过程中产生的残余热应力进行了线弹性分析。详细讨论了梯度层数目、梯度层厚度和成分梯度指数对应力大小和分布的影响，确定了各项最佳参数。非梯度功能材料（ＮＦＧＭ）与优化后的梯度功能材料的残余热应力对比结果显示：梯度功能材料缓和热应力的效果十分显著。     

Ni—ZrP2精细功能梯度材料的设计,制备和分析

基于我们以前发表的精细复合Ｎｉ－ＺｒＯ２的热渗流现象，采用薄层迭层法，设计和制备了２８种不同成分分布曲线的Ｎｉ－ＺｒＯ２ＦＦＧＭ；并用电子探针和扫描电子声显微镜分析了其成分布、应力分布和组织结构；最后得到一种成分分布为Ｙ「１．４０」（Ｘ）的Ｎｉ－ＺｒＯ２ＦＦＧＭ，它具有较显著的应力缓和效果，较高的结构完整性和致密度，本文为Ｎｉ－ＺｒＦＦＧＭ的优化设计制备和研究其成分发布及应力分布提供了一种崭新而有     

SiC/C功能梯度材料的制备和评价

以粉末冶金方法制备了块体SiC／Ｃ ＦＧＭ,该材料结合了SiC的耐腐蚀、抗冲刷和石墨的高抗热冲击性能,具备良好的抗热疲劳性能,拓展了ＳiC陶瓷的应用前景．     

功能梯度材料原理及其在固体氧化物燃料电池中的应用设想

概述了功能梯度材料（ＦＧＭ）的概念扩制备技术，提出了将ＦＧＭ原理应用于固体氧化物燃料电池（ＳＯＦＣ）的设想，并探讨了技术可能性及应用ＦＧＭ原理值得注意的几个问题。     

提高热喷涂层致密性技术的研究现状及发展方向

提高热喷层的致密性,减少其孔隙,可以防止涂层过早腐蚀,延长其使用寿命。简述了热喷涂层孔隙出现的原因;介绍了减少热喷涂层孔隙率、提高涂层耐腐蚀性能的方法;指出了提高热喷涂层耐腐蚀性能的发展方向。     

含TiB2陶瓷相热喷涂涂层的研究进展

TiB2具有高耐磨、高耐腐蚀、耐高温、抗氧化等优异性能,但由于高脆性和材料制备的困难性,使其用作结构材料还很难.通过各种工艺制备含有TiB2陶瓷相的涂层既可充分发挥材料的优异特性,满足工件所需的耐磨耐高温耐腐蚀等性能,又节省了材料节约了成本.本研究介绍了先进陶瓷材料TiB2的主要结构性能以及目前制备TiB2涂层的主要方法,着重介绍了有关国内外热喷涂法制备含TiB2陶瓷相涂层的研究进展和成果,并对不同热喷涂工艺的特点与发展趋势做了分析和讨论,最后阐述了TiB2涂层的成功应用情况及其广阔的发展前景.     

Geometry effects of substrate and coating layers on the thermal stress response of FGM structure

Summary Due to transient temperature change, the plane strain elastic-plastic problem for a functionally graded material (FGM) bonded to a homogeneous coating layer and a metal substrate is considered by the use of the finite element method (FEM). The substrate and the coating are assumed to be aluminum and partially stabilized zirconia, respectively. The FGM layer is a particulate composite of aluminum and partially stabilized zirconia with volume fractions continuously varying through the thickness. Generally in high temperature applications, the FGM system is sandwiched between a substrate layer and a coating layer. The coating layer increases the protection from heat but decreases the thermal shock resistance while the substrate layer increases the rigidity of the structure and decreases strength-related properties at high temperature. In order to compromise the thickness of both the coating and substrate layers, different values of the substrate and coating thickness are studied in order to evaluate their effects on the thermal stress response of the FGM structure. Since the main objective of the FGMs is using them in different applications with severe thermal loading conditions, the thermal stresses may be so high that some reinforcements may be fractured and/or debonded from the matrix giving a weakening effect instead of a reinforcing one. Hence, the behaviors of the reinforcements and the matrix are essential to be studied. In this regard, microscopic constitutive equations along with the temperature-dependent properties of the constituent materials are considered to enable us obtaining more realistic results of thermal stresses. Since the FGM structures are fabricated at high temperatures, thermal residual stresses are produced. In order to find out the importance of the consideration of the residual stresses arising from the fabrication process, the FGM structure with stress-free conditions is heated to the operating temperature, and its thermal stress response is compared with that one where the residual stresses are taken into account. Also, several functional forms of gradation of the constituents in the FGM layer are examined to reach the optimum profile giving the minimum stress level for the FGM structure under thermo-elasto-plastic behavior.     

Minimizing Thermal Residual Stress in Ni/Al₂O₃ Functionally Graded Material Plate by Volume Fraction Optimization

The thermal residual stress in the fabrication of functionally graded material (FGM) systems can give rise to various mechanical failures. For a FGM system under a given fabrication environment, the thermal residual stresses are determined by the spatial distribution of its constituent components. In this study, we optimize a Ni/Al₂O₃ FGM plate aiming at minimizing the thermal residual stresses through controlling its compositional distribution. Material properties are graded in the thickness direction following a power law distribution in terms of the volume fractions of constituents (P-FGM). An analytical model and a hybrid genetic algorithm with the pattern search are employed to predict and to minimize the thermal residual stresses, respectively. Simulation results show that an optimal design of the FGM plate could help fulfill its potential in reducing the thermal residual stresses.     

Evaluation of residual stresses in PVD-coatings. Part 2

The values of residual stresses in PVD-coatings of titanium, aluminum and niobium nitrides are determined by the flexible specimen method. An experimental-and-calculation procedure for separating the structural and thermal components of residual stresses is proposed that allows one to determine the thermal expansion coefficients of the coating materials and a general level of residual stresses in coatings on a substrate of any material. The dependence of the residual stress on the roughness of the substrate surface is established. The possibility of adjusting the level of residual stresses in coatings by the discrete surface topography formation is shown.     

热喷涂涂层和基体中残余应力预报与控制研究

分析研究了热喷涂涂层和基体中残余应力产生的原因并发展建立了相应的理论模型。依据该模型,不但可以计算骤冷过程和冷却过程在涂层/基体结构内引发的残余应力,而且首次分析了沉积过程中,基体/涂层因喷射冲击(即喷涂粒子高速撞击基体及形成的涂层表面)而产生的残余应力,以及因基体/涂层热膨胀系数不匹配产生的残余应力。理论计算结果与实验结果基本吻合。通过理论计算,可以预报涂层/基体中残余应力的大小,并根据需要控制涂层/基体中残余应力的分布。对即将进行的热喷涂工艺具有一定的指导意义。     

Three dimensional fracture analysis of FGM coatings under thermomechanical loading

The main objective of this study is to examine the three dimensional surface crack problems in functionally graded coatings subjected to mode I mechanical or transient thermal loading. The surface cracks are assumed to have a semi-elliptical crack front profile of arbitrary aspect ratio. The cracks are embedded in the functionally graded material (FGM) coating which is perfectly bonded to a homogeneous substrate. A three dimensional finite element method is used to solve the thermal and structural problems. Collapsed 20-node isoparametric elements are utilized to simulate the strain singularity around the crack front. The stress intensity factors are computed by using the displacement correlation technique. Four different coating types are considered in the analyses which have homogeneous, ceramic-rich (CR), metal-rich (MR) and linear variation (LN) material composition profiles. In the mechanical loading problems, the composite medium is assumed to be subjected to fixed-grip tension or three point bending. In the thermal analysis, a transient residual stress problem is considered. The stress intensity factors calculated for FGM plates are in good agreement with the previously published results on three dimensional surface cracks. The new results provided show that maximum stress intensity factors computed during transient thermal loading period for the FGM coatings are lower than those of the homogeneous ceramic ones.     

Inverse problems of material distributions for prescribed apparent fracture toughness in FGM coatings around a circular hole in infinite elastic media

This study is concerned with the inverse problem of calculating material distributions intending to realize prescribed apparent fracture toughness in functionally graded material (FGM) coatings around a circular hole in infinite elastic media. The incompatible eigenstrain induced in the FGM coatings after cooling from the sintering temperature, due to mismatch in the coefficients of thermal expansion, is taken into consideration. An approximation method of determining stress intensity factors is introduced for a crack in the FGM coatings in which the FGM coatings are homogenized simulating the nonhomogeneous material properties by a distribution of equivalent eigenstrain. A radial edge crack emanating from the circular hole in the homogenized coatings is considered for the case of a uniform pressure applied to the surfaces of the hole and the crack. The stress intensity factors determined for the crack in the homogenized coatings represent the approximate values of the stress intensity factors for the same crack in the FGM coatings, and are used in the inverse problem of calculating material distributions in the FGM coatings intending to realize prescribed apparent fracture toughness in the coatings. Numerical results are obtained for a TiC/Al₂O₃ FGM coating, which reveal that the apparent fracture toughness in FGM coatings around a circular hole in infinite elastic media can be controlled within possible limits by choosing an appropriate material distribution profile in the coatings.     

Thermal Residual Stresses in Multilayered Coatings

The mechanical integrity and reliability of coated devices are strongly affected by the residual stresses in thin films and coatings. However, due to the metallurgical complexity of materials, it is rather difficult to obtain a closed-form solution of residual stresses within multilayered coatings (e.g. functionally graded coatings, FGCs). In this paper, an analytical model is developed to predict the distribution of residual stresses within multilayered coatings. The advantage of this model is that the solution of residual stresses is independent of the number of layers. Specific results are obtained by calculating elastic thermal stresses in ZrO2/NiCoCrAIY FGCs, which consist of different material layers. Furthermore, the residual stress distribution near the edges and the stress-induced failure modes of coating are also analyzed. The topics discussed provide some insights into the development of a methodology for designing fail-safe coating systems.     

等离子喷涂热障涂层残余应力的实验与模拟研究

分别采用真空和大气等离子体喷涂工艺在GH3128镍基高温合金基材表面制备CoNiCrAlY结合层和氧化钇部分稳定的氧化锆陶瓷层组成热障涂层。采用有限元模拟计算了涂层的残余应力, 研究了基材预热对打底层与陶瓷层界面应力分布的影响规律。结果表明, 预热基材可以显著地降低陶瓷顶层内部产生的残余拉应力。采用钻孔法测量了涂层中的残余应力并与模拟结果作定量比较, 结果表明: 有限元模拟计算结果与实验测量结果能较好吻合。     

等离子喷涂ZrC基涂层逐道逐层沉积残余应力模拟与实验验证

采用商用ANSYS14.5软件, 依据复合梁增层力学模型, 采用逐道逐层累积模型模拟了C/C复合材料表面等离子喷涂ZrC基涂层沉积残余应力的特征, 分析了SiC过渡层、第二相(SiC, MoSi₂)和涂层厚度对ZrC基涂层残余应力的影响, 并进行了实验验证。结果表明, SiC过渡层有效缓解了涂层与基体的热失配应力。涂层体系的应力随着涂层厚度的增加逐渐减小, 符合应力松弛和叠加规律。在涂层内部的径向应力以拉应力为主, 基体中主要为压应力, 且在界面边缘存在压应力集中的极限区域, 易使涂层产生裂纹并沿界面扩展。该模拟采用逐道逐层累积的方法更逼近实际喷涂过程, 能更准确预测涂层的残余应力。