铜/钨酸锆功能梯度薄膜的热应力场特征有限元分析

用有限元法建立了铜/钨酸锆缓和热应力功能梯度薄膜的数学模型,讨论了梯度薄膜的层数N,成分分布指数P,梯度层厚度Hf,基片厚度Hm与纯铜层厚度Hc,以及不同工作环境温度θ对薄膜热应力分布的影响。由热力学计算可知:梯度层数越多,缓和热应力效果越好。考虑到制备工艺复杂程度,参考数值模拟结果可知:当N≥5,P=1时,可以减小热应力最大值,热应力最大值出现在基体与梯度层的界面处;当N=5,2≤P≤3,热应力最大值位于梯度层内;适量增加梯度层厚度Hf和基片厚度Hm有利于减小热应力最大值,此梯度缓冲层在室温到α相钨酸锆陶瓷的相变温度(120℃)区间内,对于各厚度的功能铜层都有良好的保护作用。     

基体条件对等离子喷涂Sm_2Zr_2O_7热障涂层热冲击性能的影响

采用有限元分析软件ANSYS对等离子喷涂Sm2Zr2O7热障涂层在金属基体材质类型、厚度、半径变化时涂层的冲击热应力进行了分析。结果表明,涂层表面及表面层/金属粘结层界面处热应力及其应力梯度随着金属基体热膨胀系数增加而增大。当基体厚度超过20mm后,其对冲击热应力的影响基本可以忽略。当基体半径达到28mm后,涂层最大径向冲击热应力趋于稳定,最大轴向热应力随基体半径增加逐渐减小,最大剪切应力不受基体半径的影响。     

等离子喷涂Sm_2Zr_2O_7热障涂层残余热应力

采用有限元分析软件ANSYS对等离子喷涂Sm2Zr2O7热障涂层在金属基体材质类型、厚度、半径变化时涂层的残余热应力进行了分析。结果表明,金属基体的热膨胀系数对Sm2Zr2O7热障涂层的残余热应力有着显著影响,金属粘结层与表面陶瓷层界面处的残余应力及其应力梯度随着金属基体热膨胀系数增加而增大。金属基体厚度和半径不是影响Sm2Zr2O7热障涂层残余应力的主要因素。     

基体条件对Sm2Zr2O7/YSZ双陶瓷层热障涂层界面残余热应力的影响

采用有限元分析软件ANSYS对等离子喷涂Sm2Zr2O7/YSZ双陶瓷层热障涂层界面残余热应力分布进行了数值仿真。结果表明:基体厚度不同时,涂层界面Sm2Zr2O7/YSZ及界面YSZ/NiCoCrAlY对应应力及应力梯度基本不变,表明应力及应力梯度与基体厚度无关;但基体材质热膨胀系数对涂层系统界面的径向、轴向及剪切应力梯度有决定性的影响,且各应力梯度随金属基体的热膨胀系数差异增加而增大,表明基体材质是影响涂层界面径向残余热应力及应力梯度的根本原因。采用多层陶瓷结构并合理选择各层材质的热膨胀系数将更加有利于降低涂层应力梯度,进而改善涂层性能,延长涂层寿命。     

单层厚度对Sm2Zr2O7/8YSZ热障涂层残余热应力的影响

采用有限单元法研究了金属粘结层厚度、热生长氧化层厚度及陶瓷层厚度对Sm2Zr2O7/8YSZ双陶瓷层热障涂层残余热应力的影响。结果表明,金属粘结层厚度为0.1mm时,涂层径向应力最小。涂层径向应力随热生长氧化层的厚度的增加而减小。当YSZ厚度在0.1～0.5mm之间时,径向热应力随YSZ厚度增加而增大,超过0.5mm后应力基本不再变化。陶瓷层最佳厚度组合是0.1mmYSZ+0.9mmSm2Zr2O7。     

Sm_2Ce_2O_7/8YSZ热障涂层残余热应力及隔热性能计算机模拟

采用ANSYS软件分析了YSZ层厚度对Sm2Ce2O7/8YSZ热障涂层残余热应力的影响以及不同服役环境温度下涂层的隔热性能。结果表明,在涂层内部存在较大的热应力;径向应力及轴向应力在距离模型中心2~17 mm的范围内保持较为稳定的压应力,而在模型边沿处突然增加;当YSZ层厚度为0.9 mm时,涂层中的剪应力沿径向距离逐渐增大,而其他厚度下剪应力在模型边沿处急剧下降。当YSZ层厚度为0.3 mm时,涂层具有最小的热应力,从涂层表面至YSZ/粘结层界面处热应力逐渐降低。整个涂层表现出良好的隔热性能,其隔热性能随服役环境温度增加而增强。     

水冷壁式粉煤气化炉炉衬应力场数值模拟研究

针对水冷壁式粉煤气化炉在使用过程中由热应力引起的耐火材料和渣层损毁现象,建立了水冷壁的局部热应力模型,运用ANSYS有限元分析软件对水冷壁式粉煤气化炉使用过程的应力场进行了数值模拟研究。结果表明:1)水冷壁式气化炉的最大应力出现在锚固钉与耐火材料的界面以及耐火材料与渣层的界面,渣层最大应力的位置在渣层表面。2)渣层厚度的增加可显著降低锚固钉与耐火材料界面处的热应力,但是会导致渣层与耐火材料层间的热应力增大。3)当热导率为2～6 W·m~(-1)·K~(-1)时,随着热导率增加,会导致热应力迅速升高;而当热导率为6～10 W·m~(-1)·K~(-1)时,热应力基本稳定。4)降温速率越快,炉衬各点的温度和热应力下降得越快。     

大气等离子喷涂ZrO_2与Sm_2Zr_2O_7热障涂层的热冲击性能

采用ANSYS软件计算了等离子喷涂Sm2Zr2O7和ZrO2热障涂层的冲击热应力,并与试验结果进行了对比。结果表明,涂层表面存在较大的径向冲击热应力,该应力在冷却5秒后达到最大值后趋于平稳,并在距离试样中心12mm处急剧下降。在表面陶瓷层/金属粘结层界面处亦存在较大的冲击热应力梯度。由于Sm2Zr2O7涂层中较大的热冲击应力使得其抗热冲击性能低于ZrO2涂层,试验结果与有限元计算结果吻合良好。     

不同基体条件下Sm_2Zr_2O_7/YSZ热障涂层的残余应力

采用有限元法研究了基体条件对等离子喷涂Sm2Zr2O7/YSZ双陶瓷层热障涂层涂层的残余热应力,并与单一Sm2Zr2O7涂层进行了比较。计算结果表明,涂层的残余热应力随金属基体的热膨胀系数增加而增大,当基体厚度超过25mm后,径向应力不再变化,基体半径对涂层残余应力的影响可以忽略。Sm2Zr2O7/YSZ涂层的热应力明显小于单一的Sm2Zr2O7涂层,增加涂层的层数可缓解残余热应力。     

Ni–Ti钎料钎焊ZrO_2陶瓷的界面组织及接头的力学性能

采用Ni–Ti钎料实现ZrO_2陶瓷自身的钎焊连接,研究接头组织结构以及钎焊保温时间对界面组织和力学性能的影响。结果表明:在1 350℃保温10 min的钎焊条件下,陶瓷与钎料界面处生成TiO+Ni_2Ti_4O反应层,TiO紧靠陶瓷呈非连续层状分布,Ni_2Ti_4O呈连续层状分布,焊缝中心区域由NiTi和Ni_3Ti构成。随着保温时间的延长,反应层中TiO逐渐减少直至消失,Ni_2Ti_4O层的厚度逐渐增大;当保温时间为40 min时,Ni_2Ti_4O层中出现明显的裂纹。接头剪切强度随着保温时间的延长呈先增大后减小的趋势,当保温时间为30 min时,接头剪切强度达到最大值88.7 MPa。     

Temperature and Stress Distributions in a Hollow Cylinder of Functionally Graded Material: The Case of Temperature-Independent Material Properties

We have presented a numerical technique for analyzing one-dimensional transient temperature distributions in a circular hollow cylinder that was composed of functionally graded ceramic–metal-based materials, without considering the temperature-dependent material properties. The functionally graded material (FGM) cylinder was assumed to be initially in a steady state of gradient temperature; the ceramic inner surface was exposed to high temperature, and the metallic outer surface, which was associated with its in-service performance, was exposed to low temperature. Then, the FGM cylinder was cooled rapidly on the ceramic surface of the cylinder, using a cold medium. The transient temperature and related thermal stresses in the FGM cylinder were analyzed numerically for a model of the mullite–molybdenum FGM system. The technique for analyzing the temperature distribution is quite simple and widely applicable for various boundary conditions of FGMs, in comparison with methods that have been proposed recently by other researchers.     

Design of a C/SiC functionally graded coating for the oxidation protection of C/C composites

To reduce the residual thermal stress between the carbon fiber-reinforced carbon (C/C) composites and the SiC coating layer, functionally graded materials (FGM) consisting of a C/SiC compositionally graded layer (C/SiC interlayer) were adopted. After designing the compositional distribution of the C/SiC interlayer which can relieve the thermal stress effectively, the deposition conditions of the entire compositional range of the C/SiC composites were determined using a thermodynamic calculation. According to the design and calculation the C/SiC interlayer and the SiC outer layer were deposited on the C/C composites by a low pressure chemical vapor deposition (LPCVD) method at deposition temperatures of 1100 and 1300 °C. The stress calculation and the experimental results suggested that the SiC-rich compositional profile in the FGM layer is the most effective for relieving the thermal stress and increasing the oxidation resistance.     

Functionally Graded Materials Under Severe Thermal Environments

Thermal shock strengths of a plate of a functionally graded material (FGM) are analyzed when the plate is suddenly exposed to an environmental medium of different temperature. A finite element/mode superposition method is proposed to solve the time-dependent temperature field. The admissible temperature jump that the material can sustain is studied using the stress-based and fracture mechanics-based criteria. The critical parameters governing the level of the transient thermal stress in the medium are identified. The strength of FGMs under transient thermal stresses is analyzed using both maximum local tensile stress and maximum stress intensity factor criteria.     

Epoxy resin/polyurethane functionally graded material prepared by microwave irradiation

The glass‐transition temperature (T_g) and modulus (E) of graded material in a plastic–elastomer system prepared with layer‐by‐layer casting in connection with microwave curing were studied. Epoxy (EP) resin and polyurethane (PU) were selected as the plastic and elastomer components, respectively. The structure of the functionally graded material (FGM) was such that EP (E = 3.2 GPa, and T_g = 162°C) and PU (E = 0.069 GPa and T_g = ?54°C) were both surfaces, with a stepwise gradient in EP and PU content existing between the two over a thickness of 9 mm. Fourier transform infrared spectroscopy and scanning electron microscopy were used to investigate the PU content and the morphologies of the FGMs separately. Finite element analysis (FEA) was used to simulate the temperature and thermal stress distribution along the graded direction under a steady‐state, nonuniform temperature field. The results of FEA showed that the temperature and thermal stress distribution decreased along the graded direction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 994–999, 2004     

流延法制备对称型ZrO2/不锈钢功能梯度材料

采用流延法制备了成分梯度为10%(体积含量,下同)的对称型ZrO2/不锈钢功能梯度材料,利用成分分布函数和经典层合板理论对成分和残余热应力的分布进行了设计分析,观察了其微观形貌,并对截面的显微硬度进行了表征.结果表明:采用流延法制备的对称型ZrO2/不锈钢功能梯度材料成分过渡良好,梯度层界面结合紧密,与对称型层状ZrO2/不锈钢复合材料相比,最大残余热应力减小,热应力缓和效果明显.     

梯度功能陶瓷圆球的抗热震性

推导和提出了第三类边界条件下梯度功能材料(functionally gradient materials,FGM)圆球的瞬态温度场及瞬态热应力场表达式.基于陶瓷材料的临界应力断裂判据,通过求解梯度功能陶瓷圆球表面达到其局部断裂强度的时间,建立了引起其表面临界热应力的临界温差△Tc的表达式,并以此作为梯度功能陶瓷圆球的抗热震参数.通过计算实例并与均质陶瓷圆球对比,分析了材料的热-物理性能分布规律对其抗热震性的影响,并提出了高抗热震性FGM陶瓷圆球的设计原则:线膨胀系数和热扩散率应由表及里增大,而弹性模量应由表及里减小.     

Development of functionally graded ZrB2–B4C composites for lightweight ultrahigh-temperature aerospace applications

In the present work, a lightweight three-layer ZrB₂–B₄C functionally graded composite material has been developed by spark plasma sintering route. The functionally graded material (FGM) is free from interlayer defects and displays a smooth transition between the individual layers. The composition of each layer was designed to reduce the overall density without sacrificing the functionality of the material. The density of the FGM is almost 40% lower than monolithic ZrB₂ and 24% lower than ZrB₂–30B₄C rendering it potentially very attractive for high-temperature aerospace applications. A detailed structural characterization of the FGM was carried out to evaluate the elemental distribution in the graded composite, as well as determine the spatial distribution of the crystalline phases. Vickers hardness was measured within each layer and in the interlayer regions to further evaluate the gradient structure and interlayer transitions. Longitudinal elastic constants of the FGM along the thickness and across the layers measured using ultrasound phase spectroscopy showed that despite the gradient structure, the FGM can be treated as a quasi-isotropic solid.     

PSZ－Mo系梯度功能材料的热应力缓和设计与制备

对ＰＳＺ－Ｍｏ系梯度功能材料（ｆｕｎｃｔｉｏｎａｌｌｙｇｒａｄｉｅｎｔｍａｔｅｒｉａｌｓ简称ＦＧＭ）在制备过程中的热应力缓和性能进行了优化设计，用有限元方法解析了ＰＳＺ－Ｍｏ系两层叠层材料（即非梯度功能材料）在制备过程中的热应力分布情况。同时解析了ＰＳＺ－Ｍｏ系ＦＧＭ在制备过程中的热应力分布及缓和规律。揭示了ＰＳＺ－Ｍｏ系ＦＧＭ在制备过程中的热应力大小与组成分布形状指数Ｐ的关系，对所研究的体系通过热应力解析，得到制备中热应力缓和最佳时的Ｐ值，同时，对ＦＧＭ的制备工艺进行了研究，用粉末法分别制备出２４ｍｍ×５．６ｍｍ和３０ｍｍ×５ｍｍ完整的ＦＧＭ试样。     

MgO／Ni系梯度功能材料的设计与制备

对ＭｇＯ／Ｎｉ系梯度功能材料（ＦＧＭ），分别用实验和微观力学模型测定和计算了用于热应力缓和设计的各物性参数。讨论了两种结果之间存在差异的原因。用有限元方法模拟了制备过程中ＦＧＭ的热应力，得到ＭｇＯ／Ｎｉ系ＦＧＭ的综合设计准则。按设计结果进一步调整粉末工艺性质，成功地烧制出ＭｇＯ／Ｎｉ系ＦＧＭ。