基于不同基体条件的Sm2Zr2O7/YSZ双层热障涂层界面残余热应力的数值仿真

采用有限元分析软件ANSYS对2Cr13基体等离子喷涂Sm2Zr2O7/YSZ双层热障涂层界面残余热应力分布进行了仿真。结果表明:在涂层Sm2Zr2O7/YSZ及YSZ/NiCoCrAlY界面存在较大的残余热应力,且应力梯度基本不变,表明应力梯度与基体厚度、半径无关。     

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。     

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。     

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。     

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。     

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。     

Sm_2Ce_2O_7-YSZ功能梯度热障涂层热冲击性能计算机模拟

采用有限元技术分析了Sm_2Ce_2O_7-YSZ功能梯度热障涂层的水淬热冲击性能,研究了金属基体材质及尺寸对其热冲击性能的影响。结果表明,在Sm_2Ce_2O_7/YSZ功能梯度热障涂层中存在较大的冲击热应力。涂层径向热应力从中心处到试样边缘逐渐递减。基体的热膨胀系数对涂层冲击应力影响最明显,涂层中热应力随基体厚度增加而增大,但基体厚度超过20 mm后热应力趋于稳定。基体半径超过14 mm后径向应力不再增大,基体半径超过10 mm后轴向应力和剪切应力不再降低。与Sm_2Ce_2O_7涂层相比,Sm_2Ce_2O_7-YSZ功能梯度涂层具有最大热应力,其结构仍需要进一步优化。     

结构对Sm_2Ce_2O_7-YSZ热障涂层残余应力及热冲击性能的影响

采用ANSYS软件分析了涂层结构对Sm_2Ce_2O_7-YSZ热障涂层热应力的影响。结果表明,在涂层表面存在较大的残余热应力和热冲击应力。径向残余热应力从试样中心至边沿逐渐降低,轴向和剪切残余应力在试样边沿明显增大。径向冲击应力与径向残余应力分布相似,但远大于径向残余应力。轴向冲击应力在试样边沿从压应力转变为拉应力,剪切冲击应力则急剧降低。涂层层数的增加有利于降低涂层的残余应力和冲击应力。     

不同基体材质的Sm_2Ce_2O_7涂层热冲应力的数值模拟

采用ANSYS软件对Ni、45钢、SiC_f/SiC、2Cr13、1Cr13Ni9Ti五种不同基体Sm_2Ce_2O_7涂层的热冲击应力进行了计算,系统研究了基体材质对热应力的影响规律。结果表明,不同基体材质涂层均存在较大的热应力,最大热应力绝对值出现在热冲击瞬间,35 s后趋于稳定,径向应力的影响远大于轴向与剪切方向;径向应力在横向距离小于12mm时保持稳定,横向距离在12～18 mm范围内,应力梯度逐渐增大;SiC_f/SiC基体在表面及表面层/粘结层界面的应力状态为压应力,且表面径向、表面及表面层/粘结层界面的轴向应力梯度均低于其他基体涂层,有利于界面的结合及防止横向裂纹的扩展;热膨胀系数的差异造成SiC_f/SiC基体涂层与其他金属基体涂层的体积形变方向不一致,同时粘结层/基体界面应力绝对值及应力梯度略大于2Cr13基体涂层,基体的热膨胀系数是影响热冲击性能的关键因素之一。     

陶瓷涂层三明治板的抗热震性

采用解析法研究了第3类边界条件下双面陶瓷涂层三明治板的瞬态温度场及瞬态热应力场.对不同Biot模数的热冲击过程中,Al2O3涂层/硬质合金(WC-8%Co,质量分数)基体/Al2O3涂层三明治板的瞬态热应力进行了数值计算.分析了涂层/基体厚度比、涂层与基体热-物理性能匹配对陶瓷涂层三明治板表面热应力峰值的影响.结果表明:陶瓷涂层三明治板的基体的热导率、线膨胀系数和弹性模量应高于涂层,这样可以降低其表面热应力,获得高抗热震性陶瓷涂层三明治板.此外,涂层厚度应尽可能小,以利于改善涂层的抗热震性.     

Effect of substrate temperature on the microstructure and properties of thick plasma-sprayed YSZ TBCs

Thick (∼1.2 mm) thermal barrier coatings (TBCs) consisting of YSZ were deposited by plasma spraying. Spraying parameters were varied in a controlled manner to produce different microstructures. The effect of substrate temperature on the microstructural features and subsequently on the Young's modulus was investigated. In addition, the residual stresses in the coatings were estimated using a numerical model and they were related to the microstructural features observed. Results showed that crack segmentation density, residual stresses in the coatings and thus coating properties are strongly affected not only by the average substrate temperature during spraying but also the variations between the minimum and maximum substrate temperature.     

Investigation of thermal residual stresses during laser ablation of tantalum carbide coated graphite substrates using micro-Raman spectroscopy and COMSOL multiphysics

Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model.     

Dy2Ce2O7和Y2Ce2O7稀土铈酸盐的制备及热导率

采用固相反应法在1600℃下保温10小时制备了Dy2Ce2O7和Y2Ce2O7陶瓷材料。分析了其相组成、微观组织和热导率。XRD结果表明,成功合成了具有萤石晶体结构的单一相Dy2Ce2O7和Y2Ce2O7。其组织结构致密,晶界清晰,无未反应物或杂质相存在。由于氧空位以及取代原子与基质原子之间的质量差异所导致的声子散射,使得Dy2Ce2O7和Y2Ce2O7具有比YSZ更低的热导率,这些结果表明,Dy2Ce2O7和Y2Ce2O7均可用作将来热障涂层用候选材料。     

Residual stresses in marine coatings under simulated service conditions

Studies have been made of the effect of cyclic temperature changes and wet/dry cycling on the residual stresses in marine coatings applied to steel substrates. A thermoplastic and a thermoset have been use as single coatings and as bi-layers consisting of the thermoset applied on top of the thermoplastic. Cyclic changes associated with differential thermal expansion/contraction between substrate and coating and with water absorption or desorption were observed, and it was found in addition that progressive changes in residual stress were sometimes superimposed on the cyclic changes. The effect was larger with the thermoplastic coating than with the thermoset. The stresses developed in the bi-layers were generally smaller than those in single layer coatings and were generally less sensitive to the cyclic changes in conditions. The effects were partly controlled by the thicknesses of the two layers in the bi-layer coatings. Stresses as high as 6 MPa were measured during the course of this work, a significant fraction of the failure strength of the coatings.     

Abrasion resistance of ceramic thin films of ZrO2/SiO2 on stretched grade polymethyl methacrylate substrates

Abrasion resistance of stretched grade polymethyl methacrylate (PMMA) was increased by using the sol–gel method to have it coated with a ZrO₂/SiO₂ thin film. Different molar ratios of Zr(OPr)₄/Si(OPr)₄ sols were prepared as precursors with propanol. These sols were used for dip-coating the stretched PMMA surfaces to establish very smooth thin films of amorphous Zr–O–Si. Fourier Transform Infrared spectroscopy (FT-IR) was employed to study vibrations of Zr–O–Si bonds within the thin film. The phase analysis was undertaken via X-ray Diffraction (XRD) method. The morphology and thickness of coatings on PMMA were investigated by means of Scanning Electron Microscopy (SEM). The results showed that coating had an amorphous structure with its thickness within the range of 80–100 nm. The water contact angle of PMMA substrates altered from 73° before coating to less than 64° after coating. Once coated, the PMMA substrate had its transparency characteristic (within the UV–vis region) increased. Furthermore, the influences of thermal treatment temperature and molar ratio of precursors (Zr(OPr)₄/Si(OPr)₄) on abrasion resistance of the coatings were studied.     

Determination of the Elastic Modulus and Residual Stresses in Ceramic Coatings Using a Strain Gage

Formulas based on the beam theory are derived for calculating the in-plane elastic modulus and residual stresses in ceramic coatings. In addition to theoretical derivation, experimental data for SiC coating/graphite substrate composites are proposed. The results indicate that the modulus of SiC coatings is 359 GPa. The residual stresses are in compression and are functions of the ratio of substrate thickness to coating thickness.     

Thermal stability enhancement of Cr2AlC coatings on Zr by utilizing a double layer diffusion barrier

Decomposition of Cr₂AlC deposited onto a Zr substrate and vacuum-annealed is observed at 800 °C as Al diffuses from the MAX phase into the Zr substrate. A double layer of ZrN and AlN has been predicted by CALPHAD calculations to act as diffusion barrier between the Zr substrate and Cr₂AlC. Experimental thermal stability investigations corroborate this prediction by confirming that the proposed double layer diffusion barrier coatings suppress the decomposition of Cr₂AlC for one hour at temperatures of up to 1000 °C.