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《塑性工程学报》2017,(3)
对含单边裂纹的40Cr Ni Mo钢构件进行脉冲放电止裂,分析了脉冲放电止裂后结晶区、相变区和基体区的显微硬度变化。结果可知,止裂后的裂纹尖端变得圆钝,曲率半径增大,应力集中得到消除,有效地阻止了裂纹的继续开裂;结晶区晶粒得到细化,相变区晶格畸变及位错密度增大导致塑性变形抗力增大,两者的显微硬度得到了不同程度的提高。应用Eshelby等效夹杂原理对脉冲放电止裂后单边裂纹尖端发生组织转变的相变应力进行了理论和数值计算,最终获得相变应力的计算方程;采用ANSYS有限元软件对于含单边裂纹构件脉冲放电止裂进行数值模拟,验证体积变化和屈服强度变化对相变应力的影响。最后,简述了含单边裂纹构件脉冲放电止裂技术对于异种材料焊接裂纹的止裂修复工程应用。 相似文献
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《组合机床与自动化加工技术》2016,(3)
应用有限元法对Si3N4基复合陶瓷刀具温度场和热应力进行了分析计算。通过建立Si3N4基复合陶瓷刀具三维温度场和热应力的有限元模型,确定边界条件,分析求解得到Si3N4复合陶瓷刀具的温度场和热应力。结果表明:普通单质陶瓷刀具随着切削速度的提高,其由切削温度引起的最大热Mises应力、最大热切应力以及最大热拉应力的增长幅度大于Si3N4基复合陶瓷刀具。说明Si3N4基复合陶瓷刀具由热应力引起的破坏比单质陶瓷刀具小,寿命长,更适合于高速切削。 相似文献
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目的 研究退火过程中La Mg Al11O19热障涂层内部残余热应力的分布情况及其对热障涂层热稳定性的影响机理。方法 基于等离子喷涂制备的La Mg Al11O19/YSZ双热障涂层物理模型,采用Abaqus建立数值仿真模型,通过温度位移耦合计算,系统分析不同退火温度下LaMgAl11O19热障涂层内部残余热应力的分布情况。通过扫描电镜,观察退火前后涂层表面及断面的微观组织形貌。根据数值模拟结果及涂层SEM图像,分析残余热应力对LaMgAl11O19热障涂层热稳定性的影响,探究引起涂层裂纹损伤失效的影响因素。结果 数值模拟结果显示,La Mg Al11O19热障涂层内部的残余热应力以径向应力为主,其值远大于轴向应力及剪切应力。退火中,径向残余热应力在径向距离0~2.4mm内缓慢增长到最大值,而在x=2.4mm至径向边缘范围内急剧降低。退火后,在涂层径向边缘位置出现应力集... 相似文献
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考虑了热障涂层在服役过程中发生的陶瓷层烧结和氧化层增厚作用,对燃气轮机起动过程中涂层热应力进行了数值研究。通过瞬态传热模拟获得起动过程温度场,运用顺序热应力耦合求解起动过程热应力。其中起动初始的陶瓷层烧结和氧化层增厚状态,通过预先模拟高温烧结和氧化层增厚过程来获得,并通过ABAQUS子程序分别实现。结果表明,起动过程中涂层瞬态温度场的变化主要受燃气温度的变化规律所影响。起动过程未见热应力激增现象,陶瓷层烧结和氧化层增厚主要对起动初期,尤其是起动过程的初始残余应力有重要影响,对起动过程中后期的影响可忽略。烧结对陶瓷层和粘结层的热应力均有较大影响,而氧化层增厚对陶瓷层热应力的影响很小,但其对粘结层热应力的影响比烧结更大。 相似文献
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Aside from its importance as a design parameter for thermal barrier coatings, measuring thermal conductivity of thermal sprayed
coatings itself provides a unique method to critically characterize the nature, quantity, and anisotropy of the defect morphologies
in these splat-based coatings. In this paper, the authors present a systematic assessment of thermal conductivity of wide
range using the flash diffusivity technique. For the case of plasma sprayed yttria-stabilized zirconia (YSZ), coatings obtained
from wide-ranging initial powder morphologies as well as those fabricated under different particle states were characterized.
Both in-plane and through-thickness properties were obtained. Other material systems that were considered include: metallic
alloys and semiconductors of interests. Issues such as reproducibility and reliability in measurements were also considered
and assessed. Finally, work in collaboration with the Oak Ridge National Laboratory (ORNL) for alternate approaches to characterization
of thermal conductivity as well as high-temperature measurements was performed.
This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials
Park, OH, 2006. 相似文献
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无冷却喷涂形成的热障涂层裂纹体系,可提高陶瓷顶层应变容限.但目前缺乏对裂纹体系的系统研究,特别是横向分叉裂纹.因此,文中研究送粉率和基体预热温度对陶瓷顶层裂纹系统的定量影响,并比较不同裂纹系统的热循环寿命.结果表明,增加送粉率,垂直裂纹密度和横向分叉裂纹长度均呈现先大后小的趋势.预热温度的提高可增加涂层中垂直裂纹数量,但横向分叉裂纹长度呈现先增后降的趋势.热循环试验表明,维持一定垂直裂纹的同时,降低横向分叉裂纹可提高涂层热循环寿命. 相似文献
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Anisotropic thermal conductivities of the plasma-sprayed ceramic coating are explicitly expressed in terms of the microstructural
parameters. The dominant features of the porous space are identified as strongly oblate (cracklike) pores that tend to be
either parallel or normal to the substrate. The scatter in pore orientations is shown to have a pronounced effect on the effective
conductivities. The established quantitative microstructure-property relations, if combined with the knowledge of the processing
parameters-resulting microstructure connections, can be utilized for controlling the conductivities in the desired way. 相似文献
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Reliability of laser flash thermal diffusivity measurements of the thermal barrier coatings 总被引:5,自引:0,他引:5
The thermal diffusivity of free standing thermal barrier coatings (TBCs) was measured by the laser flash technique. The combination
of low thermal conductivity (1 to 2 W/m K) and small TBC thickness (300 to 600 μm thick) can cause errors in the measurements.
Back surface (opposite the laser) temperatures of free standing plasma-sprayed TBCs were measured as a function of time and
laser power. The front surface temperatures were calculated using thermal transport equations. In the high power region, thermal
diffusivity decreased significantly with increasing laser power. In the moderate power region, thermal diffusivity remained
constant. In the low power region, measurement became unreliable because of noise. The detector nonlinearity was believed
to be a possible cause of deviation in the high power region. Measurements at different laser power levels should be conducted
in order to obtain reliable thermal diffusivity values for TBCs. 相似文献
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Ultrafast thermal plasma physical vapor deposition of yttria-stabilized zirconia for novel thermal barrier coatings 总被引:1,自引:0,他引:1
Heji Huang Keisuke Eguchi Makoto Kambara Toyonobu Yoshida 《Journal of Thermal Spray Technology》2006,15(1):83-91
This research aims to develop advanced thermal plasma spraying technology for the next-generation thermal barrier coatings
(TBCs) with a high power hybrid plasma spraying system. By using thermal plasma physical vapor deposition (TP-PVD), various
functional structured yttria-stabilized zirconia (YSZ) coatings were deposited. Parameters, such as powder feeding rate, hydrogen
gas concentration, and total mass flow rate of the plasma gas, were optimized, and their influences on the evaporation of
YSZ powder were investigated. Ultrafast deposition of a thick coating was achieved at a rate of over 150 μm/min. The deposited
porous coating has a low thermal conductivity of 0.7W/mK and the dense coating with interlaced t′ domains possesses a high nanohardness of 27.85 GPa and a high reflectance. These characteristics show that the TP-PVD technique
is a very valuable process for manufacturing novel TBCs. 相似文献
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采用多种方法制备不同类型的Al2O3-13%TiO2热障涂层,即等离子喷涂常规涂层、纳米结构涂层及激光熔覆纳米结构涂层.在分析三类涂层微观组织的基础上,对其隔热性能进行了比较.结果表明,即等离子喷涂常规陶瓷涂层呈典型的层状堆积特征,纳米结构涂层都为特殊的两相结构,其中部分熔化区由类似的残留纳米粒子组成,等离子喷涂纳米结构涂层的完全熔化区为片层状结构,而相应的激光熔覆涂层的完全熔化区则为细小等轴晶.在相同条件下,等离子喷涂纳米结构热障涂层具有最好的隔热性能,而激光熔覆纳米结构涂层的隔热性能要好于等离子喷涂常规涂层. 相似文献
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The behavior of macroscopic long cracks in the ceramic top coat of a thermal barrier coating (TBC) system subjected to thermal
shock loading and the influence of the cracks on the coating durability were investigated experimentally and numerically.
Thermal shock testing was conducted until coating failure. Comparisons were made with coating samples without macroscopic
cracks. The experimental results revealed that the presence of macroscopic cracks reduces the life of the TBC. The finite-element
method, with a fracture mechanics approach, was applied to analyze preexisting long cracks, and the calculations correlate
well with the experimental findings. It was found that the life of the coating is reduced with crack length as well as with
maximum cycle temperature. It was also found that the stress-intensity factors for long cracks are initially high and decrease
with the number of temperature cycles, which indicates that rapid crack growth occurs during the first number of cycles. 相似文献
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A. J. Slifka B. J. Filla J. M. Phelps G. Bancke C. C. Berndt 《Journal of Thermal Spray Technology》1998,7(1):43-46
The conductivity of a thermal-barrier coating composed of atmospheric plasma sprayed 8 mass percent yttria partially stabilized
zirconia has been measured. This coating was sprayed on a substrate of 410
stainless steel. An absolute, steady-state measurement method was used to measure thermal conductivity
from 400 to 800 K. The thermal conductivity of the coating is 0.62 W/(m×K). This measurement has shown
to be temperature independent. 相似文献