热传导对双陶瓷热障涂层隔热效果影响研究

为了更好地设计双陶瓷热障涂层结构,考察在制备和服役过程中热导率的变化对隔热效果的影响,建立了双陶瓷热障涂层半透明数学模型,采用有限元ANSYS软件模拟了稳态隔热效果.结果表明:顶层陶瓷层的热导率增大降低了隔热效果,且随顶层厚度增加隔热效果降低幅度增大;第2层陶瓷层的热导率增大降低了隔热效果,且随顶层厚度增加隔热效果降低幅度减小;陶瓷层半透明且衰减系数很小时,顶层厚度增加,隔热效果先快速后缓慢增加至不变甚至略有降低,且远低于相同条件下不透明时.顶层陶瓷层热导率变化对隔热效果影响大于第2层陶瓷层.     

粗糙陶瓷涂层与刚性平面滑动摩擦过程的数值模拟

陶瓷涂层在滑动接触过程中的温升对零部件的接触和力学性能有重要的影响.应用有限元法,建立了含多粗糙峰陶瓷涂层与刚性平面的滑动接触模型,并通过热机耦合计算对滑动摩擦过程进行了数值模拟,分析了滑动过程中陶瓷涂层、粘结层和基体的温度及应力分布规律,研究了相对滑动速度、初始压入量、摩擦系数和涂层厚度对各部分的温升、等效应力和接触应力的影响.结果表明:陶瓷涂层的最高温度出现在粗糙峰的滑动接触面上,其高温区也集中在粗糙峰部分;与静态接触相比,滑动接触改变了各部分内部应力的分布;粘结层和基体的最大等效应力和最高温度随着运动速度和摩擦系数的增大而升高,随涂层厚度的增加而降低;粘结层和基体在滑移前后的最大等效应力及最高温度均与压入量近似成线性关系.     

热震中7YSZ热障涂层结构演变

采用低温超音速等离子喷涂(LT-HVOF)在镍基高温合金基体上制备了NiCoCrAlYTa粘结层, 使用大气等离子喷涂(APS)在粘结层上`制备了7wt%Y₂O₃-ZrO₂ (7YSZ) 陶瓷层。基于动态试验即热震实验研究了粘结层的扩散氧化机制, 探讨了陶瓷层的烧结及相变过程并观察了涂层的结构演变。实验结果表明: 动态热循环下随着热震次数的增加, 粘结层组元扩散氧化形成热生长氧化物(TGO)且厚度逐渐增加。此外, 粘结层组元在温度梯度下沿陶瓷层内部裂纹向高温区扩散, 最终在陶瓷层表面裂纹区域出现大量的金属氧化物, 同时粘结层组元的扩散有助于陶瓷层的烧结, 导致其显微硬度逐渐增大, 而粘结层由于Kirkendall效应, 其内部出现大量的孔洞导致其显微硬度逐渐降低。另外, 陶瓷层在相变及热循环应力的作用下表面出现了大尺度的宏观裂纹。     

格子-Boltzmann方法模拟霜结晶生长

为了研究冷壁面上霜结晶的生长过程以及各参数的变化规律,利用格子-Boltzmann方法(LBM)方法,建立一个二维介观模型,实验验证了模型的可靠性,分析了霜层温度变化和密度增长规律,并直观模拟出霜结晶凝聚变化过程.结果表明:霜层表面温度在早期阶段迅速增加,但增加率随着结霜时间增加而减小;霜层内部温度随霜层厚度的增加呈线性增长;霜层平均密度随结霜时间增加呈现出先慢后快的规律;随着结霜过程的进行,由于越往上,霜晶体积分数越小,导致霜层内部密度随霜层厚度的上升而减小.     

界面反应对Cu35Ni25Co25Cr15多主元合金/金刚石复合材料磨损性能的影响

金刚石超硬磨具在高端芯片加工、3C陶瓷等领域发挥的作用日益重要,粘结相与金刚石的界面结合情况在很大程度上影响了金刚石超硬复合材料的力学和磨损性能。为了研究粘结相和金刚石的界面结合情况,采用放电等离子烧结方法制备了Cu₃₅Ni₂₅Co₂₅Cr₁₅多主元合金/金刚石复合材料,通过热力学计算和实验研究了粘结相和金刚石颗粒的界面反应。结果表明：烧结过程中,金属粘结相中的Cr元素与金刚石在界面处发生了化学反应,生成Cr-C化合物,且Cr-C化合物层的厚度随着烧结温度的升高而增加。当烧结温度达到950℃时,Cr-C化合物反应层均匀连续,厚度大约为1.1μm。复合材料粘结相与金刚石颗粒的粘结系数随着Cr-C化合物层厚度的增加而增大。摩擦磨损测试表明,在900℃和950℃烧结的样品表面,粘结相在摩擦过程中首先被磨除,金刚石随后露出,而Cr-C界面反应层有助于保持对金刚石颗粒的把持能力,提高复合材料的磨削性能。因此,适当的界面反应可提升金刚石复合材料的服役性能。     

陶瓷复合装甲粘结层效应和抗多发打击性能的数值模拟研究

粘结层性能对陶瓷复合装甲抗多发打击性能有重要影响。建立了研究粘结层和多发打击的数值模拟方法,解决了传统方法不能模拟“脱粘”和多发打击的问题。基于文献弹道试验,研究了环氧树脂和聚氨酯两种粘结层材料及其厚度对陶瓷/铝合金复合装甲抗7.62mm 穿甲弹单发和两发打击性能的影响。结果表明:单发打击的数值模拟可不建粘结层,而多发打击应采用建粘结层的方法;抗单发打击时,粘结层越薄,极限速度越大;抗多发打击时,陶瓷复合装甲应采用聚氨酯粘结层,且其抗两发打击的较优厚度约为0.40mm。     

ITO厚度对AlGaInP发光二极管特性的研究

采用金属有机物化学气相沉积技术在GaAs衬底上生长AlGaInP红光发光二极管器件,在表层GaP上沉积氧化铟锡透明导电层,使用扫描电镜分析器件外观、透射电镜观察器件各层结构、半导体测试机测试其光电参数、回流焊验证器件的热稳定性、X射线光电子能谱分析氧化铟锡透明导电层中In、O元素化合态;研究了不同氧化铟锡透明导电层厚度对器件光电参数、热稳定性、发光角度的影响,结果表明随着氧化铟锡透明导电层厚度增加器件电压降低、发光亮度先增加后下降,热稳定性随厚度增加而变好,发光角度随厚度增加而减小。     

AZ51镁合金交流微弧氧化膜层厚度的研究

在氢氧化钾和氟化钾组成的电解液中,采用交流微弧氧化处理技术对AZ51镁合金进行表面处理.研究了处理参数对陶瓷氧化膜层厚度的影响,确定了膜层的组织构成.结果表明:KOH浓度在300~400 g/L时,膜层厚度几乎随着KOH浓度的增加呈线性增长;KF浓度在400~1 000 g/L,膜层厚度增加最快;电压处于50~80 V时,能够促进膜层的快速生长;当电解液温度在20~70℃,随着电解液温度的升高,膜层厚度逐渐增加;膜层厚度随处理时间延长快速增长,超过100 s后趋于平缓.膜层主要由氟化镁和氧化镁组成,致密膜层的最大平均厚度约为30μm,膜层厚度超过30μm后,膜层将出现"沙化层".     

热障涂层服役温度测试与隔热机理

热障涂层(TBC)被用于航空发动机涡轮叶片表面的热防护,主要由粘结层和陶瓷层组成,准确测量陶瓷层表面与粘结层/陶瓷层界面温度分布对指导涂层高隔热结构设计与制备具有重要意义。现有非接触式与接触式测温技术可测量表面温度,接触式测温技术可测量界面温度。主要介绍了3种用于测量航空发动机涡轮叶片表面温度的技术,其中,适用于TBC表面测温的包括以光学原理为主的红外辐射、荧光、晶体、光纤测温技术;以热致变原理为主的示温漆测温技术;适用于TBC界面测温的以热电原理为主的填埋式热电偶、薄膜热电偶测温技术,并介绍了其测温的原理、优势和局限性。进一步对TBC隔热机理及性能优化进行了介绍,并对TBC表/界面测温技术及涂层结构设计方向进行了展望。     

热障涂层HCPEB改性过程中的应力研究（英文）

通过有限元分析软件Abaqus,采用三维模型,对热障涂层表面强流脉冲电子束改性过程进行了数值模拟,分析了电子束轰击过程温度变化以及涂层系统内部应力的分布情况。计算结果表明,随着外界能量的增加,涂层温度随着涂层厚度的增加而降低;当外界能量消失时,冷却过程中,由于涂层表面和周围的热辐射和热扩散作用,陶瓷层表面最先冷却,此时陶瓷层内部温度略微升高,之后陶瓷层内部热能通过陶瓷层表面进行释放,最后整个涂层冷却到室温,温度随时间变化率高达106~107 K/s。冷却至室温时,应力随着陶瓷层厚度的增加呈现先减小后增大的趋势,而在涂层表面径向应力先减小后增大,达到0.5MPa后,应力开始减小至稳态值。     

大体积混凝土温度、温度应力计算与温控措施探讨

基于有限差分法,对某核电站筏板基础工程的大体积混凝土温度场进行了计算;并在此基础上通过温度应力的计算对此工程大体积混凝土进行了抗裂验算;最后,结合此工程对大体积混凝土的温控措施进行了初步探讨。     

热双金属稳定化热处理效果的电阻分析

通过电阻和X-Ray衍射分析方法，研究了热双金属5J20110及其组元在稳定化热处理过程中电阻率和残余应力随循环次数的变化。研究结果表明经第一次循环热处理后，热双金属的残余应力下降最显著，与合金电阻率的变化趋势相同。通过电阻率的分析可以确定稳定化热处理的效果。     

Comparison of thermal conductivity data for partially stabilized zirconia with values derived from thermal diffusivity results

The thermal conductivity of partially stabilized zirconia was measured over the temperature range 320–1273 K using the radial heat flow method. The data have an absolute uncertainty of about ±2% and repeat measurements showed no evidence of changes in the thermal conductivity at high temperatures. This also was true for the thermal diffusivity data, which were obtained in vacuum over the temperature range 300–1473 K. Both sets of thermal conductivity data pass through minima at high temperatures. Quantitative differences were observed in the temperatures and thermal conductivities of the two minima. The results were analyzed by assuming parallel conduction by phonons and photons, and the phonon component was identified by fitting lower-temperature data. Extrapolating this curve allowed identification of the photon contribution to the thermal conductivity at high temperatures. The photon contribution approached a T ³ function and was larger in the thermal conductivity specimens. The difference in the photon contributions correlates with changes in the optical properties of the samples produced during the high temperature measurments.     

An apparatus for noncontact measurement of thermal conductivity by thermal radiation heating

Thermal radiation calorimetry was applied to measure the thermal conductivity of insulating solid specimens. We consider the system in which a disk-shaped specimen and a flat heater are mounted in a vacuum chamber with the specimen heated on one face by irradiation. A temperature difference between two faces was observed at elevated temperatures under steady-state conditions. An apparatus was developed using a thin graphite sheet as the heater element. Disk-shaped Pyrex glass and Pyroceram specimens, whose surfaces were blackened with colloidal graphite, were used in the measurements. Noncontact temperature measurement was performed using pyrometers and a thermocouple set in the gap between the heater and the specimen. Deviations of the estimated thermal conductivities from the recommended values were about 5% in the temperature range 250 to 800°C. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

探针法测量低温下猪主动脉导热系数研究

低温下导热系数测定对生物器官的低温保存、低温外科医学及数值模拟计算至关重要.在分析探针法测量原理的基础上,用探针法对低温下猪主动脉的导热系数进行了测量研究.实验表明探针在用甘油和蒸馏水进行标定后,可以方便准确地测量-90～-35℃温区下猪主动脉的导热系数.     

High-sensitivity capacitance method for measuring thermal diffusivity and thermal expansion: Results on aluminum and copper

Thermal diffusivity and thermal expansion in high-conducting solids can be measured by means of a capacitance method, which turns out to be simple, reliable, and accurate and yields the first property with an accuracy of 1% and the second one with an accuracy of 2%. Preliminary results, which are consistent with the literature, have been obtained on pure aluminum (99.999%) and on commercial copper, both at near room temperature.     

Comments on the measurement of thermal conductivity and presentation of a thermal conductivity integral method

A discussion is presented regarding the significance of the spatial temperature gradient approximation normally used in thermal conductivity measurement. Examples are presented illustrating the magnitude of temperature differences allowed for conductivity integral (TCI) method of analysis is presented as an alternative method which totally eliminates the need to impose temperature difference restrictions on the measurement process, so long as other errors, such as radiative heat losses, do not become excessive.     

考虑结构热变形的机床进给系统热误差研究

为系统研究精密机床进给系统热误差的形成机理及其影响因素，提出了一种考虑结构热变形的进给系统热误差建模方法。在考虑进给系统内生热源及冷却系统对丝杠螺母副的温升和丝杠热变形作用机制的前提下，同时考虑了进给系统内生热源对精密机床结构大件（床身、立柱、溜板）热态特性的影响规律。通过分析结构热变形引起的进给系统电机座和轴承座相对位置的变化，建立了综合考虑结构大件和丝杠热变形的进给系统热误差模型。以JIG630精密卧式加工中心为例，进行了考虑结构热变形和不考虑结构热变形的进给系统热误差建模与仿真分析，并开展了相应的测试验证实验。结果表明考虑结构热变形的进给系统热误差模型仿真值与实验结果具有更高的一致性。该建模方法对精密机床进给系统热平衡设计、热误差的控制与补偿具有重要参考意义。     

A noncontact method for measuring thermal conductivity and thermal diffusivity of anisotropic materials

A noncontact method for measuring the thermal conductivity and thermal diffusivity of anisotropic materials is proposed. This method is based on the fact that the surface temperature variation with time depends on the thermal properties of the material when its surface is heated locally. The three-dimensional transient heat conduction equation in the material is solved numerically. The dimensionless average surface temperature variations are obtained along each principal axis: that is, thex andy axes. The relation between the dimensionless temperature and the Fourier number is expressed by a polynomial equation and used as a master plot, which is a basic relation to be compared with measured temperature variation. In the experiments, the material surface is heated with a laser beam and the surface temperature profiles are measured by an infrared thermometer. The measured temperature variations with time are compared with the master plots to yield the thermal conductivity λ _x and thermal diffusivityx _v in thex direction and the thermal conductivity ratioE _xy (=λ _y λ _x ) simultaneously. To confirm the applicability and the accuracy of the present method, measurements were performed on multilayered kent-paper, vinyl chloride, and polyethylene resin film, whose thermal properties are known. From numerical simulations, it is found that the present method can measure the thermophysical properties λ _x , α _x andE _xy within errors of ±6, ±22, and ±5%, respectively, when the measuring errors of the peak heat flux, the heating radius, and the surface temperature rise are assumed to be within ±2, ±3%, and ±0.2 K, respectively. This method could be applied to the measurement of thermophysical properties of biological materials.