火电厂锅炉水冷壁管横向裂纹开裂原因分析

对电厂锅炉水冷壁管与鳍板焊接处开裂原因进行失效分析.结果表明:水冷壁管向火一侧表面氧化严重,管内侧存在结垢现象,同时水冷壁管珠光体发生球化,在运行过程中,在循环热应力和焊接残余应力叠加作用下,裂纹在焊缝接头处萌生,沿着拉应力区扩展,造成疲劳开裂.     

锅炉水冷壁管纵向裂纹开裂原因浅析

通过宏观检验、光谱分析、金相检验等方法对电厂锅炉水冷壁管焊接处开裂原因进行失效分析。结果表明:由于温度变化产生的热应力、焊接残余应力以及结构应力作用下,裂纹在焊缝接头处萌生,产生纵向裂纹。     

电站锅炉水冷壁管的泄漏原因及应对措施

某电站锅炉水冷壁管在运行过程中发生数次泄漏,利用化学成分分析、显微组织观察、硬度检测等方法对泄漏原因进行了分析.结果表明:失效管段化学成分、硬度满足标准要求,显微组织为铁素体+珠光体,珠光体轻度球化.泄漏点位于同一根管的多处横向裂纹处,裂纹起裂于向火侧内壁中部位置的螺旋附近.水冷壁管内壁存在垢层,炉水在氧化铁垢下方和螺...     

某电厂#3炉水冷壁管泄漏失效原因分析

某电厂 12 5MW锅炉累计运行 1196 11h后因水冷壁管泄漏而停炉检修。管子失效主要发生在前、后侧墙水冷壁标高约 13～ 15m处。根据失效分析认为 ,水冷壁管失效主要是不锈钢密封板线膨胀系数大、导热性差所致其开裂 ,但热疲劳也可能是导致水冷壁管失效的原因之一。     

某电厂#3炉水冷壁管泄漏失效原因分析

某电厂125MW锅炉累计运行119611h后因水冷壁管泄漏而停炉检修。管子失效主要发生在前、后侧墙水冷壁标高约13～15m处。根据失效分析认为，水冷壁管失效主要是不锈钢密封板线膨胀系数大、导热性差所致其开裂，但热疲劳也可能是导致水冷壁管失效的原因之一。     

600MW电站锅炉水冷壁管泄漏原因分析

通过宏观分析、化学成分分析、金相组织和断口分析,对某电厂600 MW电站锅炉水冷壁管泄漏原因进行了综合分析。结果表明,水冷壁管泄漏的根本原因是腐蚀介质和热应力联合作用产生的疲劳裂纹所致。裂纹由外壁向内壁扩展,呈楔形穿晶为主。     

某锅炉T23钢水冷壁管更换过程中焊缝裂纹原因分析

文中首先分析了导致水冷壁频繁泄漏的原因与焊前无预热及焊后无热处理的焊接工艺有关,进而制订新的水冷壁管焊接热处理工艺.在水冷壁管更换过程中,出现了热处理后焊缝表面存在横向裂纹现象,为分析裂纹原因,对裂纹管段进行金相观察,进而判定启裂裂纹性质为熄弧裂纹,且在后续热处理过程中裂纹进一步扩展.根据裂纹性质,提出对熄弧区域采取机...     

超临界锅炉水冷壁横向裂纹形成原因分析

对某超临界锅炉水冷壁管外壁横向裂纹的性质和形成原因等进行了分析,主要内容包括金相分析、硬度检测、拉伸性能试验、断口扫描电镜分析、外壁及断口附着物X射线能谱分析等。结果表明,锅炉侧墙向火侧水冷壁管外壁横向裂纹的形成原因是腐蚀性热疲劳,而炉内火焰对水冷壁的冲刷是造成热疲劳的主要原因。     

超超临界锅炉T23钢水冷壁管开裂分析

以超超临界锅炉SA213?T23钢水冷壁失效管为试验对象,通过宏观检查、化学成分分析、金相检验和硬度试验,分析失效原因。结果表明:该水冷壁管化学成分正常,材质性能未发生明显劣化;水冷壁失效原因为鳍片焊缝开裂,该裂纹为沿晶界扩展的再热裂纹,起源于焊缝熔合线附近的热影响区粗晶区域,先沿热影响区横向扩展,然后扩展至母材区域,最终导致管壁泄漏失效;热影响区粗晶区域显微组织为粗大的马氏体和贝氏体组织,硬度明显偏高于焊缝熔合线另一侧的焊缝区域,脆性增大。两者在显微组织和硬度上的明显差别,使焊缝熔合线附近的热影响区粗晶区域容易产生应力集中,在高温运行中发生晶间开裂。     

调峰机组水冷壁管焊缝背火侧开裂原因分析

通过对锅炉的运行、检修情况的调查及水冷壁开裂管样的理化性能试验分析,对某厂调峰机组水冷壁管焊缝背火侧的开裂原因进行了分析。结果表明:水冷壁管焊缝背火侧纵向开裂性质为疲劳开裂。存在硬度超标和根部凸出超标的水冷壁管环焊缝,在深度调峰期频繁超温引起的交变应力作用下逐渐在热应力最大的环焊缝背火侧中部内壁萌生纵向疲劳裂纹,直至开裂泄漏。     

热循环下梯度热障涂层热氧化物生长的应力分析

建立了一种预测多层复合梯度热障涂层热应力的理论模型,并通过有限元方法分析了梯度涂层分布指数n、热循环过程中热氧化物的生长对涂层热应力大小及分布的影响。结果表明,通过控制梯度涂层的成分分布指数可以显著降低热应力和改善应力分布。当n=1时,涂层热应力较小且变化平缓,结合性能优异。与双层非梯度涂层的热应力对比可知,功能梯度涂层能显著地缓和涂层系统的热应力和消除应力集中。另外,热循环过程中梯度热障涂层与基体界面附近生长的热氧化物急剧地提升了界面附近的热应力,复杂而又集中的热应力对梯度涂层有很大的破坏。同时采用了一种方法来抑制热氧化物的生长,结果显示该方法能较好地优化涂层的热应力和改善涂层质量。     

Microstructure and Thermal Behavior of Thermal Barrier Coatings

Yttria stabilized zirconia thick coatings were thermally sprayed from two different feedstock powders. Coating characteristics such as density, crystalline phase composition, and microstructure were evaluated. The thermal expansion coefficient and thermal diffusivity were measured as a function of temperature up to 800 °C and analyzed in terms of the microstructural features. The ability of available models to relate the measured thermal properties to the microstructural features as characterized by readily available methods was assessed. The importance of pore shape and orientation on the thermal conductivity was evidenced. The thermal contact resistance between the substrate and the coating in these samples was estimated from the thermal diffusivity data, and found to change during cooling from 800 °C.     

绝热材料的显微结构及绝热性能

着重分析了材料的显微结构对材料导热系数的影响:高孔隙率减弱固相传热作用从而使材料的导热系数减小,但是,高孔隙的也增大辐射传热作用.适当降低孔隙可减少辐射传热作用,这在高温时特别明显.尺寸<1 mm的孔隙中对流传热被制止,不再对传热起作用.在保持孔隙总量不变的前提下减小孔径可使孔隙数量增大,从而减小导热系数.小于100 nm的孔隙可以消除气体本身的热传导,从而极大地减小材料的导热系数.展示了几种不同显微结构的材料及其绝热性能.     

Thermal Performance of Low-Melting-Temperature Alloy Thermal Interface Materials

Thermal resistance of low-melting-temperature alloy(LMTA) thermal interface materials(TIMs) was measured by laser flash method before and after different stages of heating.The results showed that the thermal performance of the LMTA TIMs was degraded during the heating process.It is suggested that the degradation may mainly be attributed to the interfacial reaction between the Cu and the molten LMTAs.Due to the fast growth rate of intermetallic compound(IMC) at the solid–liquid interface,a thick brittle IMC is layer formed at the interface,which makes cracks easy to initiate and expand.Otherwise,the losses of indium and tin contents in the LMTA during the interfacial reaction will make the melting point of the TIM layer increase,and so,the TIM layer will not melt at the operating temperature.     

等离子工艺热障涂层的热疲劳分析

热障涂层作为先进的热防护技术,在航空发动机热端部件上有重要的应用,它与先进气膜冷却技术、先进单晶合金材料技术并称为航空发动机涡轮叶片三大关键技术。为了保证发动机安全可靠地工作,研究并测试热障涂层的力学参数和热疲劳特性是其工程应用的前提与基础。本文以等离子喷涂工艺制备的热障涂层为研究对象,利用共振原理和复合梁理论,获得了热障涂层表层一陶瓷层从常温到1150℃高温条件下的杨氏模量。同时,鉴于热障涂层的热疲劳失效模式为剥落,着重对热障涂层的热疲劳特性进行研究。以带热障涂层的圆管试样为模拟件进行了热疲劳试验,试验载荷选择50℃／1050℃的梯形波。利用所测试的材料参数和有限元方法进行了热变形分析,提取了热疲劳寿命控制参量,对模拟试样的热疲劳寿命进行了预测,结果显示,预测结果较为精确。     

Self-Enhancing Thermal Insulation Performance of Bimodal-Structured Thermal Barrier Coating

Nanostructured thermal barrier coatings (nano-TBCs) are being extensively studied because of their excellent thermal barrier properties. The occurrence of sintering in TBCs is inevitable in service; however, accelerated sintering of the nano-TBCs may cause premature failure. This study focuses on the changes of microstructure and thermal conductivity of bimodal nano-TBCs during thermal exposure. Results show that there are two stages in the sintering process. It was found that the thermal conductivity increased rapidly in the first stage (from 0 to 20 h), with the rate of increase in normalized thermal conductivity equal to 140% of bimodal coating. The continuous healing of the pores was the main structural change. During the following stage (20 to 100 h), the thermal conductivity decreased with the rate of increase in normalized thermal conductivity equal to ??8% of bimodal coating. The change of structure was the opening of pores. Furthermore, self-enhancing behavior of bimodal composite coatings was discovered. The phenomenon of inevitable sintering in thermodynamics can be used to introduce large-aspect-ratio pores in the in-depth direction, which can greatly slow down the increase in thermal conductivity in service and ultimately increase the lifetime of the thermal insulation. Based on a full study of the sintering mechanism of composite coatings, the present study sheds light on the structural adjustments that lead to a lower thermal conductivity and longer service life in the advanced TBC during high-temperature service.     

红外热波检测热激励源的优化

为解决热激励信号的选取问题,从热波检测的原理出发,建立了求解试件温度分布的偏微分方程组。通过分析方程组,发现热激励信号强度与温度升高值成正比关系。先从理论上对其进行推导,并使用ANSYS软件对试件内热传导过程进行数值计算。结果表明,增强热激励信号在脉冲热像法中可以成正比增大最大温差,在阶梯热像法中可以成正比增大各时刻的温差,在锁相热像法中可以成正比增大幅值差,为热激励信号强度的定量选取提供了理论依据和具体尺度。     

Failure Mechanism for Thermal Fatigue of Thermal Barrier Coating Systems

Thick thermal barrier coatings (TBCs), consisting of a CoNiCrAlY bond coat and yttria-partially stabilized zirconia top coat with different porosity values, were produced by air plasma spray (APS). The thermal fatigue resistance limit of the TBCs was tested by furnace cycling tests (FCT) according to the specifications of an original equipment manufacturer (OEM). The morphology, residual stresses, and micromechanical properties (microhardness, indentation fracture toughness) of the TBC systems before and after FCT were analyzed. The thermal fatigue resistance increases with the amount of porosity in the top coat. The compressive in-plane stresses increase in the TBC systems after thermal cycling; nevertheless the increasing rate has a trend contrary to the porosity level of top coat. The data suggest that the spallation happens at the TGO/top coat interface. The failure mechanism of thick TBCs was found to be similar to that of conventional thin TBC systems made by APS.     

提高等离子喷涂热障涂层隔热性能的方法

为进一步提高等离子喷涂热障涂层的隔热性能,对陶瓷材料的导热理论及热障涂层的热导率进行了研究.提出了包括寻求新型热障涂层陶瓷材料、添加掺杂剂、制备纳米涂层及双陶瓷层热障涂层等能够改善等离子喷涂涂层隔热性能的方法;并指出,采用等离子喷涂技术制备带颜色的稀土锆酸盐纳米双陶瓷层热障涂层,将会进一步改善热障涂层的隔热性能.     

热障涂层高温氧化生长应力预测

基于Clark氧化生长应变率理论和Wagner氧化模型给出了涂层高温生长应力公式,计算预测了热障涂层中氧化生长应力随时间的演化规律;利用光致发光分析技术对氧化层的应力进行了实验测试,并对两种结果进行了比较和分析。结果表明,本文给出的热障涂层高温氧化生长应力模型预测与实验结果符合