THERMO--MECHANICAL FATIGUE BEHAVIOR OF Ni--BASED SUPERALLOY COATED WITH Ni--Cr--Al--Y

分别采取大气等离子 (APS) 和高速火焰 (HVOF)工艺制备Ni--Cr--Al--Y涂层. 对涂覆Ni--Cr--Al--Y涂层的高温合金试样的热机械疲劳 (TMF) 行为进行了研究. 结果表明:在相同应变幅下, 2种涂层试样都是反相位热机械疲劳 (OP TMF) 寿命比同相位热机械疲劳 (IP TMF) 寿命短; 在不同应变幅下, 试样的热机械疲劳寿命与涂层的喷涂工艺相关. 通过断口和纵向剖面图的观察分析表明, 裂纹的萌生对试样的寿命有很大的影响.     

应变幅和相角度对热障涂层材料系统热机械疲劳性能的影响（英文）

热障涂层作为燃气轮机高温部件的关键材料,其服役过程中的脱落与失效机理一直是研究的热点问题。研究了应变幅和相角度对含热障涂层的镍基高温合金热机械疲劳性能的影响。研究结果表明,在相同相角度下,热机械疲劳寿命随应变幅的增大而降低。固定应变幅,同相位下样品的热机械疲劳寿命要高于反相位样品。所有样品中,裂纹萌生于热生长氧化物层,在粘结层与陶瓷层界面扩展形成分层裂纹,分层裂纹与陶瓷层内贯穿裂纹连接起来导致大面积的陶瓷层剥落,从而导致TBC层失效。另外,分析了热障涂层中的应力分布,初步建立了含热障涂层的镍基高温合金热机械疲劳寿命模型,发现含热障涂层的镍基高温合金热机械疲劳寿命与涂层中的最大应力呈指数关系。     

应变幅和相角度对热障涂层材料系统热机械疲劳性能的影响

热障涂层作为燃气轮机高温部件的关键材料,其服役过程中的脱落与失效机理一直是研究的热点问题。本文主要研究了应变幅和相角度对含热障涂层的镍基高温合金热机械疲劳性能的影响。研究结果表明,在相同相角度下,热机械疲劳寿命随应变幅的增大而降低。固定应变幅,同相位下样品的热机械疲劳寿命要高于反相位样品。所有样品中,裂纹萌生于热生长氧化物层,在粘结层与陶瓷层界面扩展形成分层裂纹,分层裂纹与陶瓷层内贯穿裂纹连接起来导致大面积的陶瓷层剥落,从而导致TBC层失效。另外,本文分析了热障涂层中的应力分布,初步建立了含热障涂层的镍基高温合金热机械疲劳寿命模型,发现含热障涂层的镍基高温合金热机械疲劳寿命与涂层中的最大应力呈指数关系。     

涂覆Ni-Cr-Al-Y涂层的镍基高温合金热机械疲劳行为

分别采取大气等离子(APS)和高速火焰(HVOF)工艺制备Ni-Cr-Al-_Y涂层.对涂覆Ni-C卜Al-Y涂层的高温合金试样的热机械疲劳(TMF)行为进行了研究.结果表明:在相同应变幅下,2种涂层试样都是反相位热机械疲劳(OP TMF)寿命比同相位热机械疲劳(IP TMF)寿命短;在不同应变幅下,试样的热机械疲劳寿命与涂层的喷涂工艺相关.通过断I=I和纵向剖面图的观察分析表明,裂纹的萌生对试样的寿命有很大的影响.     

Ti-62222合金的热机械疲劳行为

研究了Ti-62222合金在200-400℃内不同机械应变幅的热机械疲劳(TMF)行为和等温疲劳(IF)行为.结果表明,200℃的IF寿命高于400℃的IF寿命,同相位的TMF寿命高于反相位的TMF寿命.IF寿命与TMF寿命对比,同相位的TMF寿命高于200℃的IF寿命,反相位的TMF寿命高于400℃的IF寿命.在不同应变幅下,TMF应力响应曲线和IF应力响应曲线不同.SEM断口和纵向剖面金相观察表明,穿晶断裂是主要破坏方式.     

IC10合金热机械疲劳性能与寿命预测

600～1 100 ℃时对IC10合金进行同相位、反相位、135-相位和-135-相位的应变控制热机械疲劳实验.发展了一种三参数幂函数能量方法的寿命预测方法,并用于材料的热机械疲劳寿命预测.对Manson-Coffin方程、拉伸迟滞能模型(Ostergren)、基于微裂纹扩展模型的能量方法和三参数幂函数能量方法热机械疲劳寿命预测能力进行评估,结果表明:材料的热机械疲劳应力-应变滞后回线的形状与温度-机械载荷之间的相位角有关;温度-机械载荷之间的相位角对材料的热机械疲劳性能有一定的影响;三参数幂函数能量方法物理意义明确,形式简单,寿命预测结果分布在2倍的分散带内,可以用来预测IC10合金的热机械疲劳寿命.     

DD6单晶高温合金低周疲劳断裂特征的研究

对DD6单晶高温合金在高温低周（980 ℃、760 ℃）及疲劳/蠕变交互作用的断裂特征进行了研究。结果表明：DD6单晶高温合金高温低周疲劳断口往往呈多源开裂特征,裂纹萌生于试样的表面或亚表面,疲劳裂纹在刚萌生时沿着一定的小平面进行扩展,扩展区主要由垂直于裂纹扩展方向的疲劳条带和河流花样组成,瞬断区为类解理台阶形貌,裂纹扩展初期断口基本与主应力方向垂直,随着疲劳裂纹的扩展,断口呈现与主应力约成45°的平面特征;低周疲劳/蠕变交互作用的断裂特征与相同应变条件下低周疲劳断口总体形貌相似,但也一些不同之处,如断口整体氧化严重、疲劳扩展区面积明显减小。     

粘结层成分对单晶合金热障涂层寿命影响研究

采用电子束物理气相沉积工艺(EB-PVD)制备了针对第二代单晶高温合金的热障涂层,用SEM观察分析了不同成分粘结层的热障涂层热循环试验后的结构和晶体形貌,在N2条件下对比了不同成分粘结层材料与第二代单晶高温合金的热膨胀系数,分析了热循环试验后粘结层与热生长氧化(TGO)层成分、厚度及完整性情况。结果表明:NiCoCrAlYHf与第二代单晶高温合金热膨胀系数更为接近,匹配性更好;采用EB-PVD工艺制备的热障涂层在热循环试验过程中会产生大量垂直裂纹使涂层具有良好的应变容限;粘结层中Al元素含量的提高以及Hf等元素的加入,使得热循环试验后涂层TGO层的Al2O3纯度较高、生长缓慢无块状物生成,并且极大地改善了粘结层和合金基体的内氧化,涂层1 100℃循环氧化寿命达到1 200 h以上。     

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。     

粉末冶金盘材料FGH95热机械疲劳寿命预测

分别用微裂纹扩展模型、Manson-Coffin方程和拉伸迟滞能模型（Ostergren）对粉末冶金盘材料FGH95合金的热机械疲劳寿命进行了预测。结果发现,Manson—Coffin方程、微裂纹扩展模型和拉伸迟滞能寿命预测模型都能较好的对FGH95合金的热机械疲劳寿命进行预测（分散带为2倍左右）。通过分散带和标准差的定量比较发现：对于同相位和-135。相位热机械疲劳,微裂纹扩展寿命预测模型的预测结果比拉伸迟滞能模型和Manson-Coffin方程的预测结果好;而对于反相位和同相位带保持时间的热机械疲劳,拉伸迟滞能寿命预测模型的预测结果比微裂纹扩展模型和Manson-Coffin方程的预测结果好。     

NiCrAlY/Al-Al2O3/Ti2AlNb高温抗氧化和力学性能研究

采用电弧离子镀技水在NiCrAlY涂层与O相Ti₂AlNb合金之间沉积不同Al:Al₂O₃比例的Al-Al₂O₃薄膜作为扩散阻挡层.研究了900℃下恒温氧化500 h后NiCrAlY/Al-Al₂O₃/Ti₂AlNb体系中Al-Al₂O₃层阻挡合金元素互扩散的行为,以及对涂层氧化动力学曲线的影响.结果表明,没有添加扩散阻挡层的NiCrAlY/Ti₂AlNb体系,涂层和基体之间的元素互扩散十分严重,涂层丧失抗氧化能力;而添加扩散阻挡层的材料体系,涂层和基体之间的元素互扩散受到抑制,涂层的长期抗高温氧化性能得到提高.对于3Al-Al₂O₃,1Al-Al₂O₃和0Al-Al₂O₃ 3种扩散阻挡层,综合比较材料体系的抗氧化性能、阻挡层阻挡涂层和基体元素互扩散能力、以及涂层和基体之间结合力,当1Al-Al₂O₃薄膜作为扩散阻挡层时,材料性能最优异.同时,本文利用扩散阻挡系数简洁定量地表示出不同Al:Al₂O₃比例阻挡层的阻挡扩散能力.     

SiC晶须增强6061Al基复合材料的热机械疲劳性能 Ⅱ.疲劳寿命与损伤机制

研究了本积分数为１５％和２８％ＳｉＣＷ／６０６１Ａｌ基复合材料的同相和反相热机械疲劳寿命和损伤机制．结果表明：在小应变范围时,同相比反相疲劳寿命长,而在大应变时,同相疲劳寿命接近（对于２８％ＳｉＣＷ）、甚至短于（对于１５％ＳｉＣＷ）反相热机械疲劳寿命;１５％ＳＩＣＷ／６０１６Ａｌ基复合材料的反相热机械疲劳寿命高于２８％ＳｉＣＷ／６０１６Ａｌ基复合材料的寿命．两种材料的同相热机械疲劳寿命曲线存在交叉点,寿命高低取决于应变水平;同相和反相热机械疲劳的损仿均为空洞在ＳｉＣ晶须周围基体中形核、长大和连接．     

涂覆WC-17Co涂层的Ni718合金在不同环境温度中的疲劳性能

利用超音速火焰喷涂技术在Ni718合金表面制备WC-17Co涂层.利用反复弯曲试验分析25,150,300℃条件下涂覆WC-17Co涂层Ni718合金疲劳性能,利用扫描电镜、X射线衍射仪分析涂层的断口形貌和相组成,并利用剥层法测量涂层中残余应力分布.结果表明,相同应变量条件下试样的疲劳寿命随着温度的升高而降低;循环载荷作用下裂纹由涂层表面产生,向基体方向扩展,最终形成整体断裂;室温至300℃温度范围内,涂层不会发生相变,但是随环境温度上升涂层中的残余压应力呈现下降趋势,这种趋势使得涂层中裂纹的扩展速度增加,最终导致疲劳寿命下降.     

LY12铝合金微弧氧化涂层组织结构对基体疲劳性能的影响

在硅酸盐体系电解液中于铝合金表面制备出不同厚度的微弧氧化涂层,研究涂层厚度对基体疲劳寿命的影响,并揭示疲劳损伤机制.采用XRD、SEM、EDS等分析手段分析涂层的物相与组织结构.用810 Material Test System 疲劳试验机评价涂层试样的疲劳寿命.结果表明,铝合金微弧氧化涂层主要由γ-Al_2O_3和a-Al_2O_3组成,涂层内层致密,表面多微孔.随氧化时间延长,涂层厚度增大,但表面粗糙度增加.疲劳测试结果表明,微弧氧化涂层会降低基底铝合金的疲劳寿命,涂层厚度增加,疲劳寿命下降显著.相对于基体铝合金,涂层厚度为10,18,30 mm的试样,疲劳寿命分别下降了4.4%,8.5%,32.2%.疲劳断口分析认为,涂层局部过度长入基体产生缺陷部位,在循环载荷作用下,容易产生应力集中,从而萌生疲劳源,使铝合金的疲劳寿命下降.     

高温拉压环境下DZ125高温合金的热障涂层失效

采用电子束物理气相沉积法（EB-PVD）在定向凝固Ni基高温合金DZ125基体上制备了NiCoCrAlY粘结层和YSZ陶瓷层，研究了高温拉压环境下热障涂层的失效模式，并对其进行了有限元分析。实验结果表明，热障涂层的失效与仅受热载荷作用下的有很大不同，仅有热载荷作用下的热障涂层裂纹多萌生于热氧化层（TGO）内部，进而扩展引起热障涂层的失效。而高温拉压试验后热障涂层体系存在两种裂纹，分别萌生于TGO／粘结层界面和粘结层／扩散层界面附近。有限元模拟结果显示TGO／陶瓷层和TGO／粘结层处存在应力状态的转变和应力值的突变，径向应力的突变导致了界面分离现象的产生，而轴向应力的突变加速了垂直于界面裂纹的扩展，并导致了试样的最终断裂。     

Oxidation behavior of ceramic coatings on Ti–6Al–4V by micro-plasma oxidation

Compound ceramic coatings prepared on Ti–6Al–4V alloy by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO₂ solution were oxidized under different temperature in air. The phase composition and surface morphology of the coatings before and after oxidation were investigated by X-ray diffractometry and scanning electron microscopy, respectively. Meantime, the weight gains and the high temperature oxidation characteristics of the coated samples were investigated. The results show that the coatings prepared by MPO were composed of a large amount of Al₂TiO₅ and a little -Al₂O₃ and rutile TiO₂. And the oxidation process of the coated samples included the decomposition of the Al₂TiO₅ in the coating, the oxidation of the substrate and the changes of the coating structure. After high temperature oxidation, the increase of -Al₂O₃ in the coating was due to the decomposition of Al₂TiO₅, whereas the increase of rutile TiO₂ in the coating was attributable to both the decomposition of Al₂TiO₅ and the oxidation of the Ti substrate. The main crystalline of the coatings became rutile TiO₂ after the oxidation of 1000 °C for 1 h. The decomposition of Al₂TiO₅ in the coating occurred at 900 and 1000 °C, and its half decomposition time was less than 1 h at 1000 °C. Increasing oxidation temperature or extending oxidation time, the weight gains of coated samples was increased to different extent. However, the weigh gains of the coated samples was much lower than that of the substrate, so the ceramic coatings improved the oxidation resistance of Ti alloy greatly under the experimental conditions.     

等离子喷涂La2(Zr0.7Ce0.3)2O7热障涂层的抗热震性能

采用等离子喷涂制备了La₂(Zr_0.7Ce_0.3)₂O₇（LZ7C3）热障涂层,并对涂层的微观组织、相结构、成分、相稳定性、涂层热导率以及抗热震性能进行了研究.结果表明,LZ7C3涂层由单相烧绿石结构物质组成,高温稳定性较好;涂层的热导率较块材下降约20%,这是由于涂层具有较高的孔隙率所致:涂层在不同温度范围的热震寿命和失效机制不同,在室温至约1000℃间的热震寿命为116 cyc,涂层失效方式以片状剥落为主:在室温至1100℃间的热震寿命为53 cyc,涂层失效方式为片状剥落和层状撕裂;在室温至1200℃间的热震寿命为3 cyc,涂层失效方式以层状撕裂为主.     

THE INFLUENCE OF Mo DIFFUSION ON THE THERMAL BEHAVIOR OF TBCs ON Ni_3Al BASED ALLOY IC-6

Conventional two-layered structure thermal barrier coatings (TBCs) were prepared onto γ'-Ni3Al based alloy IC-6 by electron beam physical vapor deposition (EB-PVD). Isothermal oxidation and thermal cycling tests were carried out to investigate the effect of Mo content at the interface between bond coat and ceramic top coat caused by diffusion. It has been found that the alloy coated with TBCs presented the lowest oxidation weight gain value for the reason that the ceramic top coat in TBC system can effectively stop Mo oxides evaporating. The life time of TBCs has close relation with Mo content at the interface between the bond coat and top coat. Spaliation of ceramic top coat occurred during thermal cyclic testing when Mo atoms accumulated at the interface up to certain amount to decline the combination between the bond coat and top coat.     

Effects of laser shock processing,solid solution and aging,and cryogenic treatments on microstructure and thermal fatigue performance of ZCuAl10Fe3Mn2 alloy

The materials used in variable temperature conditions are required to have excellent thermal fatigue performance. The effects of laser shock processing (LSP), solid solution and aging treatment (T6), and cryogenic treatment (CT) on both microstructure and thermal fatigue performance of ZCuAl₁₀Fe₃Mn₂ alloys were studied. Microstructure and crack morphology were then examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The result showed that, after being subjected to the combination treatment of T6+CT+LSP, the optimal mechanical properties and thermal fatigue performance were obtained for the ZCuAl₁₀Fe₃Mn₂ alloy with the tensile strength, hardness, and elongation of 720 MPa, 300.16 HB, and 16%, respectively, and the thermal fatigue life could reach 7,100 cycles when the crack length was 0.1 mm. Moreover, the ZCuAl₁₀Fe₃Mn₂ after combination treatment shows high resistance to oxidation, good adhesion between the matrix and grain boundaries, and dramatically reduced growth rate of crack. During thermal fatigue testing, under the combined action of thermal and alternating stresses, the microstructure around the sample notch oxidized and became loose and porous, which then converted to micro-cracks. Fatigue crack expanded along the grain boundary in the early stage. In the later stage, under the cyclic stress accumulation, the oxidized microstructure separated from the matrix, and the fatigue crack expanded in both intergranular and transgranular ways. The main crack was thick, and the path was meandering.     

Thermal cycle behavior of plasma sprayed La2O3, Y2O3 stabilized ZrO2 coatings

The effects of La₂O₃ addition on thermal conductivity, phase stability and thermal cycle life of Y₂O₃ stabilized ZrO₂ plasma sprayed coatings were investigated. Although low thermal conductivity as well as high resistance to sintering was achieved by La₂O₃ addition, it tended to also result in lower phase stability and thermal cycle life of the coatings. Optimization of the composition and structure of the coatings improved these properties, and the optimized coatings showed prolonged thermal cycle life.