Mechanistic investigation into the role of aluminum diffusion in the oxidation behavior of cryomilled NiCrAlY bond coat

High temperature oxidation behavior of the bond coat layer is a critical factor that controls the failure mechanism of thermal barrier coatings (TBCs). Previous work reveald that TBCs with cryomilled NiCrAlY bond coats exhibited an improved oxidation behavior compared to equivalent TBCs with conventional bond coats. The cryomilled NiCrAlY bond coats contributed to a slower growth rate of thermally grown oxides (TGO) with a final thinner thickness and enhanced homogeneity in TGO composition. To better understand the improved oxidation behavior, a mechanistic investigation based on diffusion theory and quantum mechanics is performed to elucidate the role of aluminum diffusion in the oxidation behavior and how the microstructural features of the cryomilled NiCrAlY bond coats, i e, the creation of a thermally stable, uniform distribution of ultrafine Al-rich oxide dispersoids, affect the diffusion kinetics of Al and the migration of free electrons. It is revealed that these Al-rich oxide dispersoids result in a uniform diffusion of Al and slow migration of free electrons within the NiCrAlY bond coat, consequently leading to the improved oxidation behavior.     

Investigation on plasma-sprayed ZrO_2 thermal barrier coating on nickel alloy substrate

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关于基体曲率的热障涂层残余应力分析

采用空心和实心四相同心圆模型,导出了轴对称温度应力状态下的位移公式,分析了基体曲率对热障涂层残余应力的影响。结果表明:热障涂层结构中各层内既有环向应力,又有径向应力,应力大小与温降成线性关系;当陶瓷层在外层时,在氧化层/陶瓷层和粘结层/氧化层界面上产生垂直界面的拉应力,且实心模型的拉应力远大于空心模型的拉应力;当陶瓷层在里层时,空心模型中相应界面上的应力为压应力。     

金属基陶瓷涂层的耐高温及抗热冲击性能

以自制无机胶粘剂、通过添加耐高温耐磨陶瓷骨料A12 O3,WC,SiC混合后涂覆于A3钢表面制得陶瓷涂层,研究了调胶比（氧化铜与磷酸盐的配比）、骨胶比（胶粘剂与陶瓷骨料的配比）不同对金属基陶瓷涂层耐高温及抗热冲击性能的影响;并分析了金属基体与陶瓷涂层间的结合机理．结果表明：调胶比为0．5g／ml此涂层能承受1300℃以上的高温．骨胶比比为0．30：1（质量比）时,制备的陶瓷涂层抗热冲击性能最佳,能承受600～700℃的16次以上的热震试验．     

Investigation on plasma-sprayed ZrO2 thermal barrier coating on nickel alloy substrate

The thermal barrier coatings with NiCrAlY alloy bonding layer, NiCrAlY-Y₂O₃ stabilized ZrO₂ transition layer and Y₂O₃ stabilized ZrO₂ ceramic layer are prepared on nickel alloy substrates using the plasma spray technique. The relationship among the composition, structure and property of the coatings are investigated by means of optical microscope, scanning electronic microscope and the experiments of thermal shock resistance cycling and high temperature oxidation resistance. The results show that the structure design of introducing a transition layer between Ni alloy substrate and ZrO₂ ceramic coating guarantees the high quality and properties of the coatings; ZrO₂ coatings doped with a little SiO₂ possesses better thermal shock resistance and more excellent hot corrosion resistance as compared with ZrO₂ coating materials without SiO₂; the improvement in performance of ZrO₂ coating doped with SiO₂ is due to forming more dense coating structure by self- closing effects of the flaws and pores in the ZrO₂ coatings. Biography of the first author: LU An-xian, Ph.D, professor, born in Jan. 1960, majoring in inorganic non-metal materials.     

Properties of plasma sprayed NiCrAlY (ZrO_2 Y_2O_3) coating on refractory steel surface

1INTRODUCTION1Cr18Ni9Ti,i.e.188austeniticstainless steel,isakindofausteniticrefractorysteelwidely appliedinmanyfields,containingahighcontentofCrthatcanimproveheatandoxidationresistances,andalsoNicapableofformingastableaustenitic structure.However,suchstee…     

陶瓷/金属复合耐磨涂层的性能评价

应用大气等离子喷涂（APS）技术制备陶瓷／金属复合耐磨涂层试样，并对其硬度，结合强度，微观结构和耐磨性等性能进行评估，结果表明Al2O3-TiO复合涂层在耐磨性方面好于WC－NiCrAl复合涂层，而WC－NiCrAl复合涂层在结合强度性能上好于Al2O3-TiO2复合涂层。     

Behavior of NiCrAIY coating on the TC6 titanium alloy

A NiCrAlY coating was deposited on the TC6 titanium substrate by arc ion plating (AIP). The structure and morphologies of the NiCrAlY coating were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the influence of vacuum heat treatment on the element diffusion behavior was studied. The results showed that the γ'-Ni3Al phase was precipitated on the NiCrAlY coating after heat treatment. The Ni3(Al,Ti), TiNi, and Ti2Ni intermetallic layers appeared at the interface from the outside to the inside at 700°C, and the thickness of the intermetallic layers increased with the increase in temperature. At 700°C Ti and Ni were the major diffusion elements, and the diffusion of Cr was observed when the heat treatment temperature increased up to 870°C. The violent inward diffusion of Ni at 950°C resulted in the degradation of the NiCrAlY coating.     

终烧温度对陶瓷型芯性能的作用

为了阐明终烧温度与陶瓷型芯性能的关系,利用高温抗折试验机和原位观测手段,研究了不同终烧温度下陶瓷型芯性能的变化.结果表明,对于非定向陶瓷型芯而言,随着终烧温度的提高,室温抗折强度保持稳定,在1 150℃条件下陶瓷型芯的高温抗折强度最高,且其变形抗力逐渐提高;而对于定向陶瓷型芯而言,随着终烧温度的提高,室温抗折强度和高温抗折强度均逐渐降低,且其变形抗力变化不大.根据上述实验结果,非定向陶瓷型芯的终烧温度确定为1 150℃,而定向陶瓷型芯的终烧温度确定为1 120℃.     

枪速对热障涂层组织性能及残余应力的影响

为了研究等离子喷涂制备热障涂层(TBCs)时不同枪速对陶瓷面层组织性能和残余应力的影响,在GH4169高温合金基体上采用超音速火焰喷涂(HVOF)Ni Co Cr Al Y粘结层(BC层)和大气等离子喷涂(APS)8YSZ陶瓷层(TC层).通过对比不同参数样品的微观组织以及显微硬度、残余应力和热震性能差异,研究了枪速对热障涂层的影响.结果表明:枪速过低或过高时,涂层表面残余应力较大,热震性能较低;随着枪速的增大,涂层表面粗糙度逐渐增大,而孔隙率和显微硬度逐渐减小;枪速过低时,涂层出现纵向裂纹,热震失效方式为整体剥落;而枪速较大时,涂层从边缘向中心不断剥落,涂层表面出现白点.     

Effects of supersonic fine particle bombarding on thermal cyclic failure lifetime of thermal barrier coating

Thermal barrier coating ( TBC) consisting of a NiCoCrAlY bond coat ( BC) and a ZrO2-8 wt. % Y2O3 topcoat ( TC) was fabricated on the nickel-base superalloy by air plasma spray ( APS) . The BC was treated by supersonic fine particle bombarding ( SFPB) . Thermal cyclic failure and residual stress in thermally grown oxide ( TGO) scale were studied by SEM with EDS and ruby fluorescence spectroscopy ( RFS) . As shown in the results,after treated by SFPB,thickening of TGO was relatively slow,which reduced the level of growth stress. The TBC with SFPB treatment was still remained well undergoing 350 times of thermal cycle. However,after thermal cycle with the same times,the separation of TC was observed in TBC without SFPB treatment. The residual stress analysis by RFS showed that the residual stress of SFPB-treated TBC increased with the increasing number of thermal cycle. The residual stress of conventional TBC reached a value of 650 MPa at 350 times of cycle and that of SFPB-treated TBC only reached 532 MPa at 400 times of cycle. The BC with SFPB treatment after 400 times of cycle was analyzed by RFS,the high stress value was not observed in local thickened region of TGO. Thermal cycling resistance of TBC can be improved by the SFPB technology.     

STRESS ANALYSIS OF ALUMINA COATINGS ON SILICON CARBIDE BASED REFRACTORIES DURING THERMAL CYCLING

It is possible to enhance the high tempera-ture oxidation resistance and thus prolong the life time of non-oxide refractories by the application of oxide coating. In this -work, silicon nitride bonded silicon carbide refractories were coated with alumina using the plasma spraying technique. X-ray diffraction shouted r-Al2O3 to be the dominent phase in the as-sprayed alumina coatings. The stresses developed in the coating layer during post-spray heat-treatment have been analysed. It was found that the coating-was under a compressive stress below,but when heated above 1100C , the r-Al2O3 phase transformed into a-Al2O3 and this led to the formation of a destructive tensile stress(up to 1700 MPa) which caused cracks to form in and along the iveak bond between the alumina coating and SiC grains. The coatings then delaminated and of fered little protection to the refractory substrate from oxidation. Future research will be directed on the avoidance oj metastable phase formation in the plasma sprayed coating a     

反应热喷涂法制备陶瓷涂层的研究

首先通过差热-失重分析和XRD测试手段对反应热喷涂Al＋TiO2＋H3BO3混合粉体以制备Al2O3/TiB2复合陶瓷涂层的可行性进行了分析.然后对喷涂后试样涂层的耐磨性进行了研究.结果表明：Al＋TiO2＋H3BO3混合粉体差热-失重分析和在1200℃烧结后XRD测试分析均表明完全可以反应生成所需的Al2O3/TiB2复合陶瓷涂层.所制备陶瓷涂层的耐磨性要比基体提高1倍左右.     

激光制备陶瓷热障涂层的研究和发展

论述了激光制备陶瓷热障涂层的研究和发展状况 .激光制备陶瓷热障涂层包括激光重熔和激光熔覆两种方法 .激光重熔等离子喷涂热障涂层可获得等离子喷涂涂层所不具备的外延生长致密的柱状晶组织 ,提高涂层应变容限及热震性能 .激光熔覆可获得自动分层的梯度热障涂层成分及柱状晶组织 ,改善涂层的高温氧化及热震性能 .通过激光工艺参数的优化及涂层体系成分及性能的合理设计 ,可获得优于等离子喷涂 ,接近电子束物理气相沉积的热障涂层性能     

High temperature behaviors of high velocity arc sprayed Fe-Al/Cr3C2 composite coatings

Fe-Al/Cr3C2 composite coatings were manufactured using high velocity arc spraying （HVAS） technology. The high temperature erosion, wear and corrosion resistance of the coatings were investigated. The coating properties such as bonding strength, porosity, hardness as well as microstructures were characterized. The results show that the coatings have relatively high heat tremble bond strength, hardness, and typical layer-shaped coatings＇ microstructures. With the rise of temperature, the coating erosion resistance increases too; the impingement angel does effects on erosion properties, and the erosion mechanism changes from ductile to brittle behaviors at 450℃. The coatings have good room temperature wear resistance and relatively good high temperature resistance. The wear mechanism of the coatings is peeling wear behavior. The coatings have excellent high temperature corrosion resistance because of the produce of oxides during corrosion.     

亚音速火焰喷涂钛-生物玻璃涂层组织与性能研究

采用亚音速火焰喷涂方法及涂层处理技术,以Ti6A14V为基体,喷涂钛-生物玻璃,涂层经700℃晶化处理．用扫描电子显微镜（SEM）观察涂层显微结构,X射线衍射法（XRD）测试涂层相组成,采用基于GIXRD的残余应力分析方法测量涂层残余应力．结果表明：亚音速火焰喷涂钛-生物玻璃涂层沿裂纹处有晶态析出物TiO2,起到弥合裂纹的作用．添加生物玻璃G后,涂层表面有针状结构晶体Na2RO。,析出,新相Na2Ti60。,具有一定的有生物活性．涂层残余应力均为压应力,其值与生物玻璃含量成正比．     

包覆工艺制备C—SiC—B4C—TiB2复合材料的组织与性能

以鳞片石墨,B4C,SiC,TiO2为原料,利用包覆工艺在不同热压温度下制备了W（C）=50％的C—SiC—B4C—TiB2复合材料,并详细研究了热压温度对复合材料显微组织和性能的影响规律．结果表明,当热压温度高于1850℃时,复合材料由C,SiC,B4C和TiB2这四相组成;复合材料的体积密度、抗折强度和断裂韧性均随着热压温度的升高而增加．2000oC热压时,复合材料的体积密度、气孔率、抗折强度和断裂韧性分别达到2．41g／cm^3,3．42％,176MPa和6．1MPa·m^1/2;热压温度升高,复合材料的碳相和陶瓷相逐渐致密,碳相最终形成了在陶瓷基体上镶嵌的直径为40μm橄榄球状和条状这两种形貌．碳／陶瓷相的弱界面分层诱导韧化和第二相TiB2与陶瓷基体之间热膨胀系数不匹配所致的残余应力使变形过程中微裂纹的扩展路径发展变化,使复合材料的韧性提高．     

大豆蛋白对涂布白板纸涂料性能的影响

涂料的流变性能是影响涂布加工纸质量的重要因素之一,对涂布加工过程中涂层的均匀性以及获得良好的涂层性能具有决定性影响.本实验针对涂布白板纸涂料进行了研究,通过添加大豆蛋白改善涂料的流变性能及涂层的表面性能.结果表明,大豆蛋白使涂料低剪切粘度增加,剪切稀化作用增大,改善了涂料的触变性能,并且使涂布白板纸表面粗糙度下降、适印性能提高,同时涂层的表面强度也有一定的提高.     

Composition and hardness of mullite coatings formed with direct current power supply on LY12 aluminum alloy surface

The surface modification of aluminum and its alloys using plasma technology is increasingly being investigated, Thick ceramic coatings with high hardness on aluminum alloys can be prepared successfully using a micro-plasma oxidation （MPO） technique. In this work, the composition, microstructure and elemental distribution of ceramic coatings formed by MPO on LY 12 almnlnum alloy and its hardness are investigated using XRD, EPMA and microhardness instruments. The results show that the ceramic coatings consist of mullite,γ-Al2O3 and a lot of amorphous matter. The content of silicon in the coatings increases from interface to the coatings, however, the content of aluminum decreases along this direction. The maximum hardness of ceramic coatings is up to 9.2 GPa.     

Effect of bond-coat surface roughness on failure mechanism and lifetime of air plasma spraying thermal barrier coatings

This work investigates the failure mechanism of an air plasma spraying(APS) thermal barrier coatings(TBCs) with various bond coat(BC) surface toughness under constant temperature loading condition. Results show that the increased BC surface roughness decreased the lifetime. Moreover, the relationship between the TGO depth and the lifetime can be well described by linear law.The failure mechanism of the TBCs samples was studied by cross-sectional morphologies observation and using the finite element method(FEM). Cracks in the TBCs samples with higher BC surface roughness are initiated from the defects on the BC caused by Al depletion in the BC layer. However, cracks in the samples of TBCs with lower BC surface roughness condition preferentially occur at the TC-TGO interface. This finding could be attributed to the high mismatch stresses in the TC-TGO interface.