AlYSi涂层组织结构及抗燃气热腐蚀性能

采用真空电弧离子镀技术在K465镍基高温合金基材上制备了AlYSi沉积-扩散型涂层。研究了真空退火处理前后涂层的组织结构,以及涂层在900℃下的燃气热腐蚀行为。结果表明,经真空退火处理后的AlYSi涂层主要由β-NiAl相组成,与基体结合良好;K465合金在热腐蚀过程中表面产生了大量的腐蚀剥落;AlYSi涂层在热腐蚀过程中表面形成了Al2O3保护膜,显著提高了合金的抗燃气热腐蚀性能。     

K3合金复合涂层高温防护性能研究

采用电弧离子镀技术在K3镍基高温合金基材上分别沉积NiCrAlYSi涂层和NiCrAlYSi AlYSi沉积-扩散型复合涂层,研究两种涂层在1100℃下的高温氧化行为和900℃下的燃气热腐蚀行为.结果表明,NiCrAlYSi AlYSi复合涂层具有比单一的NiCrAlYSi涂层更加优良的抗高温氧化性能,而NiCrAlYSi涂层的抗燃气热腐蚀性能则优于NiCrAlYSi AlYSi复合涂层.     

真空电弧镀沉积HY7涂层及性能

本文采用真空电弧镀技术(AIP)在K465镍基高温合金基体上沉积了AlYSi(HY7)沉积-扩散型涂层,分析了涂层的组织结构及显微硬度,研究了涂层在1100℃的高温氧化行为和900℃下的燃气热腐蚀行为。通过扫描电镜(SEM)分析氧化前后试样的显微形貌,用X-射线衍射仪(XRD)分析涂层的相结构。试验结果表明,涂层主要由β-NiAl相组成,截面显微硬度自外向内呈中-高-低分布,涂层显著提高了叶片材料的抗高温氧化、抗腐蚀性能。     

单晶合金(NiCoCrAlYHf+AlYSi)复合涂层抗氧化性能研究

本文采用真空电弧镀技术(AIP)在DD9单晶高温合金基体上沉积60μm~80μm复合涂层(NiCoCrAlYHf+AlYSi),分析了复合涂层的组织及结构。对于沉积复合涂层的试样进行了1150℃循环抗氧化实验,来评价其抗氧化性能,通过扫描电镜(SEM)分析氧化前后的试样显微形貌,用X-射线衍射仪分析涂层的相结构,通过氧化速率对涂层抗氧化性能进行表征。试验结果表明:复合涂层明显改善了合金的抗高温氧化性能;1150℃循环氧化条件下,复合涂层寿命大于4200h。     

K4104镍基高温合金Al-Si涂层高温氧化过程中的元素扩散分析

采用无机盐料浆法在K4104镍基高温合金表面制备Al-Si涂层。依据GB/T13303-91《钢的抗氧化性能测定方法》标准,采用静态增重法对有涂层试样和无涂层试样进行了1000℃×200h抗高温氧化性能试验,并绘制了氧化动力学曲线。用带能谱扫描电镜对氧化膜的表面形貌和截面组织进行分析,研究有无涂层试样在高温氧化过程中的元素扩散。结果表明:Al-Si涂层和基体合金之间在高温氧化过程中的互扩散形成了厚度为120~140um的渗层。随着氧化时间的延长,外层铝含量逐渐降低,但仍能保持稳定的β-NiAl相。Si在扩散作用下形成内高外低的分布形式,形成的Cr3Si和富Si的M6C相有利于阻止涂层和基体元素之间的互扩散,降低化合物层的形成速度,体现了Al-Si涂层良好的抗高温氧化能力。     

Y2O3对渗Al—Si涂层抗氧化性能的影响

用无机盐料浆法在镍基高温合金K4104表面制备了渗Al-Si涂层并在制备过程中添加了Y2O3。采用静态氧化增重的试验方法对涂层进行了1000℃×200h抗氧化性试验,用带能谱分析的扫描电镜观察涂层氧化不同时间后的表面形貌和截面形貌及分析涂层的氧化膜和截面成分。用origin软件绘制氧化动力学曲线并拟合出氧化动力学方程。研究结果表明，渗Al-Si具有较好的抗高温氧化性能。Y2O3的添加提高了渗Al-Si涂层的抗氧化性能，提高了渗Al-Si涂层的塑性，改善了氧化膜与涂层间的粘附性。     

发动机用TiAl表面双辉等离子制备W-Mo合金层及其高温氧化行为

目前采用双辉等离子表面合金化技术在TiAl合金表面制备W-Mo涂层的研究不多。通过SEM与XRD等测试手段,研究双辉等离子表面合金化技术在TiAl基体表面制得的W-Mo合金涂层在780℃温度下的氧化行为。研究结果表明:W-Mo改性合金在初期氧化阶段快速氧化增重,经过100 h氧化后,试样增重5.2 mg/cm2,有效改善了TiAl基体的高温抗氧化性能。W-Mo合金涂层对氧气扩散起到阻碍作用,使TiAl基体抗高温氧化性能获得显著提升。氧化处理后合金涂层表面未发生改变,形成了致密、均匀的氧化膜层。TiAl基体经100 h氧化后表面氧化膜主要是一种柱状晶结构,TiAl基体氧化产物包括金红石型TiO2以及刚玉2种成分。     

高温镍基单晶合金NiCoCrAlYTa涂层的抗热腐蚀性能

以往,对高温镍基单晶合金上采用低压等离子喷涂制备的NiCoCrAlYTa涂层的热腐蚀性能研究较少.为此,采用低压等离子方法在镍基高温单晶合金上制备了NiCoCrAlYTa涂层,采用涂盐法研究了Na2SO4对试样在1 123 K空气中热腐蚀的影响,同时分析了NiCoCrAlYTa涂层的形貌及结构.结果表明:高温镍基单晶合金遭受了严重的热腐蚀,出现了内硫化和内氧化;NiCoCrAlYTa涂层由于表面生成了致密、保护性的Al2O3膜,以及涂层中Cr和Ta元素的作用而表现出优异的抗热腐蚀性能.结果证实,NiCoCrAlYTa涂层可以很好地提高单晶合金的抗热腐蚀性能.     

热障涂层对K417G合金高温低周疲劳行为的影响

研究了涂覆热障涂层的K417G合金800℃下由应变控制的高温低周疲劳行为,并对其循环应力-应变数据和应变-疲劳寿命数据进行了分析,给出了涂覆热障涂层K417G合金的高温应变疲劳参数。结果表明:K417G合金无涂层和涂覆热障涂层状态下的低周疲劳均属于应力疲劳,以弹性损伤为主;总应变幅较大时,涂覆热障涂层的K417G合金低周疲劳寿命稍优于无涂层的K417G合金。疲劳试样断口的微观分析表明:热障涂层对K417G合金低周疲劳裂纹萌生方式无明显影响;疲劳裂纹通常萌生于疲劳试样的表面或近表面,表现为穿晶扩展。     

TiAl基金属间化合物表面涂层研究进展

TiAl合金具有优异的高温力学性能,可以作为Ni基高温合金的轻量化替代材料,但氧化和磨损等行为限制了TiAl合金的高温服役时间,不利于工业化应用。通过在TiAl合金表面沉积涂层,可以使材料兼具基体的力学性能和涂层材料的表面性能,以提高TiAl合金适应不同服役环境的能力,进而拓展其应用范围。列举了TiAl合金使用的涂层材料应具有的性质;介绍了常见涂层的制备方法;以涂层成分分类,分别总结了不同涂层体系的研究现状,并展望了制备工艺和涂层性能的发展趋势。     

Effect of high-temperature protective coatings on fatigue lives of nickel-based superalloys

This study concerns MCrAlY coatings (M is Ni, Co or both) sprayed by a vacuum plasma spraying process for protection against high-temperature corrosion and oxidation of gas turbine components, such as turbine blades and duct segments. The effect of high-temperature protective coatings on fatigue lives of nickel-based superalloys were investigated at high temperature under push–pull loading and rotary bending and then compared with uncoated superalloys, such as equiaxed IN738LC, unidirectional solidified CM247LC and single-crystal CMSX-2. The high-cycle fatigue lives of MCrAlY-coated superalloys at high temperature under push–pull loading showed an inferior performance when compared with the uncoated superalloys. This was because the crack initiation site was different. The high-cycle fatigue cracks of nickel-based superalloys initiated at casting cavities which were exposed on the specimen surface, whereas the high-cycle fatigue cracks of MCrAlY-coated specimens initiated at interface defects, such as small pores and grid residue, between the MCrAlY coating and the substrate and grew into the MCrAlY coating, and then into the substrate. Similarly, the rotary bending fatigue properties of MCrAlY-coated superalloys at high temperature showed an inferior performance when compared with the uncoated superalloys. This is because of a high stress due to the higher Young's modulus of the MCrAlY coating (in comparison with the substrate) being induced at the MCrAlY coating surface. The crack initiation site was on the specimen surface in both cases of the nickel-based superalloys and the MCrAlY-coated superalloys, respectively. As a result, it was considered that, for rotary bending tests, the fatigue life reduction was due to the high stress that originated from the difference of elastic constants between the MCrAlY coating and the superalloy. Consequently, in fatigue life design it is necessary to take account of the stress levels in a coating layer.     

Aluminium and silicon base coatings for high temperature alloys—Process development and comparison of properties

The paper is concerned with systematic studies on the formation of overlay coatings on nickel and iron base superalloys to improve their resistance against high temperature oxidation and hot corrosion. In contrast to the simpler case of aluminizing nickel base alloys, the problems arising in aluminizing iron base superalloys and in siliconizing nickel base alloys have not yet been solved.A new and economical coating procedure is presented, which involves a reaction sintering process of unalloyed powder mixtures to obtain overlay coatings. The influence of the compositions of the layer and the substrate on the chemical compatibility of the whole layer composite is described in detail. It is shown that overlay coatings containing high concentrations of silicon can only be applied on nickel base superalloys if elements that are able spontaneously to form reaction barriers are present within the substrate alloy (e.g. aluminium) or in the as-preformed interlayer. Refractory metals have proved to be the most advantageous.To obtain a ductile coating, silicon-rich donor phases in the form of isolated precipitates were incorporated into a matrix containing low concentrations of silicon. These coating systems can also be applied to improve the aluminization of iron base alloys. The high temperature oxidation and corrosion behaviours of the coated samples were tested in burner gas or air at 1000°C and in molten salts at 900°C.     

Microstructural study of aluminide surface coatings on single crystal nickel base superalloy substrates

Abstract

Aluminide diffusion coatings are frequently employed to enhance the oxidation resistance of nickel base superalloys. However, there is a concern that the presence of an aluminide coating could influence the properties of the coated superalloy, especially in respect of fatigue behaviour. To understand the nature of the effects of surface coatings on the fatigue properties of superalloys, an understanding of microstructural development within both the coating and the coating/substrate interfacial zone during high temperature fatigue testing is necessary. This paper is concerned with microstructural changes in aluminide diffusion coatings on single crystal γ′ strengthened superalloy substrates during the course of high temperature fatigue testing. The ‘edge on’ transmission electron microscopy technique is employed to study cross-sections of two stage (aluminisation plus diffusion treatment) coated superalloy samples. The paper examines the degradation of the coating produced by phase transformations induced by loss of aluminium from the coating and/or aging of the coating. Aluminium removal both by interdiffusion with the substrate and by oxidation of the coating surface is considered. Microstructural development in the portion of the substrate influenced by interdiffusion with the coating is also discussed.

MST/1694     

A study on the oxidation behavior of HVOF sprayed NiCrAlY–0.4 wt.% CeO2 coatings on superalloys at elevated temperature

The high temperature oxidation behavior of HVOF sprayed ceria added NiCrAlY coatings on superalloys has been studied. Oxidation kinetics of the bare and coated superalloys in air at 900 °C under cyclic conditions was investigated. X-ray diffraction, field emission scanning electron microscope with energy dispersive spectroscopy and X-ray mapping were used to analyse the scales formed on the surface of the oxidised samples. The NiCrAlY–0.4 wt.% CeO₂ coated specimen showed negligible microspalling of the scales. The incorporation of ceria in NiCrAlY powder has contributed to the development of adherent oxide scale, in the coating, at elevated temperature and provided the better oxidation resistance.     

Hot Corrosion of Protective Coatings

Improvement in efficiencies of gas turbine engines requires a significant increase of gas inlet temperatures. This results in an increased service temperature for blade materials and consequently in enhanced oxidation and hot corrosion attack of the blade coatings, which are usually of MCrAlY type where M is Ni, Co or NiCo. This type of coating can provide protection against oxidation and hot corrosion and act as a bond coat for thermal barrier coating systems. In both cases slow growth rates and optimum adherence of the alumina scales forming on the MCrAlY coatings during high temperature exposure are significant for component life. The above mentioned properties for the alumina scales strongly depend on the coating base composition as well as on the presence of minor alloying elements. In the present paper the performance of existing superalloys during hot corrosion is briefly described followed by the results obtained on hot corrosion of MCRAlY type coatings explaining the effect of trace elements on the life of coatings in the presence of NaCl and vanadium containing environments. Optimum thickness to improve the life of superalloys with NiCoCrAlY as a bond coat and yttria stabilized zirconia thermal barrier coatings has been identified. Based on the results, an electrochemical mechanism is proposed and shows that hot corrosion of protective coatings is an electrochemical phenomenon. Hence electrochemical techniques appear to be quite useful in evaluating the coatings for hot corrosion resistance.     

Oxidation resistance: One barrier to moving beyond Ni-base superalloys

The implementation of new high-temperature materials is often hampered by their lack of oxidation or environmental resistance. This failing is one of the strongest barriers to moving beyond Ni-base superalloys for many commercial applications. In practice, usable high-temperature alloys have at least reasonable oxidation resistance, but the current generation of single-crystal Ni-base superalloys has sufficient oxidation resistance that optimized versions can be used without a metallic bond coating and only an oxygen-transparent ceramic coating for thermal protection. The material development process often centers around mechanical properties, while oxidation resistance, along with other realities, is given minor attention. For many applications, the assumption that an oxidation-resistant coating can be used to protect a substrate is seriously flawed, as coatings often do not provide sufficient reliability for critical components. Examples of oxidation problems are given for currently used materials and materials classes with critical oxidation resistance problems.     

A Novel Deflection Method for Measuring the Growth Stress of Thermally Growing Oxide Scales

A kind of new deflection technique has been developed for measuring the growth stress of thermally growing oxide scales during high temperature oxidation of alloys. The average growth stresses in oxide scales such as Al2O3, NiO and Cr2O3 formed on the surface of the superalloys can be investigated by this technique. Unlike the comventional deflection method, the novel method does not need to apply a coating for preventing one main face of thin strip specimen from oxidizing and can be used under the condition of longer time and higher temperature.     

氧化物弥散强化高温合金抗氧化性能的研究进展

氧化物弥散强化商业高温合金因氧化物颗粒在基体中的弥散强化作用而具有较好的高温力学性能,如今被广泛应用于航空航天、能源、汽车等领域的高温部件。研究发现,氧化物颗粒的掺杂不仅可以使合金基体具有优异的高温强度,还可以显著提高基体的抗氧化性能。概述了氧化物颗粒种类、尺寸和含量对高温合金抗氧化性能的影响,从合金初期氧化行为、氧化膜生长速度、生长机制、粘附性能等角度重点关注不同性质氧化物(如活性元素氧化物和非活性元素氧化物)弥散质点在氧化过程中作用机理的异同,最后对未来的研究方向做出了展望。     

微量元素对镍基高温合金微观组织与力学性能的影响

在高温环境中镍基高温合金具有良好的高温强度、抗氧化性能、抗腐蚀性能和抗疲劳性能,被广泛应用于航空航天等领域。镍基高温合金优异的综合性能与其微观组织紧密相关。综述了微量元素B, C, Y, Ce, Hf, Re, Ru, P对镍基高温合金微观组织及其力学性能的影响。针对不同的镍基高温合金,对微量元素的不同作用进行讨论分析。镍基高温合金微观组织及其力学性能与微量元素的含量及其分布有关。添加于镍基高温合金中的微量元素分布在合金基体或者其析出相中,通过偏聚于晶界处或者元素偏析等方式,改变合金的微观组织,从而影响其力学性能。     

Evaluation of mixed oxide formation and sintering behavior in thermal barrier coatings on nickel‐based superalloy

Thermal barrier coatings are widely used in aircraft turbines to protect nickel‐based superalloys from the effect of high temperature oxidation and hot corrosion. In this study, both NiCrAlY bond coat and yttria‐stabilized zirconia top coat were deposited using atmospheric plasma spray technique. After coating production, specimens were exposed to oxidation in air atmosphere at 900 °C, 1000 °C and 1100 °C for different periods of time up to 50 h. Microstructural transformations in the ceramic top coat and growth behavior of the thermally grown oxide layer were examined using scanning electron microscopy, porosity calculation, elemental mapping and hardness measurement. Formation of different types of oxides in the thermally grown oxide layer shows that this process strongly depends on deposition technique as well as on oxidation time and temperature. Hardness values of the top coat increased with a decrease in the porosity of the top coat. Uniformity and homogeneity of the thermally grown oxide layer and densification of the top coat were evaluated in terms of the structural durability of thermal barrier coating systems.