铱的合金化改性研究现状

铱具有极高的熔点、优异的高温强度以及极佳的抗氧渗透性能,通过合金化改性得到的二元铱合金的综合性能较纯铱已有显著提升。不同二元铱合金体系具有突出的高温抗氧化性能、高温力学性能或抗电弧烧损性能,被应用于高温抗氧化材料、高温结构材料、贵金属电接触材料等领域。为进一步提升性能、降低成本,在二元铱合金基础上发展出的多元铱合金充分发挥出添加元素的晶粒细化强化、弥散强化、阻挡保护等作用,展现出令人满意的成果,极具发展潜力和可设计性。     

合金元素复合化对Ti_(2)AlNb合金高温抗氧化性能影响EI北大核心CSCD

Ti_(2)AlNb合金具有良好的工艺性能、综合力学性能和较低的密度等性能优势,是新型航空发动机的重要选材之一。为拓宽Ti_(2)AlNb合金的应用范围,需对传统Ti_(2)AlNb合金进行合金成分优化和工艺组织调控以进一步增强其高温抗氧化性能。本研究在传统Ti-Al-Nb三元合金体系基础上,综合设计Mo,Zr,W等合金复合化的方法提高Ti_(2)AlNb合金的抗氧化能力,通过对新型Ti_(2)AlNb合金在750℃和850℃的氧化增重行为分析、氧化层特征结构分析、表面氧化物种类和合金成分过渡分布分析等,发现Mo合金元素引起Ti_(2)AlNb合金在750℃上升至850℃时抗氧化性能的明显下降,Zr合金元素则始终保持着Ti_(2)AlNb合金良好的高温抗氧化能力;更为深入的截面试样SEM表征可将氧化层结构细分为氧化物层、富氧扩散层和组织演变层,Zr和W合金元素对850℃高温氧化过程中不同氧化层结构具有协同抑制作用,因此提出通过Zr和W合金元素复合的方法作为新型Ti_(2)AlNb合金抗氧化合金成分优化方向。     

电弧离子镀TiC扩散障结构及抗高温氧化性能研究

采用电弧离子镀技术(AIP)在NiCrAlY涂层与镍基高温合金(DD3合金)之间沉积TiC薄膜作为扩散障层,研究了TiC对NiCrAlY涂层与基体的元素互扩散的阻碍作用和对涂层氧化动力曲线的影响。对于添加扩散障层前后的试样,进行循环抗氧化试验来评价其抗高温氧化性能,并用扫描电镜(SEM)分析氧化前后试样微观形貌和成分,用X-射线衍射仪分析涂层的相结构。试验结果表明:TiC有效阻滞DD3基体与涂层之间的元素互扩散,提高了NiCrAlY涂层和DD3合金的抗高温氧化性能。     

氧化物弥散强化高温合金及其在航空上的应用

氧化物弥散强化高温合金,简称ODS高温合金(Oxide Dispersion Strengthened Su-peralloys )是粉末高温合金的一大分枝,也是高温合金的一个重要发展方向。 高温合金的氧化物弥散强化是指在高温合金中加入一定量的热力学稳定的氧化物,使其弥散分布于基体中,形成不溶于基体的氧化物弥散相,从而使合金得以进一步强化的一种新的强化途径。     

不同打磨下内燃机用GH4169镍基高温合金的高温氧化行为

为了提高内燃机用GH4169镍基高温合金的抗高温氧化性能,用不同型号砂纸打磨的方式对其表面进行抛光处理,然后进行850℃温度下的抗氧化性能试验测试.对各试样进行了氧化增重测试,同时对氧化的截面微观形貌进行了 SEM观察,并对氧化产物结构组成进行XRD表征.研究结果表明:采用200号砂纸进行打磨处理的试样达到了最小氧化速率,经过表面抛光后的试样达到了最快的氧化速率,总体表现为表面粗糙度增大后,合金氧化速率发生了减小.以200号砂纸打磨处理后的试样具有强度很高的基体衍射峰,形成了厚度较小的氧化膜,只存在少量的氧化物.此时经过氧化处理后形成了一些NiO白色颗粒与大量黑色氧化物Al2O3,形成了粒径更小的NiO颗粒,分布均匀性也明显变差.     

微晶化及活性元素效应在合金抗高温氧化中的协同作用

总结了目前广为研究的微晶化和活性元素效应在合金高温氧化过程中的作用，并讨论了二者的协同效应。微晶化和活性元素效应均能够降低合金的高温氧化速率，提高氧化膜的黏附性。然而，微晶化中晶粒的长大趋势和促进内氧化发生的缺陷对其实际应用造成不利影响，少量活性元素的添加恰好弥补微晶化的这些缺失；活性元素添加须适量，这点限制了它作为保护性氧化膜形核中心的数量及降低氧化速率的幅度，且使得合金氧化增重较未添加活性元素试样略有增加，微晶化则不存在这样的问题，可以弥补应用活性元素效应的不足之处。本工作旨在加深对微晶化和活性元素协同效应对合金高温氧化性能影响的微观理解，为制备性能更为优异的抗高温氧化合金提供理论和实践基础。     

球磨时间对镍基ODS合金拉伸性能的影响

研究了球磨时间对Y2O3氧化物弥散强化(ODS)镍基高温合金机械合金化和拉伸性能的影响.镍基高温合金采用机械合金化和热压烧结方法制备.镍基ODS高温合金粉末是在行星式球磨机上进行球磨.采用扫描电镜及X射线衍射分析了球磨时间对镍基ODS合金粉末形貌和物相的影响.研究结果表明,Y2O3氧化物弥散强化镍基高温合金机械合金化粉末尺寸随研磨时间的增加先增大后减小,8h粉末颗粒尺寸达到最大,之后粉末颗粒尺寸逐渐减小,28h后,镍基ODS合金粉末尺寸稳定且均匀.拉伸结果表明,采用研磨28h的合金粉末制备的镍基ODS合金具有最高的抗拉强度(1300MPa).     

铌钛双稳定430不锈钢高温氧化行为研究

以铌钛双稳定430铁素体不锈钢(NTS430FSS)与SUS430铁素体不锈钢(SUS430FSS)为实验材料,研究了稳定化元素铌钛对其高温抗氧化性的影响。通过恒温氧化实验得到两种材料的氧化动力学行为曲线,结合扫描电镜、能谱分析以及X射线衍射等分析方法探究高温氧化的微观机理。结果表明,稳定化元素钛可以显著降低单位面积氧化增重,使得氧化激活能由72.6 kJ/mol提高至121.6 kJ/mol。钛的氧化物镶嵌在氧化膜与基体之间,提高了氧化膜与基体的附着力,改善了材料的高温抗氧化性能。     

EBPVD制备ODS Ni基高温合金抗氧化性能研究

采用电子束物理气相沉积技术制备了微晶氧化物弥散增强Ni基高温合金,并研究了该合金的高温氧化行为.通过最小二乘拟合得到的合金氧化动力学模型近似遵循4次方规律,并在高温氧化过程中,合金能够生成单一的Al2O3氧化膜,而且氧化膜的粘附性好,不易脱落.稀土氧化物的添加可明显地改善合金的抗高温氧化性能,提高氧化膜的粘附性.     

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。     

Identification of Iron Oxides Qualitatively/Quantitatively Formed during the High Temperature Oxidation of Superalloys in Air and Steam Environments

Mssbauer spectroscopy has been used to study the morphology of iron oxides formed during the oxidation of superalloys,such as SS-304L(1.4306S),Incoloy-800H,Incoloy-825,UBHA-25L,Sanicro-28 and Inconel-690,at 1200℃ exposed in air and steam environments for 400 h.The basic aim was to identify and compare the iron oxides qualitatively and quantitatively,formed during the oxidation of these alloys in two environments.The behaviour of alloy UBHA-25L in high temperature oxidation in both environments indicates th...     

High temperature cyclic oxidation and hot corrosion behaviours of superalloys at 900°C

Oxidation and hot corrosion are serious problems in aircraft, marine, industrial, and land-base gas turbines. It is because of the usage of wide range of fuels coupled with increased operating temperatures, which leads to the degradation of turbine engines. To obviate these problems, superalloys, viz. Superni 75, Superni 718 and Superfer 800H superalloys (Midhani grade), are the prominent materials for the high temperature applications. It is very essential to investigate the degradation mechanism of superalloys due to oxidation and hot corrosion and substantiate the role of alloying elements for the formation of protective oxide films over the surface of the superalloys. Therefore, the present work investigates the oxidation and hot corrosion behaviour of superalloys exposed to air and molten salt (Na₂SO₄–60% V₂O₅) environment, respectively, at 900°C under cyclic conditions. The weight change measurements made on the superalloys during the experiments are used to determine the kinetics of oxidation and hot corrosion. X-ray diffraction (XRD), X-ray mapping and field emission scanning electron microscope (FESEM, FEI, Quanta 200F company) with EDAX Genesis software attachment, made in Czech Republic are used to characterize the corroded products of the superalloys. It is observed that the formation of scale rich in Cr₂O₃, NiO and spinel NiCr₂O₄ has contributed for the better oxidation and hot corrosion resistance of Superni 75; whereas relatively lesser hot corrosion resistance of Superfer 800H is due to the formation of non-protective oxides of iron and sulphides of iron and nickel. The parabolic rate constants calculated for the superalloys show that the corrosion rate is minimum in air as compared to molten salt environment.     

Oxidation behaviour of single crystal nickel-based superalloys: intermediate temperature effects at 450–550°C

The oxidation behaviour of two single crystal Ni-based superalloys has been investigated at 450°C and 550°C. Isothermal oxidation was carried out for varying times and it was found that exposure resulted in a sub-micrometre thick oxide. The external and internal oxide kinetics were studied via high-resolution image analysis and both showed sub-parabolic growth rates. Thermogravimetric tests indicated that the overall oxidation growth obeys a near quartic power law while parabolic kinetics can describe the transient oxidation period. Characterisation of the resulting oxides was carried out using electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Results from thermodynamic modelling of the oxide formation are also presented to further assess the postulated mechanism of low-temperature oxidation in these Ni-based superalloys.     

Role of rare earth oxide coatings on oxidation resistance of chromia-forming alloys

Rare earths (RE) have been used to increase high temperature oxidation resistance of chromia and alumina forming alloys. The RE can be added as elements (or oxides) to the alloys or applied as oxide coatings to the alloy surface. This paper presents the effect of different RE oxide coatings and lanthanum chromite coatings on the high temperature oxidation behavior of Fe20Cr and Fe20Cr4Al alloys. The oxidation resistance of the Fe20Cr alloy increased with increase in ionic radius of the RE element in the coating. The RE oxides decreased chromia growth rate more than alumina growth rate. In extended cyclic oxidation tests that were carried out from peak temperatures of 900 °C, 1,000 °C and 1,100 °C to room temperature at cooling rates of 300 °C/s and 1,000 °C/s, the La₂O₃ coating increased cyclic oxidation resistance of the Fe20Cr alloy significantly more than the Pr₂O₃ coating. The role of RE in increasing overall oxidation resistance of chromia forming alloys is discussed.     

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.     

Basic Concepts for better heat protection systems

The mechanisms of oxide growth and adhesion on high temperature resistant alloys are discussed. Routes for achieving superior oxidation resistance are outlined. The hot corrosion resistance of high temperature alloys seems to be related to the respective oxide adhesion of the protective oxides on them. Ceramic coatings on metals offer additional heat and corrosion protection which can be markedly improved by matching the thermal expansion coefficients (TEC) of substrates to that of dense ceramic coatings.     

Effect of yttrium on high temperature oxidation behavior of Ni-Al-Mo-B alloy IC6

A variety of experimental techniques have been used to study the effect of yttrium on the high temperature cyclic oxidation behavior of a directionally solidified (DS) Ni-Al-Mo-B alloy IC6. The cyclic oxidation resistance of alloy IC6 is substantially improved by adding proper amount of yttrium, which is resulted from several beneficial roles played by yttrium. Yttrium decreases the harmful effect of sulfur to the adherence between the oxides scale and the substrate, and the depth of the diffusion layer by inhibiting cationic transportation. Yttrium promotes the selective oxidation of aluminum and decreases the proportion of NiO region in the surface oxide scale. Yttrium migrates to the oxide grain boundaries and promotes the formation of a fine close packed oxide grain structure, and hence improves the mechanical strength of the grain boundaries.     

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.