用多元线性回归法预测镍基高温合金的抗氧化性

用静态氧化法研究了3种铸造镍基高温合金K35，K44，K46在800℃及900℃的高温氧化动力学行为。结果表明，3种合金的氧化动力学曲线均符合抛物线规律，其中氧化速度常数为合金成分中每种元素作用的综合结果，用多元线性回归法计算了25种镍基高温合金在900℃氧化过程的作用系数，并给出了3种试验合金的氧化动力学回归方程，与3种合金的实验结果相比，相对误差小于13％。     

1000～1400℃下NbMoTaWV难熔高熵合金的氧化行为

采用静态氧化实验与XRD,FSEM测试技术对电弧熔炼制备的NbMoTaWV难熔高熵合金的高温氧化行为进行研究。结果表明：1000℃及1200℃下NbMoTaWV由于氧化层开裂严重失去保护性，氧化增重遵循直线氧化规律；1400℃下生成的熔融态氧化物释放氧化层的生长应力，填补Mo, V氧化物挥发留下的孔洞，使氧化层对氧气能够起到一定的阻隔作用，氧化增重遵循抛物线氧化规律。在NbMoTaWV的氧化过程中，氧气扩散进入基体内部后率先与扩散层中的Nb和Ta发生氧化反应，生成针棒状氧化物，之后与其他合金元素发生氧化反应，W的氧化物固溶在Nb和Ta氧化物中，颗粒状的Mo和V混合氧化物在高温下挥发。     

GH907高温合金表面电弧离子镀NiCoCrAlY/AlSiY复合涂层的高温抗氧化性能研究

为提高GH907高温合金在750℃下高温抗氧化性能。在GH907合金表面采用电弧离子镀技术(AIP)制备NiCoCrAlY/AlSiY复合涂层。系统开展复合涂层的高温抗氧化行为和机理研究,利用XRD、SEM和EDS等微尺度分析表征方法,全面解析氧化过程中物相的结构特征、氧化产物成分及表/截面形貌特征。结果试验表明,750℃氧化500 h后,GH907高温合金氧化层(FeO,Fe₂O₃)萌生大量裂纹,氧化层发生大面积剥落。基体呈迅速氧化增重趋势,500 h质量增重值为22.38 mg/cm²。相比之下,NiCoCrAlY/AlSiY复合涂层在氧化实验中,由于形成连续且致密的Al₂O₃屏障层,有效抑制氧气内扩散,延缓GH907高温合金发生氧化反应的影响。氧化80 h质量增重为6.37 mg/cm²,随后质量增重率趋于稳定,500 h复合涂层质量增重值仅有7.68 mg/cm²。结论由此表明,NiCoCrAlY/AlSiY复合涂层可以显著提...     

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。     

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。     

合金元素对Cu-Te-Cr合金抗氧化性能的影响

利用氧化增重法,结合SEM、XRD等不同测试手段,研究了不同碲含量的Cu-Te-Cr合金在300～600℃的抗氧化性能.实验结果表明,在纯铜基体中加入Te、Cr元素,合金发生了内氧化,提高了氧化膜和合金基体的结合强度和氧化膜的致密度,增强了氧化膜的粘附性,从而提高了铜合金的抗氧化性能;且随着温度的升高,合金的氧化趋势由抛物线规律向直线规律转变.     

Ti-45Al-10Nb合金的高温氧化行为

研究了Ti—45A1—10Nb(原子分数，％)合金在800-960℃在氧气和空气中的氧化行为．结果表明，该合金具有较好的高温抗氧化性能，其氧化增重速率与铁基耐热不锈钢相似或略优．与Ti—50A1合金相反，Ti-45A1-10Nb合金在空气中的氧化增重速率明显低于在纯氧中的氧化增重速率．X射线衍射与能谱分析表明，Ti-45Al一10Nb合金在氧气中的氧化产物主要有TiO2和Al2O3，但在空气中的氧化产物中有TiN相．这是降低氧化速率的主要原因，同时，合金元素Nb稳定了氧化层中的TiN相，因而提高了合金在空气中的抗氧化性能．     

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。     

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。     

低膨胀合金的线膨胀系数测量方法--接触式干涉法

线膨胀系数是低膨胀合金的重要性能指标，针对低膨胀合金线膨胀系数的测量精度要求较高，提出了采用接触式干涉法进行测量，并具体介绍其原理、装置、测量步骤以及对试样的要求。多年实践证明，该方法合理、简便、经济、可靠，结果达到精度要求。     

Cyclic oxidation of high-temperature alloys

Abstract

Many applications of high-temperature alloys involve high-temperature oxidation under thermal cycling conditions. The oxide scales formed have lower coefficients of thermal expansion than the metallic alloys and significant thermal stresses can arise during temperature variations. These thermal stresses add to the residual growth stresses which accompany oxide formation. Under certain conditions, stresses in oxide scales may be partly relieved by plastic deformation of scale or alloy. However, when these mechanisms cannot be operative, scale buckling or cracking occur depending on interfacial and oxide fracture strengths. Eventual oxide spallation causes rapid degradation since depleted regions of alloy are in contact with the oxidizing atmosphere. Incorporation of ‘active elements’ such as yttrium, in reducing the residual growth stresses significantly improves the cyclic oxidation resistance of high-temperature nickel-, cobalt-, and iron-base alloys. The present paper attempts to review briefly the mechanisms involved in these phenomena and the tentative cyclic oxidation models. MST/443     

Influence of microstructure on macroscopic elastic properties and thermal expansion of nickel‐base superalloys ERBO/1 and LEK94

In the present work the thermal expansion and the elastic properties of second generation nickel‐base superalloy single crystals ERBO/1 (CMSX‐4 variation) and LEK94 have been studied between about 100 K and 1273 K using dilatometry and resonant ultrasound spectroscopy, respectively. Inhomogeneity related to the large scale microstructure of the samples can act as a potential source of scatter for the propagation of ultrasonic waves. This can be overcome by choosing samples of sufficient size so that they appear as homogeneous media at the scale of the elastic wave length. Our final results are in good agreement with data reported in literature for similar alloy systems. In particular, the elastic material properties are only weekly affected by moderate variations in chemical composition and microstructure. Taking into account literature data for other superalloys like CMSX‐4, we derive general polynomial functions which describe the temperature dependence of the elastic moduli E_〈100〉, E_〈110〉 and E_〈111〉 in nickel‐base superalloys to within about ±3%. It was also observed that the alloys ERBO/1 and LEK94 show weak but significant anomalies in both thermal expansion and temperature coefficients of elastic constants above about 900 K. These anomalies are probably related to the gradual dissolution of the γ′‐precipitates at higher temperatures.     

Modelling the coefficient of thermal expansion in Ni-based superalloys and bond coatings

The coefficient of thermal expansion (CTE) of nickel-based superalloys and bond coat layers was modelled by considering contributions from their constituent phases. The equilibrium phase composition of the examined materials was determined using thermodynamic equilibrium software with an appropriate database for Ni-based alloys, whereas the CTE and elastic properties of the principal phases were modelled using published data. The CTEs of individual phases were combined using a number of approaches to determine the CTE of the phase aggregate. As part of this work, the expansion coefficients of the superalloy IN-738LC and bond coat Amdry-995 were measured as a function of temperature and compared with the model predictions. The predicted values were also validated with the published data for the single-crystal superalloy CMSX-4 and a number of other Ni-based alloy compositions at 1000 K. A very good agreement between experiment and model output was found, especially up to 800 \(^\circ \)C. The modelling approaches discussed in this paper have the potential to be an extremely useful tool for the industry and for the designers of new coating systems.     

电沉积Co-Ni-Al2O3复合镀层微观结构及高温性能

在氨基磺酸盐电解液中,利用复合电沉积技术制备得到了Co-Ni合金基中弥散分布Al₂O₃颗粒的金属基复合镀层。通过SEM,AFM以及XRD等分析测试方法,研究了Co-Ni-Al₂O₃复合镀层的表面形貌和微观晶体结构。结果发现:Co-Ni-Al₂O₃的表面形貌和微观晶体结构主要受镀层中钴含量的影响。高钴含量复合镀层具有Hcp结构,其表面形貌比具有Fcc结构的低钴含量镀层的表面更加均匀细致。Al₂O₃颗粒在Co-Ni合金中的共沉积,没有改变合金固溶体的相组成,但却改变了各晶面的优势生长。通过研究复合镀层的硬度、高温耐磨性、高温抗氧化性、热膨胀系数和热导率表明:Co-Ni-Al₂O₃具有较好的高温耐磨性和高温抗氧化能力,并且高钴含量的复合镀层相对于低钴镀层具有较低的热膨胀系数和较高的热导率。      

钛合金表面梯度Al2O3陶瓷涂层的高温抗氧化性能

钛合金应用广泛,但在高温环境中极易被氧化,降低其力学性能及寿命。利用溶胶-凝胶法在TC11钛合金上制备梯度层(ZrO_2+Al_2O_3)+表层(Al_2O_3)的复合梯度涂层,提高其高温抗氧化能力。将复合梯度涂层、单层氧化铝涂层以及基体在700℃进行100h的高温氧化,利用氧化增重数据拟合得到梯度涂层的氧化速率为0.015mg~2/(cm4·h),氧化指数为2.137,并结合氧化后EDS成分分布,发现复合梯度涂层可以提高基体的高温抗氧化性能。同时利用700℃热震实验比较了复合梯度氧化铝涂层试样和单层氧化铝陶瓷试样的热震次数,梯度层(ZrO2+Al_2O_3)的存在缓解了基体与氧化铝陶瓷涂层之间热膨胀系数不匹配而导致的易剥落的问题,延长了涂层寿命,进一步提高了基体的高温抗氧化能力。     

High temperature behavior of diffusion aluminide coating on alloy 600 superalloy

Diffusion coatings are well developed for protection of nickel-based superalloys in hot and corrosive atmospheres. In the present study, aluminide coatings are produced on an alloy 600 substrate via dipping in molten aluminium. The coatings have a two-layered structure containing a dense and compact inner layer across with a porous outer layer. Thermal oxidation and hot corrosion tests showed increased resistance by production of diffusion coatings on the superalloy. Increasing the dipping time had a positive effect on the high temperature resistance of the coated alloy.     

Oxidation Behavior of Fe-Ni-Co Based Superalloys and Influence of Yttrium Addition

1. IntroductionThe Fe-Ni-Co based 907 alloy is a controlled thermal expansion superalloy for use in casting rings andseals for aircraft gas turbine engines where the servicetemperature is up to 649oC. The coefficiellt of thermal expansion of this alloy is low, about half of that ofconventional superalloys. The absence of Cr in the alloy ensures the low thermal expansion, however leadsto an inherent lack of environmental resistance compared with other superalloys containing Cr[1]. Theoaldati…     

Development of a low-expansion bond coating for Ni-base superalloys

Ternary NiCrAl alloys were modified by the addition of Ti and Si in order to adjust their coefficients of thermal expansion (CTE) to less than 15 × 10⁻⁶ K⁻¹ (from room temperature to 1000 °C) without sacrificing essential high temperature oxidation resistance. Vacuum induction melted cast alloy samples were investigated by dilatometry and thermogravimetry (TG). Oxidative TG was conducted isothermally at 900 and 1000 °C and cyclically between 600 and 1100 °C for 100 h respectively. The CTE is reduced mainly by Ti and secondly by Cr additions. Quinary alloys which showed optimal oxidation resistance essentially exhibit phase stability in the solid state at all temperatures. Approximately 4 at.% Si is needed to attain low oxidation rates and to prevent oxide spallation as well. The beneficial effect of Si on oxidation behavior is attributed hypothetically to its ability to initiate the formation of protective alumina and subsequently silica. High Cr contents lessen the beneficial effect of Si owing to the concurrent formation of chromia and/or titania.     

A dip process for thermal barrier coating on superalloys

A new cerium oxide thermal barrier coating for superalloys has been investigated. The coating is applied by hot dipping superalloy substrates into a molten bath of low melting point Ce-Ni alloy. Annealing and selective oxidation of cerium at low oxygen activities produce a duplex coating of a continuous outer layer of cerium oxide (CeO₂) and an inner composite CeO₂-substrate layer.The effects of coating composition and processing variables on the microstructure and integrity of the coating on nickel- and cobalt-base alloys were studied in detail. Isothermal and cyclic oxidation tests showed that coating spallation could occur and was associated with the oxidation of nickel and cobalt incorporated in the coating. A model for the formation of the CeO₂ barrier and the subscale region is proposed that explains the presence of unwanted nickel and cobalt.     

高温氧化对钛合金微弧氧化陶瓷膜组成与结构的影响

针对钛合金不耐高温氧化的问题,在铝酸钠电解液体系中,利用双相脉冲直流微弧氧化技术,在TC4钛合金表面原位生长以Al2TiO5为主晶相的复合氧化物陶瓷膜,研究了1000℃高温氧化对陶瓷膜试样的相组成、结构的影响及膜层增重特点.研究表明,陶瓷膜层试样的高温氧化过程包括Al2TiO5分解、基体氧化和膜层表面形貌变化3个方面.高温氧化后,膜层的主晶相由Al2TiO5变为α-Al2O3和金红石型TiO2,同时,膜层的表面形貌发生显著的变化;由于膜层和基体的热膨胀系数不同和基体钛的氧化,使得高温氧化后膜层在冷却过程中表面出现裂纹和脱壳.陶瓷膜层极大地减少了TC4钛合金在1000℃高温氧化时的增重,因此,陶瓷膜层可用于TC4钛合金的恒温氧化防护.