容错事故燃料包壳用FeCrAl合金的研究进展EI北大核心CSCD

福岛事故后,人们迫切需要开发相应的燃料包壳材料以忍受严重事故发生时的极端工况,从而提高核电站的事故承受能力。尽管FeCrAl合金的宏观中子吸收截面要远远高于锆合金,但其在严重事故下良好的耐腐蚀性、优越的高温力学性能及抗辐照损伤能力,使其被列为事故容错燃料包壳的候选材料之一。然而,现有FeCrAl合金难以满足核电站用材料的要求,因此需对其进行优化,以获得更佳的性能。本文系统总结了近年来关于优化后FeCrAl合金的腐蚀行为、力学性能、辐照后的微观结构及力学性能变化、焊接性及加工性等方面的研究进展,分析了FeCrAl合金的高温腐蚀机理以及引起FeCrAl合金微观结构及力学性能变化的主要原因,提出了FeCrAl合金在高温腐蚀、焊接性以及加工性等过程中存在的主要问题以及未来的研究方向。     

Materials for lower temperature solid oxide fuel cells

The solid oxide fuel cell (SOFC) continues to show great promise for the generation of electricity for an increasing range of applications. The present SOFC technology is based on an all-ceramic design, which eliminates the corrosion problems associated with fuel cells containing liquid electrolytes. To obtain good electrochemical performance with the currently used materials, this all-ceramic fuel cell operates at 1000°C. Despite a significant amount of research and several successful demonstrations at the 100 kW level, commercialisation of the technology is not as rapid as anticipated. This is, in part, due to the high operating temperatures required, necessitating the use of expensive materials. As a result of these problems, there has been an effort over the past few years to lower the SOFC operating temperature. This paper will address the issues concerning the development of new materials that can operate at lower temperatures. Many of these issues have been or are being addressed in the research performed at Argonne National Laboratory, and some recent results will be discussed.     

Application and optimisation of materials in valve train

Abstract

Recently the requirements imposed on parts in the valve train have significantly increased and different trends are apparent for different fuels. These fuels can be defined as conventional fuels, heavy fuels, and (natural) gas. For conventional fuels, no major differences exist between truck and marine engine applications. Owing to an increase in peak pressure and process temperature, new designs and materials are required in these fields of application. For heavy fuel applications, corrosion presents a continuing problem because of further increasing temperatures. Improved materials, surface protection, and heat transfer could reduce problems such as seat burning and corrosion on valve stems, valve heads, and guides. Varying compositions of natural gas and problems with the mixture control require the optimisation of the tribological system of valve seat–valve seat insert and an improvement in the behaviour of valve materials at elevated temperatures. Both technically and economically there are many problems to solve. This paper addresses the techniques and results of improvement and optimisation, for example, finite element analysis and test facilities, improvement and optimisation of valve steels, and the surface protection, heat transfer, design, and interactions between valve stem guide and the valve seat-seat insert.

MST/3156     

锅炉"四管"粉芯喷涂丝抗高温氧化和热腐蚀性能的研究

针对锅炉"四管"防护问题,采用氧化增重、涂盐腐蚀增重和测量涂层表面硬度的方法,研究了3种新型粉芯喷涂丝的抗高温氧化性能、抗热腐蚀性能和涂层的硬度.结果表明,新型的粉芯喷涂丝具有良好的抗高温氧化和抗热腐蚀性能;涂层的抗高温氧化和抗热腐蚀性能随铬含量的增加而提高;其中GL1号喷涂丝在具有较好的抗高温氧化和抗腐蚀性能的同时,还具有相当高的硬度.     

12. Controlled deposition of protective aluminum films on aircraft steels

A laboratory system for controlled vacuum deposition of aluminum films was assembled in order to conduct anodic protection coating experiments on CrMo aircraft steels. High deposition rates were achieved employing a high-power electron-beam gun for source evaporation. A special substrate-heater was constructed for controlled variation of coating temperature. Process variables and their effect on the relevant properties of the films, mainly adhesion and corrosion resistances, were studied. It was found that these properties improved with increasing substrates temperature in the range of 200–450°C. Optimum conditions were obtained for the following set of process variables: temperature = 400–450°C. Films of about 5 microm thickness were obtained conditions and their structure was studied using scanning electron microscope and X-ray diffraction methods. It was found that the films had a (111) preferred orientation evidenced by 0.5–1.0 microm crystallites, with the larger sizes corresponding to the higher temperatures.     

Effect of forging process on microstructure,mechanical and corrosion properties of biodegradable Mg–1Ca alloy

The performance of Mg–1Ca alloy, a biodegradable metallic material, may be improved by hot working in order that it may be of use in bone implant applications. In this study, Mg–1Ca cast alloy was preheated to different temperatures before undergoing forging process with various forging speeds. Macro- and microstructure of the samples were examined by stereo and scanning electron microscopes (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), respectively. To determine the mechanical properties of the alloy, hardness value and plastic deformation ability of the samples were measured. To investigate the corrosion behaviour of the alloy, immersion and electrochemical tests were performed on the samples in simulated body fluid and the corrosion products were characterized by SEM/EDS. The results showed that increasing forging temperature decreased grain size led to improved hardness value and plastic deformation ability of the alloy, whereas no significant effect was observed by changing forging speed. Moreover, forging at higher temperatures led to an increase in the amount of Mg₂Ca phase at grain boundaries resulted in higher corrosion rates. It can be concluded that although forging process improved the mechanical properties of the alloy, it does not satisfy the corrosion resistance criteria required for bone healing.     

Mechanical properties of porous silicon by depth-sensing nanoindentation techniques

Porous silicon (PS) was prepared using the electrochemical corrosion method. Thermal oxidation of the as-prepared PS samples was performed at different temperatures for tuning their mechanical properties. The mechanical properties of as-prepared and oxidized PS were thoroughly investigated by depth-sensing nanoindentation techniques with the continuous stiffness measurements option. The morphology of as-prepared and oxidized PS was characterized by field emission scanning electron microscope and the effect of observed microstructure changes on the mechanical properties was discussed. It is shown that the hardness and Young's elastic modulus of as-prepared PS exhibit a strong dependence on the preparing conditions and decrease with increasing current density. In particular, the mechanical properties of oxidized PS are improved greatly compared with that of as-prepared ones and increase with increasing thermal oxidation temperature. The mechanism responsible for the mechanical property enhancement is possibly the formation of SiO₂ cladding layers encapsulating on the inner surface of the incompact sponge PS to decrease the porosity and strengthen the interconnected microstructure.     

Vanadic and chloride attack of superalloys

Abstract

The high-temperature corrosion of superalloys is associated with contaminants. When comparing contaminant conditions the contaminant flux rate (CFR) should be considered rather than the contaminant level in the fuel or environment. At temperatures above 700° C, vanadates cause fluxing of the protective oxide scales and it is shown that corrosion is determined by the CFR and temperature rather than by material selection. The effects of sulphur level in the fuel on the efficiency of magnesium additives are also considered. Chloride contamination is shown to produce scale rupture and the influence of chloride contamination under gaseous and deposit conditions is examined. In particular the differences between marine gas turbine conditions and laboratory tests to simulate hot corrosion are evaluated. It is suggested that in marine turbines fluxing mechanisms are more appropriate to the alloy than to the protective scale. Finally, the influence of chlorides on low-temperature type II hot corrosion is considered. MST/445     

Struktur und Eigenschaften nichtrostender Stähle nach einer Plasmaimmersionsionenimplantation und einer Plasmanitrierung

Structure and properties of stainless steels after plasma immersion ion implantation and plasma nitriding Stainless steels can be nitrided at temperatures ≤ 400 °C to increase their hardness and wear resistance without a decreasing of their excellent corrosion resistance. Structure and properties of the surface layers produced by plasma nitriding and plasma immersion ion implantation in this temperature range were tested. There are negligible differences in the structure of the produced surface layers in spite of different interaction principles of the used technologies. However there are clear differences between the case of different steels. The case of ferritic chromium steels mainly consists of ε-nitride. Whereas the cases of austenitic and ferritic austenitic steels are characterized by expanded austenite. The corrosion resistance of the steels is reduced by nitriding only, if evident CrN-formation occurs.     

Tensile properties and microstructure characterization of Hi-NicalonTM SiC fibers after loading at high temperature

Loading tests were performed on the Hi-Nicalon^TM fiber yarns by applying different dead loads at elevated temperatures in Ar atmosphere. After each loading test, the room temperature tensile properties of single filaments as a function of load, exposure time and temperature, were evaluated on these fibers. Strength degradation of single filament occurred after loading test, and strength retention decreased with increasing the exposure temperature and load. The microstructure observation revealed that oxidation and loading accelerated new flaw nucleation and growth resulting in stress corrosion cracks. The stress corrosion cracks acted as critical flaws and could be mainly responsible for the strength degradation. The mirror size corresponding to the critical flaw size was measured and fracture mechanics was applied to analyze failure mechanism of single filament.     

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.     

Some Characteristics of Automotive Exhaust Valve Alloys

The PH stainless steels and the nickel-base superalloys, can be evaluated for exhaust valve applications by considering their metallurgical, environmental and high temperature strength properties. The PH stainless steels are characterized by their good sulfidation and high temperature strength. Good PbO corrosion resistance is achieved with the low silicon, nickel containing alloys. Stable alloys show the greatest high temperature strength which can be improved further by a solution and age treatment. Aging below the optimum temperature of 760°C results in grain boundary sensitization and low impact properties while higher temperatures produce more of the discontinuous phase. The addition of refractory elements can be detrimental to the oxidation resistance of these alloys. The highest elevated temperature strength and best PbO and oxidation resistance is achieved with the nickel-base superalloys. These alloys are completely stable and highest strength at elevated temperatures is achieved with a solution and age treatment. These alloys show lower sulfidation corrosion resistance relative to the PH stainless steels, however this can be improved with higher chromium contents.     

Low-quality fuel problems with advanced engine materials

Demands for high efficiency and power in the future will bring the use of advanced materials including ceramics, composites and augmented metals in engines and other technologies. In many cases, these materials may be subject to corrosion by high temperature gases and molten salt deposits resulting from contaminants (eg sodium, sulphur and vanadium) in the fuel or environment. This paper gives a short overview of the state of knowledge that exists today concerning ceramics and metals corrosion by fuel contaminants, and of possible new avenues for research and materials development.     

Estimating the Triple-Point Isotope Effect and the Corresponding Uncertainties for Cryogenic Fixed Points

The sensitivities of melting temperatures to isotopic variations in monatomic and diatomic atmospheric gases using both theoretical and semi-empirical methods are estimated. The current state of knowledge of the vapor-pressure isotope effects (VPIE) and triple-point isotope effects (TPIE) is briefly summarized for the noble gases (except He), and for selected diatomic molecules including oxygen. An approximate expression is derived to estimate the relative shift in the melting temperature with isotopic substitution. In general, the magnitude of the effects diminishes with increasing molecular mass and increasing temperature. Knowledge of the VPIE, molar volumes, and heat of fusion are sufficient to estimate the temperature shift or isotopic sensitivity coefficient via the derived expression. The usefulness of this approach is demonstrated in the estimation of isotopic sensitivities and uncertainties for triple points of xenon and molecular oxygen for which few documented estimates were previously available. The calculated sensitivities from this study are considerably higher than previous estimates for Xe, and lower than other estimates in the case of oxygen. In both these cases, the predicted sensitivities are small and the resulting variations in triple point temperatures due to mass fractionation effects are less than 20 μK.     

氨基磺酸溶液中肉桂醛对碳钢的缓蚀作用和吸附热力学研究

采用失重法考察不同温度下5％氨基璜酸中,不同浓度的肉桂醛对碳钢的缓蚀作用;并对氨基璜酸介质中肉桂醛在碳钢表面吸附热力学进行了研究。肉桂醛低浓度时,随浓度增大,缓蚀作用增强;当其浓度达到一定值后,缓蚀作用基本保持不变。实验结果表明,肉桂醛在碳钢表面产生单分子层吸附,并且满足Langmuir吸附规律。△G°〈0吸附过程可以自发进行,并且随着温度的升高础增大,吸附作用降低。△H°〈O表明反应是放热过程。△S°〈0表肉桂醛在碳钢表面的吸附过程为熵减少的过程。     

Mechanical and thermal properties of HVOF sprayed Ni based alloys with carbide

The objective of the present study is to develop multi-functioned coating to the components, which are made of copper with electroplated Ni and are widely used for steel making industry. In this paper, we report the mechanical and thermal properties of Ni based superalloys with carbide sprayed by high velocity oxygen fuel (HVOF), and the detailed effects of sprayed material, spraying conditions, and initial powder structure on these properties. It was found that, among commercial Ni self-fluxing alloys (without fusing treatment), coating with a carbon content of 0.58 mass% had the most preferable properties, with a good balance of the hardness, strength, and thermal shock resistance. The thermal shock resistance depended not only on the strength of the coating but also on the volume contraction when tested at high temperatures. For the several developed Ni based superalloys with carbide, Ni20Cr8Mo5Fe–WC and Ni16Cr15Mo3–WC demonstrated the prominent adhesion strength and thermal shock resistance with high Galvanic corrosion resistance through optimized spraying condition. Also, 20 mass% NiCr–Cr₃C₂ coating sprayed by using employed relatively small primary particle succeeded in achieving the multi-superior properties; high adhesion strength, high corrosion resistance and thermal shock resistance.     

Entwicklungsmöglichkeiten und Entwicklungstendenzen auf dem Gebiet der Hochtemperatur-Legierungen

Possible Trends and Developments in the Field of High Temperature Alloys. The continuing development of super-alloys that has for some 25 years allowed a steady increase in the operating-temperature of gas turbines is now closely approaching the limit set by the ultimate operating temperatures of the materials themselves. In order to increase these limits and thus ensure continued progress in this direction new alloys and new processes need to be developed. Possible means for the improvement of conventional super-alloys have been suggested such as:

• new powder metallurgical processes
• production of cast/forged thin section blades by the “Squeeze-Casting”-process
• increasing the ductility of cast alloys by modifying the morphology of primary precipitates in the casting
• increasing the working temperature by means of precipitates having increased dissolution temperatures.

In connexion with this subject, the process of directional solidification, developed during the past 10 years, is briefly discussed with particular reference to its application in the production of columnar and single-crystal super-alloys and eutectic composite materials. The properties of directionally solidified super-alloys as well as directionally solidified eutectic composite materials are summarised in the light of present day knowledge.     

Al-Cu-Mg-Ag合金与ZL205A合金性能与微观组织对比

采用半连续铸造法分别制备了Al-Cu-Mg-Ag合金与ZL205A合金。对两种铝合金的流动性能、室温及高温拉伸性能、拉伸断口形貌、晶间腐蚀性能和微观组织进行了对比分析。结果表明:浇铸温度为720℃和740℃时,Al-Cu-Mg-Ag合金的流动性能均优于ZL205A合金的。室温、150℃、200℃、250℃下,Al-Cu-Mg-Ag合金的强度均高于ZL205A合金的,且随着温度的升高,其强度降低的幅度要明显低于ZL205A合金的,两种材料的室温伸长率基本相当。Al-Cu-Mg-Ag合金的晶间腐蚀深度在182～246 μm之间,优于ZL205A合金的274～337 μm。Al-Cu-Mg-Ag合金无析出带的宽度要窄于ZL205A合金的。      

挤压温度对Mg-5.3Gd-2.6Y-1.1Nd-0.3Zr合金的力学性能和耐生物腐蚀性能的影响

在不同温度下对均匀化处理后的Mg-5.3Gd-2.6Y-1.1Nd-0.3Zr(质量分数/%)镁合金进行挤压。利用光学显微镜和拉伸实验对比研究固溶态铸锭、不同挤压温度合金的显微组织和力学性能,采用析氢法、失重法和极化曲线实验综合测试合金在Hank’s人体模拟液中的耐生物腐蚀性能,利用扫描电子显微镜观察腐蚀后合金的表面腐蚀形貌。结果表明:随着挤压温度的降低,合金的晶粒不断细化,强度及塑性不断提高,其中390℃温度下挤压得到的合金屈服强度达到223.4MPa,较固溶态铸锭(139.8MPa)提升约60%,且挤压后的合金在Hank’s体液中具有更高的耐腐蚀性,随着挤压温度的降低,合金的耐蚀性先升高后降低,450℃挤压的棒材耐生物腐蚀性能最优,腐蚀速率为0.74mm/a。     

Effect of mono and composite coating on dynamic fracture toughness of metals at different temperatures

It is well known that during the operating condition of any metallic structural system the dynamic crack growth speed is in the order of 1–2 km/s. Industrial finishes like coating which form the integral part of manufacturing is adopted to improve fracture toughness of metals. These coated samples coated with thin films are mechanically tested by Charpy V-notch impact tester for estimating dynamic fracture toughness. Coatings improve the wear and corrosion resistance of materials; they tend to reduce the strength of materials, because of the increased residual stresses due to the coating process. Defects cannot be precluded from these coated and treated components; strength of those components in the presence of these defects can be analyzed by fracture mechanics approach. An attempt has been made to analyze the effectiveness of coating methods like electroplating, PVD (Physical Vapour Deposition), coating thickness and the service temperature on the fracture behaviour of metals. Experiments have been carried out on EN8 steel and aluminium for different temperatures and the later samples were corroded for 2400 h and tested for corrosion resistance. The specimen preparation and experimentations were carried out according to the ASTM standard E-23. Finite element analysis was done by FRANC 2D (Fracture Analysis Code) for estimating the stress intensity factor at different crack lengths along with influence of temperature and corrosion. PVD coated samples of Al–N (aluminium nitride) and nano-crystalline layer of Ti–Al–N (titanium aluminium nitride) showed improved dynamic fracture toughness properties. The same set of samples showed decrease in stress intensity factors and excellent corrosion resistance compared to conventional Ni (nickel) and Cr (chromium) coated samples. Mechanical behaviour of selected metals under heat affected zone is of also discussed in this paper, the study aims at both coated and uncoated cases. Performances of metals in cryogenic condition are also paid attention in this paper.