Y.N. Kwon and Y.-W. Chang(Center for Advanced Aerospace Materials (CAAM)
,
Pohang University of Science and Technology
,
Pohang 790-784. Korea Manuscript received 26 August 1996)
金属学报(英文版)
Superplastic forming of a thin sheet into complex shape is an important manufacturing process especially in aerospace industry. The main objective of modeling the superplastic forming process is to predict the forming pressure-time cycle to maintain the optimum strain rate and the resulting thickness distribution. There have been many attempts to model superplastic forming process using the various techniques including finite element method. However, most of these attempts so far have disregarded the strain hardening effect which occurs in several superplastic materials. In this study,we have used ABAQUS finite element code to predict the suitable processing variables during an axisymmetric cup forming of Supral 100 and 7075Al alloys to examine the strain hardening effects on forming. The performance of numerical results was then compared with the experimental results.
关键词:
:superplastic forming
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null
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null
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null
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null
T. Khan(Onera
,
B.P. 72
,
92322 Chatillon Cedex
,
France Manuscript received 26 August 1996)
金属学报(英文版)
This paper describes the key role played by superalloys in aerospace propulsion. Turbopump blades in liquid rocket engines operating under severe thermal and environmental conditions require the development of specific materials.A new superalloy,THYMONEL 8, developed by ONERA in collaboration with SEP is shown to possess a set of properties required for advanced rocket engines. For future civil aircraft engines, the development of compressor and turbine disk materials operating at still higher temperatures requires a greater contrul of the grain size,which has to be increased for improved creep resistance and higher damage tolerance. Work carried out at ONERA emphasizes the importance of high temperature deformation conditions, especially the strain rate, for obtaining a uniform grain growth.
关键词:
:superalloy
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null
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null
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null
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null
Journal of the American Ceramic Society
Search for new thermal barrier materials with high-temperature stability is very difficult because there are intractable choices among thousands of possible candidates. The present paper shows that identifying and developing new low thermal conductivity materials can be accomplished by first-principles calculations of equilibrium crystal structure and elasticity, and thereafter making theoretical prediction of minimum high-temperature lattice thermal conductivity basing on David Clarke's method for insulating materials. We highlight a new oxynitride ceramic, Y4Si2O7N2, with a low theoretical minimum thermal conductivity of 1.12 similar to W center dot m-1 center dot K-1. The theoretical result is further validated by experimental measurement of thermal conductivity of dense and bulk Y4Si2O7N2. The experimental thermal conductivity is 1.50 similar to W center dot m-1 center dot K-1 at 1300 similar to K. Furthermore, thermal properties of Y4Si2O7N2 are investigated for evaluating its potential performances.
关键词:
theoretical elastic stiffness;barrier coatings;mechanical-properties;gas;gamma-y2si2o7;crystal;y2sio5;system;phase;si3n4-sio2-y2o3
A. Mitchell Advanced Materials Research Laboratory
,
University of British Columbia
,
Vancouver BC
,
Canada
金属学报(英文版)
In the pastfew years,severalnew melting processeshavebeenindustrialised forthe produc tion ofsuperalloys,titanium alloysand high qualitysteelsfor useintheaero engineindustry.Theseincludeelectron beam , plasma,inductionskull,andthe”triple melt”process( VIM + ESR+ VAR) . These developments have allbeen instituted in responsetothe major per ceived problem oftheindustry ;that oftheincidence of random defectsin the alloys whichcause problemsinregardto predictablelifing ofthefinished partinservice. Thedirectconse quenceofthe uncertaintyislossof revenue due to premature retirement of parts which mayhavecompleted on a fraction oftheir actualservicelife; a conservatism on the partof design parameters whichleadsto uneccesary weightin thepart;and ariskofeitherservicefailuresor partrecalls whichinterruptengine performance. Thebenefitsoftheprocesschangesinrespectoftheproducts’absolute propertiesand alsoonthereproducibility and inspectability ofthose properties have been substantial. Itisclearthattheprocesses offer the industry a solution to the present dilem ma of how to treatthe ”rare”defectsfrom the pointof view of fracture mechanicslifing methodology. The use ofprocesscontrols which guarantee”zero defect”productisdevelopingintoacriticaltoolfortheextension oftherangeof a given alloy’s use. Itislikelyto permit very substantial gainsinboth componentlife and intheallowablestressin rotating parts withoutthe needtointroduce new materials carrying new problems of user confidence, production reliability and data base. Weconcludethatthenew processesareatastageof development wherethey arereadyforwideindustry usein production. They will not add significantly tothecomponentcost andthey willgive a renwed lifespan to the more familiar materials and methodsof aero engineconstruction.
关键词:
Advanced Materials
Popularization of portable electronics and electric vehicles worldwide stimulates the development of energy storage devices, such as batteries and supercapacitors, toward higher power density and energy density, which significantly depends upon the advancement of new materials used in these devices. Moreover, energy storage materials play a key role in efficient, clean, and versatile use of energy, and are crucial for the exploitation of renewable energy. Therefore, energy storage materials cover a wide range of materials and have been receiving intensive attention from research and development to industrialization. In this Review, firstly a general introduction is given to several typical energy storage systems, including thermal, mechanical, electromagnetic, hydrogen, and electrochemical energy storage. Then the current status of high-performance hydrogen storage materials for on-board applications and electrochemical energy storage materials for lithium-ion batteries and supercapacitors is introduced in detail. The strategies for developing these advanced energy storage materials, including nanostructuring nano-/microcombination, hybridization, pore-structure control, configuration design, surface modification, and composition optimization, are discussed. Finally, the future trends and prospects in the development of advanced energy storage materials are highlighted.
关键词:
lithium-ion batteries;carbon nanotube electrodes;enhanced hydrogen;storage;metal-organic frameworks;double-layer capacitors;n-h system;carbide-derived carbons;ammonia borane dehydrogenation;ordered;mesoporous carbons;high-rate performance
Surface & Coatings Technology
The Ti(Y)N coatings were successfully deposited onto 18-8 stainless steel substrates by the hollow cathode discharge ion-plating method. The influence of the rare-earth element yttrium on the TiN coating properties was studied. The results show that the adhesion of the coating to the substrate were evidently enhanced by adding a small amount (0.2 wt.%) of the rare-earth element yttrium, showing a critical load of about 390 g which is much higher than that (230 g) of the TiN coating/substrate. Investigation on the corrosion resistance of the Ti(Y)N coating and the TiN coating was performed in 0.5 N Na(2)SO(4) + 0.1 N H(2)SO(4) + 0.1 N NaCl corrosion media by means of an electrochemical potentiodynamic polarization. The Ti(Y)N coating exhibited much better corrosion resistance than the TiN coating, whose passivity maintaining current is about one order in magnitude smaller than that of the TiN coating. The Ti(Y)N coatings deposited on some HSS-based tools were presented and compared with the TiN coating. The service lifetime of Ti(Y)N coated tools is approximately 36% higher (on the pinion shape cutters) and about 50% higher (on punch side pin) compared to that of TiN coated. The Ti(Y)N coatings showed such excellent performance. It is attributed to that the transition area of Ti(Y)N/substrate consisted of three sublayers which revealed a gradual change of phase structure and composition, so that the adhesion of the coating/substrate was evidently enhanced. Moreover, Ti(Y)N coating showed a preferred orientation with (111) plane which is favorable to improve wear resistance and corrosion resistance of the coating. (C) 2010 Elsevier B.V. All rights reserved.
关键词:
Ti(Y)N coating;Adhesion;Wear resistance;Corrosion resistance;Phase;structure;Preferred orientation;tin coatings;coated tools;thin-films;deposition;steel;wear;yttrium;alloy;pvd
黄新平
,
李漠
,
吕宝军
,
赵军
,
艾兴
,
高秀生
机械工程材料
doi:10.3969/j.issn.1000-3738.2004.08.006
Y2O3-Al2O3为复合烧结助剂,以(W,Ti)C为增韧补强材料,制备了Si3N4基复合陶瓷材料.研究了Y2O3和Al2O3的配比、体积分数对Si3N4/(W,Ti)C力学性能、致密化进程和烧结性能的影响.结果表明:两者配比为2:3、总体积分数为10%时,可以获得较高的致密度和较好的烧结性能,材料力学性能最好,抗弯强度845MPa,显微硬度16.45GPa,断裂韧度7.0MPa·m1/2.
关键词:
Si3N4
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复合陶瓷
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烧结助剂
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致密化
彭石高
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丁飞
,
中国有色金属学报
采用溶胶-喷雾干燥-氢还原法制备稀土Y含量分别为0,0.4%,5%,10%和20%的超细(W,Ni,Fe,Y)复合粉末,采用XRD研究煅烧温度和还原温度以及稀土Y含量变化时复合粉末体在制备过程中的相结构变化规律.结果表明:喷雾干燥前驱体随煅烧温度的升高渐渐从非晶体向复合氧化物晶化转变,添加稀土Y的粉末前驱体经煅烧后,Y与W形成复合氧化物Y2W3O12,且稀土Y可以有效地抑制粉末颗粒长大;随着Y含量的增加,Y和W的复合氧化物明显增加,Y2W3O12在700℃才能被还原成低氧复合氧化物相:含5%稀土Y粉末中的Y2W3O12被还原生成新相Y2WO6;当稀土Y增加到10%以上时,不仅生成Y2WO6,还生成另一种新相Y6W2OB15.
关键词:
W-Ni-Fe复合粉末
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纳米粉末
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稀土
,
Y
姜迪友
,
刘三秋
稀有金属材料与工程
采用基于密度泛函理论的第一性原理方法研究了钇的含量对W-Y二元合金力学性质的影响,精确计算了W1-xYx(x=0.0625,0.125,0.25,0.5)合金的力学常数,并对其力学特性进行分析.结果表明,W-Y合金的弹性常数、体模量、杨氏模量以及剪切模量随Y含量(原子分数)的增加而成非单调性减小,表明Y对W材料的合金化降低了材料的机械强度.然而,基于力学特性B/G、泊松比v和柯西压力C等分析,Y的合金化对W的延展性和韧性有明显的提高.当Y含量x为0.25时,可有效改善W-Y合金的延展性和抗变形能力.通过态密度分析,W-Y合金的金属性随Y含量的增加先减弱而后增强.
关键词:
第一壁材料
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W-Y合金
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力学性质
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第一性原理
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密度泛函理论
