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Preparation And Characteirstic Of Neo-MoSi2-AlCr2Quasibinary System Compound Alloys

Posted on:2013-05-30Degree:MasterType:Thesis
Country:ChinaCandidate:J H RenFull Text:PDF
GTID:2231330374456004Subject:Materials science
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Refractory metal silicides MoSi2is attractive because of its high melting point(2030℃), relatively low density (6.24g/cm3), superior oxidation resistance and highthermal conductivity, as a good electric heating element material has realized industrialproduction and application. Nevertheless, MoSi2still has several problems which mustbe overcome before structural application:low ductility below1000℃, spalling ofprotective SiO2scales under thermal cycling, and not enough strength and poor creepresistance above1300℃. Generally speaking, alloying and compounding are commonmethods to reinforce and improve the mechanical properties of MoSi2. Preparedneo-MoSi2-AlCr2quasibinary system alloys with better property by add Al and Crelement which have excellent oxidation resistance alloying MoSi2. Meanwhile, theAlCr2has lower density, better oxidation resistance and the same crystal structure withMoSi2. So, MoSi2-AlCr2quasibinary system alloys expected have better interfacialmatching and oxidation resistance.MoSi2-xAlCr2quasibinary system alloys were prepared by hot pressed sintering inthis paper. The microstructure, mechanical property and low temperature oxidationresistance property of MoSi2were investigated by add different AlCr2. The followingconclusions have been drawn from this investigation:1. The main phase composition of MoSi2-base MoSi2-AlCr2quasibinary systemalloys were MoSi2and Mo(Si,Al)2. With the increase of AlCr2, the crystal structurewas gradually transformed from tetragonal C11bMoSi2to hexagonal C40Mo(Si,Al)2.Because of not find Cr simple substance in this experiment, so C40-Mo(Si,Al)2shouldbe C40-(Mo,Cr)(Si,Al)2in this paper on account of alloying element interchangetheory.2. With the increase of AlCr2, the experiment alloys not only average crystallinegrain smaller and the microstructure were uniform and dense, there was not obviousporosity and defects.3. With the increase of AlCr2, the microhardness and compactness of MoSi2-baseMoSi2-AlCr2quasibinary system alloys brought down first and increased later. Thecombination property of30at%AlCr2/MoSi2quasibinary alloy was best, itsmicrohardness and compactness were1100HV and97%.4. After oxidation100h at500℃, the pure MoSi2which were prepared by hotpressed sintering have better low temperature oxidation resistance, did not found the "Pesting" phenomenon. Add alloying element which have strong affinity with oxygen(e.g. Al and Cr) can enhance the low temperature oxidation resistance of MoSi2, thefine oxidation resistance of MoSi2-AlCr2quasibinary system alloys mainly attributedto reaction formation preservative of Al2O3and Cr2O3to prevent the oxidation offurther.5. The oxidation kinetics curve of the pure MoSi2is followed parabolic law whilethe MoSi2-AlCr2quasibinary system alloys are followed the straight–line law at thestage (20100h). After oxidation100h, the mass gain of pure MoSi2andMoSi2-AlCr2quasibinary system alloy of add10at%AlCr2were4.2898mg/cm2and1.1028mg/cm2, the average oxidation rate were4.29×10-2mg/(cm2·h) and1.10×10-2mg/(cm2·h). There was not obvious change in the low temperature oxidation resistanceof MoSi2-AlCr2quasibinary system alloys when add more AlCr2.
Keywords/Search Tags:MoSi2, AlCr2, Alloying, Phase structure, Microstructure, Lowtemperature oxidation
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