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

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.