Study Of Forming Mechanism Of Molybdenum Based Compsite Reinforced By In-situ Al₂O₃Particles

Molybdenum is a refractory metal with characteristics of high strength, highhardness, corrosion resistance and good thermal conductivity. Molybdenum and itsalloys are widely used in metallurgy, agriculture, electrical, chemical and other fields.Due to the less of hard wear-resistant phase, the high temperature wear resistance andoxidation resistance of the molybdenum alloys used in the production are poor, and itcan not meet the requirements of high temperature wear condition. The Al₂O₃/Mocomposite prepared by adding Alumina ceramic hard particles to the molybdenumsubstrate has the advantages of both the two phase, and can be used as hightemperature resistant structural materials.The forming mechanism of material preparation and sintering process weremainly studied in this paper. The mixed molybdenum powder was prepared by sol-gelmethod, and the composite materials of pure molybdenum and Al₂O₃that volumefraction of5%,10%,15%were prepared by powder metallurgy technique. Themorphology, microstructure, phase structure and density of samples of each processwere analyzed using SEM, TEM, XRD, differential thermal analyzer, metallographicmicroscope and electronic balance testing instrument. The whole experiment processand the results are of positive significance to research on Optimization of millingprocess and Sintering Mechanism of composite materials under normal pressure. Theresults are as follows:The Standard Reaction Heat of the reaction of H2reduction of Al₂O₃/MoO3mixedpowder was calculated, and the result illustrated that they didn’t reaction. And whenAl₂O₃/Mo compacts sintered at2000℃under atmospheric pressure, the two phasedidn’t reaction.The ultrafine powder of molybdenum powder mixed with nano-Al₂O₃can beprepared by sol-gel method. The aluminum oxide particles are uniformly distributed in molybdenum particles with the average size about60nm, and the powder particle sizeof about500nm. During the process of hydrogen reduction, the addition of Al₂O₃madethe molybdenum particle shape rules and promoted the transformation of irregularblocks of sheet-shaped MoO3to spherical Mo powder.The density of Al₂O₃/Mo compact decreased first and then increased with theincrease of alumina content. The effect of Al₂O₃content to on density was obviouswhen sintered at low temperature; the densification rate of Al₂O₃/Mo composite ishigher when sintering at high temperature; the density of the composite is higher thanthat of the pure molybdenum when sintered; the influence of sintering temperature onthe material density is greater than holding time.The sintering mechanism of molybdenum at atmospheric pressure is bothvolume diffusion and grain boundary diffusion. With increase of alumina content, thematerial transport mechanism of Al₂O₃/Mo composite sintering at high temperatureis volume diffusion combined with grain boundary diffusion, and the graduallychanged to grain boundary diffusion.By atmospheric isothermal sintering range1700℃to2000℃, the activationenergy of sintering of pure molybdenum,5%VolAl₂O₃/Mo,10%VolAl₂O₃/Mo,15%VolAl₂O₃/Mo composite are obtained. The addition of alumina can reduce theactivation energy of composite sintering and increase the density of material, andplayed the role of activated sintering. With the increase of alumina, the compositegrain become refinement and uniform, and the number of pores in the sintered body isgreatly reduced.