Research On Mechanical Alloying And Properties Of Al₂O₃Reinforced Mo-base Composites

Because of the good abrasion resistance at high temperature, the molybdenumcomposite materials reinforced by Al₂O₃particles （Al₂O₃/Mo composites） have a wideapplication prospect for molybdenum mandrels, extrusion and casting dies, heatingvessel and pad materials, and so on. But in the preparation process of the Al₂O₃/Mocomposites, the particles of Al₂O₃are so large and not distributed evenly thatsatisfactory reinforce effects can not be achieved.The preparation process has been optimized based on in-situ Al₂O₃mixingmethod in the current work. The sizes of Al₂O₃particles and molybdenum grains werecontrolled by combining the sol-gel method and mechanical alloying method.Moreover, the agglomeration problem of Al₂O₃particles is solved, resulting in theadherence between the Al₂O₃grains and molybdenum matrix improved. And thehomogeneity of Al₂O₃particles distributed in the molybdenum matrix is alsoameliorated. The microstructure of composite powders and composite materials wereobserved by SEM and TEM, the grain size of powder and the density and hardness ofcomposite materials were investigated.The results show that:1．During ball milling process under air environment, thecomposite powders can’t be oxidized, and there are only Mo and Al₂O₃phases. Whenother parameters are constant, the best dispersibility and the breaking degree ofcomposite grains were obtained under the ball/powder weight ratio of5:1and at therotate speed of300r/min.2．When process control agent（PCA）was not present, the size of powder grainswas especially uneven. The addition of process control agent could reduce effectivelythe ball adhering and agglomeration phenomenon of powders and improve the flouryields. A larger portion of small particles and higher flour yields were got when stearicacid was used as PCA. Being used as PCA, the anhydrous alcohol had a better effecton improving the refining rate of powders. 3．With the ball milling time increasing, the shape of the particles of Al₂O₃/Mocomposite powders was firstly spherical, and then becomes layer flake and tiny ballshape at last. The molybdenum grains are continually refined and the distortion oflattice increased. The grain sizes of Al₂O₃and Mo of the composite materials preparedby sintering are decreased. The density of composite materials increases at first andthen decreases, but the hardness is more and more large.4．Some Al₂O₃particles massed and grow up in the composite material preparedby ball milling the Al₂O₃/MoO₃powder which is prepared by sol-gel method. Ballmilling the Al₂O₃/Mo powder for60hours, which are prepared by sol-gel method, theparticles of Al₂O₃and grains of Mo in composite material are the most small, the mostevenly dispersed and have a high homogeneity, the particle size of Al₂O₃is500nmaround. Ball milling molybdenum and alumina mixture powder for60hours, the sizeof alumina particle in the composite material is less than2μm.