The Research Of Adjusting The Density Of The Carbides Powders By Mechanical Alloying Method

There are problems in the conventional methods of preparing NbC powders, such ashigh reaction temperature, high energy consumption, etc. Therefore, we proposed amethod of Mechanical alloying(MA)+vacuum annealing(VA). Used the powders ofniobium metal and graphite as raw material, at the conditions of the ball to powder ratio of20:1, PCA was graphite, milling speed was300rpm, milled8h and vacuum heated at400℃for30min, got the NbC powder completely. In the AFM microphotograph of theNbC, the particle size was about50nm. Compared with the method only using the themechanical alloying to synthetic NbC, the milling time was significantly shortened.On the basis, we done some experiments and studied a method of preparing theNbC/Fe or the NbC/Cu composite powder. The graphite powder and the niobium powderwere mixed with the atomic ratio1:1and milled for6h, then added Fe(Cu) powder whosemass was equal to total of the Nb and graphite powders and milled for another4h, aftermilled the powder was vacuum annealed at600℃for30min, then we got the NbC/Feor NbC/Cu composite powder. In the SEM microphotograph, it could be seen that thereinforcing phase NbC is generated in a situ reaction, its particles are nanoscale anduniformly distributed in the Fe or Cu matrix.The possibility of reduce the density of NbC powders was tested and studied byadding the Al element, whose atomic weight is smaller than the Nb element, to replace theNb atom in the NbC crystal lattice through the two methods of MA and MA+VA. Theresults show that when the Nb powder and graphite were mixed with the atomic ratio of1:1, and the quality of Al powder was5%of the mixture powder’s total mass, after milledfor6h, then the mixed powders was vacuum annealed at500℃for30min, the densityof the generated NbC powder’s was7.690g/cm3, which is about2%lower than theoriginal density.The analyses of the experiments’ results show that: to prepare NbC or adjust thedensity of NbC powder only by the MA method, the mechanism complied with thediffusion-solid solution theory. For the MA+VA method, it complied with the MA-SHSmechanism; vacuum annealing realized the control of Self-propagating reaction.