Abstract: High active and ultrafine B₄C-SiC composite powders were prepared by the coarse powders of B₄C and SiC through the technology of mechanical alloying. Under testing techniques of X-ray diffraction, scanning electron microscope, laser particle size analysis and infrared absorption spectrum, by which studied the influences of ball to powder weight ratio, process control agents and milling time on composite powders, the best technological conditions of MA for preparing B₄C-SiC ultrafine composite powders could be confirmed. After studying order-disorder transformation of the composite powders during the process of MA, hot pressing sintering was adopted to verify the sintering activity of the composite powders. The results indicate that the lattice unordered B₄C-50wt% SiC ultrafine composite powders can be obtained when the ball to powder weight ratio is 30:1, process control agents 2wt%, milling time 120 h and the rotation speed 250 r/min. While the composite powders are sintered at 1900℃ with pressure of 30 MPa, the density of samples is 2.62 g/cm³ and the relative density of samples attains 93%. The relative density of samples sintered with the composite powders is 8.1% higher than that of samples sintered with ordinary mixing powders. B₄C-SiC ultrafine composite powders prepared by mechanical alloying possess extremely high sintering activity.

Key words: mechanical alloying, lattice disorder, B₄C-SiC, ultrafine composite powders, hot pressing