FUNDAMENTALS OF DRY POWDER BLENDING FOR METAL-MATRIX COMPOSITES

In the manufacture of metal-matrix composites via the powder metallurg y route, blending of matrix and reinforcement materials is a critical operation which has received little attention. Past investigations hav e focussed on studies of mixing in large-scale and uniform sized syste ms (particles with diameters in the millimeter size range) and inferre d segregation behavior of powders. Several workers, however, have inve stigated the segregation tendency of particles. with different charact eristics. It has been found that particle size ratio is the most impor tant material variable. Scale-up parameters for segregation include si ze ratio, and Froude number (the ratio of inertial to gravitational fo rces). Another important conclusion is that in order to obtain a homog eneous mixture, the powder mass must be assessed for both macro- and m icro-blended states. Some preliminary experimental results have also s hown that the type and pressure of gas in the blender can have a signi ficant effect on the blending characteristics of a powder mixture. Thi s article constitutes a critical review of the relevant literature per taining to dry powder blending, in the particular context of the forma tion of metal matrix composites.