Coating of soft metal particles with ceramic fines using a dry mechanical method

This paper describes a dry coating process in which fine ceramic guest particles are mechanically compounded with soft metal host particles by embedding the guest particles on the surface of host particles using a high-speed elliptical-rotor-type powder mixer (HEM). The optimum rotor speed and processing time were determined on the basis of allowable deformation of host particles in a single compression by the rotor and the mechanical energy required for embedding all the guest particles, respectively. From measurements of the size distribution and morphology of composite particles, we confirmed that the composite particles were prepared according to powder design regardless of the physical properties of the guest particles. In order to investigate the hardness of composite particles, composite particles were deformed using HEM and the deformation was measured with an image analyzer. The coefficient representing hardness was determined from the deformation and magnitude of mechanical energy applied to the composite particles. It was proportional to the total volume of guest particles and inversely proportional to the distance between guest particles on the surface of host particles. The hardness of metal particles in which fine particles were embedded could be evaluated similar to that of particle-dispersion-strengthened materials.