A hard drive disk substrate is formed of a multi-phase ceramic-based material having at least two phases with amorphous phases being present in an amount less than 1 volume percent based on the volume of the ceramic-based material or at least one phase being free metal. A process for producing the ceramic-based disk substrate is produced by forming a flat disk of a porous ceramic and then infiltrating the porous ceramic with a metal whereby a multi-phase ceramic-based computer hard drive disk is produced. Additionally, a step of passivating the porous ceramic by elevating it to a temperature of 1300 °C to 1800 °C before the infiltrating step may be performed, such that the surfaces are passivated and the reaction kinetics can be controlled during the infiltrating step. A preferred composite material is made of a multi-phase boron-carbide composite material including grains having peaks with an average roughness value, Ra, of between 1 to 200 Å, the roughness value being formed in situ by causing a microhardness gradient of between 19 and 3200 Kg/mm2 in the various phases of the multi-phase boron-carbide composite material.