Matrix microstructure deteriorations resulting from diamond incorporation in electroplated metal–diamond composites

Abstract

Because of their desirable hardness and wear resistance, diamond composite coatings have been widely studied. This article first reports our observation results about the impact of diamond incorporation on the matrix microstructure, and then gives explanations. It is shown that the incorporation significantly worsens the microstructure, like coarsening matrix grain, inducing gaps between matrix and diamond, and promoting emergence of nodules, valleys and over-plating cases on matrix surface. These deterioration phenomena are aggravated by an increase in ‘troublesome’ diamond grain number, current density, or deposit thickness. All the facts are found to result from Lorentz forces generated by the interaction of electric current (moving cations) and magnetic fields produced by magnetic diamond grains that contain metallic inclusions. The interaction not only forces a magnetic diamond grain to stand on one of its corners, also forces a nearby cation that moves from anode to cathode (i.e., from the diamond top to the bottom) to rotate counterclockwise around the grain with an increasing radius (due to a repelling Lorentz force) before it passes the diamond middle, and then to rotate clockwise with a decreasing radius (due to an attracting Lorentz force) after passing the middle.