The bonding of diamond grits and matrix metals as powder metallurgical phenomena

摘要

In order to provide a strong bonding between diamonds and matrix, a typical matrix alloy containscopper and cobalt as base metals, and tin, chromium and titanium as additives. Copper has a highthermal conductivity to dissipate heat during grinding together with a low degree of lattice disregistryto diamond to provide bonding strength. Cobalt has rather high values of both modulus of elasticityand elastic limit, and a low coefficient of thermal expansion to be compatible to some extent with thehigh elastic properties and the low thermal expansion of diamonds during grinding. Those propertiesmake the matrix hold diamond grit tightly. Tin reacts with diamonds to form rough surfaces leading toan increased mechanical bonding strength, while chromium and titanium react with diamonds tomake carbide layers on the grits leading to a good bonding strength provided by a good wetting. In thepresence of a liquid copper alloy, iron or cobalt forms a solid solution layer containing copper as amain solute on graphite surface. The formation of the layer is driven by a difference of chemicalpotential in the system. A similar layer formation is possible on diamond surface. The layer willprovide tight holding of grits by matrix.