BORIC-ACID AS AN ADDITIVE FOR CORE-DRILLING OF ALUMINA

Interactions between chemical compounds added to cutting fluids and th e workpiece surface in the cutting zone can have pronounced effects on the material removal process during abrasive machining. These interac tions can influence the coefficient of friction, the wear of the abras ive grit, and the mechanical properties of the workpiece, thus affecti ng the machining rate. Experiments were conducted on sapphire and a hi gh-purity polycrystalline alumina to evaluate the chemomechanical effe cts of boric acid mixed with distilled water. The machining tests were performed on a precision drill with metal-bonded diamond core-drills. Following the experiments, the drilled surfaces and the debris were e xamined by scanning electron microscopy to elucidate the material remo val process. The results indicated that addition of boric acid to dist illed water increases the rate of drilling of polycrystalline alumina by a factor of two. But, boric acid was found to be ineffective in imp roving the drilling rate of single crystal alumina, i.e., sapphire. Ba sed on the results it is postulated that boric acid interacts with the amorphous oxide grain boundary phase in the polycrystalline alumina p romoting intergranular fracture; thereby, increasing the drilling rate .