Boric Acid as an Additive for Core-Drilling of Alumina

Abstract

Interactions between chemical compounds added to cutting fluids and the workpiece surface in the cutting zone can have pronounced effects on the material removal process during abrasive machining. These interactions can influence the coefficient of friction, the wear of the abrasive grit, and the mechanical properties of the workpiece, thus affecting the machining rate. Experiments were conducted on sapphire and a high-purity polycrystalline alumina to evaluate the chemomechanical effects 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 examined by scanning electron microscopy to elucidate the material removal process. The results indicated that addition of boric acid to distilled water increases the rate of drilling of polycrystalline alumina by a factor of two. But, boric acid was found to be ineffective in improving the drilling rate of single crystal alumina, i.e., sapphire. Based on the results it is postulated that boric acid interacts with the amorphous oxide grain boundary phase in the polycrystalline alumina promoting intergranular fracture; thereby, increasing the drilling rate.