REDUCING METAL CONTENT IN PCD POLYCRYSTALLINE DIAMOND LAYER BY CHEMICAL AND ELECTROCHEMICAL ETCHING

Abstract

The paper is dedicated to the study of PDC (polycrystalline diamond compact) diamond composites, which are widely used in drilling, tool and construction industries. They constitute a complex composition of diamond and cermet phases. The diamond phase consists of diamond grains of various grain-size compositions and shapes, and forms a strong, solid scaffold. The cermet phase acts as a binder. The presence of catalyst metals in the diamond layer of PDC two-layer composites deteriorates their performance properties, since the difference in the coefficient of thermal expansion between diamond grains and the catalyst can lead to material cracking during cutting, and the high temperature during the manufacture of the diamond tool and its utilization in the cutting area can lead to the reverse diamond-graphite phase transition. The paper describes the process of metal etching from the surface of the tool working area by two etching methods: electrochemical and chemical, for the purpose of improving wear characteristics of PCD diamond composites obtained using catalytic metals (cobalt and tungsten). The electrochemical etching was carried out in sulfuric acid under various current regimes and concentration; chemical etching was carried out in a mixture of hydrochloric and nitric acids and in a mixture of hydrofluoric and nitric acids. Post-etching in depth distribution of chemical composition in PCD samples was studied using the scanning electron microscopy. It was established that electrochemical etching was kinetically more active, and chemical etching was promising for industrial applications. The abrasive tests of PCD samples carried out before and after the etching showed no significant effect of both electrochemical and chemical etchings on their abrasive property.