Reducing the Metal Content in PCD Polycrystalline Diamond Layer by Chemical and Electrochemical Etching

Abstract

This article is devoted to investigating polycrystalline diamond compacts (PDCs), which find broad application in drilling, tool-and-die, and building branches of industry. They are a complex composition of diamond and cermet phases. The diamond phase consists of diamond grains of various granulometric compositions and shapes and forms a strong hard skeleton. A cermet phase serves as a binder. The presence of catalyst metals in a diamond layer of bilayer PDC composite materials lowers their operational properties, because the difference in thermal expansion coefficients between diamond grains and catalyst can lead to material cracking in the cutting process, while a high temperature when fabricating the diamond tool and its operation in the cutting zone can lead to the reverse diamond–graphite phase transition. In order to increase wear-resistance characteristics of diamond PCD composites formed using catalyst metals (cobalt and tungsten), etching of metals from the surface of the tool working zone is performed by two methods, notably, electrochemical and chemical. Electrochemical etching is performed in sulfuric acid with various current modes and concentration, and chemical etching is performed in a mixture of hydrochloric and nitric acids and a mixture of fluoric and nitric acids. The distribution of the chemical composition over the depth of PCD samples after etching is performed using scanning electron microscopy. It is established that electrochemical etching is more active kinetically, while chemical etching is promising for industrial application. Abrasive tests of PCD samples before and after etching show the absence of a noticeable effect of both electrochemical and chemical etching of their abrasive ability.