超硬合金の陽極溶解過程について

Abstract

Electrochemical behaviour of cemented carbide electrode has been experimentally investigated. In this paper some result of experiments are presented with poarization curves of cemented carbide in aqueous solution of potassium and sodium nitrate and anodic process of the materials is discussed. The data were checked by means of potentiostatic method and chemical analysis. Surfaces of the electrode were examined by electron microscopy of replica. The main results obtained are summarized as follows : 1) Characteristic curves of the current-potential in aqueous solution of KNO3 and NaNO3 show the same features. There are four (WC-Co alloy) or five (WC-TiC-Co alloy) distinct stages in the curves according to the anodic reactions.2) In the first stage, it takes place of the dissolution of cobalt in the diralent state as prored by potassium nitrite reaction and deformation of carbide component is observed (the fourth stage) after gas evolution from the solution (the third stage).3) The second stage is a passive stage which indicated by a measurable drop in current. In this stage, current changes exponentially with respect to the time. This may suggest that cobalt oxides are formed on the electrode.4) In the ash grey precipitate of WC-TiC-Co alloy, Ti4+ is detected by hydrogen peroxide reaction. Curve with two maxima for the alloy are obtained and the second maximum (the fifth stage) depend on a rate of potential increasing. The electrode surface is covered with precipitation in the stage.