X-ray microspectral analysis of ceramic binder and its contact zones with silicon-carbide grains

Abstract

In creating efficient abrasive tools, it’s important to improve the binder. Ceramic binders are the most common. When manufacturing abrasive tools from silicon carbide, a considerable quantity of ceramic binder is consumed. Nevertheless, the silicon-carbide grains break away from the binder more rapidly than, say, electrocorundum grains. The strength with which the grains are attached to the working surface of the tool largely depends on the intensity of grain‐binder interaction and also on the reaction products formed in the contact zone. Therefore, physicochemical study of the processes in the binder and in its contact region with the grain is of great scientific and practical value. The influence of the chemical processes on the state of the contact zone of the abrasive grain with the ceramic binder was considered in [1‐3]. The grains are bound together by thin binder bridges. Of course, the strength of attachment depends on the strength of the bridge, its dimensions, and the adhesive properties of the binder with respect to the grain surface. With increase in mechanical properties of the binder and increase in its quantity and adhesive properties, the retaining force on the grain increases. The interaction of the ceramic binder with silicon carbide has certain distinctive features and has not been as thoroughly studied as its interaction with other abrasive materials. Thus, the formation of decomposition products of silicon carbide at the grain surface leads, as a rule, to decrease in mechanical properties of the contact zone and in retention of the grain. This is explained in that, on oxidation, elementary silicon is converted to a SiO 2 film, which partially covers the grain and is partially dissolved in the binder. Carbon also burns, with the formation of CO and CO 2 bubbles in the binder and blistering of the tool. At the same time, stronger attachment of the silicon-carbide grains to the binder is possible on account of its reaction with the SiO 2 film. Well-founded prediction of the binder composition demands investigation of the interaction between the abrasive material and the binder and explanation of the mechanism by which the grains are attached in the tool. This primarily requires explanation of the influence of the binder components on the state of the contact zone, the homogeneity of the composition after heat treatment, and its properties. X-ray microspectral analysis is employed here. By scanning the surface with an electron probe, the distribution of the elements at the grain‐binder boundary may be obtained. Processes at the boundary are studied on models, since it is difficult, for various reasons, to obtain objective data on the binder bridges and other components of the tool. Such models take the form of silicon-carbide single crystals, with a mirror-plane area no smaller than 25 mm 2 . The single crystal is placed in a bath of corrosion-resistant steel, so that the mirror surface is vertical, and binder of the required composition is introduced under pressure. The sample is then subjected to heat treatment. In preparing the section, the boundary between the sample and the bath is not removed. Taking account of the contact-zone characteristics, optimal conditions of x-ray microspectral analysis are chosen from the section perpendicular to the interface: probe diameter 5‐38 µ m; time to measure the intensity of the characteristic radiation 10 s; voltage 25 kV. The analysis is conducted at intervals of 2 µ m. Since the compositions considered are not electrically conducting, a thin graphite layer is applied to the sample surface by spraying in vacuum.