Etching for microstructural observation of cemented submicrometer-sized carbides

When carbide grains in a metal matrix are very small (less than -1 mum), th e microstructure is difficult to observe and characterize, because the grai n interfaces cannot be distinguished easily via scanning electron microscop y (SEM) when the material is etched conventionally in a Murakami solution o r in H2O-diluted HCl. This difficulty can be overcome by etching in a newly developed etchant: 90H(2)O(2)-10HNO(3) (by vol%), After an etching of a WC -Co sample that contained submicrometer-sized grains, the individual grains were distinctly observable via SEM, During the etching, the dissolution ra tes of WC grains were different, depending on their crystallographic plane, which allowed the grain boundaries to be distinguished through observation via SEM, In addition, dissolution of the cobalt matrix occurred much faste r than did the etching of the WC grains. The WC/Co interface also was revea led clearly under high magnification, because of minimization of the electr omagnetic interaction between the cobalt and the electron beam of the SEM a pparatus.