Einfluss der chemischen Zusammensetzung und des pH-Wertes auf das Korrosionsverhalten von WC-Co Hartmetallen

By potentiodynamic electrochemistry and immerson tests, the corrosion behaviour of (WC-Co) based cemented carbides has been investigated. The nickel contend of the binder (0 - 2%), the amount of the chromium carbide (0 - 1%) and the magnetic saturation (by adjustment of a carbon deficit, low high) have been varied. Also the pH-value of the chemical solution have been varied (pH 0, 3, 4.5, 6, 10 and 14). By TEM investigations the chemical composition of the binder has been determined. A very important parameter is the magnetic saturation. A high amount of dissolved tungsten depends on a low magnetic saturation. Tungsten protects the binder against corrosion in acids. At a higher pH-value the element tungsten has a bad influence on the corrosion behaviour. Nickel improves corrosion resistance at very low and very high pH-values. In neutrale solutions nickel yields to an increased corrosion rate due nickelous ions. Chromium improves has a very good influence on the behaviour from the pH-value 4 and higher.