Erosion- and cavitation-corrosion of titanium and its alloys

The economic and effective operation of machinery and plant involved in flu ids handling is increasingly dependent on the utilisation of materials that combine high corrosion resistance and good wear resistance. This paper stu dies two wear-corrosion situations: (1) erosion-corrosion, where the wear i s due to impacting solids in a liquid medium and (2) cavitation-corrosion, where the wear is due to impacting liquid micro-jets formed by imploding ai r bubbles. The characteristics of a commercially pure titanium (CP-Ti) and three alloys in erosion-corrosion and cavitation-corrosion conditions have been studied. The erosion-corrosion characteristics of each material was as sessed using an impinging-jet apparatus. The tests were performed at an ang le of impingement of 90 degreesC at a particle velocity of 17 m/s and in a saline solution of 3.5% NaCl at 18 degreesC. A series of experiments was co nducted to determine the mass loss by combined erosion-corrosion before ind ependently determining the electrochemical corrosion contribution to mass l oss. It has been shown that exposure to liquid-solid erosion causes disrupt ion of the passive film on Ti and active corrosion occurs. In contrast, the materials exhibited passive behaviour in static conditions and when expose d to a cavitating liquid only CP-Ti became active. The role of corrosion in these wear-corrosion environments on CP-Ti and Ti-alloys is discussed in t his paper. (C) 2001 Elsevier Science B.V. All rights reserved.