Erosion– and cavitation–corrosion of titanium and its alloys

The economic and effective operation of machinery and plant involved in fluids handling is increasingly dependent on the utilisation of materials that combine high corrosion resistance and good wear resistance. This paper studies two wear–corrosion situations: (1) erosion–corrosion, where the wear is 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 air 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 assessed using an impinging-jet apparatus. The tests were performed at an angle of impingement of 90°C at a particle velocity of 17 m/s and in a saline solution of 3.5% NaCl at 18°C. A series of experiments was conducted to determine the mass loss by combined erosion–corrosion before independently determining the electrochemical corrosion contribution to mass loss. It has been shown that exposure to liquid–solid erosion causes disruption of the passive film on Ti and active corrosion occurs. In contrast, the materials exhibited passive behaviour in static conditions and when exposed 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 this paper.