Preliminary evaluation of cavitation–erosion resistance of Ti-alloys in mercury for the Spallation Neutron Source

A number of Ti-based alloys in both the mill-annealed and 20% cold-worked conditions were subjected to sonication conditions in Hg using a vibratory horn to assess relative cavitation–erosion resistance. Weight loss as a function of exposure time decreased monotonically with increasing hardness for all alloys/conditions examined, with Ti–6Al–4V (Grade 5) and Ti–6Al–2Sn–4Zr–2Mo yielding the best resistance to cavitation–erosion as evidenced by low weight losses and little or no tendency to form pits on the exposed surface. Unalloyed Ti (Grade 4) and Ti–0.12Pd (Grade 7) exhibited greater weight losses by a factor of about two and about five, respectively, with Ti–0.12Pd particularly prone to pitting development. The mean erosion rates of the best two Ti-alloys examined were about a factor of three higher than identically tested 316LN stainless steel following a low temperature carburizing treatment, but this difference is considered minor given that the rate for both materials is very low/manageable and represents a through-thickness property for the Ti-alloys. A nitriding surface treatment was also evaluated as a potential method to further increase the cavitation–erosion resistance of these alloys in Hg, but the selected treatment proved largely ineffective as measured by rapid weight loss. Recommendations for further work to evaluate the efficacy of Ti-based alloys for use in high-powered targets for the Spallation Neutron Source are given.