Impact of Yttrium on corrosion properties of titanium as a grain refiner

Abstract

The corrosion properties of grain-refined titanium (Ti) after adding yttrium (Y) were characterized to determine how the added Y and the resulting refined grains affected the corrosion resistance of commercially pure Ti (CP-Ti). Microstructural changes, such as grain refinement and Y precipitation, altered corrosion potential, open circuit potential (OCP), and corrosion resistance. Based on the mixed potential theory, adding Y to Ti caused anodic movement of the corrosion potential and OCP and the resultant Y precipitates over 1 μm placed under corrosion. Although Y precipitates larger than 1 μm appeared to be detrimental to the Ti–Y alloys’ corrosion resistance, Y segregation at the grain boundaries and the small Y precipitates in the grains increased the oxide layer’s thickness because of the micro-galvanic effect. Therefore, the grain refinement caused by Y segregation could compensate for the deteriorated corrosion performance coming from the presence of the large Y precipitates when the Y content is limited to 0.1 wt%. Therefore, by controlling the Y content as a grain refiner, not only the desired mechanical properties but the comparative corrosion resistance to CP-Ti could be achieved for plate heat exchangers.