Benefits of passive element Ti to the resistance of AlCrFeCoNi high-entropy alloy to corrosion and corrosive wear

Wear behaviors of 5-element AlCrFeCoNi and 6-element AlCrFeCoNiTi0.5 high entropy alloys (HEAs) against the Si3N4 ball respectively in 3.5 wt% NaCl and HCl (pH = 3) solutions were investigated. The role of the Ti addition in affecting microstructure, hardness, wear and corrosion of the HEA was analyzed. Results showed that the AlCrFeCoNiTi0.5 exhibited higher hardness, ascribed to the solid solution strengthening and precipitation strengthening. The wear loss of AlCrFeCoNiTi0.5 is markedly lower than that of AlCrFeCoNi under the dry condition against Si3N4 balls of 4 mm and 6 mm in diameter, respectively. The Ti addition also improved the corrosion resistance, especially the pitting corrosion resistance, of the HEA, evidenced by lowered Icorr and Ipit and elevated Rp and Rct. This was attributed to the contribution of Ti in the formation of a more protective passive film, which impeded the point defect transport and passive film breakdown. The surface potential measured by means of atomic force microscopy (AFM) shows a smaller difference between adjacent domains in AlCrFeCoNiTi0.5, which should only result in weak local galvanic coupling. Thus, the Ti addition helps suppress the pitting attack to the HEA. The solutions and size of counterpart ball have large influences on the performance of AlCrFeCoNiTi0.5 during corrosive wear. Efforts are made to clarify the mechanism for the beneficial role of Ti addition in affecting the performance of the HEA during the destructive processes.