Effect of titanium addition on the corrosion behavior of CoCuFeNiMn high entropy alloy

In this study, the effect of Ti addition on microstructure and corrosion properties of high entropy CoCuFeNiMnTix (x = 0.0–0.5) produced by the vacuum arc melting method was investigated. According to X-ray diffraction analysis, it has been found that Ti-free CoCuFeNiMn and CoCuFeNiMnTix HEAs had FCC crystal structures. It was understood from the SEM images that the CoCuFeNiMn and CoCuFeNiMnTix alloys were dendritically solidified. While the CoCuFeNiMn alloy had a homogeneous chemical composition in dendritic and interdendritic regions, Ti-rich regions were formed in the interdendritic regions with the Ti addition to the CoCuFeNiMn. The ratio of the Ti-rich region formed in the interdendritic region increased with the increase of Ti in the CoCuFeNiMnTix alloy. The corrosion resistance of the CoCuFeNiMnTix alloy decreased with the increase of Ti addition. The Ecorr and icorr values for CoCuFeNiMn alloy were found to be as −0.322 V (vs. Ag/AgCl) and 6.30 × 10−7 A.cm−2, and these values were measured as −0.982 V and 1.16 × 10−3 A.cm−2 for CoCuFeNiMnTi0.5 alloy, respectively. From the Nyquist and phase angle plots, it was understood that the 0.3% Ti ratio was the critical value for the formation of the passive TiO2 layer on the alloy surface. Ti addition's most important effect on the CoCuFeNiMn alloy's corrosion properties was determined as the transformation of pitting corrosion type to galvanic corrosion.