Effects of Mn addition on wear and corrosion resistances of AlCoCrFeNi high-entropy alloy coating sprayed by HVOF

In this study, AlCoCrFeNi and AlCoCrFeNiMn0.5 high entropy alloy coatings, denoted as the Mn0 and Mno.5 coatings, respectively, were prepared on 304 stainless steel substrate via High velocity oxygen fuel (HVOF) and their wear and corrosion resistances were investigated. The results reveal that both the coatings consist of BCC and B2 phases, indicating that the Mn addition does not cause a phase transition for the present coatings. The coatings exhibit a low porosity of less than 1%, strong interlayer adhesion and no compositional segregation. The addition of Mn significantly increases the microhardness from 520 HV 0.2 for the Mn0 coating to 617 HV 0.2 for the Mn0.5 coating. The dry sliding wear test demonstrates that the Mn0.5 coating demonstrates superior wear resistance with a significantly lower average friction coefficient of 0.433 and wear rate of 9.7×10 -5 mm 3 ·N -1 ·m -1 compared to both the Mn0 coating and 304 stainless steel. The main wear mechanisms of the coatings were identified as abrasive, fatigue and adhesive wears. Meanwhile, compared to the Mn0 coating and 304 stainless steel, the Mn0.5 coating exhibits higher corrosion resistance in 3.5 wt.% NaCl solution, with a lower self-corrosion current density ( I corr ) of 5.992×10 -7 A·cm -2 and enhanced pitting resistance, evidenced by a larger pitting potential ( E pit ) and a lower passivation current density ( I pass ) of 1.523×10 -6 A·cm -2 . XPS analysis shows that the Mn addition leads to an increased presence of Cr 2 O 3 in the passivation film on the surface of the coatings, which was more resistant to Cl - corrosion and facilitates a dense and stable passivation film compared to other oxides like Al 2 O 3 , thereby improving the corrosion resistance of the coatings. The present study highlights the beneficial impact of Mn addition on the wear and corrosion performance of AlCoCrFeNi high-entropy alloy coatings.