Tribocorrosion properties of heat-treated FeCrCoMnSix high-entropy alloy coatings

Abstract

Although non-metallic element Si has attracted much attention in the design of high entropy alloys (HEAs) and heat treatment has been proven to improve coating defects, there is still a lack of systematic research on the friction corrosion behavior of FeCrCoMnSi_x HEAs, especially coatings with different Si contents in annealed state, and their correlation with phase composition and structural defects, after annealing treatment. Therefore, the FeCrCoMnSi_x high-entropy alloy, HEA coating was fabricated on the surface of 45 steel substrates via laser cladding technology. Subsequently, the microstructure and tribocorrosion properties of the FeCrCoMnSi_x HEA alloy coatings were investigated after a heat treatment at 600 °C for 1 h. The results indicate that after the recrystallization process, the FeCrCoMnSi_x HEA coatings still predominantly consist of FCC and BCC dual-phase solid-solution phases. However, the microstructure is refined, and there are fewer defects. When a small amount of Si is incorporated into the coating, the microstructure transforms into a dense eutectic structure. In particular, the Si_0.6 coating exhibits a refined equiaxed crystal structure. After the annealing treatment, the precipitated metal silicides significantly enhance the overall hardness of the coating. The hardness of the Si_0.6 coating reaches up to 551.3 HV. Electrochemical analysis shows that after the annealing treatment, the corrosion resistance of the coatings in a 3.5 % NaCl solution is improved. The fine recrystallized structure with fewer defects and higher density delays the development of pitting corrosion. The self-corrosion current density of the Si_0.6 coating decreased from 1.1484 × 10^‐−6 A⋅cm² before annealing to 9.5076 × 10^‐−7 A⋅cm², a decrease of 17 %. The self-corrosion potential also increased from ‐−0.329 V to ‐−0.301 V. The Si_0.6 coating exhibits the best corrosion resistance, with a corrosion protection efficiency reaching 94.17 %. Moreover, the tribocorrosion analysis of the coating in a 3.5 % NaCl solution reveals that interface reactions occur under the combined action of friction and corrosion, leading to the formation of Cr and Si oxides, which reduces the coefficient of friction, COF. On the other hand, these oxides effectively improve the coating's resistance to oxidative wear and Cl^‐− erosion. Among them, the COF and wear loss of the Si_0.6 coating decrease to 0.1524 and 2.2268 × 10^‐−5 mm³/Nm respectively, compared with the unannealed Si_0.6 coating (0.202 and 4.0598 × 10^‐−5 mm³/N⋅·m), the COF decrease by 25 % and the wear loss decrease by 45 %, showing better resistance to friction and corrosion. And demonstrating excellent tribocorrosion resistance. The above studies confirm that annealing can enhance the microstructure and tribocorrosion performance of laser-cladded coatings by eliminating the defects and element segregation caused by rapid solidification.