Wear and Corrosion Properties of AlCoCrFeNi High Entropy Alloy Coatings Prepared by Plasma Activated Sintering Process

The high entropy alloys (HEAs) have excellent mechanical and chemical properties, such as high hardness and strength, wear resistance and good resistance to oxidation and corrosion. However, the higher cost of HEAs limits their large-scale industrial application. As an alternative to fabricate bulk HEAs, preparing HEAs coatings on inexpensive substrate has drawn extensive attention. The austenitic stainless steel is widely used for mechanical parts though it has poor wear resistance. Therefore, it is of interests to improve the wear and corrosion resistance of 304 stainless steel simultaneously by high entropy alloy coatings. The work aims to improve the wear resistance of 304 stainless steel substrate on the basis of further improving the corrosion resistance of 304 stainless steel according to the excellent wear resistance and corrosion resistance of high entropy alloy coating. The AlCoCrFeNi high entropy alloy coatings were rapidly prepared by the plasma activated sintering (PAS) technology with the initial powders fabricated via vacuum atomization. The microstructure of the coatings and the interfaces was observed by scanning electron microscope (SEM), and the phases were analyzed by X-ray diffractometer (XRD). The elemental distribution was identified by energy dispersive spectroscopy (EDS). The hardness wear resistance and electrochemical corrosion resistance of the coatings were tested. The bonding between the coating and substrate was perfectly metallurgical at holding temperature of 1 000 ℃, pressure of 70 MPa and holding time of 10 min, and no residual defects such as holes and cracks were found at the interface. The Al and Co elements diffused significantly across the interface, benefiting from the effect of the electric current and pressure used in the PAS process. In the range of 900͂1 000 ℃, the pores of the coating gradually decreased with the increase of the sintering temperature. The coating mainly consisted of the reticulated FCC phase where the BCC phase and B2 phase formed alternately. The average friction coefficient of the coating sintered at 1 000 ℃ (0.138) was significantly lower than that of the substrate (0.456) under the same testing loading (20 N). No obvious sticking and peeling phenomenon but slight furrows could be observed on the polished surface of the coating, which was remarkably different from the substrate. Abrasion wear was the main wear mechanism of the coating. Compared to the 304 stainless steel, the microhardness of the coating sintered at 1 000 ℃ increased obviously (562HV under 200 g with the holding time of 15 s), which was responsible to the excellent wear resistance of the coating. Both the coating and substrate underwent pitting corrosion in 3.5wt.% NaCl solution and simulated seawater, respectively. Compared with the substrate, the self-corrosion potential Ecorr of the coating sintered at 1 000 ℃ increased by approximately 0.3 V and the self-corrosion current density Icorr was reduced by two orders of magnitude in 3.5wt.% NaCl solution. Furthermore, the charge transfer resistance Rct of the coating sintered at 1 000 ℃ (564.9 kΩ·cm-2) was considerably higher than that of the 304 stainless steel (17.1 kΩ·cm-2), revealing lower kinetic of the corrosion reaction. The PAS technology enables densification and high-quality interface bonding simultaneously. As a result, the AlCoCrFeNi high-entropy alloy coating effectively improves the wear resistance and corrosion resistance of the 304 stainless steel substrate. It indicates that using high-entropy alloy to enhance the comprehensive performances of the stainless steel is a feasible way. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.