The Wear And Corrosion Resistance Of High Entropy Alloy Coating Rapidly Fabricated By Electric Field Sintering

Austenitic stainless steels are broadly used in many industries,such as the chemical,petrochemical and food processing industries which is due to their excellent corrosion resistance,high strength,formability,ductility and toughness.However,in the actual use of the process,the parts often appear performance failure because of the poor wear resistance,which greatly limits its application.Due to its unique design concept,high entropy alloy has excellent comprehensive mechanical properties,special physical and chemical properties,and has a very broad application prospect in terms of structure and function.It is a new alloy material that has attracted wide attention at present.Compared with bulk materials,high entropy alloy coatings exhibit excellent wear and corrosion resistance while significantly reducing the amount and cost of the original alloy,which has become a research hotspot in this field.Compared with the other common coating preparation methods such as the mechanical alloying,laser cladding,thermal spraying and hot pressing.In this study,high entropy alloy coatings with high density were rapidly prepared successfully,on the 304 austenitic stainless steel substrate,but at a relatively low temperature.Using atomized high entropy alloy powder as raw material by field assisted sintering technology（FAST）.The effects of process parameters on the microstructure,mechanical properties and electrochemical properties of high entropy alloy coating were studied.The feasibility of improving the service performance of 304 stainless steel by high entropy alloy coating was discussed,which provided method and ideas reference for expanding the industrial application of high entropy alloys.The results show that:（1）Under the pressure of 70 MPa,holding time of 10 min and holding temperature of 900℃～1000 ℃,the high entropy alloy coating prepared by the electric field assisted rapid sintering technology formed a good metallurgical bond between the substrate and the coatings,and no interface defects such as holes and cracks were found.The internal structure of the coating is compact and fine with uniform element distribution.The apparent diffusion of Co and Al elements across the interface is an important reason for the rapid interface bonding.（2）The phase structure of the AlCoCrFeNi high entropy alloy coatings,mainly can be divided into three different and special phases:FCC phase,BCC phase and B2 phase.The FCC phase is distributed in a grid shape in the coating,and the initial BCC phase and the B2 phase which is formed from part of the BCC’s amplitude modulated decomposition are distributed in the region surrounded by the FCC phase in in labyrinth shape.The results of energy spectrum analysis indicate that Al and Ni elements are enriched in FCC phase and Fe and Cr elements are enriched in BCC phase.With the increasing of sintering temperature,the volume fraction of FCC phase in coatings first increases and then decreases,and the corresponding hardness value also increases and then decreases.（3）The wear resistance of high entropy alloy coating and 304 austenitic stainless steel matrix is obviously different with the increasing of load.Under a small load of 5 N,the wear resistance of the coatings is similar to substrate.Meanwhile,when the load applied in the friction procession increases from 5 N to 20 N,the friction coefficient of the substrate changes little,and the wear mechanism is mainly adhesive wear and oxidation wear.But the friction coefficient of the coatings show an evident decrease with the increase of the load,which indicates that the coatings we prepared by this special sintering technology can improve the wear resistance of the substrate successfully and evidently.The wear mechanisms of the coatings prepared are mainly composed of oxidation and abrasive wear.A complex combination of the excellent solid solution strengthening,interface strengthening mechanism.with the newly absorbed second phase precipitation strengthening which is caused by B2 phase,are the main reasons to explain for the good wear resistance behavior of AlCoCrFeNi high entropy alloy coating.（4）After comparing and discuss the corrosion behavior of coatings prepared in our study and substrate which is purchased in three different electrolytes.they are 3.5 wt%NaCl solution,simulated seawater solution and electrochemical in 0.5 M H₂SO₄ solution.finally we found:in3.5 wt%NaCl solution,the coating prepared at 1000℃sintering temperature had the most obvious improvement in corrosion resistance to 304 stainless steel substrate,and actually,the self-corrosion potential E_corrhas been increased by a amplitude of about 0.2.V.Besides,the self-corrosive current density I_corr decreases by an order of magnitude;In simulated seawater solution,the corrosion resistance of the coatings is slightly higher than that of the substrate;In the above process,the corrosion of substrate is mainly caused by the pitting corrosion of Cl^-,while the corrosion of coating is mainly caused by the galvanic corrosion and the grain boundary corrosion of FCC phase.However,in 0.5 M H₂SO₄ solution,the corrosion resistance of the coating has little change when it is compared with that of the substrate.And the final results evidently show us:the AlCoCrFeNi high entropy alloy coating can effectively improve the pitting resistance and wear resistance of the substrate.