Effects Of Surface Coating On Mechanical And Corrosion Properties Of Al_0.3CoCrFeNi High-entropy Alloys

High-entropy alloys?HEAs?are generally defined as solid solution alloys by mixing five or more elements in equiatomic or near-equiatomic proportions.Due to the novel alloy-design philosophy and unique microstructure,HEAs exhibit many excellent properties,such as high strength and hardness,excellent wear resistance,and high thermal resistance.However,when simply considering mechanical properties for a certain type of alloy,for instance,the single face-centered cubic solid-solution alloys,these alloys have high tensile ductility but low strength.In order to optimize their mechanical properties,the hot processing and heat treatment are utilized to enhance their strength.In the present study,the Ni-P amorphous coating is successfully deposited on the Al_0.3CoCrFeNi HEA substrates by electroless plating,and the effects of the Ni-P coating on the mechanical and corrosion properties of the coated samples have been studied.The main results are as follows:?1?In contrast to the uncoated samples with a yielding strength of 275 MPa,the yielding strength of coated sample is 400 MPa,with a 45%improvement,which can be attributed to the very high strength for the Ni-P amorphous film.The finite-element simulation result verifies that the existence of the amorphous film can alleviate the stress on the HEA substrates.?2?A large tensile ductility was achieved in the Ni-P film,since the propagation of one primary shear band was inhibited,and the stress/strain concentration was retarded by the plastic HEA substrates.The corrosion resistance of the HEA with the Ni-P film is superior to that of the bare HEAs in the 3.5 wt.%NaCl solution due to the chemical homogeneity and the absence of microscopic defects for the Ni-P amorphous film.?3?The yielding strength,tensile strength,and surface hardness for the coated samples are improved with the increase of chemical deposition time,while the tensile plasticity is decreased.In addition,the coated sample possesses a higher yield strength when the concentration of reducing agent in electroless plating solution is 20 g/L.?4?The corrosion resistance of the coated samples at different reducing agent concentration was studied by electrochemical-measurement system in a 3.5 wt.%NaCl solutions at room temperature.The results show that the pitting resistance and corrosion resistance of the coated samples were improved with the increase of the concentration of reductant.