Study On Wear And Corrosion Behaviors Of AlFeCoCrNi High Entropy Alloy

In this thesis,the AlFeCoCrNi high entropy alloy of the as-cast and pre-strained were selected as the model materials.The microstructure of high entropy alloys with different diameters and different pre-strain levels were detected.The wear behaviors of AlFeCoCrNi high entropy alloys with different diameters in air was studied.The corrosion behavior of Al FeCoCrNi high entropy alloy samples of the as-cast and prestrained states in simulated sea water and 1mol/L hydrochloric acid was studied,The corrosion mechanism of high entropy alloy in two solutions was explored.The microstructure of high entropy alloys with different diameters and different prestrain levels were examined by transmission electron microscopy（TEM）.Numerous nano-scale precipitates existed in the high entropy alloy.The size of the precipitates gradually decreased,with increasing the cooling rate experienced during sample preparation.The crystals exhibited a needle-like shape.With the ongoing pre-straining process,no phase transformation occurred but the shape changed from round to strip.The Vickers hardness of AlFeCoCrNi high entropy alloys with different diameters was tested.The hardness of high entropy alloys increased with the increase of cooling rate.The high entropy alloy sample with 2mm diameter possess the highest hardness value.The wear resistance of AlFeCoCrNi high entropy alloy in air was evaluated systematically by combining the surface morphology of the wear surface,the mass loss and the friction coefficient.The surface roughness,mass loss and friction coefficient of AlFeCoCrNi high entropy alloy in air decreased with the increase of the cooling rate.Among the studied samples,2mm one has the minimum values,demonstrating its best wear resistance.The wear mechanism changes from the abrasive wear to the oxidation wear and adhesion wear when the high entropy alloy wears in the air.The corrosion behaviors of AlFeCoCrNi high entropy alloy in simulated seawater and 1mol/L hydrochloric acid was evaluated by impedance spectroscopy and polarization curve.The results show that the corrosion resistance of AlFeCoCrNi high entropy alloy firstly increases and then decreases with the increase in the pre-strain level,yielding a best resistance in 13 % pre-strain sample.Impedance test showed that the charge transfer resistance,impedance and capacity of the arc diameter of the 13% pre-strain sample in two solutions are largest.The corrosion resistance of 13% pre-strain sample is better than 304 stainless steel in simulated seawater and 1 mol/L hydrochloric acid.The surfaces of high entropy alloy sample with different pre-strain levels were observed by SEM.The results showed that,for all the as-cast and pre-strained AlFeCoCrNi high-entropy alloy samples,the dissolution of Al,Fe,Cr and Ni elements and the enrichment of Co element are present in the corrosion region.X-ray photoelectron spectroscopy was used to examine the electron structure of the surface of high entropy alloy samples after corrosion tests in the simulated seawater.The surface of the 13% prestrain sample was rich in Al³⁺,Ni²⁺ and Cr³⁺.