Studies On Corrosion Resistance And Mechanical Properties Of Laser Cladded CrMnFeCoNi High Entropy Alloy

In the past,the development of traditional alloy systems,such as iron-,aluminum-,nickel-,magnesium-based alloy,has been based on one major element.A novel concept of high entropy alloy(HEA),which is defined as alloys composed of 5 or more alloying elements with concentration of each at 5 to 35 at.%,represents an innovative alloy design strategy.However,most existed published works have done in bulk material state.Benefiting its excellent damage tolerance,using it as a coating material will not only broaden its application fields but also lower the cost.In this paper,HEA coating with a nominal composition of CrMnFeCoNi is fabricated by laser surface alloying and studied in detail.Microstructure and chemical composition are determined by X-ray diffraction(XRD),optical microscope(OM),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS).Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS)are used to investigate the corrosion behavior.The coating forms a simple FCC phase with an identical dendritic structure composed of Fe/Co/Ni-rich dendrites and Mn/Ni-rich interdendrites.Both in 3.5 wt.% Na Cl solution and 0.5 M sulfuric acid the coating exhibits nobler corrosion resistance than A36 steel substrate and even lower icorr than 304 stainless steel(304SS).EIS plots coupled with fitted parameters reveal that a spontaneous protective film is formed and developed during immersion in 0.5 M sulfuric acid.The fitted Rt value reaches its maximum at 24 h during a 48 hours’ immersion test,indicating the passive film starts to break down after that.EDS analysis conducted on a corroded surface immersed in 0.5 M H2SO4 reveals that corrosion starts from Cr-depleted interdendrites.Mechanical properties are also investigated with microhardness test,tensile test and indention-method toughness measurement.The microhardness of the coating is around 200 HV,the tensile strength can be as high as 496 MPa and the fracture toughness is estimated over 32.9 MPa·m1/2.In additional,the corrosion resistance and mechanical properties can be enhanced with a rapid laser remelting process by refining the grains,restraining the element segregation and reducing defects.