Influence Of Ceramics On Microstructure And Mechanical Properties Of AlCoCrFeNi High-entropy Alloys Prepared By Laser Cladding

High-entropy alloys?HEAs?are a single-phase or multi-phase solid solution which consist of 5 or more main elements.They have attracted increasing attentions because of excellent fatigue and wear resistance,high hardness and strength with reasonably good ductility.Up to now,the researches of high-entropy alloys focus on both process and elemental composition.Laser cladding technology has been widely studied in the preparation of high-entropy alloy coatings and the study of element composition is extensive.In terms of high-entropy alloys reinforced by ceramic particles,due to the complexity theoretical system of high-entropy alloys and the many kinds of ceramic particles,there are still some uncertainties on the influencing mechanism of microstructure and mechanical properties.In this study,AlCoCrFeNi-xNbC/SiC/Al₂O₃ high-entropy alloy?HEA?coatings?x=10,20,30 wt%?were prepared by laser cladding.The phase constituents,microstructure and mechanical properties of the HEAs were investigated using X-ray diffraction?XRD?,scanning electron microscopy?SEM?,electron back-scatter diffraction?EBSD?,transmission electron microscope?TEM?,microhardness and wear resistance tests.In order to provide reference for the development of high-entropy alloy design concept in the future,the effects of different contents of ceramic particles on the microstructure and properties of high-entropy alloys were studied by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,electron backscatter diffraction?EBSD?,transmission electron microscopy?TEM?,Vickers microhardness and dry sliding friction.The results show that AlCoCrFeNi high-entropy alloy coating with good macromorphology could be prepared on Q235 steel surface by laser cladding.Due to the high-entropy effect,AlCoCrFeNi high-entropy alloy coating consists of simple BCC and FCC phases.In coatings containing NbC and Al₂O₃ hard phases,high-entropy alloy coatings are composed of BCC,FCC phases and unmelted hard phases.In coatings with SiC strengthening phases,there is Cr₂Fe₁₄C phase due to the decomposition of SiC at high temperature.Meanwhile,the addition of ceramic particles can accelerate the transformation from FCC phase to BCC phase in AlCoCrFeNi high entropy alloy,thus it can inhibit the formation of FCC phase.The addition of ceramic particles plays a role of grain refinement.Because of the pinning effect of particles which at grain boundaries,solution strengthening,the increasing of nucleation rate and the increasing of small angle grain boundaries.Due to the grain refining and solution strengthening,the hardness of the coating can be greatly improved by ceramic particles.When adding NbC particles,it has the best comprehensive mechanical properties and the hardness is up to 525HV at x=20 wt.%.When adding SiC particles,the maximum average hardness of the coating is 360HV at x=30 wt%.When adding Al₂O₃ particles,the maximum average hardness of the coating is 487 HV at x=10 wt%and the average hardness is about three times that of the matrix.In the results,the increase of wear resistance is also accompanied by an increase in hardness,but there is also a certain correlation between wear resistance and friction coefficient.