Research On The Processs,Microstructure And Properties Of FeCoNiCrAlx High Entropy Alloy Laser Cladding Coating

High-entropy alloys have multiple components and the atomic fraction of each component ranges from 5%～35%,the random distribution of multi-component solid solution elements and the addition of wear-resistant,corrosion-resistant and oxidation-resistant elements make it present better performance than traditional metallic materials in terms of wear resistance,corrosion resistance and oxidation resistance,which is especially suitable for the coating field.In this study,FeCoNiCrAlx（x=0,0.1,0.3）with a single FCC structure and FeCoNiCrAlx（x=0.5,0.7,1.0）with a BCC structure were prepared by laser melting technique on Q235 steel with high entropy alloy coatings,respectively.The microstructure of high-entropy alloy coatings with different Al contents was characterized in detail using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,EBSD,and TEM and the correlation between microstructure and mechanical properties,corrosion resistance,wear resistance,and resistance to high-temperature oxidation was discussed.Firstly,the influence law of laser cladding process parameters on coating formation was investigated.The results show that too low laser power leads to low heat input,non-melting of powder particles,discontinuous forming of the cladding layer,and easy defects such as inclusions and unfused.High laser power leads to high heat input,high heat in the melt pool,increased dilution rate,and easy cracking inside the cladding layer.Too little scanning speed will also cause too high heat input to the melt pool,resulting in increased metal melting on both sides of the melt pool and increased dilution of the cladding layer.Too large a scanning speed will lead to a reduction in the amount of powder delivered per unit time and heat input,a higher melt height,a smaller melt depth,a lower interfacial bond strength and a weaker strengthening effect on the substrate.When the lap rate is controlled at 50%,the surface of the molten layer is relatively flat,without defects such as pores and slag,and the forming quality is high.The addition of Al to the material can effectively improve the strength of the alloy and resistance to high temperature oxidation,in addition,the addition of Al also plays a role in lightweighting and cost reduction.The single-phase high-entropy alloy has a simple structure,and the FCC structure has better ductility and good mechanical properties.In order to obtain a high entropy alloy coating with excellent corrosion resistance and resistance to high temperature oxidation.We prepared FeCoNiCrAlx（x=0,0.1,0.3）high-entropy alloy coatings with a single FCC structure by laser melting technique.It was found that the phase structure of all three groups of alloys consisted of a single FCC phase,but a small amount of B2 phase was found to be present in the Al0.3 alloy by EBSD results.The grain structure of the alloy changes from columnar to equiaxed crystals with the increase of Al element content,and shows anisotropy and a certain degree of grain size refinement.In addition,the addition of Al will promote the dislocation phenomenon inside the alloy,and the addition of Al can effectively improve the strength of the alloy,but the addition of Al will reduce the density of the alloy passivation film and accelerate the corrosion rate of the alloy.The addition of Al elements can also promote the generation of Al₂O₃ oxide films on the surface of the alloy and prevent further oxidation behavior of the alloy,which is conducive to improving the high temperature oxidation resistance of the alloy.The addition of Al element can promote the transformation of the phase composition of FeCoNiCrAlx high-entropy alloy from FCC structure to BCC structure,and the BCC structure has higher hardness than the FCC structure,but the addition of excessive Al element will lead to a sharp decrease in alloy plasticity and the coating is prone to cracking.Therefore,to further improve the hardness and wear resistance of the coatings and to make the coatings have certain toughness and plasticity,we prepared FeCoNiCrAlx（x=0.5,0.7,1.0）high-entropy alloy coatings with BCC structure.It was shown that the addition of Al elements can cause the transformation of FCC-FCC+BCC-BCC phase composition of the alloy.It was found that the hardness of the alloy tended to increase with the increase of Al content through performance tests on the coating.The element Al can also promote the formation of oxide film on the friction surface of the alloy and reduce the friction coefficient of the alloy,so that the wear resistance of the alloy gains significantly,and the wear mechanism of all three groups of alloys is abrasive wear.In addition,the addition of Al element intensifies the corrosion rate of the alloy,and when the content of Al element is 0.5,the alloy shows the optimal corrosion resistance.