Preparation And Tribological Properties Of CoCrFeNiMnSn_x High Entropy Alloy Coating

Q235 alloy steel is often used in construction engineering and chemical equipment and other fields.However,the unreasonable problem between the service environment and service life of a single Q235 alloy steel component is particularly prominent.Therefore,it is necessary to prepare composite coatings to improve the comprehensive mechanical properties of the component and the service life of the component.CoCrFeNiMnsystem high-entropy alloys are used as effective candidates for the preparation of coatings with composite properties due to their multi-principal components,high temperature resistance,corrosion resistance,wear resistance and other properties.In this paper,CoCrFeNiMnSn_x high-entropy alloy coatings were prepared on Q235steel substrate by laser cladding method,and the effect of Sn element content on the microstructure and friction and wear properties of CoCrFeNiMnhigh-entropy alloy coatings was deeply explored,and the reasons for the changes in the microstructure and properties of CoCrFeNiMnSn_x high-entropy alloys were explained by first-principles.CoCrFeNiMncomposite coatings were prepared on Q235 alloy substrate by laser cladding process with different laser power and powder feeding speed.The effects of different laser power and powder feeding speed on the macroscopic morphology of the coatings were studied.The optimum laser cladding process parameters of CoCrFeNiMncoating were determined by comparing the macroscopic morphology of the coating:the laser power was 1300 W,and the powder feeding speed was 1.2r/min.The effect of Sn on the microstructure and properties of CoCrFeNiMnSn_x high-entropy alloy coatings was studied.The composition and morphology of the coatings were analyzed by XRD,OM,SEM and EDS.The microstructure evolution of the composite coatings was summarized,and the friction and wear properties of the composite coating are clarified.The results show that the CoCrFeNiMnhigh-entropy alloy coating is FCC single phase.With the addition and increase of Sn element content,the coating changes from a single homogeneous phase structure of FCC structure to a combination of FCC phase structure and Mn Ni₂Sn phase structure,the volume fraction of Mn Ni₂Sn phase increases with Sn content increases and becomes larger.The average hardness of the cladding layer increases first and then decreases with the increase of Sn element content.The hardness of Sn_0.2alloy coating reaches the maximum value（417 HV）,which is nearly 45%higher than that of Sn₀ alloy coating（288 HV）.The friction coefficient and mass wear of the coating both show a trend of first decreasing and then increasing with the increase of Sn element.The friction coefficient of Sn_0.2 sample is the lowest value of 0.115,and the wear quality is the lowest value of 4.6 mg.Under dry friction conditions,the wear mechanism of Sn₀ alloy coating is mainly abrasive wear,adhesive wear and delamination wear,while the friction mechanism of Sn_0.2 alloy coating is mainly abrasive wear,accompanied by a certain amount of adhesive wear.The bonding properties of CoCrFeNiMnSn_x high-entropy alloy coatings were theoretically elucidated by first-principles calculations,and the evolution rules of microstructure and properties in composite coatings were explored.The reaserch results show that Sn_0.2 has the largest Young’s modulus（517.65 GPa）,but the smallest bulk modulus（17.485GPa）,indicating that it has the strongest compressive performance but the weakest resistance to fracture.The P,s,and d orbitals of Sn₀,Sn_0.1,Sn_0.2,Sn_0.3 and Sn_0.5 have partial wave DOS crossing the fermi level,and the hybridization of the d orbital at the fermi level is dominant.The contribution of p orbital and s orbital is small,indicating the existence of covalent bond properties in high-entropy alloys.For Sn_0.1,Sn_0.2,Sn_0.3 and Sn_0.5,the value of charge density near Sn,Mn and Ni atoms is larger,indicates that Sn,Mn and Ni atoms have strong binding force.