Study On The Wettability And Interfacial Properties Of WC/Binder Phase/Steel Substrates

As a protective coating,tungsten carbide coating is widely used on the surface of metal parts to improve the performance under wear,corrosion and high temperature.However,under the trend of replacing cobalt with nickel in the binder phase,the interfacial adhesion properties of different nickel-based alloys adhere to tungsten carbide or different steel substrates remain to be clarified.In this thesis,based on the research background of WC coatings on complex surface/abrupt cross-section made by HVOF,computational and experimental studies on the wettability and interfacial properties of binder phases-WC,WC coatings-steel substrates were carried out.The first-principles method based on density functional theory was used as the calculation method to study the influence of Co,Ni,Ni₃Al and different nickel-based binder phases on the wettability and adhesion strength of wetting on WC surface.The mechanism of the adhesive properties of the binder phase-WC interface was analyzed,and the chemical bond type at the adhesive interface of nickel-based binder phase and WC was studied.The results showed that the adhesion energy of WC/Co interface was the highest,which was 4.896 J/m²,while that of Ni₃Al was the lowest,which was3.923 J/m².The wettability and adhesion strength were in the order of Co>Co Cr>Ni Fe>Ni Co>Ni>Ni Cr>Ni Mo Cr Fe Co>Ni Mo Cr>Ni Mo>Ni₃Al.Mo and Cr elements would weaken the adhesion bond the surrounding Ni atoms and WC while Fe and Co did not,but the weakening effect of Mo and Cr in the multi-element nickel-based binder phase was weakened.The nickel-based binder phase and tungsten carbide were mainly bonded by metallic bond.From the perspectives of lattice matching,phase distinction method and virtual crystal approximation method,the first-principles method based on density functional theory was used as the calculation method to study the interfacial adhesion properties between Co,Ni binder phase and 9Cr18Mo V,Cr12Mo1V1,Cr20Mo V4（The M390steel）and 0Cr17Ni4Cu4Nb steel substrates.The results showed that the mismatch degree between the binder phase and theα-Fe,Fe₃C,VC in the steel substrates were low,which were below 5%;while the mismatch degree with martensite and carbides such as Cr₇C₃,Cr₃C₂,Mo₂C were about 7%to 20%.The higher the martensitic carbon content,the greater the mismatch with the binder phase.The results acquired by phase distinction method and virtual crystal approximation method indicated that the0Cr17Ni4Cu4Nb steel had the best bonding effect with the binder phase,followed by the 9Cr18Mo V and Cr12Mo1V1 steels,and the Cr20Mo V4 steel was the worst.The interfacial chemical bond between the binder phase and the steel substrates were mainly metallic bond,followed by covalent bondThe contact angle of Hastelloy C276 alloy,Ni and Co wetting on YG6substrates was measured by high temperature contact angle test.The interfacial morphology of powder and coating were characterized to analyze the adhesive interface of WC/binder phase/steel substrate.The high temperature diffusion test was used to analyze metal element diffusion tendency between WC coatings and steel substrates.The results showed that the contact angles of C276 and Ni wet on WC were 4.6°and 4.3°,and the contact angle of Co was extremely small.When the binder phase content was 30%,the powder sphericity was good,but the internal pores were large and unevenly distributed,and there were more contact surfaces between the binder phase and the steel substrate.When the mass fraction of the binder phase was below 20%,the powder sphericity was reduced but the internal pore size was smaller and the distribution was more uniform,and the contact surface between WC particles in the coating and the steel substrates increased.At high temperatures,Ni,Cr and Fe elements were easy to diffuse,while Co element had weak diffusivity,and Mo was hard to diffuse.