Preparation And Properties Of Self-lubricating Laser Cladding Layers Of AlCoCrFeNi High Entropy Alloys

With the development of industries such as oil and gas,aviation,and aerospace,the requirements for corrosion and wear resistance of structural components are becoming increasingly high.Using surface technology to prepare corrosion and wear-resistant coatings on the surface of structural components is an effective method to improve their corrosion and wear resistance.AlCoCrFeNi high-entropy alloy is a highly promising coating material due to its outstanding high-temperature thermal stability and corrosion resistance,thanks to its unique high-entropy effect.However,its wear resistance issue limits its application space.To address this issue,this paper improves the wear resistance of AlCoCrFeNi high-entropy alloy laser cladding by adding hard phase Ti C particles and solid lubricating phase Mo S₂,from the perspectives of increasing the hardness of the cladding layer and reducing the friction coefficient.The paper clarifies the effects of Ti C and Mo S₂ on the phase,microstructure,and microhardness of the AlCoCrFeNi cladding layer,and elucidates the effects of Ti C,Mo S₂,and their coupling on the friction and wear performance and wear mechanism of the AlCoCrFeNi high-entropy alloy cladding layer.The AlCoCrFeNi high-entropy alloy cladding layer is mainly composed of a BCC phase and a small amount of FCC phase.In the AlCoCrFeNi/Ti C high-entropy alloy cladding layer,after adding 40 wt.%,60 wt.%,and 80 wt.%Ti C,the composite cladding layer is mainly composed of BCC phase,FCC phase,and Ti C phase.Ti C,after remelting,exists in the cladding layer in the form of spherical,petal-shaped,and feather-shaped morphologies.Ti C greatly improves the hardness of AlCoCrFeNi,and the hardness of the composite cladding layer increases with the Ti C content.The surface hardness of the composite cladding layer with 80wt.%Ti C reaches 1104 HV_0.3,which is nearly twice that of the AlCoCrFeNi high-entropy alloy cladding layer hardness(577 HV_0.3),and the wear resistance is increased by nearly 20 times.The wear mechanism of the AlCoCrFeNi/Ti C composite cladding layer is adhesive wear,oxidative wear,and trace abrasive wear.Unlike adding hard particles to increase hardness and improve wear resistance,adding Mo S₂ significantly reduces the friction coefficient of the cladding layer.After adding 3～9 wt.%Mo S₂,the hardness and microstructure of the high-entropy alloy cladding layer did not change significantly and remained composed of BCC phase and a small amount of FCC phase.After adding Mo S₂,part of the Mo S₂ powder was retained in the cladding layer during the cladding process,and the rest formed sulfides such as Cr S,Fe S,Co S,and Mo₂S₃ with the high-entropy alloy elements.The two parts of sulfides formed spherical sulfur-rich self-lubricating phases in the cladding layer,which formed a self-lubricating film during the wear process,reducing the friction coefficient from 0.58 to 0.39,a reduction of over 30%.The weight loss of the cladding layer during wear was reduced from 40.91 mg to 19.70 mg,and the wear resistance was improved by more than one time.The wear mechanism of the AlCoCrFeNi/Mo S₂ cladding layer is adhesive wear and oxidative wear.By increasing the hardness and reducing the friction coefficient,the wear resistance of the AlCoCrFeNi overlay can be improved.To further improve the wear resistance of the overlay and expand its application space,an AlCoCrFeNi hard self-lubricating overlay was prepared by combining both factors.The high entropy alloy hard self-lubricating overlay AlCoCrFeNi+60wt.%Ti C/x Mo S₂（x=3,6,9 wt.%）introduced a composite of Ti C and Mo S₂,forming different phases such as Ti C phase,Ni-Cr-Co-Mo phase,BCC phase,Ti₂SC,Ti C₂,Ti S₂,Cr₇C₃,Mo₂S₃,among others.The partially melted Ti C settled in large particle form at the bottom of the overlay,while the remelted Ti C was distributed in small size throughout the overlay,causing uneven distribution of Ti C and a low hardness region rich in Fe in the overlay.The sulfides such as Ti₂SC,Cr S,Mo₂S₃ formed a composite self-lubricating phase in a strip shape.Under the coupling effect of Ti C and the composite self-lubricating phase,the overlay obtained high hardness and low friction coefficient,with a minimum wear loss of 1.20 mg and a minimum friction coefficient of 0.38.During the wear process,a self-lubricating film and an oxide film with good friction and wear reduction effects were formed on the hard self-lubricating overlay.Compared with the AlCoCrFeNi overlay,the friction coefficient decreased by 34%（from 0.58to 0.38）,the hardness increased by 1.8 times,and the wear resistance increased by 34 times.The wear mechanism was adhesive wear,oxidative wear,and trace abrasive wear.