Investigation On Microstructure And Properties Of Magnetron Sputtered Wb₂/CR Multilayer Films

Since AlB2-type WB2 film was firstly deposited by magnetron sputtering,AlB2-type WB2 film possess high hardness,high chemical stability,high wear resistant as well as self-lubrication,which indicates a potential new type of film.However,the brittleness of boride films and poor adhesion strength is the key issue to hinder AlB2-type WB2 employed widely.In this paper,the Cr-WB2,(Cr,N)-WB2 and WB2/Cr multilayer films are deposited on YG8,Si and SiO2 substrates by magnetron sputtering.By applying various analytical methods,the effect of deposition parameters such as doping content,modulation ratio and bilayer numbers on the composition,microstructure and properties of the films are studied systematically.The influence between hardness and fracture toughness on the ability to enhance the adhesion and wear resistance are emphasized.For Cr-WB2 films,with the increasing Cr addition,the preferred orientation of(101)is unchanged,the grain size is decreased,and then accompanied by the worse crystallinity.The hardness is enhanced by the addition of small amount of Cr,with the maximum of 30 GPa.The residual stress reaches the maximum of-701 MPa in the meantime.The fracture toughness increases with the increasing Cr addition and reaches the maximum of 1.264 MPa·m1/2.The adhesion strength reaches the maximum of 23 N when the hardness is highest.The friction coefficient and wear rate reach the minimum of 0.32 and 4.4×10-7 mm3/mN with the optimal Cr concentration of 5.1 at.%.For(Cr,N)-WB2 films,with the increasing N2 pressure,the concentration of N first increases and then tends to be stable,and the maximum doping amount is about 30%.The grain size decreases first and then it comes to amorphous structure.The concentration of h-BN phase increases with the decreasing CrB2 phase and WB2 phase.The hardness first decreases and then tends to be stable,while the fracture toughness reaches the maximum of 3.93 MPa·m1/2 when the N2 pressure is 0.02 Pa and then decreases.The residual compressive stress increases gradually.The adhesion strength reaches the maximum of 30 N when the fracture toughness is the highest.The wear resistance is influenced by several factors such as higher hardness,optimal residual stress and higher adhesion Strength,and the minimum of wear rate is 3.67×10-7 mm3/mN.For WB2/Cr multilayer films with fixed bilayer number at 10.With the increasing modulation ratio,both the concentration of Cr and the diffraction peak of Cr(110)decrease.The residual stress decreases which is not obviously influenced by the modulation ratio.The changing trend of the hardness and fracture toughness are different and the maximum of them are 31 GPa and 1.264 MPa·m1/2,respectively.The adhesion strength reaches the maximum of 37 N when the modulation ratio is 7.Meanwhile,the minimum of wear rate is 2.06×10-7 mm3/mN as a result of the balance of hardness and fracture toughness.For WB2/Cr multilayer films with fixed modulation ratio at 7.With the increasing bilayer number,the grain size gradually decreases and finally it comes to amorphous structure.The residual stress decreases with the increasing bilayer number.The hardness and fracture toughness first increases and then decreases with the maximum of 34 GPa and 1.246 MPa·m1/2,respectively.The adhesion strength reaches the maximum of 67 N when the bilayer number is 30.Meanwhile,the hard yet tough film possesses the lowest wear rate of 1.78×10-7 mm3/mN.