Study On Characterization Of High Adhesion WNx Nanocoatings Prepared By Magnetron Sputtering On K20 Cemented Carbide

The"13th Five-Year Plan"clearly puts forward the promotion of the development of carbide cutting materials in the direction of coated blades and precision cutting tools.Both series of coatings have been studied for many years both academically and industrially,and opening up new series of coatings is a way to improve the quality and life of the workpiece.Based on the excellent performance of WNx coatings and the high adhesion of WNx coatings on cemented carbide,the WNx nanocoatings were deposited on the K20 cemented carbides by direct current magnetron sputtering technology.This thesis investigated the effects of substrate bias,temperature and gas flow ratios on the coating's composition,microstructure and mechanical properties.The friction and wear properties of WNx coatings were studied emphatically under different loads and rotation speeds.The results show that the bias has a great influence on the properties of WNx nanocoatings.As deposited DCMS WNx nanocoating with various sputtering power all show granular micro-surface morphology.The surfaces of WNx coatings prepared under different substrate biases are all granular.The roughness reaches the maximum value of 0.065?m when the bias is-200V,which is slightly higher than substrate.The the crystal structure of WNx coatings are bcc-W phases.The bias affects the existing form of nitrogen in the coatings by influences the bombardment energy of the plasma.With the lower bias,the more nitrogen in the coating were as the form of W-N compounds and with the higher bias,the more nitrogen in the coating were as the form of solid solution.The coating grain size is 7²0 nm,and coating is composed of tiny columnar crystals,deposition rate is 1.94².04?m/h,and the substrate bias has a little influence.Due to the rotation of the sample holder during the deposition process,the cross-section of the coating consists of layers about 15 nm.The coatings exhibit residual compressive stress and the coating hardness reaches a maximum of 27.07 GPa at-200 V.The adhesion strength of the coatings were from 95.69 to 105.94 N,which demonstrates that the WNx nanocoatings exhibit excellent adhesion.The friction coefficient of WNx coating were as low as 0.32⁰.42 when wear with Si₃N₄ ball,and the wear rate is also kept below 2.26×10^-16 m³/N·m.The friction coefficient of WNx coatings increased to 0.66⁰.75 when wear against 440C ball,and the wear rate also increased.During the friction process,the WNx coating forms a deformation layer of tens micrometers on the surface.In the deformed layer,the grains are refined,and the lattice distortion was serious,and the solid solution nitrogen are escaped.Deformed layers with low-nitrogen,even nitrogen-free contact directly with the grinding ball.The temperature affects the WNx nanocoating performance by the plasma energy and the diffuse ability of the particles deposited on the substrate.Since there are many researches on the preparation of WNx coatings by magnetron sputtering at low temperature?⁴50°C?,in this thesis,the effects of temperature?high level of 450°C⁵50°C?on the performance of WNx coatings are investigated.The effect of temperature on the performance of WNx is little,so WNx coating has a large space at the process parameter of tmeperature.The grain size,Wear resistance and residual stress of WNx coating are significantly affected by temperature.As the deposition temperature increased,the grain size of the coatings increased,and the residual stress decreased.Due to the influence of phase composition and residual stress,the wear rate of WNx coating decreases with increasing deposition temperature.Nitrogen-argon flow ratios affects the WNx nanocoating performance mainly through changing the elemental composition of the plasma.The strongest adhesion strength of 111.80 N was obtained at a nitrogen-argon flow ratio of 40:120 sccm.When the nitrogen-argon flow ratio is 80:80 sccm,the main phase structure of the coating is fcc-W₂N with the minimum coating hardness value of 19.12 GPa.Friction and wear test results show that there was not show significant nitrogen loss at the center of the wear track,and the wear resistance of the coating is the best.The wear rate is only 1.99×10^-16m³/N·m.