Microstructural,Frictional,and Wear Properties of CrN/TiAlN Multilayer Coatings
Special equipment vehicles often operate under high-speed,high-impact,or other adverse environmental conditions.The surface of a rotary shaft seal on the chassis of this type of vehicle is prone to wear and tear,which can lead to sealing failure.An important method for extending the service life and prolonging the maintenance interval is the preparation of hard coatings on the working surfaces of seals.The aim of this study is to improve the wear resistance and extend the service life of rotating axes.The rotary shaft on the vehicle chassis is generally made of 45# steel.Therefore,we prepared hard coatings with different structures on a 45# steel substrate that was ground,polished,and cleaned using ultrasound and alcohol in advance.A single-layer CrN coating and multilayer CrN/TiAlN coatings with thicknesses of support layers were prepared on the 45# steel via physical vapor deposition.The microstructure,mechanical properties,and friction and wear properties of the coatings were analyzed using X-ray diffractometry,scanning electron microscopy,surface profilometry,nanoindentation,and reciprocating tribometry.The single-layer CrN coating was 0.87 μm thick,with hardness of 19.49 GPa and an elastic modulus of 160.53 GPa at a minimum.The multilayer CrN/TiAlN coatings had significantly higher hardness and elastic modulus values,which increased with the thickening of the support layer.The hardness and elastic modulus of the 4CrN/TiAlN coatings reached 39.86 and 386.72 GPa,respectively.The main reason for the increased hardness of the CrN/TiAlN multilayer coatings was Al doping.The addition of Al can refine the grain and cause crystal lattice distortion of nitride,which increases the resistance to dislocation movement and generates fine crystal strengthening and solid solution strengthening effects.In the friction and wear tests in an air atmosphere,the single-layer CrN coating was soon wom.With an increase in the thickness of the support layer,the average friction coefficient of the multilayer CrN/TiAlN coatings initially increased and then decreased,and the cross-sectional area of the wear scar and the maximum wear depth decreased.The 4CrN/TiAlN coatings exhibited optimal frictional abrasion performance,with an average friction coefficient of 0.792 5 and a cross-sectional area of wear scar of 315.09 μm2.The wear mechanisms of the 4CrN/TiAlN coatings were abrasive and slight adhesive wear.Increasing the thickness of the support layer could reduce the plastic deformation of the substrate,bridge the difference in the physical properties between the coatings and the substrate,decrease coating cracks,and improve the frictional and wear performance of the coatings.Multilayer coatings can strengthen the binding force between the film and substrate and reduce the residual stress in the coating.In multilayer structures,the interface between the two layers prevents dislocation glide,stress concentration,and cracking and detachment of the coating.It is easier to control the thickness of CrN/TiAlN multilayer coatings prepared via physical vapor deposition than that of conventional electroplated chromium coatings.Moreover,the former yields a significantly better surface hardness and modulus and is a more efficient and eco-friendly preparation process than the latter.With excellent wear resistance,multilayer coatings enable a rotary shaft seal to provide a long-term sealing effect under complex environmental conditions and high-speed rotation,thus extending the service life of the seal.In this study,we obtained CrN/TiAlN multilayer coatings with outstanding performance by controlling the coating thickness.These findings are expected to significantly improve the wear resistance of the working surface of the rotary shaft seals of vehicles.
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