Effect Of Al And Si On The Microstructure,Mechanical And Tribological Properties Of Tin And Mo₂N Based Films

A series of TiMoN, TiAlMoN, TiAlN, MoAlN, TiSiN and MoTiSiN films wereprepared by magnetron sputtering technique. The microstructures, mechanicalproperties, friction and wear properties at different temperatures of the films weremeasured by XRD, SEM and equipped EDS, nanoindentation, ball-on-disc tribometerand equipped3-D profilometer.TiMoN composite films with various Mo concentrations were deposited using RFreactive magnetron sputtering and characterized by SEM/EDS, X-ray diffraction,nano-indentation and wearing tester. The results showed that TiMoN coatings have afcc structure. When the Mo contents was less than68.37%, a TiMoN solid solutionwas formed by dissolution of Mo into the TiN lattice; When the Mo contents wasmore than68.37%, a TiMoN solid solution was formed by dissolution of Ti into theMo₂N lattice. With Mo contents increased, preferential orientation changed,microhardness increased significantly, the coefficient friction and grain size decreased,friction and wear of TiMoN coatings are excellent. Low coefficient friction can beprimarily attributed to the formation of lubricious MoO3on the wear track surface indry sliding wear conditions. The principles of a crystal chemical model relating thelubricity of complex oxides to their ionic potentials can explain this mechanism. Thefriction and wear properties of TiMoN films had a dependence with the temperature.With the increasing of the temperature, the average friction coefficient of the coatingsincreased first and then steadied and decreased lastly; the wear rate and relative massfraction of oxides on the worn coatings decreased first and then steadied andincreased lastly. Average friction coefficient and wear rate of the films at varioustemperature can be primarily attributed to the relative mass fraction of layeredlubricious oxides with low shear strength on the wornfilms.The synthesized TiAlMoN films had the face-centered cubic （fcc） structure. Thecrystallographic phase and mechanical properties of TiAlMoN films exhibited astrong dependence on Mo content. When the Mo content was below30.07at.%,（Ti,Al, Mo）N substitutional solid solutions were formed by dissolution of Mo into TiAlNlattice; when the Mo content was above44.61at.%,（Ti, Al, Mo）2N substitutionalsolid solutions were formed by dissolution of Ti and Al into Mo₂N lattice; when theMo content is34.31at.%, mixed substitutional solid solutions were formed bydissolution of Mo into Ti-Al-N lattice and dissolution of Ti and Al into Mo₂N lattice. The hardness of Ti-Al-Mo-N films increased from24.89GPa for TiAlN film to39.47GPa for Ti-Al-Mo-N films （44.61-47.38at.%Mo）. The TiAlM-N films showed aconsiderably decreased friction coefficient, compared with TiAlN film. Excellentmechanical properties of Ti-Al-Mo-N films could be primarily attributed to the phasetransition.The microstructure and mechanical properties of TiAlN films exhibited a strongdependence on the Al content in the films. When the Al content was below49.38at.%,the films had an fcc structure. The hardness increased with increasing Al content inthe films and the friction coefficient decreased with the increase of Al content. Whenthe Al content was above49.38at.%, the films had a mixed structures （fcc+hcp） andthe hardness and friction coefficient decreased with the increasing Al content.Thesynthesized MoAlN films exhibited the face-centered cubic （fcc） structure with（111）-preferred orientation. The hardness and elastic modulus of Mo-Al-N filmsdecreased with increasing Al content in the films and the highest values were32.62GPa and494.48GPa respectively, at an Al content of5.59at.%. The oxidationresistance of MoAlN films increased with the increase of Al content. The films withan Al content in the range of4.05^-9.49at.%were found to be optimized for wearresistance applications, which showed low friction coefficient values of0.31-0.35andwear rate of3.6×10^-9-8.13×10^-9mm3/Nmm. The friction coefficient and wear rate ofMoAlN films showed strong connections with the H3/E*2ratio.The synthesized TiSiN films with various Si content had an fcc structure. Thehardness of the films increased with the increasing Si content in the films and reacheda maximum value of28.38GPa at20.19at.%Si, with the further increasing of Sicontent, the hardness of the films decreased. MoTiSiN films had an fcc structure.Addition a small mount of Si could improve the hardness significantly. With thefurther increase of Si content, the hardness and the elastic modulus decreased. Theresults showed that Si can improve the friction properties of the films.