Microstructure,Mechanical And Tribological Properties Of NbN/MoN Multilayer Films

In this thesis,NbN/MoN multilayer coatings with different Mo target current and NbN coating were deposited by using direct current magnetron sputtering system.The Nb target current was fixed at 4A,while the Mo target varied from 0A-4A.Moreover,NbN/MoN multilayer coatings with different modulation periods and similar modulation ratio(?=1.5)were deposited by using direct current magnetron sputtering system.The influence of the changing of Mo target current and modulation period on the phase composition and micro-structure of NbN/MoN coatings were examined with X-ray diffraction?Atomic force microscope and Transmission electron microscope.The mechanical properties and tribological properties of NbN/MoN coatings were characterized by nano-indentation test,adhesion tests as well as the friction and wear tests.The results show that:NbN/MoN nano-multilayer films with defferent Mo target current were composed of cubic NbN(fcc)and cubic ?-Mo2N(pc)with an obvious modulation layered structure.They presented a form of columnar growth in the direction perpendicular to the substrates.NbN sub-layer and MoN sub-layer were coherent at the interface with a certain lattice mismatch(?=7.2%)due to the difference of lattice constants between NbN and ?-Mo2N.The lattice fringes successively ran throughout the interfaces and the superlattice structure formed as a result of epitaxial growth.The hardness of NbN/MoN nano-multilayer films was higher than the hardness of NbN film.The hardness of NbN/MoN nano-multilayer films achieved the highest hardness of about 40GPa when Mo target current was 1A.The friction coefficient of NbN/MoN nano-multilayer films is lower than the friction coefficient of NbN film.The friction coefficient of NbN/MoN nano-multilayer films was in the range of 0.53?0.58 with the increase of Mo target current.The main wear mechanisms of NbN/MoN nano-multilayer films were fatigue wear and abrasive wear,and a small part with adhesive wear.The increase of hardness effectively reduce the adhesion wear.The wear resistance of nano-multilayer films was improved as a result of the combination of high hardness and low friction coefficient.The wear resistance of NbN/MoN coatings is better than NbN coating.The NbN/MoN multilayers show the best tribological properties when Mo target current was 4A.NbN/MoN nano-multilayer films with defferent modulation period were composed of cubic NbN(fcc)and cubic ?-Mo2N(pc)with an obvious modulation layered structure.NbN sub-layer and MoN sub-layer were coherent at the interface with a certain lattice mismatch(6=7.2%)due to the difference of lattice constants between NbN and ?-Mo2N,the superlattice structure also formed as a result of epitaxial growth when modulation period was 10m.The hardness of NbN/MoN nano-multilayer films with different modulation period achieved the highest hardness of about 34.4GPa when modulation period was 5nm.The hardness of nano-multilayer films decreased to 30.2GPa when modulation period was 10nm.With the increase of modulation periods,the hardness nearly remained constant at about 32GPa when the modulation period was higher than 10nm.The friction coefficients of nano-multilayer films increased first and then decreased with the increased modulation periods.The comparative analysis of the results showed that the performances of NbN/MoN coatings were better which modulation period was 5.0nm.The main wear mechanisms of NbN/MoN nano-multilayer films were fatigue wear and fatigue wear.