Nano-mechanical Properties Of TiN/CrN Multilayer Films Deposited By Magnetron Sputtering

With the continuous development of industry,the diversification of service environment of mechanical parts and engineering components puts forward higher requirements on the performance of mechanical parts.Hard TiN films because of its high hardness and wear resistance are widely used in surface protection of mechanical parts.However,conventional TiN films easily peeling off from the substrate in the work process,occurred fatigue failures under the actions of cyclic loading,and behave a poor mechanical properties at high temperature.All above behaviors limit the possibility of working in aerospace engine and high speed steel for TiN films.Therefore,the researchers have developed multilayer films based on TiN films,results showed that the multi-layer structure will enhance the fracture toughness,impact fatigue resistance and high temperature mechanical properties of films.In this paper,we put TiN films,CrN films and TiN/CrN multilayer films as the research object.The TiN and CrN films prepared by magnetron sputtering technology,TiN/CrN multilayer films alternately deposited by TiN and CrN films.The effects of sputtering power on the monolayer films and the effects of periodicity on mechanical properties of multilayer films were investigated.The surface morphology,microstructure,phase composition and mechanical properties of the films were tested by scanning electron microscopy,atomic force microscopy,transmission electron microscopy,X-ray diffractometry,X-ray photoelectron spectroscopy and nanomechanical testing systems.In view of the specialty of the nanoscale multilayer structure,the nano-indentation,nano-dynamic load test and high-temperature nanoindentation module were used to investigate the mechanical properties in quasi-static,dynamic and high temperature station.Compared the mechanical properties between multilayer film with monolayer film,and different periodicity of multilayer films.Combination with multilayer film microstructure,studied the enhancement mechanism of its hardness,fracture resistance and impact fatigue resistance.The results show that mechanical properties of multilayers are better than those of monolayer films,and the hardness,fracture toughness,impact fatigue resistance and high temperature mechanical properties of multilayer films were improved with the decrease of the modulation period.The hardening mechanism of multilayer films with larger modulation period follows the Hall-pech theory.When the modulation period is less than 10 nm,the hardening mechanism is mainly the mechanism of interfacial coordination strain.The phase structure,the modulus,the deformation mechanism of the modulation layer and the interaction mechanism between the layers are all the factors that prevent crack propagation and enhance the performance of the multilayer films.The mechanical properties of films with small modulation period at high temperature are relatively stable,and the hardness of films with large modulation period and the ability of resisting the deformation are decreased.The fracture properties of the films are closely related to the load and modulation period,The critical load for the first failure of the film is determined by the competitive relationship between the crack propagation force of the film and the compressive stress of the indenter.At the same load,the films with larger modulation period are more likely to produce radial cracks and peeling.When the period beyond a threshold,the toughness of the films decreases and the film become to brittle films.The impact tests show that the impact fatigue life of the films decreases with the increase of the impact load and the modulation period.There are three stages in the film's impact fatigue failure: nucleation of crack on the surface of the film,further nucleation and growth of the crack,the edge of the impact indentation has obvious ring-like layer-like accumulation,and finally radial fracture and peeling.ring stacking appears in the edge of impact indentation,ultimately broken and peeling radially.