Preparation Of CrNx Film By Hot Cathode Ion Plating And Research On Oxidation Resistance

Metal cutting is one of the most important methods in part molding,playing an significant role in manufactural areas.In recent years,when numerical technology developed,especially the application in fast cutting and dry cutting,the requirement of the cutters has to been enhanced,the cutting energy which can be difficult to eliminate is produced between the cutting edge and the work material surface, wearing and oxidation severely,costing the processing accuracy.In order to repair the bit tool and elongate the life period,hard films are prepared by physical vapour deposition on bit tool surface.Oxidation resistance of CrNx hard films prepared by hot cathode ion-plating is investigated in this paper.CrNx films is prepared on the surface of GCr15 bearing steel and YG6 cemented carbide by the type of XH-830 ion-plating equipment in this experiment,made oxidative experiments and analysis on phase structure,constitutions,fracture pattern at different temperatures,beside of mechanical performance and oxidation resistance of films,finally oxidation mechanics of CrNx films is explored.Results of this research show:CrNx hard films made up of Cr₂N and Cr phases could be prepared by hot cathode ion plating technology.Structure of phases were different in variant temperatures:low temperature phase of Cr₂₃C₆ appeared while 400℃and disappeared above 400℃;CrN appeared while 500℃;CrN could transform to Cr₂N above 679℃,CrN disappeared,meanwhile Cr₂O₃ oxide appeared; no new phase produced between 700～800℃. Analysis of quantivalences and relative ratio of films in different oxidative temperatures by XPS indicates:Cr-O,N-O bonds generated accompanying with temperature increased,Cr-O was from Cr₂O₃ and CrO₃,but CrO₃ was not detected by XRD.N₂ was released when CrN transformed to Cr₂N and Cr₂O₃,oxygen ratio increased and nitrogen ratio decreased.The ratio of Cr,O decreased during 400～600℃,while the ratio of Cr,O approached to 1:1.5,which was equal to stoichiometry of Cr₂O₃,it was indicated that a complete oxide film produced in the process.Fracture pattern analysis shows:thickness of films with continuous,clearly interface of film-base was 4μm,presented columnar crystals.Surface of samples with a small amount stains was smooth,presented thin columnar crystal while 650℃;oxides about 0.3μm and 0.6μm were detected at 700,750℃respectively,the grain of the films presented rough columnar crystals,cavities appeared at 750℃;films with little protection resulted from many cavities appeared at 800℃.Micro-hardness and cohesion strength decreased accompanying with the temperature reducing.Micro-hardness value approach to base body's and cohesion strength value was lowest.Weight gain which started at 650℃got more with temperature heightening. Oxidation reaction rate increased as the temperature enhanced,the best inoxidizable temperature concluded at this experiment condition was 750℃.In response to comprehensive analysis of XRD,XPS,SEM,micro-hardness and cohesion strength,application effect of CrNx hard films was best at 700℃work condition.