Design Of Smart Nitride-based Nano-structure Composite Films And Study Of Their Mechanical And Tribological Properties

Transition metal nitride(TMN)films occupy an important station in some areas such as cutting and die tools due to their excellent mechanical and tribological properties.The investigation of TMN is mainly focused on the ?B,?B and ?B groups.The design of composite and smart TMN films,which exhibits excellent tribological property at the wide temperature range,is the development trend in order to meet the demands of high productivity machining,high temperature machining.The TiN in ?B group,Nb-N in ?B group and Mo-N in ?B group were chose in my thesis with a purpose of improvement of the tribological property at wide temperature range.Some elements such as Si were combined into TMN to improve the mechanical and RT tribological properties;on above basis,Magnéli elements such as Mo,V and noble metal Ag were added with a purpose of improvement of the high temperature tribological property.The aim of my thesis was the design of a new TMN system with excellent tribological property at wide temperature range.The main results were as follows:Element Al was introduced into the ?B,?B and ?B groups' nitride films and Ti-Al-N,Nb-Al-N and Mo-Al-N films with various Al content were deposited with a purpose of improvement of the mechanical and tribological properties.For the Ti-Al-N films in ?B group and Nb-Al-N in ?B group,some transition metal elements in TMN lattice were substituted by Al and substitutional solid solution was formed when the Al content in those films was below 50 at.%.The mechanical property of those films was improved due to the solid solution strengthening.However,with a further increase in the Al content,hcp-AlN phase appearing in those films led to the decrease of the hardness.For the Mo-Al-N films,the hardness of the films initially increased and reached a summit,and then decreased with the increasing of Al content in the films and the maximum value is about 33 GPa at 3.7 at.% Al.For all above films containing Al,a certain amount of Al in the TMN films could improve the capability of resisting deform.The cracks in the surface of the wear track disappeared and alleviated the interaction between the wear track and the counterpart.Therefore,the tribological property at RT of those films was improved.The addition of Al into TMN films could not improve the tribological property at high temperature due to the hard phase Al2O3 in the surface of the wear track.The oxidation resistance temperature increased with the increase of Al content in the films because Al3+ diffuses outward to the surface of the films with the inward diffusion of oxygen will form Al2O3 layer during the oxidation process.Element Si was introduced into TMN films in order to improve the mechanical and the tribological properties at RT.Magnéli elements such as Mo,V were added with a purpose of improvement of the high temperature tribological property,while still keeping the excellent red hardness.Based on the above ideas,Ti-Mo-Si-N and Nb-V-Si-N films were deposited in order to improve the adaptive capacity at wide temperature range.The substitution of Si into TMN films could improve the hardness,fracture toughness and the RT tribological property.However,amorphous Si3N4 appeared in the films with high level of Si content and degrades the mechanical and tribological properties.For the Ti-Mo-Si-N and Nb-V-Si-N films,some transition metal elements in TMN lattice were substituted by Magnéli elements such as Mo,V and substitutional solid solution was formed.The mechanical property of those films was improved due to the solid solution strengthening.The fracture toughness of the films increased with the increase of the Magnéli elements content in the films because the Magnéli elements could induce the pin dislocations in the films.The increase of the fracture toughness could increase the adhesion of the films.At RT and high temperature,some tribo-oxidation with higher value of ionic potential could be formed easily by a reaction between the wear track and oxygen/moisture in the air.Those tribo-oxidations could improve the friction property of the films significantly.However,those tribo-oxidations could be worn away easily by the counterpart during the wear testing because they had low shear strength.Therefore,the wear rate of the films was relatively high.Noble element Ag was introduced into TMN films and the influence of Ag content on the microstructure and tribological property at wide temperature range of the films was discussed.Besides this,the formation mechanism of TMN-Ag was studied based on the results of the data from the first principle and molar reaction enthalpy.TiN nucleated firstly because of the higher reactivity with nitrogen of Ti than that of Ag;and then the TiN grown gradually.The solidification of Ag was formed on the defect areas of the TiN grain and Ag nanoparticles were detected at the boundary of the TiN grains.TMN-Ag films especially the films with the high Ag content exhibited excellent tribological properties at wide temperature range.In addition,the influence of ate earth element Y on the microstructure and properties was also studied and the results showed that some transition metal elements in TMN lattice were substituted by Al and substitutional solid solution was formed.The hardness of the films increased slightly due to the solid solution strengthening.The combination of Y into TMN film could increase the oxidation resistance temperature.The wear resistance of the films was improved because the content of tribo-oxidation decreased with the increase of Y content.