Microstructure Control Preparation And Properties Of Self-Organized Nano-Multilayer AlCrNbSi(O)N Coating

In the cutting process of difficult to machine materials such as superalloys,due to the low thermal conductivity of superalloys,it is difficult to dissipate heat.The cutting temperature can reach more than 1000?,with serious work hardening,large cutting deformation and serious tool wear.In order to overcome the damage of extreme environment to tools in the process of machining difficult materials,the development of tool coatings with high hardness,high toughness and high temperature thermal stability is of great significance for high-precision and efficient manufacturing.Nitride coating has high hardness and toughness,and the effect of cutting superalloy at medium and low speed is good,but the mechanical properties decline seriously at high temperature and the oxidation resistance is poor.Oxide coating has better thermal/chemical stability and is more suitable for high-speed cutting,but the upper limit of hardness is low,mostly ion bonding and poor toughness.The AlCrSiON coating developed by combining nanocomposite structure and oxynitride self-organizing nano multilayer structure shows excellent properties in mechanical properties,high temperature stability and high temperature oxidation resistance,but it is easy to crack and fail in the process of friction behavior,and the toughness of the coating needs to be further improved.Based on the self-organized nano multilayer AlCrSiON coating with good mechanical properties and high temperature oxidation resistance,aiming at the problem of poor toughness,this paper selects the alloying method to systematically study the effect of Nb on the toughness and other key properties of the coating.Firstly,Nb was added into the nanocomposite structure coating AlCrSiN,and the effects of different Nb content on the structure and properties of the coating were systematically studied;Secondly,on the basis of previous research conclusions,N-rich monolayer,O-rich monolayer and nano multilayer coatings of self-organizing nano multilayer Al Cr(Nb)Si ON were prepared respectively,and further studied to explain its self-organizing formation mechanism and strengthening and toughening mechanism;Finally,AlCrNbSiON coatings with different oxygen content were prepared by changing the N₂/O₂ flow ratio in the deposition process.The effects of different oxygen content on the microstructure,mechanical properties,high temperature properties and Tribological Properties of the coatings were systematically studied.The main conclusions of this thesis are as follows:1)Adding Nb into AlCrSiN coating,the Nb content of the coating is between 0 at.%and 11.59 at.%.The nano hardness of the coating increased first and then decreased with the increase of Nb content.The hardness of the coating with a small amount of Nb(AlCrSiN?Nb3)was the highest,reaching 32.5±0.94 GPa;The elastic modulus of the coating as a whole shows a trend of gradually decreasing with the increase of Nb content,and the H~3/E^*2 value of the coating shows a trend of increasing?decreasing?increasing.The variation trend of film substrate bonding force of the coating is basically consistent with that of H~3/E^*2 value.With the increase of Nb content,the toughness K_IC value of the coating increases gradually.High temperature vacuum annealing experiment shows that Nb doping in AlCrSiN can further improve the high temperature thermal stability and high temperature mechanical properties of the coating.The oxidation resistance of AlCrSiN coating will decrease when Nb is added into the coating.Under the normal temperature friction test,with the increase of Nb content,the microcracks at the edge of the wear mark of the coating gradually decrease until they disappear;Under high temperature(800?),the wear resistance of all Nb containing coatings is significantly higher than that of AlCrSiN coatings.2)The N-rich monolayer,O-rich monolayer and nano multilayer coatings of AlCrSiON and AlCrNbSiON were prepared.The coatings facing the arc target were N-rich films and the coatings facing the arc target were O-rich films.The N-rich monolayer coatings of AlCrSiON and AlCrNbSiON grow with coarse columnar crystals,and the O-rich monolayer presents amorphous growth morphology as a whole.After nano multilayer combination,the O-rich layer grows along the coherent epitaxy of the N-rich layer and locally coherent and epitaxial growth.For AlCrSiON and AlCrNbSiON coatings,the mechanical properties of nano multilayer are improved compared with those of N-rich monolayer and O-rich monolayer by integrating the mechanisms of nano multilayer strengthening,coherent strengthening and modulus difference strengthening.The toughness of N-rich monolayer and O-rich monolayer of AlCrNbSiON is better than that of N-rich layer and O-rich layer of AlCrNbSiON,so the multilayer of AlCrNbSiON shows more excellent toughness.For AlCrSiON coating,the high-temperature stability of N-rich layer is poor,but the high-temperature stability of O-rich layer,so the high-temperature mechanical properties of nano multilayer are stable.The N-rich layer,O-rich layer and nano multilayer of AlCrNbSiON coating are relatively stable at high temperature.The high temperature mechanical properties of nano multilayer are similar to those of N-rich monolayer.3)AlCrNbSiON is self-organized and overlapped by N-rich layer and O-rich layer.With the increase of oxygen content,the multilayer morphology of the coating is gradually obvious,the multilayer modulation period remains constant,which is?10.7 nm,and the modulation ratio of N-rich layer and O-rich layer is gradually reduced from 5.7:1 to 3:1.AlCrNbSiON with different oxygen content shows the coherent growth of N-rich layer and O-rich layer.With the increase of oxygen content,the coherent form gradually changes from overall coherent to local coherent.With a small amount of oxygen,the hardness of the coating is improved,and the maximum value is 29.5±1.18 GPa when the flow ratio of N₂/O₂ is 294/6.The toughness of the coating after oxygen doping is better than that of AlCrNbSiN,and the toughness of the coating with a small amount of oxygen doping(N₂/O₂=294/6)and a large amount of oxygen doping(N₂/O₂=282/18)is significantly improved.Oxygen doping reduces the oxidation driving force of the coating.With the increase of oxygen content,the oxidation resistance of the coating increases gradually.AlCrNbSiON shows age hardening.Under normal temperature and high temperature(800?),the coatings with a small amount of oxygen(N₂/O₂=294/6)and a large amount of oxygen(N₂/O₂=282/18)show low wear rate.