Study On The Preparation And Properties Of TiAlN-based Coatings Deposited By Arc Ion Plating

Owing to their superior mechanical properties and thermal stability,transition metal nitride coatings have been widely used in the field of material processing to improve cutting performance and prolong the service life of cutting tools.Among them,Al Ti N with high hardness and excellent oxidation resistance is the most widely used tool coating material.However,with the development of high-speed and dry cutting,especially when machining some difficult-to-machine materials(e.g.,Ti alloys),the cutting edge temperature of the tool can reach more than 1000°C,which exceeds the service temperature of Al Ti N coating.Therefore,the search of high-performance coatings with excellent mechanical properties and wear resistance via improving Al Ti N is of great significance for broadening the use of coated tools.To serve in high-speed machining of titanium alloys,this work combines the optimization of deposition technology and material modification methods to develop Al Ti N-based coating materials,which possess better surface quality and excellent mechanical and wear resistance.First,the pulsed arc preparation process for Al Ti N coatings was optimized by varying the frequency and pulse width of the pulsed arc.Then,on the basis of optimized pulse deposition parameters,Al TiN/Cr N nano-multilayer coatings with different sublayer thicknesses were prepared by changing the currents of Al Ti target and Cr target,and then the influence of sublayer thickness on the coating structure and properties was studied.Finally,the Al Ti XN/Al Ti N(X=Cr,Si)coatings were prepared,and their mechanical properties and wear resistance as well as the milling performance of coated cutters in the high-speed machining of titanium alloy(Ti6Al4V)were investigated.The primary research results obtained in this work are as follows.1)Al Ti N coatings have single-phase face-centered cubic structures and similar chemical compositions at different frequencies.However,the frequency of the pulsed target current significantly affects the mechanical properties of the coating.With the increase of the frequency,the residual stress of the coatings increase leading to the decrease of the adhesion strength.At the same time,the increase of residual stress contributes to the increase of coating hardness and elastic modulus.In addition,Al Ti N coatings exhibit similar friction and wear properties at different frequencies.The Al Ti N coatings also have a single-phase face-centered cubic structure at different duty ratios and exhibit typical columnar grain growth morphology.With the increase of duty ratio,the adhesion strength of Al TiN coatings as well as hardness and elastic modulus increase.In addition,the room-temperature friction test shows that the minimum friction coefficient and wear rate are exhibited when the duty ratio is 50%,and the wear resistance is excellent.2)The thickness of Al Ti N and Cr N modulation layers increase with increasing Al Ti target and Cr target current,respectively.In addition,Al Ti N/Cr N multilayer coatings grow epitaxially under different Al Ti/Cr target currents and have a single-phase face-centered cubic structure.When the Cr target current is increased,the adhesion and the surface roughness of the Al Ti N/Cr N multilayer coatings increase,but the hardness decreases.When the Al Ti target current is increased,the hardness of the Al Ti N/Cr N multilayer coating increases.Al TiN/Cr N multilayer coatings have better wear resistance than Al Ti N single layer coatings.With the increase of Cr target current,the friction coefficient of the coating decreases slightly.When increasing Al Ti target current,the hardness of Al Ti N/Cr N coatings increase.Al Ti N/Cr N multi-layer coatings have superior oxidation resistance than Al TiN single-layer coatings.In addition,with the increase of the Cr target current,the oxidation resistance of the multilayer coating increases slightly.Because of the Al Ti target has little effect on the chemical composition of the nano-multilayer coatings,there is no significant difference in the oxidation resistance.3)The addition of Si and Cr can increase the hardness of Al Ti N coating.The hardness of Al Ti Si N/Al Ti N coating is 32.74±1.21 GPa.During the wear test at 600°C,the friction coefficient of the three coatings differs little,but the wear rate of the Al Ti N coating is 3.95×10~-55 mm~3/N·m.Adhesion wear and abrasive wear were the main wear mechanisms of the Al TiN coating.However,adhesion wear and oxidation wear were the main mechanisms for the Al Ti Cr N/Al Ti N and the Al TiSi N/Al TiN coatings.The milling lifetime of the coating tools is Al Ti N<Al Ti Cr N/Al Ti N<Al Ti Si N/Al Ti N.The wear mechanism of the Al Ti N coated tool is adhesion wear and oxidation wear.The wear mechanism of Al Ti Cr N/Al Ti N coated tool is adhesion wear,abrasive wear and oxidation wear.The adhesion wear,oxidation wear and boundary wear produce the wear of the Al Ti Si N/Al Ti N coatedtools.