Study On The Wear Resistance And Cutting Performance Of TiAlSiN Hard Coatings

The development of advanced machining techniques and the widespread application of difficult-to-process materials give rise to the increasing requirement for the protective coatings on cutting tools.In this thesis,the TiAlSiN nanocomposite coating with high hardness and abrasion resistance at high temperature were deposited for the potential application in superalloy machining by pulsed arc ion plating?p-AIP?via optimizing the coating process parameters.Furthermore,the influence of Si content on the wear mechanism of coated tools on cutting the superalloy was investigated.Finally,to inhibit the crack propagation of the coating during cutting materials,the TiAlN/AlTiN and TiAlN/TiAlSiN nano-multilayer coatings were deposited,which combine the characteristics of TiAlN coating with low thermal conductivity and TiAlSiN coating with high hardness and excellent thermal stability.The main research results were as follows.?1?Ti_0.45Al_0.45Si_0.10N nanocomposite coatings with various bias voltage were deposited by p-AIP and investigated concerning structure,mechanical and tribological properties.With the increase of bias voltage from-60 to-150 V,the hardness,elastic modulus,adhesion and residual stress of the Ti_0.45Al_0.45Si_0.10N coatings reveal first increase and then decrease.With a bias voltage is-90 V,Ti_0.45Al_0.45Si_0.10N coating obtains the best mechanical properties involving hardness and adhesion.Correspondingly,the Ti_0.45Al_0.45Si_0.10N coating deposited at-90V shows the best wear resistance at both room temperature and of 600?,with a wear rate of 7.0×10^-7 mm³·N^-1·m^-1and 19.6×10^-7 mm³·N^-1·m^-1,respectively.Besides,Ti_0.45Al_0.45Si_0.10N coatings exhibit a lower friction coefficient at 600°C than room temperature.?2?The microstructure,mechanical and tribological properties of TiAlSiN with various Si contents,as well as the wear mechanism of coated tools after cutting superalloy,were systematically studied.The results showed that the TiAlN coating a had a columnar crystal structure.With the addition of the Si element,the"droplets"on the surface of the film decreased,and the grain structure was refined.The Ti_0.45Al_0.45Si_0.10N coating obtained the best mechanical properties.Its adhesion strength and indentation hardness is>100 N and³5.0GPa,respectively.Alloying with Si can greatly improve the oxidation resistance of TiAlN coatings at elevated temperature,while further increasing Si content has a negligible effect.The average friction coefficient at 800°C for Ti_0.50Al_0.50N,Ti_0.40Al_0.40Si_0.20N,and Ti_0.45Al_0.45Si_0.10N was 0.60,0.43 and 0.52,respectively.Moreover,the worn mechanism of coatings includes abrasive wear,adhesive wear,and oxidation wear.For cutting performance,the lifetimes of coated inserts during turning In718 were as listed:Ti_0.50Al_0.50N<Ti_0.40Al_0.40Si_0.20N<Ti_0.45Al_0.45Si_0.10N.The primary wear mechanisms of the three coated tools were adhesive,oxidation and abrasive wear.?3?In order to further improve the cutting performance of the coatings,the TiAlN/AlTiN and TiAlN/TiAlSiN nano-multilayers were deposited to inhibit the crack propagation of the coatings.The results showed that the modulation period of TiAlN/AlTiN and TiAlN/TiAlSiN coatings were 19.47 nm and 18.93 nm,respectively.As compared to the TiAlSiN monolithic coating,the nano-multilayer structure effectively improved the mechanical properties of the coatings.The friction coefficient of nano-multilayer at 800?is lower than that at room temperature,but the wear rate is higher.After turning superalloy?In718?,the cutting distance of nano-multilayer coatings is longer than that of single layer coatings.The lifetime sequence is Ti_0.50Al_0.50N<Ti_0.40Al_0.40Si_0.20N<Ti_0.45Al_0.45Si_0.10N<TiAlN/AlTiN<TiAlN/TiAlSiN.The wear mechanisms of TiAlN/AlTiN and TiAlN/TiAlSiN coated tools are adhesive wear,abrasive wear,and oxidation wear.The breakage of the rake face is the TiAlN/AlTiN coated tool failure criterion.Because of the excellent mechanical and wear resistance properties at high temperatures,the TiAlN/TiAlSiN nano-multilayer coated tool exhibit the longest service life.