Fabrication And Investigation On Performance Of TiB₂ Based Films Deposited By Magnetron Sputtering

High requirements in service are needed for coating tools due to the fast development of high-speed,yet dry cutting.Titanium diboride?Ti B₂?film has attracted a lot of attention in recent years and has been widely used in industry due to its excellent electrical conductivity,high hardness,and high wear resistance.However,Ti B₂ film shows disadvantages of high residual stress,low oxidation resistance,and low fracture toughness,which limits its application.Focusing on the shortages of Ti B₂film in poor toughness,oxidation resistance,and high-temperature wear resistance,this thesis aims to study the fabrication and performance of Ti B₂ based films by magnetron sputtering.The mechanical properties,high-temperature wear resistance,and corrosion resistance of Ti B₂ films are enhanced via introducing nanocomposite or multilayer structures.The primary conclusions are summarized as followings:?1?Ti B_x films were prepared by Hi PIMS with varying pulse lengths.It was found that reducing the pulse length decreases the stoichiometric ratio x?i.e.atomic ratio B/Ti?of the Ti B_x.Thus,the Hi PIMS with short pulse length is used to control the stoichiometric ratio in the films.Under the condition of under-stoichiometric ratio?x<2?,Ti-B-N films with nc-Ti N and nc-Ti B₂nanocomposite microstructure were prepared by Hi PIMS with short pulse length?30?s?.Since the nanocomposite hardening effect and the inhibition of growth of soft and brittle phase a-BN,the Ti-B-N films exhibit excellent mechanical properties with a maximum hardness of 37.5 GPa.The plasma analysis technique was used to detect and analyze the plasma properties during the deposition of the Ti-B-N films.The growth mechanism of the nanocomposite microstructure was discussed as well.?2?DCMS-Ti B₂/Hi PIMS-Cr hybrid deposition was used to prepare Ti B₂/Cr nano-multilayer films with varying Cr interlayer thicknesses and deposition biases.The effects of multilayer structure and interface mixing on mechanical properties,high-temperature oxidation and tribology behavior of Ti B₂/Cr multilayer films were investigated.The results show that the introduction of a Cr metal layer with thicknesses of 2?5 nm improves toughness,adhesion strength,oxidation resistance,and high-temperature wear resistance of the Ti B₂ films.The Ti B₂/Cr multilayer films with Cr prepared at-200 V exhibit Cr/Ti B₂ interface mixing.Friction tests at RT?500°C indicate that both thickness and deposition bias of the Cr interlayers exhibit a slight impact on film friction coefficient.The friction coefficients at 500°C are lower than those at RT due to liquid lubrication induced by surface oxide B₂O₃.The Ti B₂/Cr multilayer films show higher wear resistance than that of Ti B₂ monolayer film,in which Ti B₂/Cr with 2 nm Cr interlayer deposited at-60 V and 0-200?s pulse length shows the Comparing with bias voltages of floating and-200 V?the high bias voltage causes both Cr/Ti B₂ interfacial mixing and formation of B-B bond?,the Ti B₂/Cr films with Cr interlayer prepared at the bias of-60 V shows a superior wear resistance at RT?500°C.?3?Since PVD Ti B₂ films exhibit a dense columnar microstructure and excellent electrical conductivity,Hi PIMS-Hf/DCMS-Ti B₂ hybrid deposition was used to deposit Hf/Ti B₂ multilayer films with a accumulated thickness of?3?m?Ti B₂ interlayer thickness was fixed at?20 nm?on AZ91D magnesium alloy substrates.The introduction of Ti B₂interlayers with a fine-grained and dense structure interrupt the continuous growth of the columnar Hf films.This prevents the diffusion of the corrosive medium to the AZ91D substrates effectively.The corrosion potential of the Hf/Ti B₂ multilayer films is nearly equal to the AZ91D substrates.Thus,the galvanic corrosion between film and substrate is limited.The corrosion current densities of the Hf/Ti B₂ multilayer films is significantly lower than that of the bare AZ91D substrate,showing excellent protection of the Hf/Ti B₂ against the corrosion.The 48 h neutral salt spray tests show that increasing the number of Hf interlayers helps to improve the corrosion resistance of the multilayer films.The Hf/Ti B₂ multilayer film with 5Hf interlayers possesses a corrosion current density of?8×10^-8 A/cm² and a corrosion area ratio of 0.2%after the salt spray tests,providing the most outstanding corrosion resistance for the AZ91D substrate against corrosion.The above results help to develop a widespread application of the magnesium alloys.