Thermodynamic Calculation And Experimental Research On Ti-Al-Si-C-N Coating System

With the increasing requirement of cutting tools in machining industry,uncoated cemented carbide cutting tools are gradually replaced by coated cutting tools.The CVD(Chemical Vapor Deposition)technology has become an important technology to prepare high-performance hard coatings.The traditional binary Ti C,Ti N and ternary Ti(C,N)are the most commonly used coatings,but the hardness and oxidation resistance of the above coatings are poor at high temperature.The addition of Si and Al elements can effectively improve the hardness and oxidation resistance of the coatings.More elements added produces a multiphase and complex system,which leads to a difficult situation on composition design and parameter selection in preparing process.In recent years,CALPHAD(CALculation of PHAse Diagrams)method has been widely used in the study of multi-component materials.In order to comprehensively improve the performance of Ti-base coatings by designing coatings composition and optimizing deposition parameters reasonably,it is important to obtain accurate thermodynamic database for multi-component coatings system.In this thesis,the thermodynamic database of Ti-Al-Si-C-N multi-component system is established based on experimental information by using CALPHAD method.The main work is as follows:(1)Ten binary systems Ti-Si,Ti-C,Ti-N,Ti-Al,Si-C,Si-C,Al-Si,Si-C,Si-N and C-N in Ti-Al-Si-C-N system are critically reviewed and calculated.The thermodynamic parameters of all binary systems used in present work are determined.(2)The thermodynamic and phase diagrams information of Ti-Si-C,Ti-Al-N,Ti-Al-C and Ti-Al-Si systems were evaluated.Thermodynamic optimization is finished for the above systems and more reasonable thermodynamic descriptions are given.The liquid surface projections,isothermal sections,vertical sections,solubility,heat capacity and the reaction temperature of invariable reactions are calculated.The calculated results are in good agreement with the experimental data.(3)In order to satisfy the consistency of modeling parameters and get a set of thermodynamic database systematically,slight adjustments are completed for the Ti-Si-N,Al-Si-C and Al-C-N systems in this work.The calculated phase equilibria and thermodynamic properties can well reproduce the experimental data.(4)A self-consistent thermodynamic database for Ti-Al-Si-C-N system is constructed based on the thermodynamic parameters obtained in this work.The CVD phase diagrams of Ti Si CN and Ti Al Si N coating systems are calculated.The phase compositions and element fractions of coatings are predicted through thermodynamic calculations.Two multicomponent coatings,Ti Si CN and Ti Al Si N,are deposited on WC-Co substrate using LPCVD(Low Pressure Chemical Vapor Deposition)technology.The microscopic morphology,phase structure,and element fractions of the coating are thoroughly studied by SEM(Scanning electron microscope),EDS(Energy Dispersive Spectroscopy),and XRD(X-Ray Diffraction)methods.A detailed comparison between theoretical predictions and experimental results is discussed and a good self-consistency is shown in the comparison.