Microstructure Analysis And Performance Optimization Design Of Self-lubricating Ceramic Tools

Using computer technology to simulate the microstructure evolution in the sintering process of self-lubricating ceramic tools can reveal the sintering mechanism and optimize the experimental parameters,which is of great significance to guide the design and development of new self-lubricating ceramic tools.In this thesis,based on MC（Monte Carlo）method,the microstructure changes of self-lubricating ceramic cutting tools during sintering were studied,and the best material composition and sintering conditions were obtained.Based on the finite element method,the effect of residual thermal stress field on improving the mechanical properties of cutting tools is studied,and the reliability of MC method is verified.Based on MC method,Al₂O₃/SiC/h-BN@Al₂O₃ self-lubricating ceramic tool was designed and developed,and the experimental preparation and characterization were carried out,which provided a new method for the design and development of self-lubricating ceramic tool.Based on MC method,the microstructure model of Al₂O₃/TiC/TiB₂ ceramic tool material was built with Al₂O₃/TiB₂ ceramic tool material as the matrix,and a model building method of coated solid lubricant h-BN@Al₂O₃ was designed,and then the microstructure model of Al₂O₃/TiC/TiB₂/h-BN@Al₂O₃ self-lubricating ceramic tool material was established.The effects of TiB₂,h-BN@Al₂O₃ content,sintering temperature and sintering pressure on the microstructure of the tool during sintering were studied,and the optimal experimental parameters were obtained:the optimal addition of TiB₂ and h-BN@Al₂O₃ was 10 vol%and 5 vol%respectively,and the optimal sintering temperature and pressure were 1650℃ and 32 MPa.According to the microstructure model of each component tool obtained by MC method,the finite element models of Al₂O₃/TiC ceramic tool,Al₂O₃/TiC/TiB₂ ceramic tool and Al₂O₃/TiC/TiB₂/h-BN@Al₂O₃ self-lubricating ceramic tool materials with different solid lubricant contents were established based on finite element method.The finite element method was used to simulate the residual thermal stress field of each ceramic tool during the cooling process,and the influence of different tool material composition and different solid lubricant content on the residual thermal stress field of the tool model was studied.It was concluded that the microstructure of Al₂O₃/TiC/10vol%TiB₂/5 vol%h-BN@Al₂O₃ self-lubricating ceramic tool had a reasonable maximum residual tensile and compressive stress and the residual compressive stress was connected in a flaky distribution state.It is concluded that the mechanism of toughening ceramic tools by residual stress is that the existence of residual thermal stress field greatly increases the amplitude and distribution scale of residual tensile stress in the microstructure of the tool under external force,promotes the closing of the micro-crack tip,and is conducive to improving the mechanical properties of self-lubricating ceramic tools.On the basis of the above research,Al₂O₃/SiC/h-BN@Al₂O₃ self-lubricating ceramic tool material was designed with Al₂O₃ as matrix,SiC as reinforcing phase and h-BN@Al₂O₃ as solid lubricant.Based on MC method,the material model of Al₂O₃/SiC/h-BN@Al₂O₃ self-lubricating ceramic cutting tool was built and the sintering process was simulated.The effects of particle size and content of reinforcing phase SiC,content of coated solid lubricant h-BN@Al₂O₃,sintering pressure and sintering temperature on the microstructure of cutting tool were studied.The optimum composition parameters and sintering parameters were obtained:the optimum amount and particle size of SiC were 3vol%and 0.05μm,the optimum amount of h-BN@Al₂O₃ was 5 vol%,and the optimum sintering temperature and pressure were 1650℃ and 30 MPa,respectively.Al₂O₃/SiC/h-BN@Al₂O₃ self-lubricating ceramic tool materials were prepared by using the above parameters,and the mechanical properties and microstructure of the tool materials were characterized.The bending strength,fracture toughness and Vickers hardness of the Al₂O₃/3 vol%SiC/5 vol%h-BN@Al₂O₃ self-lubricating ceramic cutting tools are 722.42MPa,6.5 MPa·m^1/2 and 20.65 GPa,respectively.The microstructure of the tool has uniform grain size and good compactness.The experiment proves that the MC method is effective in tool material design,which greatly shortens the tool material design cycle and improves the material performance.