Research On The Mechanical Impact And Thermal Shock Resistance Of Ceramic Cutting Tool Materials At The Microscale

With the development of production technology and new materials,the requirements for cutting processes have become increasingly stringent,demanding cutting tools with superior performance for high-speed cutting operations.During high-speed intermittent turning or high-speed milling,ceramic tools are susceptible to mechanical and thermal shocks,leading to tool failure.Therefore,in order to ensure the tool’s service life and reliability,ceramic tool materials need to possess excellent resistance to mechanical impact and thermal shock.In this study,Ti B₂-B₄C composite ceramic material was selected as the research object.The combination of finite element simulation and experimental research was employed to analyze the mechanical impact and thermal shock processes of the material.The mechanical properties and microstructure of Ti B₂-B₄C were investigated,and pendulum impact tests and thermal shock tests were conducted to evaluate the influence of different B₄C volume fractions on the resistance to mechanical impact and thermal shock of Ti B₂-B₄C ceramics.1)In this study,a two-dimensional Voronoi grid microstructure model of the ceramic tool material was established using ABAQUS software.The fracture path,fracture morphology,and propagation and dissipation of stress waves during the impact process were analyzed.The results showed that under the impact condition,when the B₄C content was 20 vol%,the crack propagation consumed the most energy,and the crack initiation location and propagation path were influenced by the B₄C grain content and distribution.Due to the differences in properties such as density and Poisson’s ratio,stress waves underwent reflection and transmission at the interfaces,resulting in energy dispersion and changes in the propagation path of the shock wave.Reducing internal defects and pores and reducing grain size can improve the material’s resistance to impact.2)A two-dimensional thermal shock model was established,and temperature-displacement coupled numerical simulations were conducted to analyze the transient temperature field,thermal stress field,and the effects of heat transfer coefficient and water immersion orientation during rapid cooling.The results showed that the internal temperature distribution of the model was non-uniform.Due to the different rates of surface heat transfer and internal heat conduction,a temperature gradient was formed from the inside to the outside of the model.The temperature fluctuations or large temperature differences could cause stress concentration,leading to stress concentration phenomena on the surface and grain boundaries.Increasing the heat transfer coefficient resulted in higher thermal stress and deformation on the material surface,making it more prone to thermal stress concentration and surface cracking.3)Ti B₂-B₄C ceramic tool materials were prepared using plasma sintering technology.The sintering temperature and holding time were optimized using a single-factor variable method.Ti B₂-B₄C materials with different volume fractions of the second phase were sintered under the optimized sintering process parameters.The effects of sintering temperature,holding time,and volume fraction of the reinforcing phase on the mechanical properties and microstructure of the materials were studied.The results showed that when the sintering temperature was 1700℃,the holding time was 5 minutes,and the volume fraction of the reinforcing phase B4C was 20%,the ceramic tool material exhibited optimal comprehensive performance.The fracture toughness,hardness,and flexural strength were 6.8 MPa·m1/2,22.8 GPa,and 598 MPa,respectively.4)In this study,the impact resistance of the material was evaluated using a cantilever beam pendulum impact test,and the thermal shock resistance of the material was tested using the quenching-strength decay method.The results showed that when the volume fraction of B₄C exceeded 20%,the impact strength of the material decreased.The material with a volume fraction of 20%exhibited the optimal impact strength of 19.13 J/m.The influence of the material’s microstructure and mechanical properties on macroscopic impact resistance was analyzed.The quenching-strength decay method involved quenching the prepared ceramic samples in water and then testing the residual flexural strength of the ceramic material.The results showed that when the volume fraction of the second phase B₄C was 20%,the material exhibited the best thermal shock resistance,with a critical temperature difference of approximately 500℃.