Study On Densification Theory Of Ceramic Tool Material By Ultrasonic Hot Pressing Sintering

In order to improve the densification of ceramic cutting tool materials,and improve their comprehensive mechanical properties,in this research,based on the vacuum hot pressing sintering,the ultrasonic wave is applied as the assistant sintering,and the influence of ultrasonic wave on the wettability between the metal phase and the ceramic phase is studied in theory.At the same time,the densification of the initial,middle and later stages of liquid-phase sintering under the action of ultrasonic are discussed.Finally,the influence of sintering parameters on the densification of liquid-phase sintering are revealed by MATLAB simulation.The specific research contents and results are as follows:(1)In this research,the origin,research purpose and significance of ceramic cutting tools are briefly described.The research status of wettability and compactness of hot pressing sintering domestic and abroad are reviewed.In this thesis,the research status,advantages and disadvantages of the densification process of ceramic cutting tools are summarized,the theory of hot pressing sintering is expounded.The producing principle,energy and effect of ultrasonic wave are described.(2)Under the action of ultrasonic wave,according to the principle of liquid phase sintering,wettability of liquid phase sintering and the principle of minimum energy,the equation of wettability angle is deduced,and the influence of ultrasonic heat effect on wettability angle and the change of wettability angle under the condition of applying ultrasonic wave are explored.(3)According to the mechanism of porosity,the relationship between porosity and densification,and the effect of ultrasonic wave on porosity,the structure model of porosity is established.According to the thermal effect of ultrasonic,the change of liquid viscosity with temperature is studied;the influence of ultrasonic thermal effect on surface energy is explored from the relationship among the Gibbs free energy,temperature change and specific surface energy.According to the principle of liquid-phase sintering,the stress model of particles in liquid-phase sintering is established,and the initial densification equation of sintering system is obtained.According to the sintering situation of Ti B₂-Ni ceramic system,the relative densification values under different ultrasonic frequency and liquid viscosity are calculated from the initial densification equation,and it is concluded that increasing ultrasonic frequency is helpful to densification of materials in the initial stage of sintering,the relative density of sintered materials increases with the decrease of liquid viscosity.(4)Based on the principle of powder sintering and the model of solid-liquid phase evolution,the densification equation in the middle and later stage of liquid-phase sintering is derived.From the curve of relative density change under the condition of applying and not applying ultrasonic wave,it can be seen that with the prolongation of holding time,the relative density of sintered material increases gradually,and the densification rate of applying ultrasonic wave is faster than that of not applying ultrasonic wave.The ultrasonic wave affects the densification of ceramic cutting tool material,the densification rate accelerates the densification process of ceramic cutting tool materials.(5)Through the three-dimensional plot of MATLAB simulation,it can be seen that the relative density of sintered materials is affected by the holding time,grain size,liquid viscosity,sintering pressure,sintering temperature and ultrasonic frequency.With the increase of holding time,sintering pressure and ultrasonic frequency,the relative density is larger.The smaller the grain size and liquid viscosity,the more conducive to the densification of sintered materials.When the holding time is fixed,the sintering temperature keeps rising and the relative density is basically unchanged.