Research On Online Hybrid Direct Writing Process Of Multi-component Metal Oxide Ceramics

In recent years,advanced ceramic materials have been widely used in various fields of industry due to their excellent mechanical properties and unique properties in terms of optics,electricity,magnetism,and biocompatibility.However,with the development of industry,single component ceramics with a simple structure are difficult to meet the application requirements with conflicting characteristics.Therefore,gradient ceramic materials with changes of composition and structure in a specific direction have attracted the attention of researchers.For the traditional manufacturing process,the limitation is that it is difficult to change the material composition,and the additive manufacturing technology with layered manufacturing characteristics can overcome this problem.The direct ink writing process based on ceramic slurry on-demand extrusion has significant advantages due to its simple manufacturing system and the ability to print high-solid ceramic slurry.Based on the above research background,this paper combines the manufacturing process of direct writing solid ceramics and the active microfluidic mixing process to design and optimize the additive manufacturing system with online mixing and direct ink writing,and conduct research on the process of manufacturing gradient ceramic bodies on this equipment.The main research contents are as follows:For the direct ink writing process of solid ceramics,zirconia toughened alumina ceramic（ZTA）slurries with different zirconia content are configured,and the printability is verified through rheological tests;Then,starting from the size control of a single ceramic deposition line,the pneumatic extrusion method is selected,according to the orthogonal experiment method,the extrusion air pressure has the greatest influence on the size of a single deposition line,followed by the printing speed,and the smallest influence is the height of the needle.According to this conclusion,the printing parameters of the ceramic slurry in four proportions when the diameter of the filament is 0.6mm are determined through experiments.On this basis,the printing of the ceramic solid green body is achieved by setting different line spacings and using a needle to scrape the surface.The maximum printing error in the height direction is measured to be 8.35%,and high precision is guaranteed in the length and width dimensions.The highest relative theoretical density of the sintered ceramic body obtained by the Archimedes method is 92.9%,which realizes the expectation of direct ink writing of the solid ceramic.At the same time,the fracture toughness of the sample is enhanced by zirconia,with the enhancement of zirconia,the fracture toughness of the 20wt%ZTA ceramic reaches 5.23MPa·m^1/2.The Vickers hardness of the ceramic body is affected by zirconia,and shows a downward trend as the content of zirconia increases.For the exploration of the microfluidic active mixing process,starting from the theory of Newtonian microfluidic mixing,the principle of’expanding the contact area to enhance diffusion and mixing’’was extended.According to this theory,the online mixing direct ink writing equipment suitable for ceramic slurry is designed and optimized.In the research of the mixing process,the slurry viscosity is fitted according to the Herschel-Bulkley model,and then the theoretical mixing uniform speed is calculated by the formula,and samples at different stirring shaft speeds are prepared.SEM observation shows that the zirconia particles are gradually distributed evenly with the increase of speed,and the mixing effect is best when the speed is 410rpm.In the study of the refueling delay of the mixing device,through color calibration and EDS line scanning,it is determined that the online mixing device needs to extrude a 420mm length of slurry line to complete the material change process.In the study of the accuracy and stability of the mixing device,the pure color alumina slurry and dark gray zirconia slurry are used to print ZTA ceramic bodies with different zirconia content.The color of the sample gradually darkens with the increase of zirconia content.In the XRD detection of the sample,the ratio of the peak areas of the two ceramics is found to be close to the set feed ratio.In the SEM observation of the sample at random four points,the number of zirconia particles in the same proportion sample is equivalent,and the particle distribution is uniform.In addition,the narrow mixing chamber of the mixing device also helps to reduce the appearance of agglomerates in the slurry.At the same time,as the viscosity of the slurry is reduced,the gaps in the green body are filled during printing,and the number of pores and cracks in the sample is reduced.The relative density of the four proportions of ceramic bodies has increased,fluctuating around 95%.The fracture toughness and Vickers hardness of the samples have also been improved.The fracture toughness of the sample with 30wt%zirconia content is 6.32±0.5Pa·m^1/2,and the Vickers hardness of the sample with 40wt%zirconia content is 1472.06HV,which is higher than the samples of the same proportion in Chapter 3.Based on the mixing process and direct ink writing process of the ceramic slurry,with UV light-assisted molding adopted,a ceramic sample with a gradient along the Z axis is realized by setting the buffer zone to discharge residual materials.The sample gradient is obvious in the microscopic observation,and the phenomenon of particle diffusion and mutual dissolution occurs at the boundary of the gradient,which transforms the step gradient into a gradual gradient,and avoids the damage of the ceramic body due to thermal expansion in the later sintering.