Research On Microwave Sintering Preparation And Properties Of Bronze-Based Diamond Grinding Wheels For SiC_f/SiC Grinding

Continuous fiber reinforced ceramic matrix composites have a series of advantages such as high melting point,low density,high hardness,corrosion resistance,ablation resistance,and oxidation resistance,being listed as the developing focus of a new generation of high-temperature thermal structural materials,having great application prospects in aerospace,energy and other fields.However,the precision grinding of silicon carbide fiber-reinforced silicon carbide ceramic matrix（SiC_f/SiC）composites still has many challenges.The main challenges are reflected in:（1）the grinding mechanism of SiC_f/SiC composites is still unclear,（2）lacking a stable and reliable grinding wheel of grinding processing of SiC_f/SiC composites and its preparation theory.To solve those challenges above,this paper starts with the grinding load mode of SiC_f/SiC composites,studies the mechanism of single diamond grinding SiC _f/SiC composites,then explores the relationship between load and morphology and consequently puts forward a need of grinding wheel of grinding processing of SiC_f/SiC composites.In addition,this paper adopts scientific methods such as first principles calculation,numerical simulation and experiment,and conducts research on formula configuration mechanism,grinding wheel microwave preparation process and grinding mechanism from bottom to top.And the main contents include the following four aspects:（1）To determine the optimal grinding wheel material parameters for grinding SiC_f/SiC composites,a hybrid cohesion model and a diamond grinding load mode model were established in this paper,and a single-grain grinding SiC_f/SiC composite’s study was carried out.The results show that the removal mechanism of SiC _f/SiC composites is the plastic removal and brittleness removal of the matrix material,the pull-out,deflection and fracture of the fiber s,fiber longitudinal and lateral instability deformation and fiber fracturing.There is a close relationship between the load mode and the grinding surface topography.A good grinding surface morphology is obtained as the ratio of normal force to tangential force is 0.3.The tangential strength of the interface is ranging from 217.54MPa to 249.41MPa as the grinding speed is 20m/s.（2）Based on the first principles calculation method,the numerical simulation of the interface between copper matrix and diam ond was carried out in this study,and the improvement mechanism of the interface properties between copper matrix and diamond with different formulations was explained based on the microscopic mechanism and the experimentally determined mechanical propert ies verify the accuracy of the trend of the calculated results.The mechanism of adding Cu₆Sn₅ to improve the interface properties between bronze and diamond is that the p orbital of Sn atom and the p orbital of C atom are hybridized,and the mechanism of using transition elements to improve the interface properties between bronze and diamond is that the p orbital electrons of transition elements and the p orbital electrons of C elements carry out p-p hybridization and transition element d orbital and p orbital electrons of C element form p-d hybridization.（3）In this study,the uniform grinding wheel segments be prepared by microwave and hot pressing process.During the preparing process of the studied grinding wheel,to explain the microwave heating and h eating process of multilayer copper matrix and diamond,the dielectric property of copper matrix and diamond composite was calculated by establishing a molecular dynamics model based on the first principle calculation method.Based on the dielectric proper ty of the material,the temperature rise of the multi-layer copper matrix and diamond microwave heating was numerically simulated,and the optimized solution of microwave heating uniformity was discussed.The results show that the uniformity of material he ating in the microwave cavity and the uniformity of the electric field have an opposite trend,and the optimal layered arrangement is to place the high dielectric property material layer in the middle layer.In addition,the shape of the microwave cavity a nd the arrangement of the microwave ports also affect the uniformity of microwave heating.（4）A grinding experiment was used to study the grinding of SiC _f/SiC composites with bronze-based diamond grinding wheels,and several indicators for evaluating grinding performance are proposed.Based on the realistic scene of multi-particle grinding of SiC_f/SiC composites,a stochastic model of three-dimensional distribution of abrasive particles is established,and according to the superposition causes of grinding topography during multi-particle grinding,the correction factor for distance between abrasive grains,the correction factor for residual stress and the correction factor for cavity are proposed.The research results show that the prepared grinding wheel adopts the optimized hot pressing/microwave process,which produces a multi-layer structure with controllable and adjustable properties,thereby resulting a better SiC_f/SiC composites grinding surface morphology and preliminarily meeting the requirements of precision grinding.The grinding surface roughness can be stably higher than the actual measurement results,and the excess value does not exceed 26.0%.