Design, Fabrication And Application Of Multilayered Ceramic Nozzles

According to the wear characteristics of the ceramic nozzles and the outstanding properties of multilayer ceramic composites,idea of layered structures was used to the design and prepare of ceramic nozzles.The design theory and methods of multilayer ceramic nozzles were proposed.The multilayer ceramic nozzles have been developed.The mechanical properties at the surface layer of these layered composites were measured,the microstructure was examined,and the wear behaviors of the multilayered nozzles were investigated.The erosion wear mechanisms of the.multilayer ceramic nozzles were investigated.Combination the erosive wear characteristics and stress state of ceramic nozzles,the aim of the design for the multilayer ceramic nozzles was proposed, and the physical models of multilayer ceramic nozzles with different structural parameters were established.The multilayer ceramic nozzles composites systems Al₂O₃/(W,Ti)C+Al₂O₃/TiC(AWT+AT) were determined.The value of the residual stress inside the multilayer nozzles during fabricating process was calculated by means of the finite element method(FEM), the results show that avail compressive stress fields are found to exist in the entry and exit region of dry sand blasting nozzles and coal water slurry(CWS) nozzles.The influence of structural parameters of the multilayer ceramic nozzles was studied.The theoretical optimal value of the dry sand blasting nozzles was:the best thickness ratio of 1～2 and optimal layer number of 3.The erosive wear characteristics of CWS nozzles were different from that of the dry sand blasting nozzles.The high working conditions temperature of CWS nozzles lead to the high temperature gradient and thermal stress,the thermal stress at the exit surfaces of the ceramic CWS nozzle were higher than that of other part of the nozzle.The temperature gradient and thermal stress and its distribution of the multilayer ceramic CWS nozzles in the process were analyzed. Relationship between stresses distribution and layer thickness ratio were obtained,the theoretical value of optimal layer thickness ratio should be less than or equal to 0.2.AWT+AT multilayered ceramic nozzle composites were produced by hot-pressing.The mechanical properties at the surface layer of these layered composites were measured.Results showed that the mechanical properties of the multilayer ceramic nozzle composite were greatly improved in comparison with that of the homologous nozzle composite.The surface fracture toughness of the LN0.1 multilayer nozzle composite is 10.46MPa·m^1/2,the surface Vickers hardness is 22.184GPa.While the fracture toughness of the AWT homogeneous nozzle composite is 4.8MPa·m^1/2,the Vickers hardness is 19.943GPa.The thickness ratio has an important influence over the mechanical properties of nozzle composite.In the framework of the preparation of permit,with the smaller thickness ratio,the surface composites have better mechanical properties.With the rise of layer number,the mechanical properties of surface composites have also increased,but the layer number has less effect on the mechanical properties.The microstructure analysis of AWT+AT multilayered ceramic nozzle composites showed that the thickness of each layer is uniform distribution,the layer interface is clear,the combination of layers is good.The compressive residual stresses are benefit for the increase of hardness and the fracture toughness at the surface layer of the multilayer ceramic nozzle composites.The wear behaviors of the multilayered nozzles were investigated,the cumulative mass loss,the inner diameter variation,the worn inner bore profile and the erosion rates are system studied.The results have shown that the multilayer ceramic nozzles have superior erosion resistance to that of the homogeneous nozzle under same test conditions.The wear rate of LN2 multilayered ceramic nozzles reduced 27.14%than that of the homogeneous. The thickness ratio affects the wear behaviors of the multilayer ceramic nozzles. The erosion wear resistance of the layered nozzles was influenced by the thickness ratio among constituent layers.The layered nozzles with high thickness ratio showed the low erosion wear rate.And the layered nozzles with low layer number showed the low erosion wear rate.The wear behaviors of the multilayered nozzles were compared with homogenous nozzle.Results showed that the multilayered nozzles had superior erosion wear resistance to that of the homogenous nozzle.The wear rate of LN0.1 multilayered ceramic nozzles reduced 69.01%than that of the homogeneous.The thermal stress that exist in the exit region of the multilayered ceramic nozzles are significantly relieved,does not appear the hot crack as that of homogeneous ceramic nozzle export situation.In the framework of the preparation of permit,the layered nozzles with low thickness ratio showed the low erosion wear rate.The multilayered ceramic nozzles have superior erosion wear resistance to that of the homogenous nozzle.The mechanism responsible was explained as the formation of compressive residual stresses in nozzle entry region in fabrication process of the layered ceramic nozzles,which may partially counteract the tensile stresses resulting from external loadings,and leads to an improvement of erosion wear resistance.Also the surface Vickers hardness of multilayered ceramic nozzle was greatly improved compared with that of the homogenous nozzles.Therefore,it is indicated that multilayered structures in ceramic nozzles is an effective way to improve the erosion wear resistance of the homogenous nozzles.