【作者】 员冬玲；

【导师】 邓建新；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 根据喷嘴的冲蚀磨损特性,结合层状复合陶瓷材料的优异性能,将层状复合结构的概念引入陶瓷喷嘴的设计及制造中,提出了层状复合陶瓷喷嘴的设计理论和方法,研制开发出层状复合陶瓷喷嘴,系统研究了层状复合陶瓷喷嘴的物理力学性能、微观结构以及冲蚀磨损特性等,探索了其冲蚀磨损机理。针对陶瓷喷嘴冲蚀磨损特点和应力状态,提出了层状复合陶瓷喷嘴的设计目标,建立了多种层状复合陶瓷喷嘴物理模型,并确定了其材料体系,即:Al₂O₃/（W,Ti）C+Al₂O₃/TiC（简称AWT+AT）。采用有限元法深入分析了层状复合陶瓷喷砂嘴和水煤浆喷嘴制备过程中形成的残余应力及其分布规律,结果表明:层状复合陶瓷喷砂嘴和水煤浆喷嘴在其入口和出口表面层均产生了残余压应力。研究了结构参数对层状复合陶瓷喷嘴内残余应力的影响,通过理论分析初步确定了AWT+AT层状复合陶瓷喷砂嘴的最佳结构参数:最佳层厚比为1～2,最佳层数为3层。陶瓷水煤浆喷嘴的冲蚀磨损具有其独特性,由于其工作环境温度较高,使得喷嘴使用过程中内部存在较大的温差和温度梯度并导致其出口端面存在较大的热应力。采用热-应力耦合方法对层状复合陶瓷水煤浆喷嘴使用过程中的温度梯度和热应力及其分布规律进行了分析,结果表明:与均质陶瓷水煤浆喷嘴相比,通过调节结构参数层状复合陶瓷水煤浆喷嘴内部的温度梯度有所降低,其出口端面热应力得到明显的缓解。研究了层状复合陶瓷水煤浆喷嘴的层厚比对其热应力的影响,通过理论分析得出层状复合陶瓷水煤浆喷嘴最佳层厚比应小于等于0.2。采用热压烧结工艺成功制备出多种AWT+AT层状复合陶瓷喷嘴材料,并对其性能进行了测试,研究表明:层状复合陶瓷材料比均质陶瓷材料力学性能有显著提高,LN0.1（层厚比为0.1）层状复合陶瓷喷嘴材料表面层的断裂韧性值为10.46MPa·m^1/2,硬度值为22.184GPa;而均质陶瓷喷嘴材料AWT的断裂韧性值为4.8MPa·m^1/2,硬度值为19.943GPa。层状复合陶瓷喷嘴材料的层厚比对材料力学性能有重要影响,其变化规律为:在制备工艺允许范围内,层厚比越小,层状复合陶瓷材料表面层的力学性能越好。随着层数的增加,表层材料的力学性能也有提高,但层数对材料力学性能影响较小。对AWT+AT层状复合陶瓷喷嘴材料显微结构分析表明,材料层界面清晰可见;各层材料的厚度较为均匀一致,厚度相差不大;层与层间结合情况良好。层状复合陶瓷喷嘴材料表层的残余应力是导致其综合力学性能提高的主要原因。对陶瓷喷砂嘴冲蚀后的重量损失、喷嘴内径随时间的变化、喷嘴内孔轮廓变化和体积冲蚀磨损率等进行了系统试验研究。结果表明:层状复合陶瓷喷砂嘴的抗冲蚀磨损性能比均质喷砂嘴有显著提高。LN2（层厚比为2）层状复合陶瓷喷砂嘴的体积冲蚀磨损率比均质陶瓷喷砂嘴AWT的体积冲蚀磨损率降低了27.14%。层状复合陶瓷喷砂嘴的结构参数对其冲蚀磨损率起着重要的作用:随着层厚比的增加,其冲蚀磨损率逐渐减小。随着层数的增加,其冲蚀磨损率逐渐增加。对层状复合陶瓷水煤浆喷嘴在水煤浆燃烧锅炉内的使用情况进行了现场冲蚀磨损试验研究,结果表明:层状复合陶瓷水煤浆喷嘴的抗冲蚀磨损性能比均质陶瓷水煤浆喷嘴有显著提高。LN0.1（层厚比为0.1）层状复合陶瓷水煤浆喷嘴的体积冲蚀磨损率比AWT均质陶瓷水煤浆喷嘴的体积冲蚀磨损率降低了69.01%。层状复合陶瓷水煤浆喷嘴出口端面热应力得到明显的缓解,没有出现均质陶瓷水煤浆喷嘴出口那样的热崩裂现象。层厚比对层状复合陶瓷水煤浆喷嘴冲蚀率有重要影响,在制备工艺允许范围内,层厚比越小,其冲蚀磨损率越低。与均质陶瓷喷嘴相比,层状复合陶瓷喷嘴的抗冲蚀磨损性能有显著提高,主要是由于层状复合陶瓷喷嘴的采用了层状结构,制备过程中在其表面层形成了有利的残余压应力,从而缓解了喷嘴实际使用过程中的高应力状态。另外,层状复合陶瓷喷嘴表层材料的硬度和断裂韧性比均质陶瓷喷嘴的硬度和断裂韧性显著提高。因此层状复合陶瓷喷嘴应力状态的改善和力学性能的提高是造成其抗冲蚀能力显著高于均质陶瓷喷嘴的主要原因。更多还原

【Abstract】 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.更多还原