【作者】 陈常连；

【导师】 张联盟；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2005， 硕士

【摘要】 放电等离子烧结作为一种制备材料的新技术,可以对多种新型材料实现快速烧结,并可最大限度地保持材料原有的特性。本文即是利用SPS这一特点,分别以MgO、MgO与SiO₂、MgO与Al₂O₃、MgO与AlPO₄作为烧结助剂和复合烧结助剂,于烧结温度不高于1500℃,制备了系列α-Si₃N₄陶瓷,对其物相、显微结构、力学性能和介电性能进行测试分析,重点研究了SPS条件下,α-Si₃N₄陶瓷的液相烧结过程和致密化机理,以及密度的调控与其介电性能之间的关系。 研究表明,MgO能有效促进α-Si₃N₄陶瓷致密化进程,烧结温度1500℃时,4%的加入量,致密度可达96%,但烧结的起始温度为1350℃:MgO与SiO₂复合烧结助剂进一步降低了氮化硅材料的起始烧结温度（1150℃）;MgO与Al₂O₃复合烧结助剂,烧结温度1450℃时,烧结样致密度可达96%以上,材料开始烧结温度为1200℃,致密化主要在1400℃-1450℃完成;MgO和AlPO₄复合烧结助剂不但降低了氮化硅的起始烧结温度（1100℃）,而且能使α-Si₃N₄在较宽的温度范围内实现烧结,可通过对烧结条件和A1PO₄加入量调控烧结样的致密度。 烧结样的XRD和SEM测试和分析表明,主晶相仍为α-Si₃N₄,晶粒没有或几乎没有长大,表明SPS快速烧结技术有助于抑制晶粒的长大,实现材料的细晶化,保持粉料原有的主物相。 SPS工艺条件下,氮化硅材料的致密化主要是由于颗粒的重排实现的,可分为颗粒的初始重排,颗粒的扩展重排和气孔闭合阶段,液相的粘性流动、液相粘度的迅速降低、晶界的滑动及气孔的排除是促进烧结体致密化的主要因素,但各阶段侧重点有所不同。 烧结样的力学性能主要取决于其相对密度。以MgO与AlPO₄作复合烧结助剂,可以显著提高低致密度烧结体的力学性能,当材料的致密度为631.61%时,材料的抗弯强度仍然可达89MPa以上。 对材料的介电性能测试分析表明,材料的介电常数介于4.5～8.5之间,材料的致密度达至一定程度（93%以上）后,烧结助剂的种类和含量的变化,对介电常数的影响不大,介电常数基本上维持为一定值;材料的介电损耗介于0.001～0.03之间,它受材料致密度的影响较大,对烧结助剂的种类和含量较为敏感,AlPO₄的加入可显著降低烧结样的介电损耗。更多还原

【Abstract】 As one of the novel techniques for fabricating materials, Spark Plasma Sintering （SPS） could finish rapid sintering for diverse materials and preserve the characteristic to the best extent. In light of this advantage, in this work, a series of α-Si₃N₄ ceramics were prepared below 1500℃ with MgO, MgO&SiO₂, MgO&Al₂O₃, MgO&AlPO₄ as the sintering aid respectively. Phase composition, microstructure, mechanical property and dielectric performance were explored, and the emphasis was focused mainly on the liquid sintering process and densification mechanism of α-Si₃N₄, and the dependence of dielectric property on density.It is found that MgO can effectively help to the densification of α-Si₃N₄ at 1500 ℃, with 4wt% of MgO, the relative density reaches 96%, but the starting sintering temperature is as high as 1350℃ with MgO&SiO₂ as mixed sintering aid, the starting sintering temperature is reduced to 1150℃; when using MgO& Al₂O₃ as the sintering aid, at 1450℃ , the relative density could be above 96% and the starting sintering temperature is around 1200℃. the densification process finishes between 1400-1450℃. the mixed sintering aid MgO&AlPO₄ not only brings down the starting sintering temperature （¹100℃）, but also enables sintering to be conducted in a wider temperature range, and the relative density could be tuned by sintering condition and content of AlPO₄.XRD（X-Ray Diffraction） and SEM（Scanning Electron Microscopy） indicate that the major phase is α-Si₃N₄ and grain fails to grow any larger, which prove that SPS helps to prevent the grain from growing, preserve the main phase and realize the downsize of grain.In SPS process, the densification of Si₃N₄ is caused by the realigning of grains, which could be cut into the following steps: the initial realigning, the extensive realigning and elimination of closed pores. The liquid viscosity flowing, the quick decrease of liquid viscosity, the slip of grain boundary and vanish of pores are main contributors to densification, whereas the role of each of them differs in each step.The mechanical property relies on the relative density. The mixed sintering aid MgO&AlPO₄ can enhance the strength of sintered samples with a low density. Although the relative density is as low as 63.61%, the bending strength stays above 89MPa.The dielectric constant ranges 4.5⁸.5. As long as the density is high to certain extent（e.g. 93%）, the dielectric constant tends to certain value and the species of sintering aid and its content difference influences little on the dielectric constant. The dielectric loss varies from 0.001 to 0.03, which is sensitive to the relative density, sintering aid and its content. The addition of AlPO₄ remarkably reduces the dielectric loss of the sintered sample.更多还原