【作者】 马静梅；

【导师】 叶枫；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2010， 博士

【摘要】 本文采用热压烧结工艺和放电等离子烧结(SPS)工艺,制备了BAS/SiC、BSAS/SiC和BAS/(Si3N4-SiC)复合材料。采用XRD、SEM、TEM和HRTEM等测试方法对所制备的复合材料进行了物相及组织结构分析;采用三点弯曲、单边切口梁及压痕等方法测定了复合材料的室温力学性能。系统地研究了BAS含量、烧结工艺对复合材料的组织结构及性能的影响,揭示了SiC基复合材料的断裂行为及强韧化机理。并在其基础上,进一步研究了复合材料的高温抗氧化行为及其损伤机理。成功地将BAS玻璃陶瓷引入到SiC陶瓷中,获得了致密的SiC基陶瓷复合材料。BAS不仅能有效地促进SiC陶瓷的致密化,而且自身还能完全晶化成高熔点的六方钡长石。SiC晶粒均匀地分散于连续的BAS相中,烧结温度的提高和BAS含量的增加均能进一步提高SiC基复合材料的致密度。BAS/SiC复合材料具有良好的综合力学性能,1900oC热压烧结制备的40wt.%BAS/SiC复合材料的抗弯强度和断裂韧性可分别达到597MPa和7.0MPa·m1/2,且室温力学性能可维持到1200oC。其主要的韧化机理为裂纹的偏转、SiC晶粒的拔出与桥连。Sr部分取代BAS中的Ba,虽能进一步促进材料的致密化,但未能有效地促进BAS由六方相→单斜相的转变。BAS/SiC和BSAS/SiC复合材料的显微组织受BAS含量的影响不大,说明SiC晶粒的生长是受界面反应控制的。TEM分析结果表明,复合材料中BAS和SiC晶粒直接结合,无明显的界面反应层或非晶层,说明在烧结过程中BAS和SiC之间没有发生化学反应,SiC和BAS具有良好的化学相容性。BAS/SiC复合材料具有优异的高温抗氧化性能。氧化测试结果表明,BAS/SiC复合材料氧化增重曲线呈抛物线变化规律,高的BAS含量能提高材料的抗氧化性能,40wt.%BAS/SiC复合材料经1200oC下氧化8小时后增重仅为0.31mg/cm2。利用放电等离子快速烧结(SPS)技术,成功地制备出致密的BAS/(Si3N4-SiC)复合材料。Si3N4晶粒的加入显著提高了BAS/SiC复合材料的力学性能,30wt.%BAS/(20Si3N4+50SiC)复合材料中,30wt.%BAS/SiC复合材料的抗弯强度由527MPa提高到659MPa;30wt.%BAS/SiC复合材料的断裂韧性由5.5 MPa·m1/2提高到6.7MPa·m1/2,其力学性能的提高主要归结于自生β-Si3N4棒晶对复合材料的强韧化效应。更多还原

【Abstract】 BAS/SiC, BSAS/SiC and BAS/(Si3N4-SiC) composites were synthesized by hot-press sintering and spark plasma sintering method. Crystalline phases and microstructure observations were characterized by X-ray techniques, SEM, TEM and HRTEM method. Room-temperature mechanical properties of the composites were measured by a three-point bend and single-edge-notch beam method. Fracture mode, strengthening and toughening mechanisms of the SiC matrix composites were studied. Oxidation behavior and toughening mechanisms at high temperature of the composites were also studied.BAS was first introduced to the sintering of SiC ceramics. The results showed that BAS could serve as an effective liquid sintering aid to promote densification of SiC grain during sintering process, and could entirely crystallize to high melting hexacelsian. SiC grains are homogenously distributed in the continuous BAS matrix. With increasing the sintering temperature and BAS content, the densities of the composites increase. The excellent mechanical properties were obtained for the BAS/SiC composites. The flexural strength and fracture toughness of 40wt.%BAS/SiC composites HP-ed at 1900oC was up to 597MPa and 7.0 MPa·m1/2, respectively, and its room-temperature flexural strength can maintain to 1200oC. The strength and toughening mechanisms were realized by crack propagation, crack bridging and SiC pullout of the BAS/SiC and BSAS/SiC composites.The densites of the composites were increased with Sr instead of Ba of the BAS phase partly. Microstructure of the BAS/SiC and BSAS/SiC composites hardly affect by BAS content, which indicates the growth of SiC grains are controlled by interface reaction. TEM observation indicated that no reaction layers or armosphere layers were observed, there was no reaction between SiC particles and BAS phase. SiC grains are compatible with BAS phase.Excellent oxidation resistance was obtained at high temperature for BAS/SiC composites. It was found that the oxidation rate of the composites followed a simple parabolic growth law. The weight change of 40wt.%BAS/SiC was 0.31mg/cm2 after oxidation at 1200oC maintaining 8h.Fully dense BAS/(Si3N4-SiC) composites were successfully fabricated by SPS method. The addition ofβ-Si3N4 particles increased the mechcanical properties of the BAS/SiC composites. the flexural strength and fracture toughness of the 30wt.%BAS/(20Si3N4+50SiC) omposites were up to 659MPa and 6.7MPa·m1/2, respectively, comparing with 527MPa and 5.5MPa·m1/2 of 30wt.%BAS/SiC composites, which induced good strengthening and toughening effect of self-reinforces rodβ-Si3N4 particles of the composites.更多还原