Introduction of strengthening and toughening mechanisms into intermetallic and ceramic matrix composites

纤维增强金属间化合物和陶瓷基复合材料有望成为下一代高温材料。然而，强度和韧性不足以应用。实际应用需要进一步的强韧化和提高可靠性。本文的主要工作是通过引入裂纹止裂机制来获得高强度和高韧性。(1)建立了描述微损伤累积过程及其对整体应力应变曲线、强度和断口形貌影响的新模型。用这种方法可以获得高强度和高韧性的材料设计指标。(2)从实验和理论上阐明了残余应力、试样尺寸和加载条件对纵向裂纹的影响，为韧化提供了有益的指导。(3)通过实验阐明了界面条件对无缺口和缺口强度的影响，并由此得出了止裂的必要条件。(4)在以耐热微晶玻璃为基体的Si-Ti-C-0/BMAS复合材料中，界面处碳层的形成是导致缺口尖端钝化的主要原因。首次估算出纵向裂纹的临界能量释放率约为100 J/m ~ 2。(5)以界面控制和韧性金属的引入为增韧目标，制备了具有高弹性模量、高强度和低缺口敏感性的C/C-Mg复合材料。

Fiber-reniforced intermetallic and ceramic matrix composites are expected as the high temperature materials for next generation. The strength and toughness are, however, not sufficient for application. Further strengthening and toughening, and improvement of reliability are required for practical use. The aim of the present workwas to achieve high strength and toughness by introducing crack arrest mechanisms.Main results are summarized as follows.(1) Newmodelwas developed fordescriptionofmicro-damageaccumulationprocess and its influenceonoverall stress-straincurve, strengthand fracturemorphology. With thismethod, indications formaterial design to achieve high strength and toughness could be obtained.(2) Influences of residual stresses, sample size and loading condition on longitudinal cracking were clarified experimentally and theoretically, which supplied useful indications for toughening.(3) Influences of inter facial condition on unnotched and notched strengths were clarified experimentally, from which the necessary condition for crack-arrest was obtained.(4) In the Si-Ti-C-0/BMAS composite with heat-resistant crystallized glass matrix, the formation of carbon layer at interface was found to act to cause longitudinal cracking, which leads to blunting of the notch-tip. The critical energy release rate of longitudinal crackingwas first estimated to be around 100J/m2.(5) To aim toughening by inter facial control and introduction of ductile metal, C/C-Mg composite was prepared, which showed high Young's modulus, high strength and low notch-sensitivity.