Development of High Performance Ti Alloy Composite by Controlling Microstructure and Inter face.

未来的航空航天结构需要在高温下具有高比强度和刚度的先进材料。本论文对通过控制组织和界面来开发高性能钛合金及其复合材料进行了研究，主要结论如下：（1）提出并研究了通过控制组织和界面来开发高性能钛合金及其复合材料的新概念。(2)以下是关于单向SiC纤维增强Ti-24 Al-11 Nb（at%）基复合材料的热疲劳的说明：（i）由热疲劳引起的可见裂纹的轮廓，（ii）裂纹密度随热循环的变化，（iii）通过EPMA和SEM与经受长期等温暴露的纤维/基体界面相比，经受热循环的纤维/基体界面的变化，（iv）弹性性能的变化和由热疲劳损伤引起的稳定裂纹扩展的阻力的变化，（v）基于推出试验的界面剪切强度的变化，（vi）环境对（i）至（v）的性质的影响。(3)总结上述系统的研究，热疲劳失效的机制和力学已经澄清和建议。

Future aerospace structures require advanced materials with high specific strength and stiffness at elevated temperatures. In this study, development of high performance Ti alloy and composite has been studied, by controlling microstructures and interface.The main conclusion reached are summarized as follows :(1) A new concept to develop high performance Ti alloy and composite was proposed and studied, by controlling microstructures and interface.(2) The followings have been clarified on the thermal fatigue of an unidirectional SiC fiber rein-forced Ti-24Al-11Nb (at%) matrix composite :(i) outline on visible cracks induced by thermal fatigue,(ii) change of the cracks in density with thermal cycling,(iii) change of the fiber/matrix interface subjected to the thermal cycling, compared with that subjected to long term isothermal exposure, by means of EPMA and SEM,(iv) change of elastic properties and that of the resistance to stable crack growth resulting from thermal fatigue damage,(v) change of the interfacial shear strength on the basis of push-out tests,(vi) effect of environment on the properties from (i) to (v).(3) Summarizing the above systematic investigations, mechanisms and mechanics of thermal fatigue failure have been clarified and proposed.