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

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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.