Evolution of Macroscopic and Microscopic Themal Cycle Damages in SP700/SCS-6 Titanium Alloy Matrix Composite
Masakazu OKAZAKI, Akira IKADA and Yasuhiro YAMAZAKI
Abstract:Damage evolution process of a new generation titanium alloy matrix composite, SP-700/SCS-6, was studied when the composite was subjected to thermal cycles at elevated temperatures. Two types of damages were focused on: one is the macroscopic damage, or thermal cycle cracking induced by the repeat of thermal stress; and the other is the microscopic damage, or microstructural change of the fiber/matrix interface characterization. The investigation on the former showed that the cracks were originated and propagated, associated with the following behavior: the crack propagation rates almost linearly increased with the crack length at the early growth stage, and then they gradually decreased and finally arrested in the most cases. This behavior was shown to be rationalized on the basis of fracture mechanics law. The analysis of the interface by means of a transmission electron microscope and an energy dispersive X-ray spectrometer (EDS) demonstrated that the products of the interface reaction zone, as well as the thickness, were changed by the repeat of thermal cycles. However, the thickness was still significantly thinner, compared with that in other kinds of titanium alloy matrix composite systems. Key Words:Thermal cycle, Crack propagation, Fracture mechanics, SP-700/SCS-6 composite, EDS, Interface, TMF, Damage