Difference of Fracture Behavior on Isothermal Low Cycle Fatigue between SP-700/SCS-6 Titanium Alloy Matrix Composite and Monolithic Matrix Alloy

摘要

The isothermal low cycle fatigue (LCF) fracture behavior of a new generation titanium alloy matrix composite, SP-700/SCS-6, were investigated compared with the monolithic matrix alloy. To study the effects of the test temperature and the loading frequency on the LCF fracture behavior in SP-700/SCS-6, the LCF tests were performed under strain-controlled condition at room temperature and 450℃. In the LCF tests two strain wave shapes were applied : the fast-fast wave in which the loading frequency was 0.5 Hz, and the slow-slow wave in which it was 1/360 Hz, respeetively. The conclusions obtained from the experimental results are summarized as follows : (1) The LCF lives of the composite were almost comparable to those of the matrix alloty, on the basis of strain range. In other words, the performace of the present composite material can be absolutely improved, since the stiffness and the deformation resistance can significantly increased by the composition. (2) The fatigue cracks were initiated from the matrix part at the specimen corner. The fiber pull-out was not so significant on the fracture surface. (3) The LCF lives of the composite at 450℃ were longer than those at room temperature. This trend was in contrast to the monolithic matrix alloy which exhibits a normal temperature dependence in the LCF lives. (4) The LCF lives of the composite under the slow-slow wave was noticeably shorter than those under the fast-fast wave at high temperature. This trend was familiar to the conventional monolithic materials.