High cycle fatigue behaviors and deformation mechanisms in Ti47Al2Cr2Nb alloy at room temperature and 700 °C

Abstract

This study systematically investigated the high cycle fatigue behaviors and deformation mechanisms in Ti47Al2Cr2Nb alloy at room temperature and 700 °C through scanning electron microscope and transmission electron microscope. The results showed that high temperature deteriorated the fatigue performances, especially under the higher stress levels. Large scatter in fatigue lifetimes under the lower stress levels was observed at high temperature. After 107 cycles, the high cycle fatigue limit at 700 °C was about 20 MPa lower than that at room temperature. Fracture morphologies showed that brittle fracture presented at both temperatures and fatigue cracks initiated from the surfaces. Fracture modes at room temperature included trans-lamellar and trans-γ grain fractures, while those at 700 °C included trans-lamellar, interlamellar and inter-γ gain fractures. Fatigue deformation at both temperatures mainly occurred in the γ phase, dislocation multiplication and slip bands were found in the deformation microstructures. Dislocation slip was the main deformation mechanism at both temperatures. A few mechanical twins were observed in the deformation microstructures of room temperature. Slip bands and mechanical twins transferred through γ/γ true-twin interfaces with a deflection while they transferred through γ/γ rotational boundaries straightly. Mechanical twins had a blocking effect on slip bands, resulting in the dislocation arrays in slip bands piling up at the intersections.