Investigation of crack initiation mechanism of a precipitation hardened TC11 titanium alloy under very high cycle fatigue loading

Publication date: Available online 22 January 2020Source: Materials Science and Engineering: AAuthor(s): Tao Gao, Hongqian Xue, Zhidan Sun, Delphine RetraintAbstractTC11 alpha-beta titanium alloy (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) is widely used in the construction of aero-engine components. In service, these components are subjected to cyclic loading due to vibrations. This work aims to assess the fatigue properties of a TC11 alloy and to reveal the effect of silicide precipitates and α2 phase (Ti3Al) on fatigue behavior including failure mechanism in very high cycle fatigue (VHCF) regime. For this purpose, tension-compression fatigue experiments were carried out with an ultrasonic fatigue testing system. Fatigue crack initiation and early propagation mechanisms were finely investigated using Field Emission Gun Scanning Electron Microscopy (FEG-SEM). The results show that this alloy exhibits a high fatigue strength at 109 cycles with a fatigue limit up to 618 MPa. Fracture surface observation indicates that the fatigue failure can be categorized into three modes: (a) surface failure in short life regime, (b) subsurface failure and (c) internal failure with the presence of a fish-eye pattern for long life regime. The internal and subsurface crack initiation regions are characterized by microvoids, dimples and peaks without the presence of crystallographic facets in the VHCF regime. This signifies that ductile damage mechanism instead of brittle one is the dominant failure mode f...
Source: Materials Science and Engineering: A - Category: Materials Science Source Type: research