Fatigue crack propagation behavior of high strength titanium alloy

Abstract

High strength Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe（Ti-5321） alloy is a new type of high strength tolerance titanium alloy designed and developed to meet the demand of high performance titanium alloy for new generation aircraft in China. Ti-5321 alloy with equiaxed microstructure（EM），basket-weave microstructure（BW） and fine basket-weave microstructure（F-BW）was obtained by forging and heat treatment，and the tensile properties and fatigue crack growth behavior were studied. Fatigue crack propagation mechanisms in Paris and unstable propagation regimes were revealed by analyzing the microstructures and fracture morphology using optical microscopy (OM) and scanning electron microscopy (SEM). The results show that the samples with EM，BW and F-BW exhibit the excellent fatigue crack propagation resistance with the tensile strength of 1200 MPa. The sample with F-BW presents the highest fatigue crack propagation resistance in Paris and rapid growth regimes，while the sample with EM presents the lowest fatigue crack propagation resistance. In F-BW， the crack mainly propagates through and along α phase. Crack tends to propagate across colony oriented for （\begin{document}$ \bar{1} 011$\end{document}） pyramidal slip and propagates along colony oriented for （\begin{document}$10 \bar{1} 0$\end{document}） prismatic planes.

Keywords

• ti-5321 alloy
• fine basket-weave microstructure
• fracture morphology
• fatigue crack growth mechanism