Effect of microstructure on high cycle fatigue behavior of Ti-5Al-5Mo-5V-3Cr-1Zr titanium alloy

High-cycle fatigue (HCF) behavior of Ti-5Al-5Mo-5V-3Cr-1Zr (Ti-55531) alloy with both lamellar microstructure (LM) and bimodal microstructure (BM) was studied at room temperature. The results indicate that BM presents much higher strength, lower ductility and slightly higher HCF strength (10(7) cycles, R = -1) than those of LM. Typical dislocation structures including straight prismatic slip lines, curved dislocation lines, dislocation tangles and twins can be discovered in fatigued specimens with two different microstructures. Primary alpha (alpha(p)) particles and secondary alpha (alpha(s)) lamellae accommodate more cyclic deformation than retained beta (beta(r)) laths. Grain boundary (GB) alpha layers have more effect on promoting crack initiation in LM than that in BM. As a result, fatigue microcracks mainly initiate at the interface between GB alpha films and prior 6 grains or at the alpha(s)/beta(r) interphase for LM. However, microcracks primarily nucleate at the alpha(p)/beta(trans) (beta transformed microstructure) interface or at alpha(p) particles in BM. The combination of transgranular and intergranular crack propagation could be observed in the two microstructures. Crack front profile of macrocrack in LM is rougher than that of BM during the stable propagation region. (C) 2016 Elsevier Ltd. All rights reserved.