Tensile and low-cycle fatigue behavior of commercially pure titanium and Ti-5AI-2.5Sn alloy at 293 and 77 K

Tensile tests and symmetrical push-pull fatigue tests were carried out with samples of commercially pure titanium and Ti-5Al-2.5Sn at 293 and 77 K, respectively. The microstructures were examined in detail by transmission electron microscopy. Pure titanium shows higher strength and ductility, longer low-cycle fatigue life at 77 K than at 293 K. Fatigue life of Ti-5Al-2.5Sn alloy keeps almost same with temperature decreasing. Pure titanium exhibits complex cyclic hardening/softening behavior at room temperature, while cyclic hardening is observed at 77 K. Ti-5Al-2.5Sn alloy cyclically softens at 293 K irrespective of strain amplitudes, and shows approximate saturation stage in peak stress besides the initial softening at low strain amplitudes with temperature decreasing to 77 K. Slipping predominates in monotonic deformation of both pure titanium and Ti-5Al-2.5Sn alloy at 293 K, while in cyclic deformation both slipping and twinning take place. Twinning becomes the main deformation mode in pure titanium at 77 K, and for Ti-5Al-2.5Sn alloy, twinning was also observed to operate in deformation at 77 K. Three types of twinning, {10 (1) over bar2}, {10 (1) over bar 11}, {11 (2) over bar2}, were identified in pure titanium and in Ti-5Al-2.5Sn alloy as well. (C) 2001 Elsevier Science B.V. All rights reserved.