titanium alloys![Sample our Physical Sciences journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/110819/TOC-Subject-Sample-2021-Physical-Sciences.jpg"})
Abstract
Titanium alloys are known to creep at room temperature at stresses below the macroscopic yield stress. In this study a two-phase α/β alloy, Ti-6Al-2Sn-4Zr-2Mo (Ti-6242), and a single phase binary alloy, Ti-6Al, were observed to exhibit a dramatic asymmetry between tension and compression during room temperature creep. It was observed that the aero-engine alloy, Ti-6242, accumulated about five to six times higher creep strains in tension than in compression. A much smaller asymmetry was observed for the 0.2% yield strength such that it is higher in compression. It is shown that the present observations cannot be explained by the activation of predominantly ⟨c + a⟩ slip. Further, CRSS measurements from single colony crystals of Ti-6242Si oriented for basal ⟨a⟩-type slip showed that there is a significant asymmetry between tension and compression, with the CRSS observed to be higher in compression. Studies on the single-phase α alloy Ti-6Al with low oxygen content suggest that the interstitial content could also play a significant role in determining the behaviour of these alloys. The single phase alloy also exhibited tension-compression asymmetry in creep, although it was observed to be less pronounced compared to the two phase alloy. HRTEM results suggest that the core structure of ⟨a⟩-type dislocations is altered by the addition of alloying elements, especially oxygen, and that the tension–compression asymmetry is primarily due to the behaviour of ⟨a⟩-type dislocations.
Acknowledgements
The authors would like to acknowledge the Air Force Office of Scientific Research under grant number F496200-02-1-0013 for financial support. They would also like to thank Prof. K.J. Hemker and Dr. M. Zupan of Johns Hopkins University for providing the facilities and their help with the microsample tensile testing. M.F.S also acknowledges the use of the electron optics facility in the Metallurgy Division of NIST under the direction of J.E.. Bonevich for the HRTEM observations.