Observation of tension-compression asymmetry in α and α/β titanium alloys

• Published in: Philosophical magazine (2003. Print) Vol. 85; no. 2-3; pp. 279 - 295
• Main Authors: NEERAJ, T, SAVAGE, M. F, TATALOVICH, J, KOVARIK, L, HAYES, R. W, MILLS, M. J
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Abingdon Taylor and Francis 11.01.2005
• Subjects: Condensed matter: structure, mechanical and thermal properties; Creep; Elasticity, elastic constants; Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Physics; Grain boundaries; Scanning electron microscopy; Inorganic compounds; Creep; Compressive testing; Tensile tests; Screw dislocations; Experimental study; Multi-element alloys; Tin alloys; Titanium alloys; Monocrystals; Transmission electron microscopy; Aluminium alloys; Asymmetry; Shear stress; Stress effects; Molybdenum alloys; Transition element alloys; Zirconium alloys
• ISSN: 1478-6435; 1478-6443
• DOI: 10.1080/14786430412331315707

Titanium alloys are known to creep at room temperature at stresses below the macroscopic yield stress. In this study a two-phase alpha/beta alloy, Ti-6Al-2Sn-4Zr2Mo (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 alpha 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 tensioncompression asymmetry is primarily due to the behaviour of (a)-type dislocations.