Orientation Effect on Mechanical Properties of Commercially Pure Titanium at Room Temperature
- PDF / 652,997 Bytes
- 10 Pages / 594 x 792 pts Page_size
- 97 Downloads / 210 Views
TION
IN common with work on other metals, early literature on deformation mechanisms in titanium looked at the activation of particular slip and twinning modes in suitably oriented single crystals. The critical resolved shear stress (CRSS) for prism-hai and basal-hai slip in titanium was established over a wide range of temperatures and compositions (Conrad[1] for a summary). Prism-hai slip was found to be by far the easiest slip mode up to very high temperatures. However, these deformation modes cannot accommodate a strain component along the c-axis. Therefore, pyramidal-hc + ai slip and twinning, which are able to accommodate strain along the c-axis, are very important. Similarly to slip, the possible twin modes observed in titanium were determined very early on (the most common modes are shown in Table I), but there is still very little quantitative data on their activity. There have only been a couple of notable studies of twinning in a-titanium single crystals. One study[2] found that 11 22 twinning could accommodate almost all the applied strain at room temperature (RT) under favorable loading conditions, indicating its potential as a major deformation mode in polycrystals. The other the resolved shear stress for 1012 study[3] determined and 11 21 twinning in crystals of three distinct orientations that yielded by either one of these twin M. BATTAINI, Postgraduate Student, and E.V. PERELOMA and C.H.J. DAVIES, Associate Professors, are with the Victorian Centre for Advanced Materials Manufacturing and the Department of Materials Engineering, Monash University, Victoria 3800 Melbourne, Australia. Contact e-mail: [email protected] Manuscript submitted March 24, 2006. 276—VOLUME 38A, FEBRUARY 2007
modes. Comparison of the data showed that a CRSS did not apply for either twin mode, which is in contrast to its use in crystal plasticity modeling as an approximation of an activation criterion. Due to experimental difficulties in activating pyramidal-hc + ai slip independently, there are very little data on this mode. Unfortunately, this single crystal data may vary enough from polycrystalline data to limit its use, because grain boundaries are obstacles to dislocation motion and may also act as dislocation sources. A couple of recent studies in polycrystalline titanium have shown that pyramidal-hc + ai slip has considerable activity.[4,5] In polycrystals, the twin modes most commonly reported at RT are 1012 and 11 22 respectively, for deformation perpendicular and parallel to the dominant c-axis orientation.[4–10] Other twin modes were found to have high activity under certain conditions. Mullins and Patchett[6] found 1124 twinning accounted for about one third of all twinning in uniaxial tension along the longitudinal direction of [10] transverse split basal textured sheet. Muruyama also qualitatively observed 1124 twinning to be a major twin mode in transverse split basal textured sheet. However, this was in plane strain compression (PSC) with compression in the norma
Data Loading...
