Coefficient of thermal expansion anisotropy and texture effects in ultra-thin titanium sheet

Abstract

Several measurements have been made for the coefficient of thermal expansion (COTE) of titanium in both single crystal and polycrystalline samples. The most commonly observed preferred crystallographic orientation of cold-rolled Ti has been presented by Clark and others to be a 209 to 40{degree} tilt of the c-axis in both transverse directions. This rolling texture is common among HCP metals with a c/a ratio lower than the ideal, and it results from the two most common slip systems active in Ti at room temperature. These were first reported by Anderson, Jillson, and Dunbar, who found that the critical resolved shear stress (CRSS) for slip in the {l_angle}11{bar 2}0{r_angle} direction on the (0002) basal plane is 110 MPa, and the CRSS for slip in the {l_angle}11{bar 2}0{r_angle} direction on the {l_brace}10{bar 1}0{r_brace} first order prism planes is 50 MPa. Thus the Ti unit cell is oriented for easiest slip when it lies in a position near the CRSS maximum for the first order prism plane slip system, while still permitting cross slip on the basal plane.