Single-crystal growth of Ti-Nb-Ta-Zr-O alloys and measurement of elastic properties

Single crystals of beta-type Ti alloy system Ti-Nb-Ta-Zr-O have been grown successfully in an At gas flow by a floating zone method. The growth orientations were determined approximately by using seed crystals with the desired orientations. The various growth conditions were realized by choosing the gas purity, the gas flow rate, and the growth rate as variables. Composition analysis of the grown crystals was done to check any variation from the values of the raw material along with the bulk homogeneity, followed by measurements of the lattice parameter and the hardness, which provides the following results: (1) the composition of oxygen varies with respect to the flow rate, or is increased as the purity is degraded, (2) the lattice parameter is increased with increasing composition of oxygen, (3) which is also the case with the hardness. Measurements of Young's moduli were performed to investigate the elastic properties. The results indicate that the crystals exhibit the anisotropy which was expected previously. The elastic constants were estimated from the moduli, giving the ideal stress 1.7-1.9 GPa which is on a level with the real strength. Additionally, the tensile stress-strain curve for the crystallographic direction < 1 1 0 > exhibited nonlinear elasticity and hysteresis. (C) 2009 Elsevier B.V. All rights reserved.