Composition/phase structure and properties of titanium-niobium alloys

This study attempts to develop Ti-Nb alloys with elastic moduli that approach that of human bone. The experimental results reveal that the microstructure of a Ti-Nb alloy that contains 14 mass% Nb consists of alpha and beta phases, with alpha phase being the dominant one. The proportion of the alpha phase decreases gradually as the Nb content increases, and the microstructure becomes completely the beta phase when the Nb content exceeds 34 mass%. Moreover, the omega phase can be detected using XRD and TEM in alloys with a Nb content from 30 to 34 mass%. Over the Nb range studied (14 to 40 mass%), the elastic modulus decreases from 14 to 26 mass% Nb, and then increases to a maximum at 34 mass% Nb, before falling again as Nb content is increased further. The elastic modulus of the Ti-Nb alloys is closely related to the microstructure (or Nb content) of the alloys. The fall in the elastic modulus with the increasing Nb content from 14 to 26 mass% is associated with a gradual decrease in the proportion of the alpha phase in the microstructure, while the precipitation of the omega phase accounts for the increase in the elastic modulus over the intermediate range of Nb (30 to 34 mass%). The tensile strength of Ti-Nb alloys increases slightly from 14 to 26 mass% Nb, and then increases markedly with a Nb content of up to 34 mass%, before falling drastically as Nb content is increased further. A similar pattern was obtained for 0.2% proof stress, while the elongation vs. %Nb curve was just the reverse of the T.S. vs. %Nb curve, as expected. A Ti-Nb alloy with a relatively high Nb content (above 36 mass%) is preferred to other compositions for use in medical implants with a reduced stress shielding effect.