Microstructural Control for Characteristics of Biomedical Ti-39Nb-6Zr-0.45Al Alloy

Ti-39Nb-6Zr-0.45Al alloy was developed for biological applications as exchangeable hard tissue. This alloy has very low elastic modulus, but lower strength than Ti-6Al-4V alloy. This study was performed for improving the strength by various heat treatments and microstructural characteristics and mechanical properties of Ti-39Nb-6Zr-0.45Al alloy were investigated. Heat treatments were conducted at 350 °C, 400 °C, 450 °C, 500 °C, 550 °C and 600 °C, followed by water quenching. Microstructures of Ti-39Nb-6Zr-0.45Al alloy showed two types of different features. One of the features was not visible for grains at low temperature heat conditions (350 °C, 400 °C and 450 °C), because of the effect of cold swaging. On the contrast, at high temperature conditions (500 °C, 550 °C and 600 °C), the grains were visible. Tensile properties had similar tendency to hardness properties under all low temperature conditions. The samples showed high strength and low elongation under low temperatures, but showed the opposite results under high temperature conditions. These results were due to thermal ω phases and secondary α phases inside the matrix of this alloy. ω phases, which were precipitated under low temperature heat treatments, induce high strength and low elongation. In case of high temperature conditions, ω phases disappeared into the matrix and secondary α phases with fine size appeared. γoung's moduli of the samples under all the conditions were lower (about 60 GPa) than those of the as-swaged (about 70 GPa). Consequently, the heattreated Ti-39Nb-6Zr-0.45Al alloy had high strength and very low elastic modulus for biomedical applications.