Microstructures and properties of biomedical TiNbZrFe β-titanium alloy under aging conditions

A metastable beta-titanium alloy Ti-28Nb-13Zr-0.5Fe (TNZF alloy for short) was designed for implant biomedical application. The forged specimens were solute-treated at 850 C followed by water quenching and then aged at 350 degrees C, 450 degrees C, and 550 degrees C for 2-6 h in order to evaluate the effect of phase transformation during ageing on the biomechanical compatibility of the alloy. The quenched microstructure consists of lath alpha '' martensite and beta phase. A large quantities of shuttle-like omega phase precipitate at 350 degrees C, leading to the drastic increase of strength and elastic modulus and the decrease of plasticity. Ageing at 450 degrees C for 4 h, small amount of elliptic omega phase and dot alpha phase precipitate from beta matrix. With increasing ageing time alpha precipitations begin to coarsen and precipitation free zones (PFZs) form around prior beta grain boundaries. Needle-like a phase precipitates on grain boundaries and intra-grains when aged at 550 degrees C. Both PFZs and grain boundary a precipitates are prone to bring about the intergranular fracture and thus have adverse effects on the tensile strength and fracture plasticity. The quenched microstructure has good combination properties of high strength, high plasticity and low elastic modulus. (C) 2009 Elsevier B.V. All rights reserved.