Effect of Nb content on microstructure, tensile properties and elastic modulus of Ti-XNb-10Ta-5Zr alloys for biomedical applications

Abstract

Effect of Nb content on microstructure, tensile properties and elastic modulus of Ti-XNb-10Ta-5Zr alloys made by a sinter-forged method for biomedical applications was investigated. Ti-30Nb-10Ta-5Zr, which is the simplified compositional alloy of Ti-29Nb-13Ta-4.6Zr developed for biomedical applications, has been selected as the basic alloy composition and, Nb contents of the alloy were varied from 0 through 40 mass%. Blended elemental powder metallurgy method was applied to fabricate these alloys. The alloying elements powders were mixed and pressed to form green products by a cold isostatic pressing (CIP) machine. Green products were then sintered at 1573 K for 57.3 ks in a vacuum of about 1.33 × 10-3 Pa. Subsequently, they were forged and swaged at 1223 K in air. Finally, heat treatment at 1123 K for 1.8 ks in air to remove residual strain was done on the swaged bar. Tensile tests and elastic modulus measurements and mocrostructural observations on different Nb content were carried out. The microstructure of the alloy containing 0 mass%Nb shows single α phase. Other phases such as α″ phase, ω phase and β phase become to be recognized with increasing Nb composition of Ti-XNb-10Ta-5Zr alloys. Microstructures of the alloys containing over 30 mass%Nb show single β phase. Elastic moduli of Ti-XNb-10Ta-5Zr alloys decrease with increasing Nb contents. However, 15Nb, 20Nb and 25Nb alloys, whose microstructures contain ω phase, show a tendency of the increase of elastic moduli. These tendencies of elastic moduli are the same with general binary titanium alloy systems. The alloy containing 25 mass%Nb, whose microstructure have ω phase, shows the largest elongation. Tensile properties of the alloys containing over 30 mass%Nb, which have same microstructures, change a lot. These phenomena are caused by the change of deformation mechanism of β phase.