Ti 29Nb 13Ta 4.6Zr (TNTZ) which was developed for biomedical applications, is a b type titanium alloy with a relatively low Young's modulus. However, its fabrication cost is high because the alloying elements of Nb and Ta, which are b stabilizers with high melting points, are expensive and rare metals. In this study, Ti Mn system alloys were developed as low cost titanium binary alloys for biomedical applications, and their mechanical properties (tensile strength and Young's modulus) and biocompatibility (bone contact ratio) were investigated to evaluate their possible use as next generation metallic biomaterials.Ti 12Mn has a tensile strength of approximately 950 MPa, which is similar to those of annealed Ti 6Al 4V ELI (Extra Low interstitial) and insufficiently aged TNTZ. Ti 9.2Mn has the lowest Young's modulus of approximately 90 GPa among the alloys investigated. The mean values of bone contact ratios on Ti 12Mn were obtained 12, 52 and 96 weeks after the implantation of rabbit femurs and were found to be slightly lower than the values for commercially pure Ti, although a small amount of Mn element was detected at a interfacial bone tissue with the concentration gradient at 96 weeks after implantation. However, there appeared to be no significant effects of the release of Mn to the bone tissue on bone formation.From these results, it is considered that Ti Mn system alloys are promising biomaterials with attractive mechanical properties and relatively good biocompatibility.
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 massNb shows single a phase. Other phases such as a″ phase, v phase and b phase become to be recognized with increasing Nb composition of Ti XNb 10Ta 5Zr alloys. Microstructures of the alloys containing over 30 massNb show single b phase.Elastic moduli of Ti XNb 10Ta 5Zr alloys decrease with increasing Nb contents. However, 15Nb, 20Nb and 25Nb alloys, whose microstructures contain v 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 massNb, whose microstructure have v phase, shows the largest elongation. Tensile properties of the alloys containing over 30 massNb, which have same microstructures, change a lot. These phenomena are caused by the change of deformation mechanism of b phase. (Received July 14, 2003; Accepted September 26, 2003) Keywords: titanium alloy, mechanical properties, elastic modulus, microstructure, biomaterial, powder metallurgy
As a new type of metallic biomaterial, porous pure titanium filled with a medical polymer has been developed for obtaining a low Young's modulus similar to that of bone. This type of biomaterials will inhibit the deterioration of mechanical properties due to the presence of pores, and provide biofunctionalities that are intrinsically possessed in certain polymers. However, the inhibition of the deterioration of mechanical properties is not satisfactory because of the poor interfacial adhesiveness between the titanium particles and the medical polymer. Therefore, in the present study, silane coupling treatment is employed in order to improve the interfacial adhesiveness, and silane coupling treated (Si treated) porous pure titanium (pTi) filled with polymethylmethacrylate (PMMA) is fabricated. Subsequently, the effect of the silane coupling treatment on the mechanical properties of the pTi filled with PMMA is investigated.The tensile strengths of the Si treated pTi filled with PMMA are higher than those of pTi and non Si treated pTi filled with PMMA. In the fractographs of non Si treated pTi filled with PMMA obtained after the tensile test, the detachment of titanium particles from PMMA is observed; this occurs because of poor interfacial adhesiveness between titanium particles and PMMA. However, in the case of the Si treated pTi filled with PMMA, the interfacial adhesiveness between titanium particles and PMMA is improved by the silane coupling treatment. This leads to the dispersion of the stress concentration at necks between particles, resulting in an improvement in the tensile strength of pTi. On the other hand, PMMA filling hardly affects Young's modulus of pTi because Young's modulus of PMMA is lower than that of pTi.
Formation of the reaction product layer on the surface of biomedical titanium alloys, Ti 29Nb 13Ta 4.6Zr (TNTZ) and Ti 6Al 4V ELI (Ti64), during gas nitriding was investigated. These alloys were exposed to nitrogen atmosphere at 1023, 1073, 1123 and 1223 K. After the gas nitriding, a reaction product layer was observed on the surface of both alloys, and was analyzed using an X ray diffraction (XRD), Auger electron spectroscopy (AES) and X ray Photoelectron spectroscopy (XPS). The layer was comprised of two phases, which were outer oxide layer (mainly TiO 2 ) and inner nitride layer (mainly TiN or Ti 2 N). In these layers, the thickness of the oxide layer particularly depended on the kinds of alloys. According to the thermodynamics and point defect theory, the growth rate of oxide layer is expected to be increased by the presence of Al in TiO 2 . Namely, the dissolution of Al into TiO 2 may increase the number of oxygen vacancies, resulting in acceleration of oxygen diffusion inward. On the other hand, the elements that accelerate the growth of the oxide layer are not contained in TNTZ. Thus, the oxide layer formed on Ti64 was thicker than that of TNTZ. In a similar way, the elements that accelerate the growth of the nitride layer are not contained in both TNTZ and Ti64. Thus, the nitride layers with similar thicknesses may be formed on TNTZ and Ti64 during gas nitriding.
CP titanium and titanium alloys have been used as biomaterials. Recently, b type titanium alloy, which has good biocompatibility, low modulus, excellent balance of strength and ductility, is widely expected to use for biomedical applications. Very recently, Ti 29Nb 13Ta 4.6Zr alloy is newly designed and developed for biomedical applications. The new alloy is composed of non toxic elements such as Nb, Ta, and Zr. In present study, various phases appeared in the new alloy according to the various aging treatments were characterized by hardness tests and microstructural observations. Tensile and fatigue properties of the new alloy were also investigated with relating microstructure. Precipitated phases distributed homogeneously over the whole specimen are a and v phases, when the new alloy is aged at 673 K for 259.2 ks after solution treatment at 1063 K for 3.6 ks. The best balance of strength and elongation in the new alloy was obtained by the condition of 673 K for 259.2 ks after solution treatment at 1063 K for 3.6 ks. Fatigue limit of the new alloy aged at 673 K for 259.2 ks is around 700 MPa.
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