Microstructure and biomechanical properties of Ti-3Zr-2Sn-3Mo-25Nb biomedical alloy with nanostructure by ARB Process

摘要

Biomedical Ti alloy materials have been widely applied in surgical implants and internal intervening devices. These materials not only require better biocompatibility, but also the lower elastic moduli should be guaranteed to prevent from the "stress-shielding" and implants failure. At present work, the 1 mm Ti-3Zr-2Sn-3Mo-25Nb(TLM) plates after solid solution heat treatment at 610oC/1h, 710oC/1h, 810oC/1h were cold rolled into 0.2mm foils which the deforming rate is 80%, then the 0.2mm foils were cut, surface cleaned and then composed in composite plates with the layers of 2,4,8 separately. Finally the foils with the same thickness of 0.2mm were prepared by cold-rolling step by step by Accumulative Roll-Bonding process (ARB) from the above-mentioned composite plates with different thickness 0.4mm, 0.8mm and 1.6mm. The samples cut from the above-mentioned materials were subjected to a variety of heat treatment. The specimens for tensile mechanical properties, optical metallography, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were prepared and determined using standard techniques and methods. The results are shown that the average grains dimension of TLM alloy foils (0.2mm) can reach about 80nm after 97.5% severe plastic deformation (SPD). The TLM alloy foils of 0.2mm in thickness could be easily prepared by severe plastic deformation processing of ARB. With increasing of the deforming rates, the grains could be fined to 80nm for the composite foils with 8 layers, and the tensile strength Rm, yielding strength Rp0.2 and modulus of elasticity E rise gradually. With the temperature of solid solution treatment increasing, the tensile strength Rm, yielding strength Rp0.2 and elongation A5 lower gradually, whereas the modulus of elasticity E rise slowly. Especially, the lowest E value could reach 38GPa which is very close to that of natural bone. And with increasing of the deforming rates, the boundary among layers for TLM alloy composite foils have achieved melting fusion welding by mechanical atom diffusion bonding which leads to the increasing of the tensile strength Rm, yielding strength Rp0.2 and modulus of elasticity E. Thereby the materials strengthening mechanism is different between ARB and STA, one is dispersion strengthening (or precipitation strengthening) for STA heat treatment, and the other is nano-grain strengthening for ARB process.