Formation of nano-sized grains in Ti-10Zr-5Nb-5Ta biomedical alloy processed by accumulative roll bonding (ARB)

Abstract

Formation of nano-sized grains in a new Ti-10Zr-5Nb-5Ta (wt.%) alloy without cytotoxic elements, through innovative accumulative roll bonding (ARB) process was the subject of investigation. The investigations consisted of structural and mechanical characterization of the alloy, processed by 4 ARB cycles at ambient temperatures. The micro-structural investigations were performed before and after each ARB cycle, using a SEM analyzing system, an X-ray diffractometer and a HRTEM analyzing system. The investigations of mechanical properties were based on tensile strength, Young’s modulus, tensile elongation and micro-hardness measurements. Nano-sized grains were successfully obtained after 4 ARB cycles. The analyzed samples initially showed an ultra fine grain (UFG) structure, transformed during ARB cycles to a nano-sized grain (NG) structure, suitable for improving the alloy’s bioactivity. Consequently, the ARB process increases the strength of the samples: the values of tensile strength drastically increase in the initial stage of the ARB process, after which they tend to become saturated; the Young’s modulus constantly increases; the tensile elongation greatly decreases after 2 ARB cycles; the micro-Vickers hardness values are constantly high during ARB process. K e y w o r d s: Ti-Zr-Nb-Ta alloy, grain refining, accumulative roll bonding, structure characterization, mechanical properties testing, nano-crystalline structure