Mechanical properties of a medical β-type titanium alloy with specific microstructural evolution through high-pressure torsion

The effect of high-pressure torsion (HPT) processing on the microstructure and mechanical biocompatibility includes Young's modulus, tensile strength, ductility, fatigue life, fretting fatigue, wear properties and other functionalities such as super elasticity and shape memory effect, etc. at levels suitable for structural biomaterials used in implants that replace hard tissue in the broad sense (Sumitomo et al., 2008 [4]). In particular, in this study, the mechanical biocompatibility implies a combination of great hardness and high strength with an adequate ductility while keeping low Young's modulus of a novel Ti-29Nb-13Ta-4.6Zr (TNTZ) for biomedical applications at rotation numbers (N) ranging from 1 to 60 under a pressure of 1.25 GPa at room temperature was systematically investigated in order to increase its mechanical strength with maintaining low Young's modulus and an adequate ductility. TNTZ subjected to HPT processing (TNTZ(HPT)) at low N exhibits a heterogeneous microstructure in micro-scale and nano-scale consisting of a matrix and a non-etched band, which has nanosized equiaxed and elongated single beta grains, along its cross section. The grains exhibit high dislocation densities, consequently non-equilibrium grain boundaries, and non-uniform subgrains distorted by severe deformation. At high N which is N>20, TNTZ(HPT) has a more homogeneous microstructure in nano-scale with increasing equivalent strain, cm Therefore, TNTZ(HPT) at high N exhibits a more homogenous hardness distribution. The tensile strength and 0.2% proof stress of TNTZ(HPT) increase significantly with N over the range of 0 <= N <= 5, and then become saturated at around 1100 MPa and 800 MPa at N >= 10. However, the ductility of TNTZ(HPT) shows a reverse trend and a low-level elongation, at around 7%. And, Young's modulus of TNTZ(HPT) decreases slightly to 60 GPa with increasing N and then becomes saturated at N >= 10. These obtained results confirm that the mechanical strength of TNTZ can be improved while maintaining a low Young's modulus in single beta grain structures through severe plastic deformation. (C) 2013 Elsevier B.V. All rights reserved.