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Abstract: A novel -type titanium alloy, Ti–29Nb–13Ta–4.6Zr (TNTZ), has been developed as a candidate for biomedical applications. TNTZ exhibits non-toxicity and a low Young’s modulus close to that of bone (10–30 GPa). Such a low Young’s modulus of this alloy is achieved by comprising a single metastable phase. Greater mechanical biocompatibility, which implies higher mechanical strength and hardness while maintaining a low Young’s modulus, has been aimed for TNTZ. Therefore, strengthening by grain refinement and increasing dislocation density is expected to provide TNTZ high mechanical strength while keeping a low Young’s modulus because they keep the original phase. In this case, high-pressure torsion (HPT) processing is one of the effective ways to obtain these properties simultaneously in TNTZ. Thus, in this study, the effect of HPT processing on the microstructure and mechanical hardness of TNTZ was systematically investigated at rotation numbers () of 1 to 20 under a pressure of around 1.25 GPa at room temperature. On the cross sections of TNTZ subjected to HPT processing (TNTZHPT) after cold rolling (TNTZCR) at any rotation number, a heterogeneous microstructure consisting of a matrix and a non-etched band, which is not corroded by etching solution, can be observed. The thickness of non-etched band increases as rotation number and distance from specimen center increase. Both matrix and non-etched band comprise a single phase, but their grain geometries are different each other. Equiaxed grains and elongated grains are observed in the matrix and the non-etched band, respectively. The equiaxed grain diameter, which is ranged from 155 nm to 44 nm, in the matrix decreases with increasing rotation number. Contrastingly, the elongated grains with a length of around 300 nm and a width of 30 nm, which are nearly constant with rotation number, are observed in the non-etched band. The mechanical hardness of TNTZHPT is consistently much higher than that of TNTZCR. The mechanical hardness distribution on the surface of TNTZHPT is heterogeneous in the radial and depth directions, while that of TNTZCR is homogeneous; the mechanical hardness is higher in the peripheral region than in the central region on the surfaces of TNTZHPT at all . Further, the mechanical hardness distribution on the cross sections of TNTZHPT at all is also heterogeneous in depth direction; the mechanical hardness is higher in the peripheral region than in the central region. The heterogeneous mechanical hardness distribution depending on the position on the surface and cross section of TNTZHPT is considered to be related to grain refinement and imposed strain due to HPT processing. [Copyright &y& Elsevier]

Abstract: A high strength Cu–NbC composite conductor for electrical applications was fabricated from Cu, Nb and C elemental powders using high pressure torsion (HPT). After HPT, samples showed close to full density (>99%). SEM observations revealed that atomic scale mixing occurred in the following order: deformation of Cu particles, the formation of Cu/Nb lamellar structure, fracturing of Nb lamella into sub-micron particles and the formation of uniform structure with fine distribution of Nb particles. The in situ formation of NbC in the copper matrix during HPT was detected. Annealing at 600 and 700°C resulted in substantial increases in microhardness and tensile strength and a slight decrease in electrical conductivity with increasing NbC volume fraction. The best combination of electrical conductivity (54% IACS) and tensile strength (810MPa) ever reported for such a composite was obtained in the Cu–2vol% NbC composite after annealing at 700°C. [Copyright &y& Elsevier]

In order to elucidate the microstructural refinement mechanism and the effect of secondary phase on the microstructural evolution of β -type titanium alloy, severe plastic deformation was conducted on samples of a precipitation-hardened Ti–29Nb–13Ta–4.6Zr (TNTZ). Specifically, TNTZ that was precipitation-hardened through an aging treatment (TNTZ AT ) was subjected to high-pressure torsion (HPT) processing (TNTZ AHPT ). The microstructure of TNTZ AHPT , which has been evaluated as a function of the torsional rotation number, N , exhibits ultrafine elongated β grains. The needle-like α precipitates in TNTZ AT , which exhibit a diameter of approximately 12 nm, are homogeneously distributed within the β grains. The dislocation density and subgrain diameter, estimated by X-ray line profile analysis, saturate at approximately 4.2 × 10 16 m −2 and 12.2 nm, respectively, at N ⩾ 10. The β grains contain nanostructured subgrains having non-uniform morphologies surrounded by blurred and wavy boundaries. A saturated hardness distribution at approximately 450 HV indicates that microstructural homogeneity has been achieved at N ⩾ 10. The α precipitates enhance the β grain refinement and microstructural homogeneity is achieved in TNTZ AHPT at N ⩾ 10, whereas this occurs at later stages ( N > 20) in TNTZ which is solution-treated and therefore does not contain any α precipitates. [ABSTRACT FROM AUTHOR]

Abstract: 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 1.25GPa 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 (TNTZHPT) 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 β 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, TNTZHPT has a more homogeneous microstructure in nano-scale with increasing equivalent strain, εeq . Therefore, TNTZHPT at high N exhibits a more homogenous hardness distribution. The tensile strength and 0.2% proof stress of TNTZHPT increase significantly with N over the range of 0≤ N ≤5, and then become saturated at around 1100MPa and 800MPa at N ≥10. However, the ductility of TNTZHPT shows a reverse trend and a low-level elongation, at around 7%. And, Young's modulus of TNTZHPT decreases slightly to 60GPa 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 β grain structures through severe plastic deformation. [Copyright &y& Elsevier]

Abstract: Several pairs of Zr55Cu30Ni5Al10 bulk metallic glass (BMG) plates and pure copper plates with volume ratio of 1:1 were put together and subjected to high-pressure torsion process with 10, 20 and 50 rotations separately to prepare BMG/Cu composites. For the samples processed with 10 and 20 rotations, the microstructures were not very homogeneous and some metallic glass blocks can still be observed near the center of the samples. While after 50 rotations, the microstructure becomes rather homogenous throughout the samples. Both glass phase and copper phase were transformed into small pieces and mixed uniformly with each other. No intermetallic compounds either from chemical reaction or crystallization from the glass phase could be detected for all the samples regardless of the rotation numbers. This study indicates that high-pressure torsion technique can be used as a new approach to fabricate bulk metallic glass matrix composites. [Copyright &y& Elsevier]