Papers by Keyword: TiNi Alloy

Abstract: Today, one of the problems of modern implants is their high rigidity, which can lead to bone resorption at the interface between the implant and the bone and to the gradual detachment of the implant. In addition, implant detachment can occur due to the positive Poisson's ratio of the implant along its entire length. This phenomenon is described in detail in [1]. As a possible solution to these problems, it is proposed to use lattice structures with negative Poisson's ratio from TiNi alloy. This alloy has a fairly low modulus of elasticity - about 48 GPa. The use of a porous (lattice) structure of an implant made of TiNi alloy will reduce the modulus of elasticity and bring it closer to the modulus of human cortical bone – 12-17 GPa [2], and possibly the modulus of elasticity of cancellous bone – 0.1-5 GPа [3]. In this work, a computer numerical simulation of strut based lattice structures with several variants of unit cell topology with a negative Poisson's ratio is carried out. For the obtained structures, the following characteristics were calculated - elastic modulus (Young's modulus), modulus of elasticity in shear, Poisson's ratio. The modeling process is implemented using the ANSYS 2019 R2 SpaceClaim finite element analysis package. The data obtained confirmed the promising possibility of modeling and fabricating lattice structures with a low elastic modulus and negative Poisson's ratio from a TiNi alloy. Also, on the basis of this data, conclusions about the influence of the topology and porosity of unit cells on the resulting characteristics of the lattice structure were made.

Abstract: The microstructure and mechanical properties of the ultrafine-grained Ti–50.8 at.% Ni alloy after thermal cycling treatment with the number of cycles up to 250 was investigated. A fractographic analysis of the samples after tensile tests was carried out. The fracture pattern of the alloy in the UFG state has a viscous character with microdepths on the fracture surface. The average size of microdepths decreases as the number of thermal cycles increases up to n= 250.

Abstract: The paper presents the results of a study the hydrogen effect on the structural-phase transformations and the superelasticity in binary ultrafine-grained (UFG) TiNi based alloy after diffusion redistribution hydrogen as a result of aging at room temperature. The redistribution of hydrogen in the process of long-term aging after electrolytic hydrogenation of UFG wire specimens the Ti_49,1Ni_50,9 (at.%) stabilizes the B2 structure. Superelasticity in samples aged at room temperature after hydrogenation is significantly deteriorated.

Abstract: In this study, we enhanced the corrosion fatigue life of a TiNi shape-memory alloy wire using a thermal oxidation treatment technique that can generate a passive layer on the wire surface. We followed the following procedure for the thermal oxidation treatment. First, the as-received material with an oxide film was mechanically polished to remove the film using an abrasive paper and a buffing compound. Second, the material was heat-treated in an electrical furnace filled with an N₂-20 vol% O₂ gas for 1 h at 673 K. Subsequently, the material was allowed to cool in the furnace. The results of this treatment are summarized as follows. (1) A passive layer was uniformly generated on the surface of the TiNi shape-memory alloy wire via thermal oxidation on a macroscopic scale; this significantly improved its corrosion resistance. (2) Thermal oxidation extended the corrosion fatigue life of the treated material more compared with HT in air. In addition, we found that the layer generated via the thermal oxidation treatment can maintain adhesion to the base material even when subjected to a bending strain greater than 1%.

Abstract: This work has as objectives the structural analysis and mechanical behavior of a TiNi (46.5Ti-53.5Ni (wt%) / 51.6Ti-48.4Ni (at%)) alloy displaying Shape Memory Effect, manufactured by Light Metals Institute, in Russia, as a ∅ 5.12 mm wire. Samples were annealed at 300 to 550oC, and air cooled afterwards. X-Ray and scanning electron microscopy structural analysis was performed. Mechanical tests by compression testing were made, up to 10% strain, with control unloading, and afterwards continued up to fracture. The alloy has shown itself sensitive to the heat treatment and applied strain. In the alloy, after annealing at different temperatures in the interval of 300 to 550oC, phases B19’, R and Ti₂Ni, were identified. Along higher annealing temperatures, up to 550oC, R phase was replaced by B2. In this alloy, strain induced Martensitic Reversible Transformations (MRT) type B2/R→B19 ́/R_def were induced.

Abstract: The chapter is devoted to a study of the influence of neutron irradiation on the martensitic transformations and shape memory effects in TiNi-based shape memory alloys. Irradiation of the samples was carried out in the low-temperature helium loop of a WWR-M fusion reactor at Petersburg Nuclear Physics Institute in Gatchina (Russia). The experimental data showed that the variation in transformation temperatures depended on the irradiation temperature. The main factors influencing the variation in transformation temperatures during irradiation were disordering of the solid solution at low temperatures, radiation ordering at high temperatures, and thermally activated annealing of radiation damage. All of these mechanisms were taken into account in the differential equation given in the present work for description of the transformation temperature variation during irradiation at different temperatures. It was found that irradiation up to a fluence of 7⋅10¹⁸ cm^-2 did not suppress the transformation plasticity and shape memory effects in TiNi alloy in spite of the variation in transformation temperatures. It was observed that the shape memory effect may be initiated by irradiation up to a fluence of 5⋅10²⁰ cm^-2 at a constant temperature (under isothermal conditions) due to a decrease in transformation temperatures.

Abstract: The effects of micro-arc oxidation (MAO) voltage (370V, 400V, 420V) on the surface morphology, adhesion of film/substrate, corrosion resistance and fretting friction and wear properties after micro-arc oxidation and heat-treatment for 48h of TiNi alloy were investigated. The results show that, as the voltage gradually increases: (1) micro-arc oxidation coatings form, when the voltage increase to 420V, the coating shows a significant micro-arc oxidized porous characteristics; (2) the Ca/P ratio in the coatings also increases, so the Ca/P ratio can be controlled by adjusting the voltage of micro-arc oxidation; (3) the corrosion resistance of MAO coatings can be significantly improved by increasing the output voltage, the corrosion rate and the corrosion potential of 420V are smaller two magnitude than 370V’s; (4) the coating of 420V shows lower friction coefficient with higher resistance, narrower wear scar width; (5) the MAO coatings have formed different types of hydroxyapatite crystals (HA) after immersed in high temperature and pressure reactor for 48h, and the phase composition of the coating are mainly apatite.

Abstract: Changes in the structure and properties of a TiNi alloy, which possesses shape memory effect by means of reversible martensitic transformation (RMT), after annealing at different temperatures in the interval of 300 to 550oC, were investigated. These changes were characterized by chemical analysis, X-ray diffraction, electrical resistivity, microhardness and differential scanning calorimetry. The results showed that the as-fabricated TiNi alloy presented a multiphase structure. An additional high temperature phase was revealed upon 550oC annealing. The alloy displayed sensible changes in its electrical resistivity that were attributed to the influence of the several existing phases. A tendency for the increase in the RMT critical temperatures was also observed with increasing annealing temperature.

Abstract: In this paper, BaZrO_3, which is successfully used to prepare the YBCO single crystal superconductor, is introduced into the melting of titanium alloys. The density of the home-made BaZrO₃ crucible reaches 97% of theoretical density, and TiNi alloy is melted using this crucible by the vacuum induction method. It is found that the home-made BaZrO₃ crucible possesses excellent thermal shock resistance. After melting, the surface of the ingot is smooth and it can be separated from the crucible easily, there is no reaction layer and elemental diffusion between the refractory and the melt is not observed, the oxygen content of the melt is about 600 ppm, and the increase of other impurity elements (i.e., Ba, Zr) is negligible. This implies that the BaZrO₃ is a promising candidate for refractories for melting the TiNi alloy.

Abstract: The present article is dedicated to the study of thermoelastic martensitic transformation in the TiNi equiatomic composition by low-frequency internal friction. Considered the influence of oscillation frequency, strain amplitude and heating rate on the internal friction peak of the martensitic nature.