Papers by Keyword: TiNi

Abstract: The deposition of composites with tailored optical properties is investigated. This would employ structures consisting of combined metallic and oxides nature. A thin layer of TiNi is obtained by using RF magnetron sputtering on a stainless-steel substrate, followed by oxidation at 400°C and 800°C for four and one hours, respectively. The optical properties of the thin films were characterized by optical spectrophotometer, and Fourier Transform Infrared Spectroscopy (FTIR). The morphology, topography, and structure were studied by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD). The results show that TiO₂ has been produced through the oxidation process of the sputter-deposited TiNi thin film at high oxidation temperature. The TiNi thin films showed a significant improvement in optical properties after oxidation, as the absorbance increased, and the emittance was reduced. This work introduces oxidized TiNi thin films as candidates for solar selective absorber.

Abstract: Implants made of porous SHS-TiNi alloys are successfully used in medicine to replace solid tissues of the human body. Self-propagating synthesis reaction of TiNi alloy was carried out through layer-by-layer combustion. XRD analysis of the phase composition and structural parameters of porous N_i50Ti₅₀ alloy, as well as microscopic studies, were carried out. The structural methods employed in the study showed that the surface of porous SHS-TiNi alloys is a complex of dense layers of amorphous-nanocrystalline intermetallic oxycarbonitrides saturated with O, N, C intercalation impurities. The study of the surface layer S showed that the layer S consists of three layers: the foam layer F and two sublayers. Samples were studied for the nonuniform potential distribution in the cross section of interpore partitions. It was shown that they correlate with the structural phase inhomogeneity of the SHS-TiNi alloy. The structural studies carried out using different methods allowed us to reliably establish the presence of surface nonmetallic phases in the form of surface films and grain boundary inclusions formed during the self-propagating reaction synthesis of the porous TiNi alloy. High biochemical compatibility is ensured by specific surface layers of the porous alloy formed in the process of its metallurgy, which do not require additional surface modification.

Abstract: In situ synthesized TiB_x/TiC reinforced composite coatings were prepared on Ti-6Al-4V substrate by laser in situ deposition using 10B₄C-18TiNi-72Ti-6Al-4V (wt. %) powder blends as the feedstock materials. The microstructural analysis of the composites was performed using scanning electron microscope, and phase analysis was done with X-ray diffraction. The results showed that the composite coatings contained long needle TiB, irregular block TiB₂ and disperse particles/dendrites TiC, the thick rod phase which was a inlay structure consisted of TiB₂ and TiC. These composite reinforced phases were evenly distribution in the (TiNi+Ti₂Ni+α–Ti) substrate.

Abstract: The results of studies on the influence of ultrasonic vibrations (UVs) on shape memory effect (SME) in NiTi alloys are presented. The appearance of shape memory effect is due to changes in the temperature and mechanical stress. They can operate simultaneously under the ultrasonic treatment. It has been found that the ultrasonic vibrations can initiate shape recovery processes in a material with shape memory effect. The reversion of the accumulated deformation occurs at the direct and reverse martensite transformations under the influence of ultrasonic vibrations. Since the process is accompanied by ultrasonic heating, small thermal mechanical hysteresis loops have been observed during the direct transformation. The deformation reversion can be explained by ultrasonic heating of the sample due to the dissipation of vibrations and the formation of austenite.

Abstract: Structural properties of porous TiNi-based materials produced by SHS method and sintering have been investigated. The material having different pore wall surface topography, porosity and pore size distribution was shown to be produced depending on the powder metallurgy method for porous TiNi-based alloy. All the materials having porosity of 55-70%, mean pore size 90-150 μm, as well as normal pore size distribution are most preferable. Ultimate strength and breaking point were determined to depend on porosity, pore size distribution, pore intersections and phase chemical composition of the material. Strength properties of the sintered alloy are twice as much compared to the SHS-produced ones due to homogeneity of its macrostructure, low chemical heterogeneity and TiNi₃ precipitations strengthening the TiNi matrix.

Abstract: The strain recovery character and transformation behavior of a TiNi alloy are investigated by means of mechanical testing and DSC measurement before and after vibration. The DSC results show that the second reverse transformation peak temperature of TiNi alloys after vibration under constraint increases slightly during the subsequent heating, and the transformation heat decreases, while the transformation heat of the first reverse transformation increases. After constrained vibration, the first decline of the two-stage recovery strain obtained during the second heating process is obviously smaller than the one without vibration, and the total recoverable strain also decreases. For the prestrained martensitic TiNi fiber after a heating-cooling cycle, the two-way memory strain increases about 1.2% after vibration. All these phenomena are considered to be closely related to the vibratory stress relief during vibration.

Abstract: The influences of different annealing temperatures and pre-strains on the coupling effect between TiNi matrix and the Nb nanowire were studied by means of synchrotron X-ray diffraction in form of variation in lattice strain of the nanowire upon temperature changing for four groups of samples. For every annealing temperature, variation in Nb (110) lattice strains initially increasing with increasing pre-strain and then decreased after 12% pre-strain. A maximum variation in Nb (110) lattice strain was observed approaching 2.4% within the sample 450°C-20min annealed and 12% pre-strained. Such variations in lattice strain of the embedded nanowires upon temperature changing provided the composite great potentials as structural-functional integrated two-way actuators.

Abstract: The electronic energy structure of Ti-Ni and TiNi-Cu alloys has been studied experimentally by XPS and NEXAFS and theoretically by the full-potential local-orbital minimum-basis code. The study has revealed formation in the valence band of the Ti50Ni50 alloy of a common d-band through hybridization of the d-states of Ti with those of Ni, which is localized within a narrow binding-energy interval. This brings about an intra-atomic redistribution of Ti electron density in the Ti50Ni50 alloy compared to the pure metal: decrease of the occupancy of the Ti d-shell is countered by an increase in the number of Ti p-electrons. The occupancy of the Ti d-shell in the TiNi-Cu alloys, where Ni atoms are partially substituted by Cu, and in the Ti-Ni alloys with an excess of the Ni is more than in the equiatomic Ti50Ni50 alloy. The occupancy of the Ni and Cu d-shells in the Ti-Ni and TiNi-Cu alloys is independent of the atomic composition. The Ti d-shell sensitivity to variation of the nearest atomic environment is apparently due to their relatively itinerant behavior in the studied alloys. The results obtained suggest that the increase of the stiffness of an interatomic bond in the TiNi-Cu alloys with increasing Cu content and in the Ti-Ni alloys with increasing Ni content is possibly associated with the filling of Ti bonding d-states.

Abstract: Ab-intio investigations of atomic and molecular oxygen on TiNi(110) surface are performed by using the projector augmented wave method with generalized gradient approximation for the exchange-correlation functional. Our results confirm the formation of a Ni-rich interface TiO2(100)/TiNi(110), for which the formation energies (Hf) of point defects at the interfacial layers were estimated. It is shown that Hf of swap Ti-Ni defect has a lower energy than that for the Ni antisites at the interfacial layers. The formation energies of point defects in bulk TiNi, monoclinic TiO, and rutile TiO2 are also calculated. Our results demonstrate that Hf of Ni-antisites in TiO is twice less than that in TiO2. The formation of small Ni clusters is also discussed.

Abstract: Processes, occurring on annealing of TiNi alloy, processed by high pressure torsion (HPT), were the focus of this research. Some peaks of heat release were found on heating the deformed samples up to 550 °C. If the initial structure of the alloy was amorphous (after 3.5 turns of HPT), then structural relaxation, crystallization and grain growth occurred on heating. When alloys had a crystalline structure (after rotation by 15 and 90 degrees), recovery, recrystallization and further grain growth took place on heating. It was observed that the TiNi alloy, subjected to 3.5 turns of HPT and subsequent heating up to 550 °C, underwent unusual kinetics of martensitic transformations. The austenite B2 phase transformed to the martensite B19' phase in two ways: B2→R→B19' and B2→ B19'.