Abstract—The mechanical and functional properties of a composite material consisting of a polyethylene matrix reinforced with a titanium nickelide wire are investigated. This composite material has a high fracture strength under static and cyclic bending. The effective ultimate strength of the composite material during interlaminar shear exceeds 3.6 MPa. Depending on the structural state of titanium nickelide, the fatigue life of the composite material is 2–50 times longer than that after similar reinforcement with a corrosion-resistant steel wire. The viscoelastic behavior of polyethylene is found to affect the superelasticity and the one-way shape memory effect of the composite material. Despite the low adhesive strength of the polyethylene/titanium nickelide interface, this composite material can exhibit the one-way shape memory effect with a shape recovery η ≈ 0.95.

Rapidly solidified fibers are a unique metallurgical semi-finished product used to manufacture filters, damping materials and implants. At present, there is virtually no information on the production of fibers from commercial titanium alloys. In this work, we produce fibers from the high-strength titanium alloy Ti-5Al-5V-5Mo-1Cr-1Fe, wt. %. The phase composition and microstructure of the fibers are studied by X-ray structural analysis and electron microscopy. Tensile testing, bending and microhardness measuring are used to investigate fiber properties. It has been found that after rapid solidification a fine-dispersed microstructure of the alloy is observed with an average grain size of 22 mu m in the longitudinal and transverse sections. The fibers have high tensile strength (>1000 MPa) and microhardness (317.7 +/- 3.7 HV0.05) but low plasticity. At the same time, they are able to endure enormous deformation (up to 50 %) during bending without destruction. With such deformation degree, stress-induced beta ->alpha" martensitic transformation is observed.

The laws of changing the shape of cylindrical springs made of a titanium nickelide-based alloy are considered as a function of the level of counteracting stresses and thermal cycling boundaries. Stresses from 20 to 110 MPa are shown to cause completely reversible deformation of the material; at higher stresses, unrecovered deformation accumulates. During thermal cycling, a decrease in heating temperatures in the range As–Af and an increase in cooling temperatures in the range Ms–Mf are accompanied by a decrease in the reversible deformation of the material.

The characteristics of the shape memory effect of a silicone rubber–titanium nickelide composite material under bending deformation have been studied. It is shown that the critical deformation ( ε _cr^0.2 ), upon reaching which 0.2 ε _cr^0.2 = 9

The paper analyzes the possibility of creating a titanium porous fiber material for implants, which is made of fibers of various transverse sizes and has gradient pore architecture. The architecture of the porous space, structure, and mechanical characteristics of such material have been studied. It is shown that the strength of the porous fiber material can be improved by increasing the temperature of diffusion bonding and by performing hydrogen heat treatment. The specifics of the mechanical behavior and fracture of the material samples were studied by performing a fixed-end bending test.

The effect of volume fraction and size of Ti4Ni2Ox particles on pitting, crevice, and fretting corrosion processes is studied by testing implanted elements of titanium nickelide based alloys as part of spinal pedicle screw devices in a 0.9% NaCl solution, tested elements being produced from ingots melted by various technologies (vacuum induction melting; combined skull melting with subsequent vacuum-arc remelting). It is shown that the vacuum induction melting method, which provides higher purity of the resulting material, in particular with respect to oxygen, and reduces the Ti4Ni2Ox volume fraction, is preferable for increasing titanium nickelide based alloy corrosion resistance in a biological environment. It is established that a reduction in volume fraction (and size, dmax) of Ti4Ni2Ox particles from 5.1 +/- 1.2 vol.% (dmax = 10 mu m) to 3.5 +/- 0.7 vol.% (dmax = 7 mu m) results in the pitting potential increasing from 552 +/- 70 to 854 +/- 123 mV and the fretting corrosion current decreasing from 11 +/- 2.7 to 6.7 +/- 2.8 mu A. At the same time, the content of Ni ions in a test corrosion medium after crevice and fretting corrosion studies decreases from 84 +/- 6 to 64 +/- 5 and from 74 +/- 6 to 57 +/- 4 mu g/liter, while the area of corrosion sites decreases by 1.3 and 1.8 times respectively. It is shown that a further reduction in Ti4Ni2Ox particle volume fraction down to 1.2 +/- 0.2 vol.% (dmax = 5 mu m) does not have a significant effect on corrosion resistance indices.

The characteristics of the shape memory effect of the VT22I titanium alloy under torsional deformation have been investigated. The critical deformation (γcr0.3), at which 0.3% of unrecovered deformation accumulates, was used as the main characteristic of the effect. It is shown that in the VT22I alloy this value is 3—4 times less than in alloys based on NiTi, which is due to an intensive increase in resistance to movement of the interface «martensite—austenite» and low slip stresses in a disordered solid solution.

The strain and temperature characteristics of the shape memory effect are studied in bending tests of a composite material with the nylon 66 matrix reinforced with nickel-titanium wire containing 55.7 wt % Ni. It is shown that deformation mechanisms in the matrix and the reinforcing filler influence the shape memory behavior of the composite. The В2 → В19′ martensitic transformation and dislocation slip processes occurring in nickel titanium and resulting in unrecoverable deformation determine thermomechanical properties of the composite. The plastic deformation and stress relaxation mechanisms in the polyamide matrix should also be taken into account, as they can either promote or prevent the shape memory effect in the reinforcing filler at different stages of the composite deformation. It is proposed that the main performance characteristics of shape memory composites are the critical strain ε cr 0.2 , at which 0.2% of unrecoverable strain is accumulated, and the shape recovery start and finish temperatures determined after prestraining to ε cr 0.2 in a cooled state. The strain and temperature characteristics of the shape memory effect are compared between the composite material and the reinforcing filler. The viscoelastic behavior of the composite matrix is shown to decrease the critical strain from 9% in the reinforcing NiTi filler to 5% in the composite. The composite material exhibits a slight decrease (by approximately 5°C) in the shape recovery temperatures compared to the reinforcing NiTi filler.

It is shown that the pressure treatment of titanium nickelide alloys should be carried out in two stages. At the first stage, ingots are deformed in order to transform the brittle cast structure, while at the second stage, the necessary shape is imparted to a semi-finished product along with the required structure and material properties. The deformability of TiNi alloy ingots largely depends on the content of impurities and the uniformity of a chemical composition, which is determined by the purity of a charge material and the smelting method. The deformability can be increased on the basis of using a titanium sponge in terms of a charge and smelting ingots either by an induction method in a cold crucible unit or by the combination of skull melting with subsequent vacuum-arc remelting. At the second pressure treatment stage during the acquisition of deformed semi-finished products with the required structure and shape memory effect properties, it is necessary to consider temperature-time conditions for the development of polygonization and recrystallization processes, as well as the precipitation of Ni-rich Ti3Ni4 intermetallics.

The operability of shape memory spring actuators made of titanium nickelide under constant and variable counteraction to shape recovery is investigated. Methods for calculating the maximum specific energy of the actuators using the properties of the material are proposed. These properties are shown to be the critical strains and stresses (in martensitic and austenitic states) corresponding to the beginning of slip processes and depending on the ratio of the test temperature to the shape recovery temperatures.

The deformation- and thermal-cycle resistance of titanium nickelide-based alloys is considered. We proposed to estimate these characteristics using both fracture and the degradation of the functional characteristics of the material (shape recovery temperature, unrecoverable strain, etc.). The functional characteristics are found to be determined by the critical stresses and strains of the material, which depend on its structure and the test temperature.

It is shown that the structure of alloys based on titanium nickelide, obtained by industrial technology, invariably contains titanium-rich phases of type Ti2Ni/Ti4Ni2(O, N), even if the nickel concentration in the B2-phase exceeds the equiatomic composition. The volume fraction of these phases depends on the smelting method, the purity of the charge, and the technology used for subsequent ingot processing. Regression equations linking shape recovery temperatures with the concentration of nickel in the B2-phase in the quenched state are presented. On the basis of these equations, a method for calculating the volume fraction of Ti3Ni4 type particles released during aging is proposed.

Theoretical calculations and experimental studies were carried out making it possible to predict the maximum value of reversible deformation of a composite material based on a polymer matrix reinforced with titanium nickelide fibers.

— The effect of the structure, the temperature, and the deformation scheme on the deformation behavior of titanium nickelide-based alloys is studied. One of the most important characteristics of the material is shown to be the temperature dependence of the critical strain corresponding to the onset of intense development of slip mechanisms.

— The composite material consisting of a carbon fiber reinforced plastic matrix and reinforcing titanium nickelide elements is studied and subjected to static and cyclic three-point bending tests. At the same rigidity, the elastic deformation and the fatigue life of the material are found to increase with the volume fraction of titanium nickelide. The developed material can be used to produce prosthetic–orthopedic medical articles.

The mechanical properties and fracture of a TiNi alloy (Ti-55.8 wt % Ni) have been investigated under vacuum heat treatment at 700–1200°C. Three-point bending and low cycle fatigue tests were conducted on heat treated wire samples under extreme loading conditions (large strains and alternating bending loads) to determine the effect of the annealing temperature on the superelastic behavior of the alloy. It was found that an increase in the heat treatment temperature leads to grain coarsening in the alloy, but the coarsening effect on its superelastic behavior is insignificant at low bending strains (4.0–4.5%). With heat treatment temperature variation from 700 to 1200°C, the shape of the alloy stress-strain curves remains almost unchanged for all bended samples, but with increasing heat treatment temperature the martensitic shear stress and residual strain slightly increase. In low cycle bending tests, the alloy ductility reduces significantly after heat treatment above 1100°C. Fractographic analysis of the tested alloy samples revealed different fracture surface structures depending on the heat treatment conditions, but the same fracture mechanism. In all cases, fracture occurs by quasi-cleavage, and the microcrack nucleus is associated with Ti2Ni/Ti4Ni2O inclusion particles or surface defects. The general results indicate the possibility of diffusion welding of TiNi alloys at a temperature of 1000–1100°C, without pronounced changes in their mechanical properties and ductility.

Abstract—A composite material consisting of a silicone rubber matrix and nickel–titanium wire reinforcement added at different volume fractions is prepared, and its debond strength and thermomechanical behavior are studied. The debond strength of the composite can be increased by reducing the surface roughness of the embedded nickel–titanium wire to Ra = 0.16 μm. The loading rate has a considerable effect on the residual strain in this material. The composite materials with the reinforcement content of 10 to 31% subjected to a 10% pre-strain can fully recover their shape on heating, suggesting the presence of memory shape effect in these materials.

The short-term creep processes in a Ti–55.7 wt % Ni alloy are investigated. Wire samples of this alloy after preliminary annealing at 450–700°C are deformed by torsion under constant loading in an air atmosphere in the temperatures range 450–550°C. The effect of structural parameters (grain size, presence of fine Ti3Ni4 particles) on the creep mechanism and rate is shown. Grain-boundary diffusion is found to be one of the main creep mechanisms.