Search Results (24)

The effect of thermomechanical processing (TMP) parameters on the structural-phase evolution and properties of Ni-enriched Ti–50.8 at.% Ni shape memory alloy was investigated. Compression deformation was performed at T = 300–500 °C, accompanied by the development of dynamic aging (DA) processes, to true strains of e = 0.5–1.3, followed by post-deformation static aging (SA) at 430 °C for 1 and 10 h. The structural-phase state and properties were characterized using optical and transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, and Vickers hardness measurements. The results confirmed that DA processes were activated during compression but proved insufficient for pronounced Ti₃Ni₄ precipitate growth compared with SA. The temperature range of 430–500 °C promoted the most intensive DA processes and facilitated ultrafine-grained structure formation. The processing route combining DA at 500 °C with short-term SA (1 h) resulted in the finest precipitates of Ti₃Ni₄ phase and most homogeneous substructure. These findings demonstrate that the proposed TMP strategy enables effective tailoring of precipitate dispersion, evolution of transformation temperatures and mechanical properties (hardness), providing a viable manufacturing pathway for tailoring TiNi SMA performance in advanced biomedical and engineering applications. Full article

Objectives: The aim of this study is to demonstrate the efficacy of the modified technique of radical organ-preserving surgery of invasive cervical cancer (CC) in patients of reproductive age. Methods: This study included 118 patients of reproductive age (34.9 ± 4.8 years) with a morphologically verified diagnosis of invasive CC (T1a-1bNxM0). All patients underwent organ-preserving surgery in the scope of radical trachelectomy. A shape memory mesh implant woven in the form of a stocking from superelastic nickelide titanium thread with subsequent fixation with separate sutures around the perimeter was used to form the uterine closure apparatus and to strengthen the utero-vaginal anastomosis. The mesh implant was made of superelastic thin nickelide titanium threads with a diameter of 60–40 microns on a metal knitting machine. All patients were prospectively followed up for a mean of 120 months. Results: No intraoperative or postoperative complications were revealed when using a shape memory implant made of titanium nickelide during radical trachelectomy to form a locking apparatus and strengthen the anastomosis zone. No cervical stenoses or mesh failures were noted in any case. The 5-year overall and recurrence-free survival rates were 100% and 98%, respectively. Two patients indicated recurrence; it occurred in 3 and 36 months. There were 42 spontaneous pregnancies, and 29 resulted in full-term delivery, whereas 2 and 11 ended in miscarriage and early abortion, respectively. Currently, 18 patients are at different stages of the use of assisted reproductive technologies. Conclusions: The shape memory implant made of titanium nickelide integrates well into the surrounding tissues and successfully imitates the effect of the cervix. The use of this sparing-surgery technique has shown reasonably good results in carrying the pregnancy to term and good reproductive outcomes. Full article

The present study was carried out using a cold-drawn wire of Ni_50.8Ti at.% subjected to post-deformation solution treatment at 700 °C for 1 h to obtain a fine-grained recrystallized structure. Subsequent aging was carried out at a temperature range of 300, 430, and 500 °C for 1, 10, and 20 h. The time–temperature aging mode strongly affects the aging-induced microstructure. Variation of the aging-induced microstructure (using various aging modes) permits precise tuning of the characteristic temperature of the martensitic transformations and their specific temperature ranges upon cooling and heating. The latent heat and hysteresis exhibit different evolution vs. aging durations; this finding remains fair when using different aging temperatures. The aging mode strongly affects the stress–temperature behavior: (i) a dramatical expansion of the temperature range of realization of the transformation yield stress (σ_tr); and (ii) the magnitude of σ_tr at a chosen test temperature is generally determined by the position of the M_s temperature. An additional contribution of competing factors is discussed. The efficiency of the aging temperature under isochronous aging is significantly higher than the efficiency of the aging time under isothermal aging. Aging at 430 °C for 10–20 h provides the highest resource for the recovery strain. The strain–temperature behavior strongly depends on the relative position of the R_s and M_s temperatures (onset of B2→R and R→B19′ transformations, respectively). The regularities obtained can be used to predict the set of functional and mechanical properties of titanium nickelide. Full article

This paper presents a model of the bending behavior of a bi-layer cantilever composed of titanium nickelide and a magnetoactive elastomer embedded with magnetically hard particles. The cantilever is initially subjected to an external magnetic field in its high-temperature state, followed by cooling to a low-temperature state before the magnetic field is removed. This sequence results in residual bending deformation. Basic relations describing the material behavior of titanium nickelide and the magnetoactive elastomer are presented. A variational formulation for the problem under consideration is written down. The problem is solved numerically using the finite element method. The influence of the applied magnetic field magnitude and the thickness of the titanium nickelide layer on the cantilever deflection magnitude is studied. The dependence of the residual cantilever deflection on the applied magnetic field is obtained. The possibility of this structure as a controllable gripping element for applications in robotics and micro-manipulation is demonstrated. Full article

This article presents the results of studies of the features of the development of thermoelastic martensitic transformations during cooling/heating in the free state and under load of Ti₅₀Ni_49.7−XNb_XMo_0.3 alloys (X = 0.5, 1.0 and 1.5 at% Nb) with shape memory effects. Using X-ray diffraction analysis, it was found that all the alloys studied at room temperature contained a multiphase mixture consisting of intermetallic compounds with the TiNi (B2, B19′), Ni₅₆Ti₂₉Nb₁₅, and Ti₂Ni compositions. Scanning electron microscopy was used to study the microstructure of TiNi (Nb,Mo) alloys and it was found that the distribution of fine Ni₅₆Ti₂₉Nb₁₅ particles in the matrix depends significantly on the concentration of the alloying element. A correlation was established between changes in the structural-phase state in TiNi (Nb,Mo) alloys and the occurrence of the B2↔B19′ martensitic transition in the free state and under load. Based on physical and mechanical studies, the temperature ranges of the martensitic transformations (MT) in the free state and under load were established. Based on the thermodynamic description of the MT and the analysis of the characteristic temperatures of the MT, it was found that the MT mechanism is strongly dependent on the concentration of the alloying element. Full article

The effect of quasi-continuous (QC) equal-channel angular pressing (ECAP) in various pre-aged states on the structure formation and mechanical and functional properties of a hyper-equiatomic titanium nickelide (TiNi) shape memory alloy is studied. QC ECAP with a channel intersection angle of 110° is carried out at a temperature of 450 °C after aging for 1 and 5 h for three passes. To investigate the obtained structure and properties, the following research methods are applied: transmission electron microscopy, XRD analysis, calorimetric study, tension and hardness tests, and a special technique for the determination of functional properties. QC ECAP allows for the considerable refinement of structural elements and results in obtaining a mixed fine-grade structure, with structural elements of average sizes of 92 nm after pre-aging for 1 h and 115 nm after pre-aging for 5 h. Pre-aging for 5 h before QC ECAP, in combination with QC ECAP and post-deformation aging at 430 °C for 1 h, provides the best combination of mechanical and functional properties: a dislocation yield stress of 1410 MPa, ultimate tensile strength of 1562 MPa, and total recoverable strain of 11.6%. These values are comparable with the best results obtained for titanium nickelide and expand opportunities for the application of smart shape memory devices. Full article

The regularities and features of the evolution of the grain–subgrain structure, phase composition and mechanical properties in Ti_49.8Ni_50.2 (at.%), depending on the temperature of isochronous annealings at 573–973 K are herein studied. The state of the Ti_49.8Ni_50.2 (at.%) alloy samples after abc pressing at T = 573 K with the given true strain e = 9.55 was taken as the initial state. It is shown that the grain–subgrain structure of the samples after annealing for 1 h in the temperature range of 573–673 K changes slightly. In samples annealed at 673 K, regions with the microband structure similar to the microstructure of a fast-frozen turbulent liquid flow were found. It has been established that during annealing at 773 K the beginning of an active recrystallization process is realized; the size of grains does not exceed the submicrocrystalline scale (~200 nm). At 873 K, the recrystallization process occurs in the entire volume of the samples; the grains with an average size of 2 ± 0.5 µm are almost equiaxed. The microstructure of the samples after annealing at 973 K (with average grain sizes of 5 ± 0.5 µm) is qualitatively similar to the microstructure of the samples after annealing at 873 K. It was found that the phase composition of the samples as a result of isochronous annealing at 573–973 K changes from R and B19’ immediately after abc pressing to a three-phase state: B2, R and B19’ phases. It is shown that the highest values of yield stress σ_y, ultimate tensile strength σ_UTS (1043 MPa and 1232 MPa, correspondingly) and low ductility (the deformation to fracture ε_f = 48%) are observed in the initial samples. Increasing the temperature of post-deformation annealing and, correspondingly, the development of recrystallization, led to a decrease in σ_y, σ_UTS and an increase in ε_f to the values of these characteristics in the coarse-grained samples (σ_y = 400 MPa, σ_UTS = 920 MPa and ε_f = 90%). Full article

In the present work, the possibility of applying severe torsion deformation (STD) to a bulk near-equiatomic NiTi shape memory alloy in order to accumulate super-high strain and improve mechanical and functional properties was studied. STD was performed using the multidirectional test system “BÄHR MDS-830” at a temperature of 500 °C (the upper border temperature for the development of dynamic polygonization) in 14 and 30 turns with accumulated true strain values of 4.3 and 9.1, respectively. Structural phase state and properties were studied using differential scanning calorimetry, X-ray diffractometry, transmission electron microscopy, hardness measurements, and thermomechanical bending tests. STD at 500 °C allowed for the accumulation of high strain without failure. As a result of STD in 30 turns, a submicrocrystalline structure with an average grain/subgrain size of about 500 nm was formed. This structure ensured the achievement of high maximum completely recoverable strain values of 6.1–6.8%. The results obtained show the prospects of applying severe torsion straining deformation to titanium nickelide in terms of forming an ultrafine-grained structure and high properties. Full article

Coatings based on calcium phosphate with thicknesses of 0.5 and 2 μm were obtained by high-frequency magnetron sputtering on NiTi substrates in an argon atmosphere. The coating was characterized using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and in vitro cytocompatibility and bioactivity studies. A biphasic coating of tricalcium phosphate (Ca₃(PO₄)₂) and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) with a 100% degree of crystallinity was formed on the surface. The layer enriched in calcium, phosphorus, and oxygen was observed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Scanning electron microscopy showed that the surface structure is homogeneous without visible defects. The 2 µm thick coating obtained by sputtering with a deposition time of 4 h and a deposition rate of 0.43 µm/h is uniform, contains the highest amount of the calcium phosphate phase, and is most suitable for the faster growth of cells and accelerated formation of apatite layers. Samples with calcium phosphate coatings do not cause hemolysis and have a low cytotoxicity index. The results of immersion in a solution simulating body fluid show that NiTi with the biphasic coating promotes apatite growth, which is beneficial for biological activity. Full article

This study aimed to determine the incidence of dentinal microcracks after instrumenting the root canals of maxillary premolars using two novel rotary instrumentation systems. Micro-computed tomography (microCT) scans and images generated by sectioning and observation with a stereomicroscope were used to assess the specimens. Twenty-two freshly extracted maxillary premolars were collected and the specimens were divided into two groups of eleven. The tested radicular shaping systems were XP-Endo shaper and TRUShape (i.e., single file). The specimens were scanned with microCT pre- and post-instrumentation, and the newly formed microcracks were detected. The post-instrumentation scans were also compared with images obtained by sectioning method and stereomicroscope inspection, comparing the incidence of microcracks in either microCT scans or images. The results identified an overall incidence of 0.49% of newly formed microcracks, with no statistically significant differences (p = 0.689) between the shaping systems (0.11% for TRUShape and 0.87% for XP-Endo shaper). There were statistically significant differences (p < 0.001) between the microcracks incidence in microCT scans and the sectioning method (16.6% more for the latter). In conclusion, the results show that neither TRUShape nor XP-Endo shaper created dentinal microcracks during root canal instrumentation. The sectioning method with stereomicroscope evaluation overestimates the presence of microcracks with a statistically significant difference compared to microCT scans. Full article

This study aimed to compare the intracanal lateral force and cutting efficiency associated with two engine-driven nickel-titanium (NiTi) systems during root canal shaping. Bovine single-rooted teeth models were assembled to a custom-made splitting force measuring platform while being endodontically treated with rotary (ProTaper Gold [PTG]) or reciprocal systems (WaveOne Gold [WOG]) by two clinicians. The cutting efficiency test was run for each group by a free-falling endomotor on dentin discs for 3 min. The resulting force, files, and stroke force peaks were recorded. Data were analyzed by the Shapiro-Wilk test and ANOVA. Statistical significance was set at alpha = 0.05. Intracanal lateral forces (p < 0.01), cutting efficiency (p < 0.01), and time efficiency (p < 0.01) were significantly different between the NiTi groups. The maximum lateral splitting force was detected using the PTG shaping full-length file (S1) and during the WOG final stroke. Thus, caution is advised when reciprocating single-file systems approach the apical third or when using a large taper and wide-diameter rotatory instruments. The WOG had significantly less maximum horizontal splitting force and significantly greater cutting efficiency but less time efficiency than the PTG system. Full article

Recently, film materials based on the combination of noble metals have showed promising results for surface modification of medical implants, allowing both to improve biocompatibility and to acquire the increased antibacterial effect. An important challenge here is to combine the developed coating morphology, which is favorable for biological response, with a high protective function, which, on the contrary, requires a compact coating microstructure. In this work, we aimed to solve this problem with respect to the TiNi implant material. We have tested two types of compact thin sublayers: Iridium (Ir’), formed by metal-organic chemical vapor deposition (MOCVD), and gold (Au), formed by physical vapor deposition (PVD). Subsequently these sublayers were coated with a developed-columnar-iridium (Ir) by MOCVD. Features of the microstructure, chemical and phase composition of all these film materials were studied using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The changes in the characteristics of TiNi martensitic transformation due to MOCVD experiments were also studied by differential scanning calorimetry (DSC). The biocompatibility of Ir’/TiNi, Au/TiNi, Ir/Ir’/TiNi, Ir/Au/TiNi samples was assessed by cytoxicity testing (Man-1 cells) and measuring of nickel content in the biological extracts. The application of both sublayers effectively reduces the release of nickel, which was previously shown for Ir/TiNi samples. This prevents the toxic effect. Note that the Ir’ sublayer better protects against nickel release, while the Au sublayer promotes cell proliferation. Full article

For the first time, we performed functionalization of the surface of porous titanium nickelide alloys with bambusuril[6]-based macrocyclic compounds by different methods in order to provide the basis for saturation with therapeutic agents to impart antibacterial activity and accelerate its osteogenesis. It has been shown for the first time that the vacuum modification method is preferable for bambusuril deposition, since it provides a uniform deposition of organic matter on both the outer and inner surfaces of the pores. The effect of bambusuril deposition methods on the continuity, structure, and cytocompatibility of the porous titanium nickelide surface was evaluated. In vitro tests proved high biocompatibility and low toxicity of porous TiNi treated with BU[6] under vacuum. The SEM study of the structure of the surface layer of TiNi modified with BU[6] under the vacuum method showed that BU[6] agglomerates are uniformly deposited on the inner and outer surfaces of TiNi pores, which will provide an even saturation of BU[6] cavities with various pharmaceuticals, including antibiotics and inhibitors. Full article

We present a brief overview of the structural and phase transformations and mechanical properties of bulk binary TiNi shape memory alloys, which demonstrate attractive commercial potential. The main goal of this work was to create a favorable microstructure of bulk alloys using both traditional and new alternative methods of thermal and thermomechanical processing. It was found that the implementation of an ultrafine-grained structure by different methods determined an unusual combination of strength, ductility, reversible deformation, reactive resistance of these alloys to subsequent tensile or torsion tests at room temperature, and, as a consequence, the highly reversible effects of the shape memory and superelasticity. It is shown that the alloys Ti_49.8Ni_50.2 and Ti_49.4Ni_50.6 are incapable of aging, and, after being subjected to ECAP, were characterized by their high strength (σ_u up to 1200 MPa) and ductility (δ up to 60–70%). A combined treatment of multi-pass rolling and HT of the Ti_49.5Ni_50.5 and Ti₄₉Ni₅₁ alloys prone to aging have provided even greater strength (σ_u up to 1400–1500 MPa) with slightly lower ductility (25–30%). The microstructure, phase composition, and martensitic transformations in Ti-Ni alloys with varying Ni concentrations ranging from 50 to 51 wt.% were investigated by TEM, SEM, and X-ray methods. The mechanical behavior of the alloys was studied during tensile and torsion tests. Full article

The phase composition, microstructure, and multiple shape memory effect of TiNi_50−xV_x alloys were studied in this work. The phase composition of the TiNi_50−xV_x system is the TiNi matrix, spherical particles of TiNiV, the secondary phase Ti₂Ni(V). Doping of TiNi alloys with vanadium atoms leads to an increase in the stability of high-temperature B2 and rhombohedral R-phases. An increase in the atomic volume with an increase in the concentration of the alloying element V from 1 to 4 at.% was established. Vanadium doping of the Ti–Ni–V system alloys leads to an increase in the temperature interval for the manifestation of the multiple shape memory effect. It has been established that the value of the reversible deformation of the multiple shape memory effect both during heating and during cooling increases linearly from 2 to 4% with an increase in the vanadium concentration. Full article