Параметры эффекта памяти формы в сплавах на основе TiNi с серебром

Статья представляет исследования влияния добавки серебра с разной концентрацией до 1,5 ат.% на сплавы на основе TiNi. Построены температурные зависимости накопления и возврата деформации при многократном эффекте памяти формы (ЭПФ) сплавов (TiNiMoFe)Ag и определены параметры ЭПФ (температуры начала и конца накопления и возврата деформации, остаточная и обратимая деформации, ширина петли гистерезиса). Показано, что увеличение концентрации серебра приводит к росту ширины петли гистерезиса и величины обратимой деформации. Изменение состава в В2 структуре приводит к смещению характеристических температур превращения исследуемых сплаво

Cyclic stability of two-way shape memory effect in aged Ni50.3Ti32.2Hf17.5 polycrystals after various thermomechanical treatments

In the present paper, the cyclic stability of the high-temperature two-way shape memory effect was studied in high-strength Ni50.3Ti32.2Hf17.5 polycrystals after various thermomechanical treatments—training (thermocycling under stress) and stress-induced martensite aging. The effect of training and stress-induced martensite aging on the microstructure, the two-way shape memory effect, and its cyclic stability was determined. It was found out that both thermomechanical treatments induce the high-temperature two-way shape memory effect at T > 373 K, with a strain of 1.5% in tension. The influence of cyclic tests (up to 100 stress-free cycles of cooling/heating) on the two-way shape memory effect strain, the transformation temperatures, and the microstructure was established. Different degradation mechanisms of the two-way shape memory effect were established after thermocycling and stress-induced martensite aging

The influence of the surface layer on the combination of properties of thin TiNi alloy wires

We have studied the influence of the surface layer on the parameters of the multiply repeated shape memory effect, developing stresses, characteristic temperatures, and intervals of martensitic transformations in thin (1 mm diameter) wires made of TiNi-based alloys. Examination of the surface layer structure showed that, in 1-mm-diameter TN-1V grade alloy wire, the oxide layer is about 15 μm thick and consists mostly of titanium, nickel, oxygen, and carbon. Removal of this surface layer leads to an increase in the maximum accumulated deformation, shift of the temperature interval of formation toward higher temperatures, and increase in the strength and plasticity characteristics

Influence of wire geometry on the mechanical behavior of the TiNi design

The present article is aimed at studying the deformation behavior of TiNi wire and knitted metal TiNi mesh under uniaxial tension and revealing the role of wire geometry on their main mechanical characteristics and mechanisms of deformation behavior. The temperature dependence curve of the electrical resistance indicates that a two-stage martensitic transformation of B2!R!B190 is occurring, and is responsible for the superelasticity effect. The TEM results showed that at room temperature, the TiNi wire has a nanocrystalline structure composed of B2 austenite grains. A change in the deformation mechanism was established under the uniaxial tension, where the TiNi wire exhibits the effect of superelasticity, while the knitted metal TiNi mesh made from this wire is characterized by hyperelastic behavior. Fracturing of the knitted metal TiNi mesh requires significant loads of up to 3500 MPa compared to the fracture load of the TiNi wire. With the uniaxial tension of the wire, which maximally repeats the geometry of the wire in knitted metal mesh, an increase in mechanical characteristics was observed

The effect of subsequent stress‐induced martensite aging on the viscoelastic properties of aged NiTiHf polycrystals

This study investigated the effect of stress‐induced martensite aging under tensile and compressive stresses on the functional and viscoelastic properties in Ni50.3Ti32.2Hf17.5 polycrystals containing dispersed H‐phase particles up to 70 nm in size obtained by preliminary austenite aging at 873 K for 3 h. It was found that stress‐induced martensite aging at 428 K for 12 h results in the appearance of a two‐way shape memory effect of −0.5% in compression and +1.8% in tension. Moreover, a significant change in viscoelastic properties can be observed: an increase in internal friction (by 25%) and a change in elastic modulus in tensile samples. The increase in internal friction during martensitic transformation after stress‐induced martensite aging is associated with the oriented growth of thermal‐induced martensite. After stress‐induced martensite aging, the elastic modulus of martensite (EM) increased by 8 GPa, and the elastic modulus of austenite (EA) decreased by 8 GPa. It was shown that stress‐induced martensite aging strongly affects the functional and viscoelastic properties of material and can be used to control them

Surface structure and properties of hydroxyapatite coatings on NiTi substrates

Hydroxyapatite coatings were deposited for 1, 2, and 3 h on NiTi substrates using plasmaassisted radio frequency sputtering. The matrix consisted of NiTi B2 and NiTi B19’ phases and Ti2Ni, Ni3Ti, and Ni4Ti3 intermetallic compounds. The surface coating was monoclinic hydroxyapatite. Increasing the deposition time to 3 h made it possible to form a dense hydroxyapatite layer without visible defects. The phase contrast maps showed that the coating consisted of round grains of different fractions, with the smallest grains in the sample deposited for 3 h. The wettability tests showed that the coating deposited for 3 h had the highest surface energy, reflected in the proliferation density of the MCF-7 cell line

The effect of stress-induced martensite aging in tension and compression on B2–B19′ martensitic transformation in Ni50.3Ti32.2Hf17.5 high-temperature shape memory alloy

The present study investigates the high-temperature shape memory effect (SME) in heterophase Ni50.3Ti32.2Hf17.5 polycrystals with nanosized H-phase particles after stress-induced martensite (SIM) aging in tension and compression. SIM aging created the conditions for fully reversible two-way SME with a strain of up to 50% of the one-way shape memory strain. SIM aging altered the viscoelastic properties of material, in particular, the elastic moduli of austenite and martensite increased, as did internal friction. Increased interface mobility is suggested as the reason for internal friction growth

The influence of aging on shape memory effect in Ti‑50.7at.%Ni and Ti‑51.7at.%Ni single crystals

The shape memory effect (SME) during stressassisted thermal cycles under compressive load in [001]-oriented Ti-50.7at.%Ni and Ti-51.7at.%Ni single crystals aged at 823 K for 1 h has been studied. Ti3Ni4 particles with a diameter of 300–400 nm were precipitated with volume fractions of 11 and 22% and interparticle distances of 300–500 nm and 50–150 nm, respectively. In quenched single crystals, the SME parameters were determined by the transformation type (thermal-induced martensitic transformation (MT) or strain glass transition). In contrast, the SME parameters of aged single crystals were determined by the volume fraction of particles and interparticle distances. Differing volume fractions of particles and interparticle distances led to different temperatures ( M0s ) for the formation of B19′-martensite, different strain (εrev), different dependences of the interval of forward MT ( Δσ1) and thermal hysteresis ( ΔT1= Aσf−Mσs and ΔT2= Aσs−Mσf) on applied stresses, and changes in the morphology of martensite crystals. Practically, these differences do not affect the stresses (σmin and σmax) required to achieve the minimum strain and maximum reversible strain (εrev) and strain growth coefficient (dεrev/dσ). The influence of aging on the dependence of the SME parameters on the chemical composition was analysed in comparison with quenched crystals

Improved mechanical properties of porous nitinol by aluminum alloying

Aluminum alloying effects (up to 2 at %) on the macrostructure, microstructure, and mechanical properties of porous nitinol (NiTi) obtained by self-propagating high-temperature synthesis (SHS) were studied. It has been established that Ni and Ti interactions with liquid Al (0.5–1 at % Al) in the SHS process significantly change macrostructure, decrease the size of the interpore bridges, and increase their number, resulting in a larger effective cross-sectional area. An increase in the aluminum content above 1 at % leads to larger interpore bridges in the SHS product. The microhardness of TiNi(Al) increases from 305 HV50 g to 422 HV50 g with aluminum concentration, while the fraction of the TiNi(Al) (B2 + B19′) phases decreases from 75% to 50%. The Ti2Ni(Al) phase fraction increases from 25% to 50% with Al concentration. The 64 MPa tensile strength and 2.9% fracture strain of porous Ti50Ni49Al1 alloy are higher than without Al. The increase in strength is due to the formation of a more homogeneous macrostructure and solid solution strengthening of the alloy-forming phases