Papers by Author: K.E. Inaekyan

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Authors: Sergey Prokoshkin, Andrey Korotitskiy, Vladimir Brailovski, K.E. Inaekyan
Abstract: The Ti-50.26 and 50.61at.%Ni alloys were cold-rolled with true strains from e=0.3 to 2.1. Post-deformation annealing in the 200 to 500°C temperature range after a moderate deformation (e=0.3) produced a polygonized dislocation substructure with various dislocation density and subgrain size, while after severe plastic deformation (e=1.7-1.9), a nanocrystalline structure with various grain size was formed in the B2-austenite. An X-ray diffraction study shows that lattice parameters of B19'-martensite formed from (a) partially recovered and polygonized or (b) nanocrystalline austenites differ from the corresponding parameters of the martensite formed from quenched (recrystallized) austenite. This difference increases with nanocrystalline grain refinement and with an increase in residual dislocation density and subgrain refinement. The maximum martensitic transformation strain has the highest value for the martensite formed in recrystallized austenite, and this value decreases with nanograin refinement and with an increase in dislocation density and subgrain refinement.
Authors: I. Khmelevskaya, Sergey Prokoshkin, Vladimir Brailovski, K.E. Inaekyan, Vincent Demers, Irina Gurtovaya, Andrey Korotitskiy, Sergey V. Dobatkin
Abstract: The main functional properties (FP) of Ti-Ni Shape Memory Alloys (SMA) are their critical temperatures of martensitic transformations, their maximum completely recoverable strain (er,1 max) and maximum recovery stress (sr max). Control of the Ti-Ni-based SMA FP develops by forming well-developed dislocation substructures or ultrafine-grained structures using various modes of thermomechanical treatment (TMT), including severe plastic deformation (SPD). The present work shows that TMT, including SPD, under conditions of high pressure torsion (HPT), equal-channel angular pressing (ECAP) or severe cold rolling followed by post-deformation annealing (PDA), which creates nanocrystalline or submicrocrystalline structures, is more beneficial from SMA FP point of view than does traditional TMT creating well-developed dislocation substructure. ECAP and low-temperature TMT by cold rolling followed by PDA allows formation of submicrocrystalline or nanocrystalline structures with grain size from 20 to 300 nm in bulk, and long-size samples of Ti-50.0; 50.6; 50.7%Ni and Ti-47%Ni-3%Fe alloys. The best combination of FP: sr max =1400 MPa and er,1 max=8%, is reached in Ti-Ni SMA after LTMT with e=1.9 followed by annealing at 400°C which results in nanocrystalline (grain size of 50 to 80 nm) structure formation. Application of ultrafine-grained SMA results in decrease in metal consumption for various medical implants and devices based on shape memory and superelastiсity effects.
Authors: Andrey Korotitskiy, K.E. Inaekyan, Vladimir Brailovski, Sergey Prokoshkin
Abstract: Ti-50.26at.%Ni shape memory alloy samples were subjected to cold rolling (CR) with true strains encompassing from moderate (logarithmic strain e=0.25) to severe (e=2.1) deformation. СR with e = 0.5 and more initiated a partial austenite amorphization. The evaluation of structural changes in the material during its long-term storage was performed using Vickers microhardness (HV) technique. It was shown that during storage at room temperature up to 9 months, microhardness varied following a dome-shaped trend, thus reflecting commonly encountered interaction between two concurrent time-dependent phenomena, the first responsible for the material hardening, and the second, for the material softening. To represent such phenomena, a simple mathematical model was proposed and experimentally validated.
Authors: Irina Gurtovaya, Sergey Prokoshkin, K.E. Inaekyan, Andrey Korotitskiy, Vladimir V. Stolyarov, Alex M. Glezer, S. Makushev, I. Khmelevskaya, U. Ugurchiev, S. Manaenkov
Abstract: Application of electroplastic deformation (EPD) by rolling to bulk long-sized samples of Ti-50.7 at.%Ni alloy allows increasing of the deformation strain without macrofailure by 1.5 to 3 times in comparison to cold rolling without electrical current application. Structure formation and functional properties were studied after various EPD regimes: current density (84 to 168 А/mm2) and impulse duration (80 and 160 ms). When the stage of mixed nanocrystalline and amorphous structure formation is reached as a result of EPD, a post-deformation annealing at 400 °С leads to a nanocrystalline structure formation in austenite and highest recovery stress values generation by the martensite.
Authors: K.E. Inaekyan, Sergey Prokoshkin, Vladimir Brailovski, I. Khmelevskaya, Vincent Demers, Sergey V. Dobatkin, E.V. Tatyanin, E. Bastarache
Abstract: Substructure and structure formation as well as functional properties of thermomechanically treated Ti-Ni wire have been studied using differential scanning calorimetry, X-ray diffraction, transmission electron microscopy and mechanical. The low- temperature themomechanical treatment (LTMT) was carried out by rolling at room temperature in a true strain range e = 0.3 to 1.9. It was shown that severe plastic deformation (e=1.9) of Ti-50.0at.%Ni alloy results in partial amorphization and formation of nanocrystalline austenite structure during post-deformation annealings up to 400 °C. As a result, the fully recoverable strain and recovery stress become much higher than the values reachable after traditional LTMT (e=0.3 to 0.88) with post-deformation annealing which creates a poligonized dislocation substructure.
Authors: Vladimir Brailovski, Sergey Prokoshkin, E. Bastarash, Vincent Demers, K.E. Inaekyan, I. Khmelevskaya
Abstract: The thermomechanical processing consisting in severe cold rolling (true strain 0.7–1.9) followed by a post-deformation annealing (200-700oC) is applied to Ti-50.0 and 50.7at%Ni alloys. The thermal stability of the amorphous phase as well as the influence of post-deformation annealing on the structure, substructure and temperature range of martensitic transformations are studied using TEM and DSC techniques. For a given level of cold work, the equiatomic alloy has a higher volume fraction of amorphous phase than the nickel-rich one. For both alloys, the higher the volume fraction of the amorphous phase, the higher the thermal stability. For a given post-deformation annealing temperature, the DSC martensitic transformation peaks from the material subjected to amorphization cold work are sharper and the hysteresis between the direct and reverse transformations is narrower than those for a material subjected to strain hardening cold work. This observation confirms the absence of the well-developed dislocation substructure in the severely deformed alloy subjected to nanocrystallization heat treatment, which is consistent with TEM results.
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