scholarly journals Mechanical behavior and fractographic analysis of a TiNi alloy with various thermomechanical treatment

2019 ◽  
Vol 298 ◽  
pp. 00019 ◽  
Author(s):  
Anna Churakova ◽  
Anna Yudahina ◽  
Elina Kayumova ◽  
Nikita Tolstov
Keyword(s):  
Dislocation Density ◽  
Thermal Cycling ◽  
Thermomechanical Treatment ◽  
Martensitic Transformations ◽  
Coarse Grained ◽  
Tini Alloy ◽  
Phase Hardening ◽  
Cold Upsetting ◽  
Cycling Treatment ◽  
Ultrafine Grained

Influence of thermomechanical treatment (deformation, thermal cycling treatment in the temperature range of martensitic transformations B2-B19’) on the TiNi alloys’ mechanical behaviour and fracture was studied. Different states were considered, they are initial coarse-grained (CG), ultrafine-grained (UFG) after ECAP (with a grain size of 200 nm), the state after ECAP and cold upsetting by 30% - UFG state with high dislocation density. It was shown that thermal cycling causes some increase in dislocation density, strength and microhardness in all the states. Thermal cycling of UFG alloys allows forming the states with non-equilibrium grain boundaries, with additional dislocations of “phase hardening”. The nature of the fracture was analysed in the TiNi alloy in various states.

scholarly journals Microstructural and Mechanical Stability of a Ti-50.8 at.% Ni Shape Memory Alloy Achieved by Thermal Cycling with a Large Number of Cycles

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 227 ◽  
Author(s):  
Churakova ◽  
Gunderov
Keyword(s):  
Mechanical Properties ◽  
Shape Memory Alloy ◽  
Thermal Cycling ◽  
Shape Memory ◽  
Temperature Change ◽  
Mechanical Stability ◽  
Martensitic Transformations ◽  
Coarse Grained ◽  
Ultrafine Grained ◽  
Number Of Cycles

The influence of thermal cycling (TC) with a large number of cycles on the microstructure, the parameters of martensitic transformations (MTs), and the mechanical properties of a Ti-50.8 at.% Ni shape-memory alloy in coarse-grained (CG) and ultrafine-grained (UFG) states was investigated. The effect of microstructural and mechanical stability was found in both coarse-grained and ultrafine-grained states starting from the 100th cycle of martensitic transformations. In addition, an unusual temperature change was observed in martensitic transformations occurring with the formation of an intermediate R phase.

scholarly journals Interrelation of microstructure and thermodynamic parameters in TiNi alloy during multiple martensitic transformations

2019 ◽  
Vol 298 ◽  
pp. 00002
Author(s):  
Anna Churakova
Keyword(s):  
Thermodynamic Parameters ◽  
Rapid Heating ◽  
Martensitic Transformations ◽  
Coarse Grained ◽  
Tini Alloy ◽  
Thermal Cycles ◽  
Fast Heating ◽  
Heating And Cooling ◽  
Coarse Grained State ◽  
Consistent Increase

The effect of multiple martensitic transformations on the microstructure and thermodynamic parameters of the alloy of the TiNi system was investigated. It was shown that in the Ti50Ni50 alloy, with an increase in the number of thermal cycles with rapid heating and cooling up to n = 100, a consistent increase in the dislocation density occurs, and a decrease in the width of martensitic plates is observed. And also, that in TCs with fast heating and cooling of the Ti50Ni50 alloy in a coarse-grained state, a change in the trend in the temperatures of martensitic transformations is observed — with an increase in the number of thermal cycles to n = 50, they decrease, and at n> 50 the temperatures increase.

Nanostructured Shape Memory TiNi Alloy Processed by Severe Electroplastic Deformation

2008 ◽  
Vol 584-586 ◽  
pp. 507-512 ◽  
Author(s):  
Vladimir V. Stolyarov
Keyword(s):  
Cold Rolling ◽  
Mechanical Behavior ◽  
Shape Memory ◽  
Fracture Strain ◽  
Coarse Grained ◽  
Tini Alloy ◽  
Current Effect ◽  
Electroplastic Rolling ◽  
Ultrafine Grained ◽  
A Current

Electropulse current effect during cold rolling on deformability, nanostructure formation and mechanical behavior in coarse-grained (CG) and ultrafine-grained (UFG) TiNi alloys enriched by nickel is investigated. The UFG sample subjected to cold rolling with current has a fracture strain (е = 1.91) which is higher than that without a current (е = 0.59). As a result of cold rolling with a current and a subsequent annealing at 400-450 °C, nanostructure is formed in both alloys, which leads to a significant enhancement of yield and ultimate stresses. It has been shown that the efficiency of electroplastic rolling depends on the purity of the alloys.

scholarly journals Comparison of the corrosion behavior of the TiNi alloy in the coarse-grained and ultrafine-grained state

2021 ◽  
Vol 2124 (1) ◽  
pp. 012026
Author(s):  
E M Kayumova ◽  
A A Churakova ◽  
O R Latypov
Keyword(s):  
Corrosion Rate ◽  
Corrosion Behavior ◽  
Volume Fraction ◽  
Significant Proportion ◽  
Gravimetric Method ◽  
Corrosion Products ◽  
Coarse Grained ◽  
Tini Alloy ◽  
Ultrafine Grained ◽  
Coarse Grained State

Abstract This article studies the corrosion behavior of the TiNi alloy in the coarse-grained and ultrafine-grained states. The study of the influence of the initial microstructure on the corrosion behavior of the TiNi alloy was carried out by the gravimetric method in the NaCl and H2SO4 solution for a month. Studies was shown that as a result of the action of a corrosive medium from a sample in a coarse-grained state, it undergoes greater destruction, pitting corrosion was observed, at the same time, in an ultrafine-grained sample only traces of corrosion products are observed on the surface of the samples. Investigations with an inverted light microscope in a dark field made it possible to observe corrosion products and determine their volume fraction. Evaluation of the corrosion rate showed that in the coarse-grained state it is 126 times higher than the corrosion rate in the ultrafine-grained state. Analysis of X-ray phase analysis showed that in the coarse-grained state after corrosion tests, a significant proportion of the TiNiH1.4 phase is observed, while in the ultrafine-grained state all phases correspond only to the TiNi phases. The TiNi alloy contains an Ti2Ni phase enriched Ti both in the coarse-grained state and in the ultrafine-grained state. Moreover, in a coarse-grained state, its share is 2 times higher.

Change of Microstructure and Analysis of Fracture of the Ti-50.8 at.% Ni Alloy in the Ultrafine-Grained State after Multiple Martensitic Transformations with a Large Number of Cycles

2021 ◽  
Vol 1016 ◽  
pp. 354-358
Author(s):  
Anna Churakova ◽  
Dmitriy Gunderov
Keyword(s):  
Martensitic Transformations ◽  
Tensile Tests ◽  
Fracture Pattern ◽  
Cycling Treatment ◽  
Thermal Cycling Treatment ◽  
Ultrafine Grained ◽  
Ni Alloy ◽  
Number Of Cycles ◽  
Average Size ◽  
Change Of Microstructure

The microstructure and mechanical properties of the ultrafine-grained Ti–50.8 at.% Ni alloy after thermal cycling treatment with the number of cycles up to 250 was investigated. A fractographic analysis of the samples after tensile tests was carried out. The fracture pattern of the alloy in the UFG state has a viscous character with microdepths on the fracture surface. The average size of microdepths decreases as the number of thermal cycles increases up to n= 250.

Deformation Behavior of Ultrafine Grained Iron

2006 ◽  
Vol 503-504 ◽  
pp. 317-322 ◽  
Author(s):  
Setsuo Takaki ◽  
Kenji Kawasaki ◽  
Y. Futamura ◽  
Toshihiro Tsuchiyama
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Yield Stress ◽  
Grain Refinement ◽  
Work Hardening ◽  
Coarse Grained ◽  
Deformation Condition ◽  
Initial Yield Stress ◽  
Ultrafine Grained ◽  
Dislocation Strengthening

Work hardening behavior and microstructure development during deformation by cold rolling were investigated in iron with different grain size. Grain refinement makes the introduction of dislocation easier. For instance, under the same deformation condition (5% reduction in thickness), dislocation density is the order of 1014m-2 in a coarse grained material (mean grain size; 20μm), while it reaches 7×1015m-2 in an ultrafine grained material (0.25μm). It is well known that the yield stress of metals is enlarged with an increase in dislocation density on the basis of the Bailey-Hirsch relationship. However, it should be noted that the ultrafine grained material never undergoes usual work hardening although the dislocation density is surely enhanced to around the order of 1016m-2: 0.2% proof stress is almost constant at 1.4 ~ 1.5GPa regardless of the amount of deformation. The dislocation density of 1016m-2 is thought to be the limit value which can be achieved by cold working of iron and the yield stress of iron with this dislocation density (ρ) is estimated at 1.1GPa from the Bailey-Hirsch relationship; σd [Pa] = 0.1×109 + 10 ρ1/2. On the other hand, yield stress of iron is enhanced by grain refinement on the basis of the Hall-Petch relationship; σgb [Pa] = 0.1×109 + 0.6×109 d-1/2 as to the grain size d [μm]. This equation indicates that the grain size of 0.35 μm gives the same yield stress as that estimated for the limit of dislocation strengthening (1.1GPa). As a result, it was concluded that work hardening can not take place in ultrafine grained iron with the grain size less than 0.35 μm because dislocation strengthening can not exceed the initial yield stress obtained by grain refinement strengthening.

scholarly journals The Investigation of Mechanical and Functional Properties and Microstructural Features of Coarse-Grained SME Ti49.0Ni51.0 Alloy during Multiple Martensitic Transformations and Annealing

2021 ◽  
Vol 346 ◽  
pp. 02011
Author(s):  
Anna Churakova ◽  
Elina Kayumova ◽  
Dmitry Gunderov
Keyword(s):  
Grain Size ◽  
Thermal Cycling ◽  
Yield Stress ◽  
Martensitic Transformations ◽  
Tensile Tests ◽  
Mechanical Tests ◽  
Coarse Grained ◽  
Initial State ◽  
Subsequent Aging ◽  
Mechanical Tensile

The paper was investigated the effect of preliminary multiple martensitic transformations on the microstructure and mechanical and functional stability during subsequent annealing in the range of aging temperatures of the Ti49.051.0 alloy in the coarse-grained state. The structure in the initial state has an austenitic structure with a grain size of 30 ± 5 μm; after TC, the structure is martensite with a grain size of 30 ± 5 μm. According to the results of mechanical tensile tests, thermal cycling leads to an increase in the yield stress, which is associated with the generation and accumulation of dislocations. An increase in the number of cycles to n = 100 led to a slight decrease in the yield stress, which may be due to the saturation effect during thermal cycling. Subsequent aging at T=400 °C after thermal cycling showed that the yield stress increases. At the same time, the results of mechanical tests showed that, in general, the preliminary TC (n = 100) with subsequent aging contributes to an increase in the yield strength and strength. The structure revealed after thermal cycling and subsequent low-temperature annealing confirms the precipitation of aging strengthening particles Ti3Ni4.

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