Thermomechanical fatigue of nanostructured Ti–Ni shape memory alloys

Demers, Vincent; Braïlovski, Vladimir; Прокошкин, С. Д.; Inaekyan, К.

doi:10.1016/j.msea.2009.01.055

“…But in the region between d 0 (d min ) and 12.5 nm, equation (8) does not adequately describe the material softening. In the case of the model , the approximation according to (3) and (4), (Fig. 4a) shows an appropriate correlation with the experimental results in the whole grain sizes range.…”

Section: Analysis Of the Experimental Results For Ti-5026%ni Alloysupporting

confidence: 62%

“…Recently, it was found that thermomechanical processing consisting of severe plastic deformation (SPD) and post-deformation annealing (PDA) allows creation of a nanocrystalline structure in Ti-Ni SMA, which results in a significant improvement of their functional properties [1][2][3]. In a series of works, the stability of the amorphous/nanocrystalline structure formed by severe cold rolling (CR) was studied during room-temperature aging [4], and a peculiar dome-shape that nanocrystalline metallic alloys do not follow the classical Hall-Petch behaviour and that below a certain grain size, softening instead of hardening is observed [5,6].…”

Section: Introductionmentioning

confidence: 99%

Microhardness of binary near-equiatomic Ti-Ni alloys after severe cold rolling and post-deformation annealing

Inaekyan

¹

,

Braïlovski

²

,

Прокошкин

³

et al. 2009

ESOMAT 2009 - 8th European Symposium on Martensitic Transformations

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Abstract. Comparative HV-microhardness and TEM studies of Ti-50.0at%Ni and 50.26at%Ni alloys subjected to cold-rolling (e=0.3, 1 and 1.72) and post-deformation annealing at 100-700°C (1 hour) are presented. Based on the TEM-measured grain size data for Ti-50.0at%Ni alloy as a function of an annealing temperature (T PDA ) higher than 250 o C, it was possible to evaluate the grain size (d) of the near-equiatomic Ti-Ni alloys at T PDA <250 o C, using exponential extrapolation distribution of the d-T PDA data. It was shown that below a critical grain size (d c = 10 nm), the smaller the grain size (as a result of the decrease in annealing temperature), the lower the microhardness. This softening phenomena can be described, with good correlation between the approximation and experimental data, by the normal-abnormal Hall-Petch transition caused by the influence of the intercrystalline regions and by the melting temperature grain-size dependence.

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“…5g,h,i). (c); B -fixed-support recovery (d), (e) and (f); C -constant-stress recovery (g), (h) and (i); e = 0.75 (a), (d), (g), e = 1 (b), (e) and (h); e = 1.5 (c), (f) and (i) (adapted from [5]). …”

Section: Ti-5026at%ni Alloy As Actuator Materialsmentioning

confidence: 99%

Functional properties of nanocrystalline, submicrocrystalline and polygonized Ti–Ni alloys processed by cold rolling and post-deformation annealing

Braïlovski

¹

,

Прокошкин²,

Inaekyan

³

et al. 2011

Journal of Alloys and Compounds

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Abstract. Thermomechanical processing consisting of cold rolling (e=0.3-2.0) and post-deformation annealing (300-450oC, 1h) was applied to binary Ti-Ni alloys to produce nanocrystalline structures (NS) or polygonized dislocation substructures (PDS), or their mixture. The evolution of the material structure and properties was studied using TEM, X-ray, microhardness, calorimetry and tensile testing techniques. Recovery stress and strain of the 50.26at%Ni alloy and superelastic strain of the Ti-50.6at%Ni alloy were measured under static and fatigue conditions. It was found that higher true yield stress of NS alloys not only increases the recovery stress potential, but, since it is combined with a relatively low transformation yield stress; it increases the completely recoverable strain. NS alloys generate recovery stresses that are twice as high as those of PDS alloys (1200 MPa), completely recoverable strains that are 10% greater (up to 6% in tension), and they demonstrate a higher cyclic stability of functional properties. This improvement comes with the cost of a lower NS alloy fatigue damage tolerance, aggravated by the presence of microcracks caused by cold working. Binary Ti-Ni alloys, processed by annealing of an intermediately cold-worked (e=0.75…1) alloy and containing mixed nanocrystalline structure and polygonized dislocation substructure, allow a high fatigue life combined with relatively high and cyclically stable functional properties.

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“…Mechanical characterization was carried out using microhardness (Instron Tukon, 500g) and tensile testing (Enduratec ELF 3200 and MiniBionix MTS) techniques. To characterize the Ti-50.26at%Ni alloy performances as actuator material, corresponding samples were then subjected to thermomechanical cycling using a custom-made test bench [5], whereas to characterize the Ti-50.6at%Ni alloy performances as superelastic material, they were mechanically cycled at a constant temperature T d = A f +10 o C. Testing of Ti-50.26at%Ni alloy as actuator material…”

Section: Methodsmentioning

confidence: 99%

“…This is a classical trade-off situation: the higher the cold rolling intensity, the finer the material structure and the higher the functional properties of Ti-Ni shape memory alloy (SMA), but this improvement is reached in tandem with a greater the risk of microcrack appearance and therefore, a lower fatigue resistance [5]. This article focuses on the advantages and limitations of the CR-PDA technique, applied to binary Ti-Ni SMA, by comparing their single cycle and multiple cycle shape memory and superelastic properties.…”

Section: Introductionmentioning

confidence: 99%

Functional properties of nanocrystalline, submicrocrystalline and polygonized Ti-Ni alloys processed by cold rolling and postdeformation annealing

Brailovskia

¹

,

Прокошкин

²

,

Inaekyan

³

et al. 2009

ESOMAT 2009 - 8th European Symposium on Martensitic Transformations

Self Cite

0

View full text Add to dashboard Cite

Abstract. Thermomechanical processing consisting of cold rolling (e=0.3-2.0) and post-deformation annealing (300-450oC, 1h) was applied to binary Ti-Ni alloys to produce nanocrystalline structures (NS) or polygonized dislocation substructures (PDS), or their mixture. The evolution of the material structure and properties was studied using TEM, X-ray, microhardness, calorimetry and tensile testing techniques. Recovery stress and strain of the 50.26at%Ni alloy and superelastic strain of the Ti-50.6at%Ni alloy were measured under static and fatigue conditions. It was found that higher true yield stress of NS alloys not only increases the recovery stress potential, but, since it is combined with a relatively low transformation yield stress; it increases the completely recoverable strain. NS alloys generate recovery stresses that are twice as high as those of PDS alloys (1200 MPa), completely recoverable strains that are 10% greater (up to 6% in tension), and they demonstrate a higher cyclic stability of functional properties. This improvement comes with the cost of a lower NS alloy fatigue damage tolerance, aggravated by the presence of microcracks caused by cold working. Binary Ti-Ni alloys, processed by annealing of an intermediately cold-worked (e=0.75…1) alloy and containing mixed nanocrystalline structure and polygonized dislocation substructure, allow a high fatigue life combined with relatively high and cyclically stable functional properties.

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Thermomechanical fatigue of nanostructured Ti–Ni shape memory alloys

Cited by 66 publications

References 25 publications

Microhardness of binary near-equiatomic Ti-Ni alloys after severe cold rolling and post-deformation annealing

Microhardness of binary near-equiatomic Ti-Ni alloys after severe cold rolling and post-deformation annealing

Functional properties of nanocrystalline, submicrocrystalline and polygonized Ti–Ni alloys processed by cold rolling and post-deformation annealing

Functional properties of nanocrystalline, submicrocrystalline and polygonized Ti-Ni alloys processed by cold rolling and postdeformation annealing

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