Marforming and tempering of binary Ni–Ti alloys including precipitation effects

Wurzel, D.

doi:10.1016/s0921-5093(99)00338-x

Cited by 21 publications

(21 citation statements)

References 2 publications

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“…[1] Thermomechanical treatment is essential to control the transformation temperatures, phase strengths, and monotonic and cyclic response and to improve shape-memory characteristics, and, thus, it has been the subject of numerous investigations. [2][3][4][5][6][7][8][9][10][11][12] The most common thermomechanical treatments are ausforming and marforming, in which defects are introduced into the austenitic and martensitic structures, respectively. Subsequent heat treatments may or may not be applied, depending on the desired end microstructures and the resulting transformation and mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

“…[2,3,5,13] In particular, the ultimate goal of these thermomechanical processes is (1) to control transformation temperatures in such a way that the desired transformation path can be obtained (thermally induced or stress-induced transformation at a given temperature), (2) to increase the transformation stress of the stress-induced parentto-martensite transformation while the SME and/or PE are expected to be preserved, and (3) to enhance thermomechanical fatigue resistance.…”

Section: Introductionmentioning

confidence: 99%

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The effect of severe marforming on shape memory characteristics of a Ti-rich NiTi alloy processed using equal channel angular extrusion

Караман

Karaca

Luo

et al. 2003

Metall Mater Trans A

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A Ti-49.8 at. pct Ni alloy was severely deformed at three different temperatures using equal-channel angular extrusion (ECAE). Three deformation temperatures-room temperature (below the martensite finish temperature), 50°C (below the austenite start temperature), and 150°C (above the austenite finish temperature)-were selected such that the initial deforming phase (B2 austenite or B19' martensite) and the initial governing deformation mechanism (martensite reorientation, stress-induced martensitic transformation, or dislocation slip in martensite) would be different. The X-ray analysis results revealed that all processed samples mostly contained a deformed martensitic phase, regardless of the initial deforming phase and the deformation mechanism. Although the martensite start temperature did not change, the austenite start temperature decreased significantly in all deformation conditions, probably because of the effect of the internal stress field caused by the deformed microstructure. All deformation conditions led to an increase in the strength levels and some deterioration of shapememory characteristics. However, a subsequent low-temperature annealing treatment significantly improved pseudoelastic strain levels while preserving the ultrahigh strength levels. The sample deformed at room temperature followed by the low-temperature annealing resulted in the most promising strength and shape-memory characteristics under compression, such that a 5.3 pct shape-memory strain at a 2200 MPa strength level and a 3.3 pct pseudoelastic strain at a 1900 MPa strength level were achieved. The differences between the strength levels and the shape-memory characteristics after severe deformation at different temperatures were attributed to the different amounts of plastic deformation and the resulting deformation textures, since at each deformation temperature the deformation mechanism was different. It is concluded that the severe marforming using ECAE could easily improve strength levels of NiTi alloys while preserving the shape-memory and pseudoelasticity (PE) characteristics and, thus, improve the thermomechanical fatigue behavior. However, lower deformation temperatures are necessary to hinder formation of macroshear bands, and ECAE angles larger than 90 deg should be used to reduce the amount of strain applied in one pass.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The effect of severe marforming on shape memory characteristics of a Ti-rich NiTi alloy processed using equal channel angular extrusion

Караман

Karaca

Luo

et al. 2003

Metall Mater Trans A

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“…Consequently, thermomechanical treatments are necessary in NiTi alloys to achieve the desired pseudo elastic behavior. Previous studies have shown that for one PE-loop, malformed or mixed deformed and annealed specimen provide a high reversibility [1,2]. In case of high rolling reductions ((p = 0.44), both thermomechanical treatments lead to similar microstructures and, therefore, to comparable fatigue behavior (Fig.…”

Section: Mechanical Fatiguementioning

confidence: 90%

“…Range I (MF) and II (XF): Depending on the annealing conditions, favorable functional and structural properties were created [1,2]. Range III (AF): Only pseudo plasticity is improved.…”

Section: Introductionmentioning

confidence: 99%

Effects of different thermomechanical treatments on fatigue of NiTi shape memory alloys

Wurzel

2001

J. Phys. IV France

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Fully recrystallized NiTi sheets were deformed in four different temperature ranges: fully transformed martensite (T < M f ), transforming austenite (M s < T < Md), low temperature, stable austenite (M d < T < 1/3 T s ) and austenite at elevated temperatures (T > 1/3 T m ). The types and distributions of defects produced in these materials depend on the deformation temperature. The characteristic defect structures resulting from the low temperature deformation lead to different microstructures even after annealing. The thermomechanically treated as compared to the fully recrystallized NiTi alloys were subjected to thermal, mechanical and thermomechanical fatigue tests. Their microstructural origin was interpreted by TEM investigations. In conclusion it is proposed that a low ratio of pseudo-yield stress to true yield stress is responsible for good fatigue resistance. Regarding fatigue it is better to increase the yield stress by a small grain size than by a high dislocation density (work hardening).

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“…For testing, the fabricated porous NiTi specimens were machined to cylindrical shapes with a nominal diameter of 13 mm and a length of 35 mm. After the fabrication of the porous specimens they have not been subjected to any further processing such as marforming 27 or ausforming. Load from a hydraulic MTS load frame was applied through two compression plates.…”

Section: Mechanical Properties Of Hipped Porous Nitimentioning

confidence: 99%

<title>Effect of transformation induced plasticity on the mechanical behavior of porous SMAs</title>

2002

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The fabrication of porous NiTi Shape Memory Alloy (SMA) from elemental Ni and Ti powders using Hot Isostatic Press (HIP) is presented in this work. Porous NiTi alloys with different porosity levels and different mechanical properties are obtained and analyzed. Their behavior under compressive mechanical loading is modeled using a micromechanical averaging model. The model treats the porous NiTi alloy as a two-phase composite: dense SMA matrix and pores. The behavior of the fully dense SMA matrix is modeled using a thermomechanical model with internal state variables. The development of transformation and plastic strains during the martensitic phase transformation is taken into account. The results from the model are compared with the experimental data.

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Marforming and tempering of binary Ni–Ti alloys including precipitation effects

Cited by 21 publications

References 2 publications

The effect of severe marforming on shape memory characteristics of a Ti-rich NiTi alloy processed using equal channel angular extrusion

The effect of severe marforming on shape memory characteristics of a Ti-rich NiTi alloy processed using equal channel angular extrusion

Effects of different thermomechanical treatments on fatigue of NiTi shape memory alloys

<title>Effect of transformation induced plasticity on the mechanical behavior of porous SMAs</title>

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