In situ characterization of martensite variant formation in nickel–titanium shape memory alloy under biaxial loading

Niendorf, Т.; Lackmann, J.; Gorny, B.; Maier, Hans Jürgen

doi:10.1016/j.scriptamat.2011.08.011

Cited by 20 publications

(9 citation statements)

References 24 publications

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“…The composition of α phase and martensitic α phase is different: martensite α contains high β phase stable elements and the α phase contains high α phase stable elements. Similar phenomena have been found in some literature using BSE to observe the microstructure of other alloys [21][22][23]. When the sample was cooled to 943°C (Figure 4(a)), the microstructure of the surface of Ti6Al4V-0.55Fe alloy is mainly composed of martensite α .…”

Section: Microstructural Analysissupporting

confidence: 85%

Phase transformation behaviours and mechanical properties of Ti6Al4V-0.55Fe alloy during continuous cooling

Zhu

Liu

et al. 2022

Materials Science and Technology

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The phase transformation and mechanical properties of Ti6Al4V-0.55Fe alloy were investigated during the continuous cooling process. The curves of α phase precipitation exhibit a typical S-shaped pattern, which indicated that β→α phase transformation is a nucleation-growth-controlled process. The average activation energy is 231 kJ mol−1 calculated by Kissinger–Akahira–Sunose method. The Avrami exponent during β→α transformation significantly changes with the increasing transformed volume fraction. It is found that the thickness of α phase lamellar decreased, while the strength and hardness increased with the increasing cooling rate. Moreover, the fracture morphology of the samples gradually changes from ductile fracture to brittle fracture under the cooling rate from 1 to 15 K min−1, which illuminates that the plasticity of the alloy will decrease.

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Section: Microstructural Analysissupporting

confidence: 85%

Phase transformation behaviours and mechanical properties of Ti6Al4V-0.55Fe alloy during continuous cooling

Zhu

Liu

et al. 2022

Materials Science and Technology

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“…27 The few studies on polycrystals, on the other hand, speak of very complicated morphologies and stress fields. 28,31 For example, in Cu-Zn-Al and Ni-Ti, a myriad of small plates of different variants can be found within a single grain and variants in adjacent grains can couple. 27,28 Furthermore, the amount of martensite that is observed to form is limited by "locking" of the variant structure as sequential grain transformation occurs.…”

Section: Introductionmentioning

confidence: 99%

Grain boundary and triple junction constraints during martensitic transformation in shape memory alloys

Ueland

Schuh

2013

Journal of Applied Physics

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We investigate the role of grain constraint upon martensitic transformation through in situ scanning electron microscope tensile experiments on shape memory microwires with a small number of grains and grain junctions. The martensite transformation morphology becomes more complex with increasing grain constraint: In unconstrained monocrystalline regions, the transformation is simple, single variant, and complete; near grain boundaries, the transformation is only partial, containing regions of untransformed austenite; near a triple junction, the morphology is complex, the transformation is partial and also multi-variant. These observations speak of transformationinduced stress concentrations that are more severe around triple junctions than around grain boundaries. Finite element modeling also provides an estimate for constraint effects on martensitic transformation yielding higher stresses near triple junctions than near grain boundaries. Towards the goal of developing polycrystalline Cu-based shape memory alloys that avoid intergranular fracture, our results support three design objectives: (1) Removal of triple junctions, (2) reduction of the total grain boundary area, and (3) geometry design containing unconstrained regions where the transformation can be most easily accommodated. V

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“…These mechanistic aspects have been extensively studied individually. For example, microholes and notches are known to induce multiaxial stress states and multiple martensite variants in their vicinity [13] and also to act as the nucleation sites for cracks [14], while grain boundaries are known to constrain deformation due to phase transformation [15]. Crack growth in SMAs has been extensively studied both at the individual crystal scale as well as in a statistical sense, using empirical [16][17][18][19] as well as modeling-based techniques [20,21].…”

Section: Introductionmentioning

confidence: 99%

Influence of Structure and Microstructure on Deformation Localization and Crack Growth in NiTi Shape Memory Alloys

Paul

Fortman

Paranjape

et al. 2018

Shap. Mem. Superelasticity

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Porous NiTi shape memory alloys have applications in the biomedical and aerospace fields. Recent developments in metal additive manufacturing have made fabrication of near-net-shape porous products with complicated geometries feasible. There have also been developments in tailoring site-specific microstructures in metals using additive manufacturing. Inspired by these developments, we explore two related mechanistic phenomena in a simplified representation of porous shape memory alloys. First, we computationally elucidate the connection between pore geometry, stress concentration around pores, grain orientation, and strain-band formation during tensile loading of NiTi. Using this, we present a method to engineer local crystal orientations to mitigate the stress concentrations around the pores. Second, we experimentally document the growth of cracks around pores in a cyclically loaded superelastic NiTi specimen. In the areas of stress concentration around holes, cracks are seen to grow in large grains with [1 1 0] oriented along the tensile axis. This combined work shows the potential of local microstructural engineering in reducing stress concentration and increasing resistance to propagation of cracks in porous SMAs, potentially increasing the fatigue life of porous SMA components.

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In situ characterization of martensite variant formation in nickel–titanium shape memory alloy under biaxial loading

Cited by 20 publications

References 24 publications

Phase transformation behaviours and mechanical properties of Ti6Al4V-0.55Fe alloy during continuous cooling

Phase transformation behaviours and mechanical properties of Ti6Al4V-0.55Fe alloy during continuous cooling

Grain boundary and triple junction constraints during martensitic transformation in shape memory alloys

Influence of Structure and Microstructure on Deformation Localization and Crack Growth in NiTi Shape Memory Alloys

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