Journal ArticleDOI
Fracture of precipitated NiTi shape memory alloys
TLDR
In this paper, the fracture mechanisms in single crystal and polycrystalline Ti-50.8at%Ni shape memory alloys containing Ti3Ni4 precipitates were studied using the scanning electron microscope (SEM).Abstract:
The fracture mechanisms in single crystal and polycrystalline Ti-50.8at%Ni shape memory alloys containing Ti3Ni4 precipitates are studied using the scanning electron microscope (SEM). Aged materials with three different precipitate sizes (50 nm, 150 nm, and 400 nm), which have interfaces ranging from semi-coherent to incoherent, are considered. The mechanisms of material fracture identified in the single crystal NiTi are: 1. Nucleation, growth, and coalescence of voids from the Ti3Ni4 precipitates, 2. Cleavage fracture on {100} and {110} crystallographic planes, 3. Nucleation, growth, and coalescence of voids from fractured Ti-C inclusions. Cleavage and ductile tearing mechanisms also operate in polycrystalline NiTi, however, since the Ti-C inclusions are an artifact of single crystal growth processes, mechanism 3 was not discovered in the polycrystalline materials. Cleavage fracture and ductile tearing are found to act in conjunction, with the relative dominance of one over the other depending on the local precipitate size and concentration. As the Ti3Ni4 precipitate size increases to about 400 nm, the overall fracture is dominated by failure mechanism 1, and the cleavage markings become diffuse. Finally, we assert that the high tensile ductility of drawn NiTi polycrystals is due partially to the fact that drawn bar and wire stock usually have a strong {111} fiber texture. Such a texture promotes the initiation of the transformation at low stresses and concurrently prevents primary cleavage on the {100} or {110} planes.read more
Citations
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Elastocaloric cooling capacity of shape memory alloys – Role of deformation temperatures, mechanical cycling, stress hysteresis and inhomogeneity of transformation
TL;DR: In this paper, the effect of loading states (tension and compression), long-term cycling, strain localization, and deformation temperatures in shape memory alloys (SMAs) were studied.
Journal ArticleDOI
Elastocaloric cooling potential of NiTi, Ni2FeGa, and CoNiAl
TL;DR: In this article, a dual camera technique of digital image correlation and thermography was utilized to track the transformation bands and temperature gradients to gain insight about the unloading, endothermic process.
MICROSTRUCTURE OF NiTi SHAPE MEMORY ALLOY DUE TO TENSION-COMPRESSION CYCLIC
TL;DR: In this paper, the authors focused on the martensite microstructure developed as a result of mechanical cycling and showed that, before and after mechanical cycling, the Martensite variants are well self-accommodated to each other with the h011itype II twinning as the main lattice invariant shear.
Journal ArticleDOI
Micromechanical modelling of the effect of plastic deformation on the mechanical behaviour in pseudoelastic shape memory alloys
X.M. Wang,Baoxing Xu,Zhufeng Yue +2 more
TL;DR: In this paper, a new three dimensional micromechanical model is proposed by coupling both the slip and twinning deformation mechanisms, which is implemented as User MATerial subroutine (UMAT) into ABAQUS/Standard.
Journal ArticleDOI
Strain and texture evolution during mechanical loading of a crack tip in martensitic shape-memory NiTi
TL;DR: In this article, in situ synchrotron X-ray diffraction measurements are used to create two-dimensional maps of elastic strain and texture, averaged over a compact-tension specimen thickness, near a crack tip in a martensitic NiTi alloy.
References
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Book
Shape memory materials
Clarence Marvin Wayman,和弘 大塚 +1 more
TL;DR: Otsuka et al. as mentioned in this paper introduced shape memory alloy actuators and their application in medical and dental applications, including shape memory ceramics, shape memory polymers, and shape memory alloys.
Journal ArticleDOI
Tension–compression asymmetry of the stress–strain response in aged single crystal and polycrystalline NiTi
TL;DR: In this paper, the tensile and compressive stress-strain behaviors were established on aged single crystals ([100, [110], and [111] orientations) and polycrystalline NiTi materials.
Journal ArticleDOI
Fatigue of NITI thermoelastic martensites
K.N. Melton,O. Mercier +1 more
TL;DR: In this paper, the authors studied the mechanical fatigue of NiTi shape memory alloys and found that the fatigue limit is lower than predicted from the phenomenological law relating growth rates to the elastic modulus.
Journal ArticleDOI
Symmetry, texture and the recoverable strain of shape-memory polycrystals
TL;DR: In this paper, the authors show that the shape-memory behavior of polycrystals depends on the texture of the polycrystal, the transformation strain of the underlying martensitic transformation and especially on the change of symmetry during the underlying transformation.
Journal ArticleDOI
The influence of texture on the shape- memory effect in polycrystals
TL;DR: In this article, a model is developed to show that texture is a crucial factor in determining the shape-memory effect in polycrystals, and that even the qualitative behavior of combined tension-torsion can critically depend on the texture.