The thermoelastic martensitic transformation in β′ Ni-Al alloys: II. Electron microscopy

Chakravorty, S.; Wayman, C.M.

doi:10.1007/bf02643971

Cited by 83 publications

(17 citation statements)

References 8 publications

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“…Later several long period stackings of these twins were reported (for references see chapter 2). The first extensive report on the crystallography of the martensitic transformation was presented by Chakravorty & Wayman [9]. The habit plane was experimentally determined to be close to the ( 2 14 15) family of the P phase, confirming the theoretical predictions of the Bowles-Mackenzie theory [10,11].…”

Section: Introductionsupporting

confidence: 48%

Martensitic and Related Transformations in Ni-Al Alloys

Schryvers

1995

J. Phys. IV France

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Abstract:The present paper gives a review of results of recent studies investigating the fundamentals of the martensitic and related phase tr-ansformations in Ni-A]. For the former case, the emphasis will be on the microstructure of martensite plates. The latter include the metastable Ni2A1 o-like and stable Ni5A13 bainitic phases. These phases will be discussed in view of their atomic structure, nucleation, growth and effect on the martensitic transformation. A separate chapter will deal with precursor effects.

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Section: Introductionsupporting

confidence: 48%

Martensitic and Related Transformations in Ni-Al Alloys

Schryvers

1995

J. Phys. IV France

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“…The twinning plane is found to be ð1 " 11Þ, which is the same as that reported for NiAl, CoNiAl, and NiMnGa alloys. [33,40,41] Figures 7(b) and (c) display TEM images of the stabilized martensite in the fatigued [123]-oriented CoNiGa single crystal. The pinned martensite in both cases appears to have strong stress fields, as indicated by the contrast change at the martensite-austenite interface, and substantial dislocation activity is also evident.…”

Section: Tem Observationsmentioning

confidence: 98%

Pseudoelasticity and Cyclic Stability in Co49Ni21Ga30 Shape-Memory Alloy Single Crystals at Ambient Temperature

Dadda

Maier

Niklasch

et al. 2008

Metall Mater Trans A

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As-grown Co 49 Ni 21 Ga 30 [001]-and [123]-oriented single crystals were subjected to cyclic compression loading at room temperature above the austenite finish temperature of 15°C. Straincontrolled experiments were performed using both incremental strain steps and constant strain amplitudes. Cyclic deformation with a maximum strain amplitude of 2.5 pct resulted in rapid accumulation of irrecoverable strains in the [123]-oriented crystals. However, after a few cycles, the samples demonstrated cyclic stability with fully recoverable transformation. By contrast, the [001]-oriented crystals displayed excellent cyclic stability with hardly any change in stress-strain characteristics. In-situ optical microscopy and electron backscattered diffraction analysis were employed to clarify the events that take place at different stages of a typical loading-unloading history. The in-situ observations also revealed that the initiation and growth characteristics of stress-induced martensite (SIM) are heterogeneous on the microscopic scale in CoNiGa alloys. In addition, theoretical transformation and detwinning strains, and resolved shear stress factors (RSSFs), were calculated based on the energy minimization theory and are compared to the experimentally obtained orientation-dependent transformation stress and strain levels. It is shown that the selection of an appropriate orientation is one of the key criteria to optimize the pseudoelastic (PE) response and cyclic stability of CoNiGa alloys.

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“…A toughness of approximately 9 MPa-^m_ has been reported for quenched single-phase B-alloys with 61.5 at.% Ni because of martensitic transformation toughening (Kumar, Mannan, and Viswanadham 1992). However, because of the small volume increase during the NiAI to martensite transformation (Chakravorty and Wayman 1976), only a small increase in toughness results from this mechanism. The toughness and ductility of Ni-rich Ni-Al alloys can be increased best by the formation of a two-phase microstructure.…”

Section: Microstructural Modificationmentioning

confidence: 98%