Premartensitic microstructures in NiAl ordered β2 phase: I - Effects induced by cooling

Tanner, L.E.; Pelton, Alan R.; Vantendeloo, G.; Schryvers, D.; Wall, M.

doi:10.1016/0956-716x(90)90537-q

Cited by 32 publications

(8 citation statements)

References 33 publications

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“…Crystal structures suggested for the NiAl Martensite [41][42][43] may require a certain type of ordering of antisite defects in the Ni-rich NiAl. Short-range ordering of the constitutional vacancies in the Al-rich NiAl is also expected from experiment.…”

Section: Introductionmentioning

confidence: 99%

Constitutional and thermal point defects inB2NiAl

et al. 2000

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The formation energies of point defects and the interaction energies of various defect pairs in NiAl are calculated from first principles within an order N, locally self-consistent Green's-function method in conjunction with multipole electrostatic corrections to the atomic sphere approximation. The theory correctly reproduces the ground state for the off-stoichiometric NiAl alloys. The constitutional defects ͑antisite Ni atoms and Ni vacancies in Ni-rich and Al-rich NiAl, respectively͒ are shown to form ordered structures in the ground state, in which they tend to avoid each other at the shortest distance on their sublattice. The dominant thermal defects in Ni-rich and stoichiometric NiAl are calculated to be triple defects. In Al-rich alloys another type of thermal defect dominates, where two Ni vacancies are replaced by one antisite Al atom. As a result, the vacancy concentration decreases with temperature in this region. The effective defect formation enthalpies for different concentration regions of NiAl are also obtained.

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Section: Introductionmentioning

confidence: 99%

Constitutional and thermal point defects inB2NiAl

et al. 2000

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“…The appearance of a defect‐induced precursor state in the form of either a tweed‐like pattern as discussed above or nanocluster configurations is quite common in martensitic systems such as Ni–Al , Co–Ni–Ga or Ni–Ti–Fe . More recently the interest has shifted to similar features as those described above but in the case of the isotropic near‐equiatomic Ni–Ti . In this system, for a concentration above 51.3 at% Ni the martensite is found to be suppressed due to the large number of point defects, locally straining the lattice in small nanopockets thereby prohibiting the martensite to form .…”

Section: Resultsmentioning

confidence: 62%

“…Due to the sensitive nature of the many parameters playing a role in these phenomena, obtaining accurate quantitative data at the atomic level has not been obvious. For example, when interpreting conventional TEM images such as the original cross‐hatched tweed patterns in, e.g., Ni‐Al , care needs to be taken about the actual imaging conditions. Indeed, the observed length scale of the modulations is not only related to the underlying strain or disorder pattern but also to the actual orientation of the sample in the used two‐beam bright‐ or dark‐field procedure .…”

Section: Resultsmentioning

confidence: 99%

“…For example, when interpreting conventional TEM images such as the original cross‐hatched tweed patterns in, e.g., Ni‐Al , care needs to be taken about the actual imaging conditions. Indeed, the observed length scale of the modulations is not only related to the underlying strain or disorder pattern but also to the actual orientation of the sample in the used two‐beam bright‐ or dark‐field procedure . Since the strain in the matrix is expected to degrade away from any stress or disorder locus, a streak of diffuse intensity rather than a sharp reflection nearby affected diffraction spots in reciprocal space is observed.…”

Section: Resultsmentioning

confidence: 99%

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Lattice deformations in quasi‐dynamic strain glass visualised and quantified by aberration corrected electron microscopy

Martinez

Aert

et al. 2014

Physica Status Solidi (b)

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Phone: þ32 326 532 47, Fax: þ32 326 533 18Advanced transmission electron microscopy and statistical parameter estimated quantification procedures were applied to study the room temperature quasi-dynamical strain glass state in Ni-Ti alloys. Nanosized strain pockets are visualised and the displacements of the atom columns are quantified. A comparison is made with conventional high-resolution transmission electron microscopy images of point defect induced strains in Ni-Al alloys.[001] Cs-corrected HRTEM image of Ni 51.7 Ti 48.3 B2 austenite with highlighted nanosized strain pocket of a few nm in diameter.

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“…Endo-and exothermic peak around 470 K upon heating and cooling was observed respectively, with a hysteresis of 23 K. Integrating − C p /T in the cooling process leads to the temperature dependence of the excess entropy as shown in figure 3. [19,26,35]. Previous thermal expansion measurements on a Ni 62.5 Al 37.5 single crystal showed pretransformation effects starting 115 K above the transition point [22].…”

Section: Differential Scanning Calorimetry Experimentsmentioning

confidence: 82%

The martensitic phase transition in Ni–Al: experimental observation of excess entropy and heterogeneous spontaneous strain

Zhang¹,

Salje²,

Schryvers³

et al. 2008

J. Phys.: Condens. Matter

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Experimental studies of the martensitic phase transition of Ni 63.5 Al 36.5 by means of differential scanning calorimetry and x-ray diffraction show a coexistence interval of 30 K for the austenite and martensitic phase. Within a smaller interval of 10 K near the upper limit of the stability of the martensitic phase no strain broadening of x-ray diffraction lines was observed for either phase. With decreasing temperature, diffraction profiles broaden, with a maximum reached when the sample is fully transformed into the martensitic phase. This observation is analyzed in terms of heterogeneous strain broadening due to imperfect microstructural self-accommodation of the martensitic grains. No strain broadening occurs when the martensitic phase is not fully interconnected but forms isolated islands inside an austenite matrix. It is concluded that large stress fields result from the coalescence of martensitic regions in the sample. The calibration of the excess entropy from the measurements of the specific heat confirms the Landau potential of Salje et al (2007 Appl. Phys. Lett. 90 221903). Imperfect self-accommodation does not contribute to a measurable increase of the entropy of the sample.

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Premartensitic microstructures in NiAl ordered β2 phase: I - Effects induced by cooling

Cited by 32 publications

References 33 publications

Constitutional and thermal point defects inB2NiAl

Constitutional and thermal point defects inB2NiAl

Lattice deformations in quasi‐dynamic strain glass visualised and quantified by aberration corrected electron microscopy

The martensitic phase transition in Ni–Al: experimental observation of excess entropy and heterogeneous spontaneous strain

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