Decomposition kinetics of Ni-11.8at.% Ti at 853 K

Lambrigger, M.; Calderón, H.A.; Kostorz, G.

doi:10.1016/0921-5093(92)90010-x

Cited by 10 publications

(7 citation statements)

References 26 publications

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“…Pairs of SPDs are operating on neighbouring (1 1 l)fcc planes, and the following two (11 l)fcc remain unchanged [9]. In this way transformation blocks of four (1 1 l)fcc planes develop, which form a microtwin with an ABAC stacking sequence.…”

Section: Discussionmentioning

confidence: 99%

Plasticity of the spinodally decomposing Ni-11.8 at.% Ti alloy

Lambrigger

1993

J. Phys. IV France

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The spinodal decomposition of supersaturated Ni -11.8 at.% Ti single crystals (fcc structure) was studied during ageing at 853 and 1073 K. All the samples were homogenised at 1423 K and then waterquenched to room temperature prior to ageing. The quenched samples were found consisting of short-range ordered matrix and slightly L12 -ordered Ti-rich domains.During the first sixty hours of ageing at 853 K, a "metastable situation" was found, where the microstructure of the samples did not change very much. Between sixty and five hundred hours of ageing, concentration waves developed, which grew in amplitude and wavelength with increasing ageing time. Later on, coarsening started, leading to metastableY' particles (L12 -structure), which began to become incoherent after 4000 h of ageing. The kinetics of Ni -11.8 at.% Ti single crystals at 1073 K were investigated in order to study the phase transformation to the stable 9 -Ni3Ti phase (DO24 -structure). Not fully DO24 -ordered nuclei with ABAC stacking sequences were observed. Furthermore, defective stacking sequences, derived from the ABAC stacking sequence, were found to occur frequently. A mechanism based on Shockley partial dislocations is suggested for the transformation of the fcc structure to the ABAC stacking sequence of the DO24 -structure. The mechanical properties of quenched and aged Ni -11.8 at.% Ti single crystals were investigated by compressive, tensile and fatigue tests performed at room temperature. The quenched specimens showed planar glide in all types of tests, and even strain bursts, which are typical for short-range ordered single crystals, were recorded during fatigue tests. Superdislocations and dislocation pile-ups were observed by Transmission electron microscopy in quenched samples, which were deformed in compression. The samples aged at 853 K, which were consisting of a microstructure containing concentration waves, showed a very localised deformation behaviour. Instabilities were observed in compressive tests, and in tensile and fatigue tests a low ductility was noted. In all types of tests a very high yield strength was measured. It may be assumed, that these special mechanical properties are the result of the tendency to nucleate the stablev phase. The dislocation structure of samples consisting of a microstructure with concentration waves, was found to be dominated by regularly dissociated a/2<110> dislocations. This dissociation into Shockley partial dislocations takes place in the Ti-rich domains. The dislocations may be considered to act as microprobes which are very sensitive to the Ti concentration. A model based on planar slip is presented, which describes the formation of defective microtwins, i.e. ABAC stacking sequences containing a/2<110> dislocation segments, out of regularly split, paired dislocations under an external stress in a microstructure consisting of concentration waves. These microtwins are the basic elements of the ABAC stacking sequence of the stable? phase.Article published online by EDP Sciences and av...

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Section: Discussionmentioning

confidence: 99%

Plasticity of the spinodally decomposing Ni-11.8 at.% Ti alloy

Lambrigger

1993

J. Phys. IV France

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“…On the basis of the static displacement parameters no clear indication (for example from 211 neighbors, as the L1 2 to D0 24 transformation can be formally achieved by the motion of Shockley partials [26]) can be found for a transition from L1 2 to D0 24 . Precursors of the transition might also occur in the dynamic displacements.…”

Section: Static and Dynamic Displacementsmentioning

confidence: 99%

“…Configuration C16 is much more enhanced in Ni±Ti than in Ni±Al. A large ratio between the enhancement factors of C16 and C17 found for both Ni±Ti samples (but not for Ni±Al) might be a prerequisite for the transformation from L1 2 to D0 24 [26] as it would lead to unfavorable Ti±Ti nearest neighbors.…”

mentioning

confidence: 92%

Short-Range Order in Ni-Rich Ni–Ti Studied by Diffuse Neutron Scattering

Bucher

Schönfeld

Kostorz

et al. 1999

phys. stat. sol. (a)

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“…Two discs (PC1, PC2) with Ti concentrations of 10.1(1) and 11.3(1) at.%, as determined by X-ray fluorescence analysis and by comparing them with a set of Ni-Ti standards, were subsequently annealed at 1470 K for 1 h, at 900 K for 24 h, solution treated at 1470 K for 1 h and quenched in water. A special vertical quenching furnace was used for heat treatments as fast quenching rates are crucial in the study of the early stages of decomposition in Ni-Ti (Cerri et al, 1988;Lambrigger et al, 1992a). Alloy rods were also used to grow single crystals of a diameter of 12 mm in an …”

Section: Methodsmentioning

confidence: 99%

“…In their lateral extension these plates seem to be restricted to the size of the metastable precipitates. Their formation may be explained by a shear transformation from the L1 2 to the D0 24 structure (Lambrigger et al, 1992b). Conservation of composition is considered a prerequisite for a purely displacive transformation.…”

Section: The Stable η Phasementioning

confidence: 99%

Small-angle neutron scattering investigation of the early stages of decomposition in Ni-rich Ni-Ti

Kompatscher¹,

Schönfeld²,

Heinrich³

et al. 2000

J Appl Cryst

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In-situ small-angle neutron scattering was performed on polycrystals and single crystals of Ni-10 to 12 at.% Ti at temperatures between 900 and 1240 K. A plateau in the integrated intensity as a function of aging time for polycrystalline Ni-11.3 at.% Ti at 900 K indicates the presence of a precursor state γ" preceding the formation of the metastable γ' state, with a Ti concentration of 16.5(1.0) at.% in the particles. In the scattering patterns of a Ni-12.0 at.% Ti single crystal aged at 1200 and 1240 K, strong scattering intensities along <100> related to the coherent γ"/γ' states, and sharp streaks along <111> related to plates of the stable η phase appear successively. At 1240 K, the presence of the L1 2 -related intensities along <100> is unexpected, as this temperature lies above the metastable miscibility gap suggested in the literature.

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Decomposition kinetics of Ni-11.8at.% Ti at 853 K

Cited by 10 publications

References 26 publications

Plasticity of the spinodally decomposing Ni-11.8 at.% Ti alloy

Plasticity of the spinodally decomposing Ni-11.8 at.% Ti alloy

Short-Range Order in Ni-Rich Ni–Ti Studied by Diffuse Neutron Scattering

Small-angle neutron scattering investigation of the early stages of decomposition in Ni-rich Ni-Ti

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