Growth kinetics and mechanism of the massive transformation

Perepezko, John H.

doi:10.1007/bf02644967

Cited by 51 publications

(16 citation statements)

References 37 publications

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“…In this view, it is suggested tion, have been observed in a range of metals and ferrous that planar, low-energy, massive-matrix interphase boundand nonferrous alloy systems. [1][2][3][4][5][6][7][8][9][10][11][12] The effective levels of aries are common during growth, and that these interfaces undercooling at which such transformations occur and, thus, migrate in directions normal to the interface plane only by the driving forces involved are usually sufficiently large that the formation and lateral movement of growth ledges. [2] the product phase takes a massive, approximately equiaxed Systematic characterization of massive-matrix interphase form with dimensions typically in the range of several boundaries in the Ag-Al alloy system [10] using transmission microns.…”

Section: Introductionmentioning

confidence: 99%

Orientation and structure of planar facets on the massive phase γ m in a near-TiAl alloy

Nie

Muddle

2002

Metall Mater Trans A

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The orientation and structure of planar facets on the ␥ m massive phase formed in a Ti-46.5 at. pct Al alloy have been characterized using a combination of transmission electron microscopy (TEM) and electron diffraction. The planar ␥ m /␣ 2 interfaces are irrational with respect to both the ␣ 2 matrix phase and the ␥ m phase, and there is neither evidence of a rational orientation relationship across such facets, nor resolution of a linear defect structure within the interface planes in conventional electron diffraction patterns and amplitude-contrast images, respectively. However, when imaged parallel to a particular direction in the interface, these irrationally oriented interfaces are invariably parallel to the Moiré plane, which is defined by the intersection between two sets of closely-packed planes in the ␥ m and ␣ 2 phases. The relationship is such that there is an effective continuity of these lattice planes across the interface and a one-dimensional coherency within the planar interface. This is interpreted to imply that such interface facets adopt a configuration of reduced energy and that they are not random and fully incoherent, as often described. It is suggested that these planar facets may migrate in a glissile manner normal to the interface plane by nucleation and rapid lateral movement within the interface plane of interfacial defects that have the form of Moiré ledges, which are defined by the spacing of the Moiré pattern that may be formed by overlap of the relevant crystal planes across the interface.

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Section: Introductionmentioning

confidence: 99%

Orientation and structure of planar facets on the massive phase γ m in a near-TiAl alloy

Nie

Muddle

2002

Metall Mater Trans A

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“…In the present study, the effect of Al content in binary alloys has been examined and the results show that the massive reaction from a to "y occurs at high cooling rates from 46.54 to 50 Al. The massive transformation has been extensively studied in the past and examples of this transformation can be found in many systems (16)(17)(18)(19). Essentially, a massive transformation takes place by diffusional nucleation and growth and involves a change in crystal structure without a change in composition, and in principle, can be observed in any system where the pertinent phase fields overlap in composition (16,17).…”

Section: Discussionmentioning

confidence: 99%

“…The massive transformation has been extensively studied in the past and examples of this transformation can be found in many systems (16)(17)(18)(19). Essentially, a massive transformation takes place by diffusional nucleation and growth and involves a change in crystal structure without a change in composition, and in principle, can be observed in any system where the pertinent phase fields overlap in composition (16,17). Moreover, it is possible for a massive reaction to be considered as occuring in the metastable two-phase field, such as that below a invariant reaction temperature (eg., eutectoid temperature) (17).…”

Section: Discussionmentioning

confidence: 99%

“…Essentially, a massive transformation takes place by diffusional nucleation and growth and involves a change in crystal structure without a change in composition, and in principle, can be observed in any system where the pertinent phase fields overlap in composition (16,17). Moreover, it is possible for a massive reaction to be considered as occuring in the metastable two-phase field, such as that below a invariant reaction temperature (eg., eutectoid temperature) (17). Both the TEM observations showing the structural change and the microprobe analysis establishing composition invariance attest to the occurrence of the massive reaction from a to y at high cooling rates.…”

Section: Discussionmentioning

confidence: 99%

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Air Force Engineering Research Initiation Grants (1990-1991)

Freiman¹

1992

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“…[7] across the massive-product/matrix interface. [2,3] Detailed Numerous studies [10][11][12][13][14][15][16][17][18][19] in near-equiatomic Ti-Al systems studies have been made on the effect of crystallography on have shown that a massive solid-state transformation of the both nucleation and growth in the Cu-Zn system. [4,5,6] The hexagonal ␣ phase into the tetragonal L1 0 ␥ m phase can nuclei of the massive-product ␣ phase at ␤:␤ grain boundoccur when the cooling rate is sufficiently high.…”

Section: Introductionmentioning

confidence: 99%

The massive transformation in titanium aluminides: Initial stages of nucleation and growth

Wittig

2002

Metall Mater Trans A

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Rapid solidification by twin-anvil splat quenching captures the initial nucleation and growth of the ␣ → ␥ m massive transformation in titanium aluminides. Splat quenching Ti 52 Al 48 and Ti 50 Al 48 Cr 2 from the liquid at slightly below the melting point produces an equiaxed ␣ solidification structure. Solid-state cooling rates that approach 10 6 K/s arrest the ␣ → ␥ m massive transformation with 1-to 5-m-sized ␥ m nuclei, especially in the Ti 50 Al 48 Cr 2 alloy. Classical massive-transformation heterogeneous nucleation occurs at ␣:␣ grain boundaries with an orientation relationship of [111] ␥ //[0001] ␣ and {110} ␥ //{1120} ␣ . The ␥ m nucleus then grows into the adjacent ␣ grain without the orientation relationship by forming an incoherent ␣:␥ interface with {111} ␥ facets. Orthogonal variants of the tetragonal c-axis in the ␥ m product suggest that the massive transformation initially produces an fcc structure which subsequently orders into the L1 0 phase. Nucleation of ␥ m is not only observed at ␣:␣ grain boundaries and triple points, but also within the ␣ grains. The intragranular ␥ m nucleation, which is believed to be heterogeneous, occurs with the same orientation relationship as for the intergranular nuclei. However, the intragrain nuclei do not form {111} ␥ facets and retain a curved ␣:␥ m interface. Although analysis of the {111} ␥ faceted growth using weak-beam dark-field (WBDF) imaging shows no evidence for any type of misfit-compensating dislocations, lattice imaging of the {111} ␥ facets with high resolution transmission electron microscopy (HRTEM) reveals that the planar interface exhibits a slight curvature, produced by atomic steps of (111) planes. These experimental data have been used to estimate a ratio of ledge spacing ( ) to ledge height (h) for the {111} ␥ facets as /h ϭ 41, which is similar to calculated values for a ledge growth mechanism of massive transformations in Cu-Zn and Ag-Cd alloys.

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Growth kinetics and mechanism of the massive transformation

Cited by 51 publications

References 37 publications

Orientation and structure of planar facets on the massive phase γ m in a near-TiAl alloy

Orientation and structure of planar facets on the massive phase γ m in a near-TiAl alloy

Air Force Engineering Research Initiation Grants (1990-1991)

The massive transformation in titanium aluminides: Initial stages of nucleation and growth

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