The calculation of a parent grain orientation from inherited variants for approximate (b.c.c.–h.c.p.) orientation relations

2002 ◽  
Vol 35 (4) ◽  
pp. 401-405 ◽  
Author(s):  
M. Humbert ◽  
N. Gey
Keyword(s):  
Phase Transformation ◽  
Grain Orientation ◽  
The Body ◽  
Orientation Relation ◽  
Hexagonal Close Packed ◽  
Orientation Relations ◽  
Parent Orientation

The orientations of parent β grains are evaluated from several α variants inherited from the same parent during the body-centred cubic (b.c.c.) to hexagonal close packed (h.c.p.) phase transformation. The proposed calculation, based on orientation correlating and orientation averaging, is particularly useful when the inherited variants are not strictly related to the parent orientation by a strict Burgers orientation relation or when the orientations of the inherited volumes vary slightly at different locations of the variant. This method of parent identification from variant orientations is an improvement of a previously published method.

Determination of the Orientation of a Parent β Grain from the Orientations of the Inherited α Plates in the Phase Transformation from Body-Centred Cubic to Hexagonal Close Packed

1995 ◽  
Vol 28 (5) ◽  
pp. 571-576 ◽  
Author(s):  
M. Humbert ◽  
F. Wagner ◽  
H. Moustahfid ◽  
C. Esling
Keyword(s):  
Phase Transformation ◽  
The Body ◽  
Orientation Relation ◽  
Favourable Case ◽  
Hexagonal Close Packed ◽  
Uniqueness Of The Solution

Knowledge of the orientations of several α plates inherited from the body-centred-cubic–hexagonal-close-packed phase transformation of a β grain allows us to determine the orientation of the latter, provided that a strict orientation relation between the two lattices exists. This contribution discusses the problem of the uniqueness of the solution and leads to the conclusion that the number of different α orientations required for that purpose is three in the less favourable case but is reduced to two in the most favourable case.

Calculation of the Parent hcp Grain Orientation from Inherited Variants in the hcp to t and in the hcp to cc Phase Transformations Application to the α-γ Transformation in TiAl-Based Alloys

2005 ◽  
Vol 495-497 ◽  
pp. 1219-1224 ◽  
Author(s):  
Michel Humbert ◽  
S.R. Dey ◽  
Emmanuel Bouzy ◽  
Alain Hazotte
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Grain Orientation ◽  
Orientation Relation ◽  
Parent Orientation

The orientations of the inherited tetragonal (resp. cubic) variants are calculated from the parent hcp orientation in the case of a strict orientation relation. The numbering of the variants is proposed, as well as the misorientations between them. Conversely, a method for calculating the parent hcp orientation from a sufficient number of inherited variants is proposed. It is based on orientation correlating and orientation averaging, and it is particularly useful when the inherited variants are not exactly related to the parent orientation by a strict orientation relation or when the orientations of the inherited volumes slightly vary at different locations of the variant. The method is illustrated by considering the a to g phase transformation taking place in TiAl-based alloys

Restitution of the Shapes and Orientations of the Prior Austenitic Grains from Inherited Alpha' Orientation Maps in Steels

2011 ◽  
Vol 172-174 ◽  
pp. 911-915 ◽  
Author(s):  
Nathalie Gey ◽  
Pierre Blaineau ◽  
Lionel Germain ◽  
Michel Humbert ◽  
David Barbier ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Grain Orientation ◽  
Automated Analysis ◽  
Orientation Relation ◽  
Reconstruction Procedure ◽  
Α Phase ◽  
Bainitic Steels ◽  
Large Spread ◽  
Orientation Maps

We propose to reconstruct the g orientation maps from the α maps inherited by the bainitic or martensitic γ→α phase transformation. Our approach comprises two main steps (1) identification of reliable fractions of parent grains – each γ fraction is determined from neighbouring variants related to a unique γ orientation with a low tolerance angle; (2) expansion of these fractions by collecting adjacent variants being in orientation relation (OR) with the calculated g orientation - using a higher tolerance around the strict OR. Moreover, this fully automated g map reconstruction is further improved by an additional semi-automated analysis of α/γ maps. This reconstruction procedure was applied to the α microtexture of bainitic steels. The reliability of the calculations was checked by comparing each γ grain orientation and their corresponding α variants. The results show that even with a large spread around OR, the shape and orientation of most of the γ grains are accurately calculated.

X-Ray Investigation of a 2H-3C Phase-Transformation in Silicon Carbide Single Crystals

1970 ◽  
Vol 14 ◽  
pp. 67-77 ◽  
Author(s):  
P. Krishna ◽  
R. C. Marshall
Keyword(s):  
Phase Transformation ◽  
Hydrogen Reduction ◽  
Reciprocal Lattice ◽  
Inert Atmosphere ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hexagonal Close Packed ◽  
Dark Green ◽  
New Phase ◽  
Thermal Stability Of

AbstractThis paper reports the results of a detailed X-ray diffraction study of a new phase-transformation observed in SiC crystals grown by a vapour-liquid-solid mechanism involving the hydrogen-reduction of methyltrichlorosilane. The 10.ℓ reciprocal lattice rows of these crystals, as recorded on X-ray diffraction photographs, reveal sharp reflections corresponding to the hexagonal close-packed 2H (ABAB….) structure and sometimes also corresponding to the cubic close-packed 3C (ABCABC…) structure. These reflections are invariably connected by a diffuse but continuous streak whose intensity is a measure of the random faulting on the basal planes. The crystals were needle shaped and the structure sometimes varied along their length.Several crystals were annealed in an inert atmosphere at progressively higher temperatures and their 10.ℓ reciprocal lattice row re-examined to determine the annealing behaviour as well as possible structural transformations. For a number of dark green needles having a faulted 2H structure the 2H reflections disappeared around 1400° C and the 10.ℓ reciprocal lattice row revealed only a continuous streak with increased intensity around positions for 3C reflections. On further heating the structure went over to a strongly faulted 3C. Around 1600°C the appearance of a 6H structure became discernible while highly diffuse 30 reflections still persisted. The reversible part of the transformations, if any, could not be observed. Some of the structures were, however, found to be much more stable and did not transform even up to 1650° C.The above results, in particular the discovery of a 2H-3C phase-transformation around 1400°C, throw fresh light on the thermodynamic stability of the different SiC types. The mechanism of the 2H-3C transformation, the possible influence of faults and impurities and the thermal stability of various SiC structures are discussed on the basis of the experimental results stated above.

Ground State Symmetry of an Electrorheological Fluid Containing Two Types of Particles

1998 ◽  
Vol 09 (04) ◽  
pp. 591-606 ◽  
Author(s):  
A. Lukkarinen ◽  
K. Kaski
Keyword(s):  
Dielectric Constant ◽  
Ground State ◽  
Base Fluid ◽  
Electrorheological Fluid ◽  
The Body ◽  
Tetragonal Symmetry ◽  
Point Dipole ◽  
Free Energies ◽  
Hexagonal Close Packed ◽  
Different Types

The ground state symmetry of an electrorheological fluid is studied numerically using a finite element method. The free energies of body-centered cubic, body-centered tetragonal, simple hexagonal, hexagonal close-packed, simple cubic, simple hexagonal, and honeycomb structures are calculated for systems containing homogeneous particles with the dielectric constant greater or smaller than that of the base fluid. In accordance with other studies, the body-centered tetragonal symmetry was found to be the most favored lattice symmetry. The ground state of an ER system containing two types of particles, i.e., particles with the dielectric constant greater and smaller than that of the base fluid, was found to consist of separated particle columns each of which has only one type of particles. These separated particle columns preferred body-centered tetragonal symmetry. However, simple hexagonal and honeycomb symmetries were found to be energetically quite close to a body-centered tetragonal symmetry. In addition, simple hexagonal and honeycomb symmetries do not need phase separation between different types of particles and are thus more likely to form. Dynamical effects were studied using a point dipole model. Within the time-span studied the system seemed to form a polycrystalline structure.

Deformation-induced γ → DI-α2 phase transformation occurring in the twin-intersection region of TiAl alloys

2007 ◽  
Vol 22 (9) ◽  
pp. 2416-2422 ◽  
Author(s):  
C.L. Chen ◽  
W. Lu ◽  
L.L. He ◽  
H.Q. Ye
Keyword(s):  
Phase Transformation ◽  
Room Temperature ◽  
Compositional Analysis ◽  
Hexagonal Close Packed ◽  
Partial Dislocations ◽  
Close Packed Structure ◽  
The Matrix ◽  
Hexagonal Close Packed Structure ◽  
Packed Structure ◽  
Face Centered

Deformation-induced γ → DI-α2 phase transformation was verified to occur in the twin-intersection region of a Ti–45Al–8Nb (at.%) alloy compressed at room temperature. High-resolution image observations of the deformation-induced DI-α2 phase suggested that the orientation relationship between the DI-α2 and γ phases remained the typical one: (0001)DI−α2//{111}γ, [11¯20]DI−α2//〈101]γ. The conversion of stacking sequence from ordered face-centered tetragonal to ordered nonequilibrium hexagonal close-packed structure was accomplished by the movement of a/6〈11¯2] Shockley partial dislocations on every other {111}γ plane. Compositional analysis based on energy dispersive spectra revealed that the DI-α2 phase had the same composition as the matrix γ phase. No compositional diffusion occurred because the plastic deformation was carried out at room temperature. The strong stress concentration in the intersection region was the major force to induce the γ → DI-α2 phase transformation in the process of room-temperature compression.

Sign in / Sign up

Export Citation Format

Share Document