Correlation between Growth Twinning and Crystalline Reorientation of Faceted Growth Materials during Directional Solidification

Abstract

The correlation between growth twinning and crystalline reorientation of faceted growth materials during directional solidification was demonstrated through matrix calculation and Thompson regular tetrahedron model diagrams. The correlation is that the crystalline reorientation results from the mirror symmetry operation of initial orientation on different twin planes. In total, seven possibilities of crystalline reorientation caused by single-twinning from ⟨110⟩, ⟨111⟩, and ⟨112⟩ initial axial orientation were predicted, four of which were verified experimentally in the representative Tb 0.3 Dy 0.7 Fe 2 alloys. G rowth twinning (GT) has attracted much attention owing to its effects on the growth pattern, microstructure, crystalline orientation, and thus the property. The effects of GT on crystal growth were first discovered from Ge in the 1950s 1 and has been extensively observed in metals, intermetallic compounds, semiconductors, and oxides, especially for the faceted growth materials with a large entropy of melting, for instance, Ge, 1−4 Si, 5−13 AlSi, 14−19 and TbDyFe. 20−25 Growth with GT is usually a major growth pattern for the faceted growth materials because twinning grooves can reduce the growth supercooling degree.Remarkable property anisotropy exists in almost all faceted growth materials. The excellent properties usually appear along specific crystalline orientation. For example, the magnetostriction along ⟨111⟩ orientation (λ 111 ) is about 20 times of that along ⟨100⟩ orientation (λ 100 ) in TbDyFe giant magnetostrictive alloys. 26 Thus, the control of crystalline orientation along certain direction is of crucial importance for faceted growth materials.However, the phenomenon that the crystalline orientation can be changed by GT is frequently observed in faceted growth materials. 14,24,27 Especially for directional solidification process, the axial orientation is usually changed even with a single crystal seed. For instance, it is observed that the axial orientation changes from ⟨110⟩ initial axial orientation to ⟨114⟩ in TbDyFe alloys, 23,24 and a two-{111}-twin system growth model is proposed. 24 However, because of lacking systematic theoretical analysis, the correlation between GT and crystalline reorientation remains still unclear. Investigating all possibilities of reorientation from different initial axial orientations could provide a better understanding for crystalline orientation control and properties.In this communication, we analyzed the correlation between GT and reoriented growth from ⟨110⟩, ⟨111⟩, and ⟨112⟩ initial axial orientations in faceted growth materials with facecentered-cubic (fcc) structure. All the possibilities of crystalline reorientation from these three orientations were calculated by matrix and intuitively shown through a Thompson regular tetrahedron model, and the results were confirmed experimentally in a representative alloy of Tb 0.3 Dy 0.7 Fe 2 .High-purity starting element terbium, dysprosium, and iron with a purity level of 99.99% were remelted four times by ar...

Possible Twinning Operations during Directional Solidification of Multicrystalline Silicon

“…The correct T matrices should be the ones for the misorientation axis/angle pair of ⟨1̅ 10⟩/70.5°, which was observed in the experiment. 13 On the other hand, in the method mentioned in ref 12 which we adopted, the growth orientation (column vector) of the…”

“…Fortunately, the transformation matrix (T matrix) is a useful tool for the analysis, because it focuses on the orientation relationship instead of the structural one. The use of the mirror symmetric operation for T matrices was reported recently, 12,13 but still some experimental results could not be explained by the proposed T matrices. Because the previous matrices were calculated based on the two grains being misoriented by 180°, they were not sufficient at all.…”

Recent Advances in Magnetostrictive Tb-Dy-Fe Alloys

“…Therefore, the transformation of the preferred axial orientation was explained by the different space-occupying capacities caused by the different morphological configurations for <101> and <112> axially oriented grains [24]. The growth twins of Tb-Dy-Fe alloys changed the crystal orientation, which was related to the crystal orientation of mirror symmetry [22]. Previous studies have shown that different solidification rates correspond to different solidification morphologies; that is, with the increase in the solidification rate, the preferred axial orientation changed from <101> to <112> and was then reoriented to <101> [23].…”

Orientation Selection and Microstructural Evolution in Directionally Solidified Tb0.3Dy0.7Fe1.95

“…Therefore, an in-depth understanding of directional solidification of the (Tb,Dy)Fe 2 intermetallic is the topic of interest with a special emphasis on orientation selection and microstructural evolution. Several researchers, including the authors, [4][5][6][7][8][9][10][11][12][13][14][15] are pursuing investigations in this area, and the efforts have led to an improved know-how of the physical metallurgical aspects of this material. However, the key issue that remains unresolved is to grow the material successfully with h111i texture.…”

“…On the other hand, zone melting or modified Bridgman techniques offer scope for obtaining specimens of larger dimensions. Although reports on formation of different texture components through these methods are available, [4][5][6][7][8][9][10][11][12][13][14][15] an integrated theory on the underlying mechanism is yet to evolve that can explain the orientation selection as a function of solidification parameters.…”