Research Project: Üç Fazlı Ötektik Mikroyapılarının Gerçek Zamanlı Deneysel İncelenmesi
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Contributors
Funders
ID
TB.00134
Authors
Şerefoğlu, Melis
Researcher
Publications
Dynamics of spacing adjustment and recovery mechanisms of ABAC-type growth pattern in ternary eutectic systems
(Elsevier B.V., 2017) Mohagheghi, Samira; Şerefoğlu, Melis; N/A; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; No; College of Engineering; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
In directionally solidified 2D samples at ternary eutectic compositions, the stable three-phase pattern is established to be lamellar structure with ABAC stacking, where A, B, and C are crystalline phases. Beyond the stability limits of the ABAC pattern, the system uses various spacing adjustment mechanisms to revert to the stable regime. In this study, the dynamics of spacing adjustment and recovery mechanisms of isotropic ABAC patterns were investigated using three-phase In-Bi-Sn alloy. Unidirectional solidification experiments were performed on 23.0 and 62.7 mu m-thick samples, where solidification front was monitored in real-time from both sides of the sample using a particular microscopy system. At these thicknesses, the pattern was found to be 2D during steady-state growth, i.e. both top and bottom microstructures were the same. However, during spacing adjustment and recovery mechanisms, 3D features were observed. Dynamics of two major instabilities, lamellae branching and elimination, were quantified. After these instabilities, two key ABAC pattern recovery mechanisms, namely, phase invasion and phase exchange processes, were identified and analyzed. After elimination, ABAC pattern is recovered by either continuous eliminations of all phases or by phase exchange. After branching, the recovery mechanisms are established to be phase invasion and phase exchange.
Quasi-isotropic and locked grain growth dynamics in a three-phase eutectic system
(Pergamon-Elsevier Science Ltd, 2018) Mohagheghi, Samira; Şerefoğlu, Melis; N/A; Department of Mechanical Engineering; No; College of Engineering
The anisotropy of the interphase boundaries has a substantial impact on the eutectic pattern formation. Using rotating directional solidification (RDS) technique, two distinct eutectic grains, namely quasi-isotropic (floating) and crystallographically-locked grains, were identified in three-phase In-Bi-Sn alloy system. The growth dynamics of these grains were investigated in thin samples. The ABAC-type growth pattern, where A, B, C are eutectic phases, is preserved in the quasi-isotropic grains upon evolution of the pattern over the entire crystallographic orientations in RDS experiments. In the locked grains, however, the regularity of the ABAC pattern is disturbed due to the existence of two-fold singularities, i.e. cusps over a well-defined angular range at the surface energy plot. Nevertheless, the ABAC pattern is recovered after the sequence of the unlocked/transient/locked/transient states. The characteristics of both grains are analogous to the nearly steady-state pattern formed upon standard directional solidification experiments. The quasi-isotropic and locked grains in a three-phase ternary eutectic system essentially have the similar dynamical features as the two-phase binary eutectic systems although the microstructural details are highly complex in the three-phase system. These similarities designate that the formation of quasi-isotropic and locked patterns is merely due to the inherent characteristics of the eutectic grains.
Stability of three-phase ternary-eutectic growth patterns in thin sample
(Elsevier, 2018) Şerefoğlu, Melis; Yücetürk, Sinan; Bottin-Rousseau, Sabine; Faivre Gabriel; Akamatsu, Silvere; Department of Mechanical Engineering; No; College of Engineering
Near-eutectic ternary alloys subjected to thin-sample directional solidification can exhibit stationary periodic growth patterns with an ABAC repeat unit, where A, B, and C are the three solid phases in equilibrium with the liquid at the eutectic point. We present an in-situ experimental study of the dynamical features of such patterns in a near-eutectic IneIn2BieSn alloy. We demonstrate that ABAC patterns have a wide stability range of spacing l at given growth rate. We study quantitatively the ldiffusion process that is responsible for the spacing uniformity of steady-state patterns inside the stability interval. The instability processes that determine the limits of this interval are examined. Qualitatively, we show that ternary-eutectic ABAC patterns essentially have the same dynamical features as two-phase binary-eutectic patterns. However, lamella elimination (low-l stability limit) occurs before any Eckhaus instability manifests itself. We also report observations of stationary patterns with an [AB]m[AC]n superstructure, where m and n are integers larger than unity.
