Research Project: Real-time study of pattern formation dynamics şn nonvariant eutectic solidification microstructures
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Contributors
Funders
ID
EC.00053
Authors
Şerefoğlu, Melis
Researcher
Publications
Effects of interphase boundary anisotropy on the three-phase growth dynamics in the β(In) - In2Bi - γ(Sn) ternary-eutectic system
(Institute of Physics (IOP) Publishing, 2019) Mohagheghi, Samira; Şerefoğlu, Melis; Hecht, U.; Bottin-Rousseau, S.; Akamatsu, S.; Faivre, G.; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; No; College of Engineering; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
We present an experimental investigation on the effects of the interphase energy anisotropy on the formation of three-phase growth microstructures during directional solidification (DS) of the β(In)-In2Bi-γ(Sn) ternary-eutectic system. Standard DS and rotating directional solidification (RDS) experiments were performed using thin alloy samples with real-time observation. We identified two main types of eutectic grains (EGs): (i) quasi-isotropic EGs within which the solidification dynamics do not exhibit any substantial anisotropy effect, and (ii) anisotropic EGs, within which RDS microstructures exhibit an alternation of locked and unlocked microstructures. EBSD analyses revealed (i) a strong tendency to an alignment of the In2Bi and γ(Sn) crystals (both hexagonal) with respect to the thin-sample walls, and (ii) the existence of special crystal orientation relationships (ORs) between the three solid phases in both quasi-isotropic and anisotropic EGs. We initiate a discussion on the dominating locking effect of the In2Bi-β(In) interphase boundary during quasi steady-state solidification, and the existence of strong crystal selection mechanisms during early nucleation and growth stages.
On the growth dynamics of nearly-locked grain in the three-phase in-bi-sn eutectic system
(Springer, 2019) Mohagheghi, Samira; Şerefoğlu, Melis; Department of Mechanical Engineering; No; College of Engineering
Solidification microstructures are significantly affected by the anisotropy of crystal/crystal interphase energy. A recent experimental work on a three-phase eutectic system by the authors suggested that two distinguishable eutectic grains, i.e., quasi-isotropic and locked, form when crystal/crystal interphase energies contain negligible and strong anisotropy, respectively (Mohagheghi and Serefoglu in Acta Mater 2018, vol. 151, pp. 432-42, 2018). In two-phase eutectic systems, in addition to these two grain types, another class of eutectic grain called nearly-locked (NL) was reported. In order to investigate the existence of the NL grain in three-phase eutectic systems, real-time directional solidification (DS) and rotating directional solidification (RDS) experiments are performed on thin samples of In-Bi-Sn eutectic alloy. It is found that NL grains also form in three-phase eutectics and they contain some characteristic features of both quasi-isotropic and locked grains. The anisotropy is strong enough to tilt the lamellar pattern with respect to the thermal gradient axis, as in the case of locked grains; however, the NL grains also retain some of the characteristic features of the quasi-isotropic grains, such as lambda-diffusion, systematic eutectic spacing adjustment, and recovery mechanisms. As a result, these grains tend to form a relatively uniform ABAC-type growth pattern, similar to quasi-isotropic grains. Using the equilibrium shapes extracted from the interphase traces of RDS patterns, the gamma plot of the anisotropic interphase, which contains 2 twofold smooth and distinct minima, is determined.
