Effects of interphase boundary anisotropy on the three-phase growth dynamics in the β(In) – In2Bi – γ(Sn) ternary-eutectic system

S Mohagheghi,S Akamatsu,G Faivre,U Hecht,M Şerefoğlu,S Bottin-Rousseau

doi:10.1088/1757-899x/529/1/012010

Abstract

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.

Highlights

In a directionally solidified eutectic material, the distinct crystal phases in the solid most often present several types of orientation relationships (ORs)
Summary and conclusions We used the rotating directional solidification (RDS) method for in-situ observation of the microstructure growth dynamics in thin samples of β(In)-In2Bi-γ(Sn) three-phase system, and ex-situ electron backscatter diffraction (EBSD) analysis for determining the orientation of the crystals growing in a coupled manner
The floating growth dynamics are insensitive to the ORs

Summary

Introduction

In a directionally solidified eutectic material, the distinct crystal phases in the solid most often present several types of (special) orientation relationships (ORs). The free energy of the interphase boundaries can be substantially anisotropic, and that interfacial anisotropy, in particular, the number and the inclination of low-energy planes, depend on the OR. This has a great impact on the formation of both eutectic growth microstructures and eutectic grains (EGs) [1]. During RDS, a thin alloy sample is slowly rotated with respect to the axis of the fixed unidirectional temperature gradient, in such a way that solidification occurs while the orientation of the crystals is continually varied. In a binary eutectic system, the trace of the interphase boundaries

Methods

Results

Conclusion