Melting behaviour of tri-phasic Bi44In32Sn23 alloy nanoparticle embedded in icosahedral quasicrystalline matrix

Abstract

Tri-phasic nanoscaled (Bi,In,Sn) alloy nanoparticles (NPs) embedded in the icosahedral quasicrystalline (IQC) matrix were synthesized by the rapid solidification route. The microstructure of the NPs was analyzed using transmission electron microscopy (TEM), which typically reveals the combination of three phases; rhombohedral (Bi), body-centered tetragonal BiIn and hexagonal (γ-Sn) in each NP. TEM study also indicates that (Bi) and BiIn bear a reasonably good lattice match with surrounding IQC, whereas (γ-Sn) does not develop any specific orientation relationship. In order to understand the melting behavior of tri-phasic NPs, extensive DSC (differential scanning calorimetry), in-situ TEM (transmission electron microscopy) and in-situ XRD (X-ray diffraction) has been carried out. The DSC result reveals substantial depression of melting temperature (∼20 °C) as compared to bulk. In-situ studies also indicate the solid-state transformation of (γ-Sn) into (β-Sn) prior to melting. As the temperature advances, melting initiates at the triple junction of (Bi)/BiIn and matrix. BiIn first melts completely, and the melt front grows into the (β-Sn) phase of the NP. Subsequently, the melt propagates into the interior of (Bi) rich region. The present study provides an insight into the formation of non-equilibrium (γ-Sn) phase instead of (β-Sn) and the mechanism of the melting behaviour of three-phase NP embedded in IQC.