Observation of peritectic reaction in Ag-Sn alloys

Abstract

In general, peritectic reaction is known that the secondary phase grows as it surrounds the primary phase. However, relationship between primary and secondary phase is still uncertain. Therefore, to clarify this, an experimental work has been preformed using Ag-35 mass%Sn alloy. The alloy was melted in an alumina crucible and then cooled at a constant cooling rate. The specimen temperature was measured with a thermocouple. Thereafter, the specimen was dropped into a water bath at a various temperature to quench the solid/liquid interfacial morphology and solute distribution. Then the specimen was polished and was etched, if necessary. The result of the thermal history, supercooling and recalescence was observed near the peritectic temperature. The observation by scanning electron microscope (SEM) unveiled many fine protrusions ( = ε-phase) on a primary ζ-phase, which is quenched at early state of peritectic reaction. In addition, concentration profile was measured by energy dispersive X-ray spectrometry (EDX) and ζ, ε and liquid phases were identified. As a result, it was confirmed that ε-phase grew along the surface of ζ-phase and it did not grow into the ζ-phase. Further, result of electron backscatter diffraction (EBSD) analysis, ε-phase was found to be single crystal within the range of this study.