Analysis of thermal stability after occurrence of absolute solute trapping in undercooled Co–Cu alloy

Abstract

Thermal stability after recalescence of the single-phase supersaturated granular grains prepared in Co-15 at.%Cu immiscible alloy melt was investigated. As for undercooled Co–Cu alloy, a transition from dendritic to granular crystals occurred when ΔT ≥ ΔT∗, which was induced by an abrupt change in the dendritic growth mechanism from solute-controlled to purely thermally-controlled growth. However, the recalescence effect led to grain growth and solute segregation of trapped Cu to grain boundaries. On this basis, a thermo-kinetic model applicable for nano-scale materials was extended to the system of micro-scale undercooled Co–Cu alloy. The model showed close agreement with the experimental results. It is concluded that Cu atoms captured by solute trapping re-segregated to grain boundaries, which was responsible for the reduction in grain boundary energy and improvement in thermal stability in undercooled Co–Cu alloy.