EVOLUTION OF MICROSTRUCTURE IN A RAPIDLY SOLIDIFIED AL-FE-V-SI ALLOY

Microstructural development in a rapidly solidified Al-Fe-V-Si alloy has been investigated by transmission electron microscopy (TEM). The as-cast microstructure varies depending on casting conditions and also through the thickness of melt-spun ribbon. The microstructure of the completely zone A ribbon consists of the microcellular precipitation of a microquasi-crystalline phase, with globular particles of clustered microquasi-crystalline phase near the air side of the ribbon. For the ribbon with mixed zone A and zone B, in contrast, an intercellular particle is composed of silicide phase, but the formation of globular particles of microquasi-crystalline phase (somewhat decomposed) is again observed near the air side of the ribbon. During heating, as observed by annealing studies and by in situ hot-stage TEM studies, intercellular microquasi-crystalline particles are quite unstable and decompose at a very fast rate, resulting in a coarse distribution of silicide particles. This decomposition of the intercellular microquasi-crystalline particles assists the decomposition of globular particles of clustered microquasi-crystalline phase in completely zone A ribbon, resulting in a very coarse distribution of silicide particles after annealing. For the ribbon with mixed zone A and zone B, decomposition of globular particles of clustered microquasi-crystalline phase results in the precipitation of silicide particles along the cell boundaries.