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

Microstructural development in a rapidly solidified Al-Fe-V-Si alloy h as been investigated by transmission electron microscopy (TEM). The as -cast microstructure varies depending on casting conditions and also t hrough the thickness of melt-spun ribbon. The microstructure of the co mpletely zone A ribbon consists of the microcellular precipitation of a microquasi-crystalline phase, with globular particles of clustered m icroquasi-crystalline phase near the air side of the ribbon. For the r ibbon with mixed zone A and zone B, in contrast, an intercellular part icle is composed of silicide phase, but the formation of globular part icles of microquasi-crystalline phase (somewhat decomposed) is again o bserved near the air side of the ribbon. During heating, as observed b y annealing studies and by in situ hot-stage TEM studies, intercellula r microquasi-crystalline particles are quite unstable and decompose at a very fast rate, resulting in a coarse distribution of silicide part icles. 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 i n a very coarse distribution of silicide particles after annealing. Fo r the ribbon with mixed zone A and zone B, decomposition of globular p articles of clustered microquasi-crystalline phase results in the prec ipitation of silicide particles along the cell boundaries.