Effects of process parameters on melt-spun AgCu

Abstract

Process parameters in chill block melt spinning (CBMS) play an important role in product formation during rapid solidification. The effect of variations in wheel speed and melt superheat on ribbon dimensions and microstructures of Ag-19wt.%Cu melt spun under high vacuum conditions were examined. The ribbon thickness varied linearly with (solidification time) 0.5, and the solidification rate increased with increasing wheel speed. The initial solidification microstructures had a fine equiaxed two-phase morphology on the wheel side which developed into a directional growth. Examination of serial sections parallel to the wheel side revealed a helical two-phase growth pattern in the mid-thickness of the ribbon which subsequently adopted a mixed cellular-dendritic solidification mode. The helical morphology appears to be related to the morphological instability associated with a banded microstructure. Near the free surface an equiaxed microstructure again developed as a result of dendritic fragmentation induced by melt shear flow. Wheel speed and melt superheat affected the extent of the different microstructures. Through control of processing parameters in CBMS, under high vacuum conditions, a degree of control on ribbon dimensions and structural development has been achieved.