The Effect of the Rate of Cooling from High-Temperature Single-Phase Region on the Microstructure and Magnetic Properties of AlNi Alloys

Abstract

The microstructure of as-cast and melt spun AlNi alloys was studied by transmission (TEM) and scanning electron microscopy as well as atomic force microscopy (AFM). The magnetic properties of the alloys were measured using a vibrating sample magnetometer. The water quenched and melt spun AlNi samples were characterized by zone microstructure formed as a result of solid solution decomposition into β- and β2 phases within the miscibility gap. Therefore, the subsequent aging of as-quenched alloy leads to the development of the zone microstructure instead of the decomposition of single-phase solid solution. The absence of preferential precipitations and discontinuous precipitation (DP) reaction was observed at grain boundaries (GB) of as-cast AlNi alloy after aging. The antiphase domains (APD) have been observed for the first time in the AlNi ribbons prepared by melt spinning. The effects of GB and APD boundaries on the decomposition of a solid solution in the AlNi ribbons were investigated. At first, a thin β-phase layer is formed along GB and APD boundaries. Then the decomposition leads to the formation of β2-phase layers on the both sides of β-phase layer. The GB and APD boundaries, which are decorated by precipitates of β- and β2 layers, become visible in the TEM and AFM micrographs. A DP reaction at GBs has been observed for the first time in the AlNi ribbons after supplementary aging. The cellular microstructure at GBs consisting of alternating lamellas of β′- and β′2 phases was formed after aging the ribbons at 773 K (500 °C) for 10 minutes.