Temperature Oscillations in Eutectic Alloy Melt for the Bridgman‐Stockbarger Configuration

Abstract

The characteristics of the temperature field in AlZn, AlGe, PbSn, and Sb—InSb low‐melting alloy eutectics were determined by means of the Bridgman‐Stockbarger method of directional solidification with a specimen fixed in a graphite ampoule and a moving furnace. The device could be rotated in such a way, that an arbitrary angle α between the axial temperature gradient in the melt and the gravity field vector could be set. Periodic and/or nonperiodic temperature fluctuations indicating periodic and/or nonperiodic turbulent convection up to an angle α = 80° were studied in the individual systems. At larger angles laminar convection can be expected. The frequency of the temperature oscillations is the same along the entire length of the specimen, whilst the amplitudes of the temperature oscillations depend on the situation of the measurement in the specimen. It has been found that the zone of unstable periodic convection is reduced with an increase of the axial temperature gradient and a decrease of the H/d ratio for a cylindrical ampoule. The convection instability threshold in the ampoule increases with the deviation of the ampoule axis from the axis of the vertical unstable arrangement, i.e. from the direction of the gravity vector. The threshold of the laminar flow instability and the onset of turbulent flow increases with the H/d ratio, i.e. an ampoule with a higher H/d ratio stabilizes laminar flow.