In-situ and real-time investigation of the columnar-equiaxed transition in the transparent alloy system neopentylglycol-camphor onboard the sounding rocket TEXUS-47

Abstract

The low-gravity experiment TRACE (TRansparent Alloys in Columnar Equiaxed solidification) has been performed onboard the sounding rocket TEXUS-47 to enable the investigation of dendritic growth and the dendrites' columnar to equiaxed transition during solidification. Low-gravity conditions provide solidification under diffusive heat and mass transfer conditions and without sedimentation or buoyancy of equiaxed dendrites or nucleation seeds to simplify the boundary conditions for dendritic microstructure simulation. In addition the transparent organic alloy system Neopentylglycol (NPG) - (D)Camphor (DC) was used to allow for a real-time and in-situ observation of the microstructure evolution with standard optics. For the flight experiment all relevant experimental parameters like thermal gradient, solidification velocity and undercooling within the bulk liquid and at the columnar dendritic tips have been determined by image analysis or from thermocouple recordings within the solidifying alloy. This allows a very detailed comparison with results of existing models for dendritic growth and for columnar-to-equiaxed transition. Here we present a summary of the experimental findings in comparison with results of some of the theoretical models.