Convectionless directional solidification in an extremely confined sample geometry

A method for the investigation of directional solidification in cylindrical metallic samples with diameters of 2 µ m and lengths of 5 cm, embedded in glass capillaries is presented. We estimate the Rayleigh number of the melt inside these samples to the order of magnitude of signifying completely suppressed convection. Inclined mounting with an angle of between the sample axis and the mounting surface resulted in the creation of elongated nearly longitudinal sections of the sample. Thus it was possible to both depict significant lengths of the sample and to locate distinguished positions along the sample’s length. During directional solidification of an Au-63at%Zn alloy sample with a diameter of 2 µ m the primarily solidifying phase was γ′, with secondary β forming along the surface of the solidified metal fiber and in separated regions along its middle. Bubble formation from gases dissolved in the melt plays a significant role during microstructure formation at this length scale. Quenching induces the formation of shrinkage pores due to additional solidification fronts ahead of the directionally solidifying solid/liquid interface.