Solidification-Induced Formation of 3D Ge Frameworks in Al-Ge Alloy Microparticles

The solidification behavior and microstructural evolution of Al-Ge microparticles were investigated on Si, SiO₂, Al₂O₃, amorphous carbon, and ZrO₂ substrates. Micrometer-sized particles with a hypereutectic composition were produced by melting and resolidifying 40 nm thick Al-Ge films. Their size, wetting angle, crystal structure, and internal morphology were characterized by SEM and TEM techniques. We demonstrate that Al-Ge particles exhibited strongly substrate-dependent wetting, with contact angles ranging from 46° on SiO₂ to 123° on ZrO₂. Nevertheless, all particles developed a similar internal microstructure consisting of a fully interconnected, irregular Ge network within an Al matrix, indicating complete phase separation during solidification. The eutectic network was quantified by its ligament thickness. No correlation was found between ligament thickness and substrate type or contact angle, indicating that the coral-like internal Ge network forms independently of particle wetting. Instead, the ligament thickness increased with particle size and during post-solidification annealing. The network gradually coarsened up to 310 °C, followed by its complete breakdown and transformation into an equilibrium Janus morphology at 370 °C. These findings provide new insight into the solidification of irregular eutectic systems and suggest a route for tailoring three-dimensional internal microstructures in eutectic microparticles.