Spiral eutectic growth dynamics facilitated by space Marangoni convection and liquid surface wave

Eutectic alloys display excellent application performances since the essential function of coupled microstructures is quite different from that of single-phase and peritectic alloys. However, due to the strong natural convection within liquid alloys under normal gravity, the eutectic growth process on earth usually produces traditional rod-like or lamellar composite microstructures, which hinders the exploration of distinctive coupled growth patterns. Here, we carried out the rapid solidification of hypoeutectic Zr64V36 alloy to explore novel coupled growth dynamics aboard the China Space Station under a long-term stable microgravity condition. An extreme liquid undercooling of 253 K was achieved for this refractory alloy, displaying a strong metastability in outer space. We find that a radial coupled pattern grew out of the nucleation site, accompanying a ripple-like surface microstructure. This resulted from the rapid eutectic growth within a highly undercooled alloy in combination with a liquid surface wave excited by the electrostatic field under microgravity. Especially, a spiral coupled growth mode occurred during radial eutectic growth and surface wave spreading, which were controlled by the Marangoni convection effect on the fluid flow pattern and eutectic growth dynamics. Our findings contribute to the coupled growth investigation by modulating gravity levels to develop multi-pattern microstructures.