Liquid alloys can solidify with patterns like zebras or leopards. This structure opens up new opportunities in metallurgy. The study by scientists from the University of New South Wales and the University of Auckland is published in the journal Nature Nanotechnology.
Around 1952, the famous mathematician Alan Turing developed a conceptual model to explain the patterning process of a two-component system. Such patterns are hereinafter also referred to as Turing patterns.
Patterning is also widely used in artificial systems and industry, especially in the field of metallurgy. There is a whole area called “metallography”, which specializes in the study of microscale structures and compositions of metals and alloys. If you split a multicomponent alloy and look at its cross-sections, it is likely that you will see alternating stripes or overlapping spots of different metal components in the cut. However, despite the fact that the structure and models of solidification of liquid alloys have been known for a long time, the phenomenon of the formation of their surface pattern has remained unexplored for a long time.
Researchers studied the exact types of patterns found on the surface of solidified metal alloys. The team used two-component metallic mixtures: gallium-based alloys containing small amounts of bismuth. These alloys melt easily in the hand, making experimental observation and control easier.
“We could observe the surface solidification process under a conventional optical microscope, and I was surprised when I first saw a solidification front on the surface of a liquid metal, creating continuous patterns behind it,” says Dr. Jianbo Tang, lead author of the work.
Using electron microscopes, the scientists examined highly ordered patterns, including alternating stripes, curved fibers, arrays of dots, and some exotic hybrids of stripes and dots. The researchers were surprised that during the formation of these structures, the content of bismuth with a low concentration in the surface region increased significantly. Such surface enrichment found in this study is contrary to conventional metallurgical concepts.
The researchers linked the discovered solidification phenomenon to the unique surface structure of liquid metals and used supercomputers to simulate this process. In computer simulations, small bismuth atoms, apparently, randomly moving in the sea of gallium atoms, accumulated on the alloy surface.
“This previously ignored phenomenon of surface solidification improves our fundamental understanding of liquid metal alloys and their phase transition processes. This self-contained surface process can be used as a drawing tool to design metal structures and create devices for advanced applications in future electronics and optics, ”added Professor Kurosh Kalantar-Zade, co-author of the study.