Eutectic systems have shaped mankind for millennia — bronze, solder, casting alloys — and yet, for all their industrial pedigree, the nanoscale mechanics of how they actually melt has remained stubbornly out of reach. Experimental resolution simply could not keep up with the physics. A new preprint from our group closes that gap, using in situ STEM with MEMS-based electrothermal chips to film an aluminium–copper alloy melting in real time, at nanometre and millisecond resolution. The results are striking: melting does not sweep uniformly across the material. It ignites in the hotter central region, creeps outward, and grain boundaries act as the spark — local copper enrichment at boundaries triggers eutectic liquid formation before the surrounding matrix has even begun to melt. The Al₂Cu phase goes first, then the rest follows.
Once liquid forms, the physics shifts dramatically. Copper redistribution driven by the Marangoni effect — surface-tension gradients pulling liquid from hot to cold — moves material across 258 micrometres in minutes, orders of magnitude beyond what solid-state diffusion could ever achieve in the same timeframe. This is a pioneer nanoscale observation of this process, and the methodology opens a window onto melting phenomena relevant to additive manufacturing, welding, sintering, and beyond.
This work is led by Martin Hasenburger, who joined us for his PhD studies in In situ Electron Microscopy & Materials Physics after completing his studies at TU Graz, his alma mater. He is proving himself to be one of the most driven and creative young experimentalists we have had the pleasure of working with. Combining deep technical fluency in advanced physics topics with a genuine instinct for asking the right scientific questions, Martin is exactly the kind of early-career researcher this world needs more of. Chapeau!
Citation:
M. Hasenburger, R. Daniel, P. Dumitraschkewitz, T. M. Kremmer, M. A. Tunes, S. Pogatscher, Direct nanoscale observation of melting and solute redistribution in a hypoeutectic Al-Cu alloy with in situ STEM, arXiv:2606.12107 [cond-mat.mtrl-sci] (2026). https://doi.org/10.48550/arXiv.2606.12107
Materials at Extremes 