Secret Glue and Hidden Cracks in Steel express
Steel is not a monolith but a mosaic of microscopic grains fused together. Their seams, the grain boundaries, are the most vulnerable spots: this is where cracks begin. Impurity atoms, even in negligible amounts, accumulate at these seams like sand between gears, and they can either lubricate the mechanism or jam it completely.
The authors "probed" the behavior of eight light elements, from ubiquitous hydrogen to sulfur, at six typical grain boundaries in iron using quantum calculations. They found out who acts as glue (carbon and boron) and who acts as a wedge (helium, oxygen, sulfur). Nitrogen, phosphorus, and hydrogen turned out to be "gray cardinals": their influence is weaker, but not harmless either.
The main practical outcome is an open database with results from thousands of calculations. It will serve as a training ground for machine learning (although the article is about materials, not medicine, the approach is similar: neural networks learn from labeled data), which will accelerate the creation of new alloys. Instead of months of experiments — a few hours of computer simulation, and the engineer already knows which additive to introduce into steel to make a bridge last an extra hundred years.
Boron, which acts as glue in steel, under other conditions is the basis of superhard materials close to diamond. The nature of the same element can change dramatically depending on its environment.
In Isaac Asimov's novel "The Gods Themselves," aliens use isotopic differences to obtain energy — similarly here: a tiny difference in the position of an atom at a grain boundary determines whether a structure falls apart or not.