Jörg Neugebauer

In a thin aluminum film, millions of tiny metal grains are packed together like grains in granite. Where three such grains meet, a triple junction arises — a line along which three boundaries intersect. Previously, it was considered merely a meeting point, but now, peering into the atomic scale, scientists have seen: it is an independent defect with its own personality.

Metal is like a rope made of many strands: pull too hard and it snaps. Engineers have long sought a way to make it both strong and flexible at the same time. Typically, additives that increase strength make the metal brittle. But a team of materials scientists found a loophole: they added a small amount of nitrogen to the CrMnFeCoNi alloy, just one atom in a hundred, and got an unexpected result.

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.