How solid metals actually form

A team from MIT has analysed how metal crystals form down to the nanometre level.

A team of researchers at the Massachusetts Institute of Technology (MIT), USA, have found what happens at a nanometre scale when crystal grains form in metal during an extreme deformation process.

Metallurgists have a variety of methods to make metal grains smaller, generally through strain such as deformation. The main method is recrystallisation, where the metal is deformed and heated, which creates defects that are highly disordered.

MIT Professor Chistropher Schuh says that the new work determines how this takes place at very high speed at the smallest scales.

By using a laser-based system the team was able to shoot 10µm particles and measure how fast they were going and how hard they hit. Cutting them open afterwards revealed how the grain structure evovled, to a nanometre level.

Their new pathway, called nano-twinning assisted recrystallistaion, is a variation of a metal phenomenen called twinning, where a crystalline structure flips its orientation.

Describing their experiements with copper Schuh says, 'This is sort of a hyper-forging type of phenomenon that we’re talking about.'