Magnesium diffusion modelled

Materials World magazine
10 Mar 2017

A new model for diffusion in magnesium alloys could be used to examine a range of materials.

Using new computational techniques, researchers at the University of Illinois at Urbana-Champaign, USA, have constructed the first exact model for diffusion in magnesium alloys, which can also be used to predict how atoms diffuse in many other materials. Einstein first described the fundamental mechanism of diffusion, but it has only been modelled exactly for a few crystals.

‘Computer analysis of the magnesium crystal revealed hidden broken symmetries that impact how different atoms would move in magnesium,’ said Dallas Trinkle, an associate professor of materials science and engineering at Illinois. Combined with state-of-the-art quantum mechanics calculations, Trinkle and PhD student Ravi Agarwal predicted the diffusion of both common and rare earth metals.

‘Most substitutional solutes in solids diffuse via vacancies, however, widely used analytic models for diffusivity make uncontrolled approximations in the relations between atomic jump rates that reduce accuracy,’ said Agarwal. ‘Symmetry analysis of the hexagonal close-packed crystal identifies more distinct vacancy transitions than prior models, and a Green function approach computes diffusivity exactly for solutes in magnesium. We found large differences for the solute drag of aluminium, zinc, and rare earth solutes, and improved diffusion activation energies – highlighting the need for exact analytic transport models.’

Trinkle added that the results ‘will allow the creation of new, lightweight structural metals for automotive and aerospace applications.’