Investigation of Icosahedral Short Range Order (ISRO)-mediated nucleation in deep undercooled aluminium alloys

One way to enhance the characteristics of metallic alloys is to refine their microstructure. Promoting the nucleation in the undercooled zone in order to create an equiaxed growth and smaller grain can help achieving this. Some additions of hundreds of ppm of some elements in Al-based or Au-based alloys induce a huge diminution of the grainsize, but also an augmentation of twinned grain boundaries with five neighbouring grains in orientation relation. Those twinned grains could be the result of the creation of an ISRO in the liquid. The ISRO-mediated nucleation in aluminium is a theory that involves the nucleation of an ISRO phase in the liquid that promotes crystallization of alpha-aluminium phase on it. This could explain the high number of twinned grain boundaries. However, this phenomenon has never been directly observed experimentally. This experiment aims to achieve these observations by analysing the local atomic environment of selected elements in our alloys by means of EXAFS.