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.

提升金属合金特性的一种方法是细化其微观结构。通过促进过冷区的形核以实现等轴生长和更细晶粒，有助于达成这一目标。在铝基或金基合金中添加数百ppm的某些元素，不仅能大幅减小晶粒尺寸，还会增加与五个具有取向关系的相邻晶粒相连的孪晶界数量。这些孪晶晶粒可能是液态中形成ISRO（ISRO）的结果。铝中ISRO介导的形核是一种理论，该理论认为液态中会形成ISRO相，进而促进α-铝相在其上结晶。这可以解释孪晶界数量较多的现象。然而，这一现象从未在实验中被直接观测到。本实验旨在通过EXAFS分析合金中选定元素的局部原子环境，以实现上述观测。