Eutectic alloy microstructure: atomic force microscopy analysis

The exciting microstructures found in several eutectic alloys are a result of a cooperative growth, which is connected to the atomic transfer in the melt ahead the solid/liquid interface. In a eutectic system, the growth of solid phases depends on the simultaneous rejection of constituents to the liquid phase, which causes adjustments of the melt composition and hence, mass transport by diffusion normal to the growth direction. Generally, eutectic microstructures are examined by using optical (OM) and scanning electron microscopy (SEM). While OM may not provide the necessary resolution, the eutectic microstructure may present three-dimensional features, as a result of etching, which is not always possible to be observed by SEM. As an alternative, this paper describes the use of atomic force microscopy (AFM) in understanding micro-scale feature of a eutectic microstructure. For such a purpose, directionally solidified samples of a Ni-Al-V lamellar eutectic, a Ni-Al-Mo fibrous eutectic and a Ni-Al-Nb three-phase eutectic were examined. The results obtained provided a new picture of multi-phase microstructures and allows one to understand their new characteristics.