ABSTRACT
In the present work, transmission electron microscopy (TEM) and scanning Auger microscopy (SAM) techniques have been used to study the structure and composition of an interlayer of 95% Ni–5% Al plasma sprayed between a low-alloy steel substrate and a plasma sprayed alumina layer. TEM images of this interlayer reveal a microstructure formed by a discontinuous stacking of curved layers, each one corresponding to a splat. These splats consist on different crystalline zones confined between thin amorphous layers. Small columnar crystals (height 0.1 μm, width 25 nm) form, as well as larger columnar crystals (height 1 μm, width 0.5 μm) and equiaxed ones (mean diameter of 0.5 μm), depending on the distance from the initially cooled surface. These microstructures are argued in terms of the solidification processes that do occur during the formation of the interlayer. SAM experiments reveal that at the interface Ni/Al–steel substrate, there is no diffusion of the signal of Ni, neither Al inside the steel.
