The microstructures of surface alloys A and B are
similar. From the bottom to the top of the surface alloys,
we observe first a thin layer (a few micrometres thick)
exhibiting epitaxial solidification with planar front
growth; this is a consequence of the solidification rate
which begins with a zero value at the interface between
the melted and non-melted regions. The rapid increase
in the solidification rate destabilizes the plane front
leading to the formation of austenite dendrites surrounded
by the eutectic y-M& (Fig. l(b)). The mean
compositions of these two alloys as determined by
electron probe microanalysis (EPMA) are reported in
Table 3.