Atomic force microscopy study of sapphire-YAG eutectic fiber

The superior strength at high temperature of directionally solidified eutectic materials, the so-called melt-growth composites, such as sapphire-YAG is attributed in large measure to their "Chinese script" microstructure. The mechanical properties of fibers of such materials, grown for example by the micro-pulling-down technique, depend strongly on the nature of the morphology at the surface. Using atomic force microscopy to study fibers grown by the micro-pulling-down technique, we show that the script microstructure extends to the surface. Atomic force microscopy revealed that the surface differs from the bulk in both volume ratio and domain size, which could not be observed by SEM. The surface volume ratio varies with growth rate, and tends to approach the properties of the bulk as the growth rate increases.