Influence of thermally induced structural transformations on hardness in Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy

Effect of heat treatment on mechanical behavior of Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy was investigated by measuring microhardness. It was shown that the as-prepared amorphous alloy has an unexpectedly high microhardness. This can be attributed not only to boron dispersed in the alloy, but also to the structure which exhibits aspects of a nanocomposite of nanoparticles dispersed in an amorphous matrix. As the alloy crystallizes at temperatures above 540 °C, microhardness decreases continuously as a function of heating temperature. This is attributed to separation of boron out of the amorphous matrix into nanocrystals of Fe2B phase. Further decrease in microhardness is attributed to crystallite growth with the accompanying change in the dominant nature of the interfaces from amorphous/crystal to crystal/crystal, and creation of a porous structure. When the crystallization is complete, the alloy exhibits microhardness close to that of a hypothetical mixture of α-Fe and Fe2B phases of the same composition.

► Iron-based amorphous alloy has been heated at different temperature for 1 h.
► As-prepared alloy has a microstructure similar to that of a nanocomposite.
► Nanocomposite of nanocrystals in amorphous matrix is formed during crystallization.
► Microhardness has been measured after heating at different temperatures.
► Structure and microhardness have been correlated.