Amorphous and Partially Crystalline Alloys Produced by Rapid Solidification of The Melt in Multicomponent (Si,Ge)-Al-Transition Metals Systems

Summary

The present chapter describes Si,Ge-Al-TM (TM-transition metals) amorphous alloys produced by rapid solidification. Although Al-Si-Fe and Al-Ge-Cr alloys have similar composition ranges for the formation of an amorphous phase in the Al-rich area and the largest possible among the Al-Si,Ge-TM systems metalloid concentration in the amorphous phase achieved, influence of transition metals on the amorphous phase formation between Ge- and Si-based (Si,Ge-Al-TM) alloys is significantly different. Composition range of an amorphous single phase in the Si-Al-Fe system was extended up to 50–60 at % Si by the alloying with Ni, Cr and Zr transition metals while the addition of different transition metals to Ge-Al-Cr alloys with 55–60 % Ge causes appearance of crystallinity. Moreover, microstructure of the Si-based alloys produced by rapid solidification changes from homogeneous amorphous to heterogeneous — (amorphous+crystalline Ge solid solution) by the addition of Ge. The Ge particle size increases with increasing Ge content from 5–7 nm at 7 at % Ge to 30–40 nm at 40 at % Ge. The amount of Si dissolved in Ge decreases with increasing Ge concentration. At the same time replacement of Ge by Si for Ge-Al-Cr-Si causes the precipitation of Ge particles from the amorphous matrix. In contrast to Si-Al-TM-Ge alloys where homogeneous distribution of c-Ge particles in an amorphous matrix was observed, the distribution of the Ge particles in the Ge-Al-Cr-Si alloy is inhomogeneous. This phenomenon as well as the properties of the obtained materials are also discussed in the present chapter.