Compositional range, thermal stability, hardness and electrical resistivity of amorphous alloys in Al-Si (or Ge)-transition metal systems

Abstract

An amorphous single phase was found to be formed in wide compositional ranges in rapidly solidified Al-Si-transition metal (M) and Al-Ge-M alloys. The compositional ranges are in the range from 12 to 53 at. % Si or Ge and 8 to 23% M and Al-Si-Co and Al-Ge-Fe alloys have the widest glass-formation ranges. Because the interaction between aluminium and silicon or germanium atoms is thought to be repulsive from the immiscible equilibrium phase diagrams, the glass formation is probably due to an attractive interaction of M-Si (or Ge) and Al-M pairs. Hardness, H _v, and crystallization temperature, T _x, increase with increasing M content and the highest values reach 1120 DPN and 715 K, while the change with silicon or germanium content is much smaller for H _v and is hardly seen for T _x. Additionally, the H _v and T _x have maximum values for Al-Si (or Ge)-M (M=Cr, Mn or Fe), decrease with the decrease and increase in the group number of M element and are the lowest for Al-Si (or Ge)-Ni alloys. The compositional dependence is interpreted under the assumption that T _x and H _v of the aluminium-based amorphous alloys are mainly dominated by the attractive interaction of M-(Si or Ge) and Al-M pairs. Room-temperature resistivity, ϱ _RT, increases in the range of 220 to 1940 μΩ cm with increasing silicon or germanium and M contents. The change in ϱ _RT with the group number of M elements shows a maximum phenomenon for manganese. It has thus been clarified that the characteristics of the Al-Si-M and Al-Ge-M amorphous alloys have the different compositional dependence as compared with those for conventional metalmetalloid amorphous alloys, probably because of the unusual interaction among the constituent elements.