The alloying effects of Ge and Si on thermal stability and crystallization behavior of Al-Y binary amorphous alloys

Abstract

(Al90Y10)100-xGex (x = 0,1,2,2.5), (Al90Y10)98Si2-yGey (y = 0,0.5,1,2) and (Al90Y10)97.5Si2.5-zGez (z = 0,0.625,1.25,2) amorphous alloys were crystallized in a differential scanning calorimeter and the crystallization products were identified by X-ray diffraction. Addition of Ge to Al90Y10 induced severer chemical heterogeneity in the amorphous alloy than addition of Si due to the bigger difference of binding force between Ge-Al and Ge-Y. Consequently, the onset temperature of crystallization decreases more quickly with the increasing Ge addition. The Ge addition reduced precipitation of metastable Al4Y phase but promoted direct crystallization of stable Al3Y phase form the remaining amorphous matrix. The primary crystallization of α-Al split into two stages with 2.5 at% Si added to the base alloy, but this phenomenon did not occur in the Ge-contained amorphous alloy. It is suggested that severe chemical inhomogeneity in Al-based amorphous alloys is only necessary but not the sufficient condition for the abnormal crystallization.