On Different Mechanisms of Primary Crystallization in Al-Ni-La-Zr Amorphous Alloys

Abstract

The devitrification sequences and mechanism are reported for a seriesof Al-Ni-Rare Earth amorphous alloys containing addition of Zr. Theprimary precipitation of a primitive cubic intermetallic occurs oncontinuous heating of amorphous alloys containing at least 6 at.% Laas shown in Al87Ni7La6 and Al87Ni6La6Zr, whereas Al is formed inAl97Ni7La5Zr. The transformation can turn eutectic-like in both theabove alloys with formation of the intermetallic and Al when it isaccomplished on isothermal annealing. This induces a surprising effecton the subsequent matrix crystallization which is shifted to hightemperature with respect to conventional scans made on continuousheating. The implications of the findings for diffusion in the matrix,nucleation and growth mechanisms are discussed.