Devitrification studies of Zr–Pd and Zr–Pd–Cu metallic glasses

Influence of short-range order on devitrification in Zr70Pd20Cu10 metallic glasses

“…The difference plot for the MM alloy shows all of the features of the high temperature stable MoSi 2 phase only. In fact the difference plots show the reflections of nucleating phases much clearer than the image plate data which was used previously [8].…”

“…In these plots we clearly observe different nucleating phases between the two alloys. If we compare the difference plots to those of the stable and metastable phase which were observed in these alloys previously published [8], it is clear that the difference plot for the MS alloy compares very favorably with the i-phase which forms metastably above the first exotherm in the DSC. The difference plot for the MM alloy shows all of the features of the high temperature stable MoSi 2 phase only.…”

“…This structure is more stable than the quasicrystalline phase but less stable than the MoSi 2 -type structure. Thermal analysis showed that these two alloys underwent nucleation and growth of distinctly different phases at temperatures nearly 100 K apart [8,9]. The Zr 70 Pd 30 MS alloy shows a transformation to a metastable icosahedral (i) phase at 708 K for a heating rate of 40 K/min and then to the Al 2 Cu-type structure at 782 K over a temperature range of 25 K (Fig.…”

“…1). The MM alloy exhibited only one exothermic event at 803 K; a direct transformation to the MoSi 2 -type structure from the amorphous structure without any intermediate phases [8]. While the thermal analysis was conclusive that the MM alloy underwent a nucleation event, the XRD data and the RMC simulations suggested that the MM alloy had a higher degree of chemical ordering than the MS alloy and there was evidence of topological ordering beyond 1 nm which would support some medium-range ordering (MRO) for the MM alloy [7].…”

“…RMS of the pair distribution function suggested that MRO is topologically similar to the MoSi 2 -type structure ðP4=mmmÞ; but chemically closer to the Al 2 Cu-type structure ðP4=mcmÞ which undergoes nucleation and growth of the MoSi 2 -type structure. To more fully understand the atomic rearrangements which occur during the devitrification process of these chemically identical but differently prepared alloys, we developed a system to obtain time-resolve high wave-momentum ðQ ¼ ð4p sinðuÞ=lÞÞ diffraction data [8]. Using an area detector, we were able to obtain usable Q out to 125 nm 21 .…”