Two-stage amorphization reaction in Ni–Nb–Zr system

• Mechanical alloying induced amorphization in Ni–Nb–Zr system was studied in details.
• Amorphization occur by two consecutive reactions at Ni–Zr and Ni–Nb interfaces.
• The thermodynamically stable phase was predicted using extended Miedema’s model.
• The results of Miedema’s model agree well with experimental outcomes.

Ni60Nb20Zr20 powder mixture was subjected to mechanical alloying (MA) using a low energy ball mill, allowing slower processing and easier progressive observation of amorphization at intermediate milling times. The amorphization during MA was studied by X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). MA of Ni60Nb20Zr20 alloy involves two consecutive amorphization reactions. MA first leads to a Ni–Zr amorphization reaction with a strong thermodynamic driving force as well as fast kinetics compared with Ni–Nb amorphization. On further milling the kinetic requirements for Ni–Nb amorphization reaction are provided. The resulting two amorphous phases homogenize at longer milling times. XRD traces showed no crystalline intermetallic compound prior to the amorphization reaction. Furthermore the thermodynamically stable phase was predicted using semi-empirical Miedema model and the results were compared with the structure formed in MA of Ni–Nb–Zr powder mixture.

ΔG298K of (a) amorphous phase, (b) intermetallic compound and (c) solid solution showing that the amorphous phase is thermodynamically more stable than solid solution or intermetallic compound in Ni60Nb20Zr20 alloy.Figure optionsDownload as PowerPoint slide