Study of the fabrication and thermally induced transformation of amorphous Mg50Ni50 obtained by mechanical alloying

This work studied the amorphization process by mechanical alloying of a Mg50Ni50 alloy and its later thermal transformation into stable equilibrium phases. The amorphous alloy was produced using a SPEX 8000D mill, under controlled Ar atmosphere, with a ratio in ball mass: material of 20:1, from powders of Ni and cuttings of Mg. The evolution of the phases during the amorphization process was qualitatively determined by X-ray diffraction. The results showed that a noticeable microstructural refinement of the Mg and Ni occurs at the start of the milling, and that this accumulation of defects amorphitizes part of the system, producing an amorphous precursor, which mechanically crystallizes the Mg2Ni. As the milling time increases and more energy is added to the system, the structure of the Mg2Ni collapses giving way to the appearance of the amorphous Mg50Ni50 phase. With reference to the thermal transformation of the amorphous solid to the stable equilibrium phases, the joint results obtained by differential scanning calorimetry and X-ray diffraction, indicate that this occurs in two stages: at temperatures close to 350oC the amorphous Mg50Ni50 transforms into a mixture of phases, composed of Mg2Ni and a residual amorphous, which at temperatures close to 450oC undergoes the transformation into MgNi2. A temperature-heating rate-transformation (T-HR-T) diagram was built for the passage of the amorphous Mg50Ni50 into Mg2Ni and MgNi2 using the calorimetric data (au)