Optimisation of the ball-milling and heat treatment parameters for synthesis of amorphous and nanocrystalline Mg 2Ni-based alloys

Abstract

Amorphous and nanocrystalline Mg 1.9M 0.1Ni (M=Ti,Zr,V) alloys were synthesized by mechanical alloying (MA) and by MA followed by annealing. The phase composition, microstructure and morphology of the as-milled powder, and the milled and heat treated powders were determined by XRD and SEM/EDX. Thermal stability, crystallization and grain growth processes in the nano-/amorphous alloys were investigated too. The milling and heat treatment conditions for obtaining amorphous or nanocrystalline alloys were optimised for different alloy compositions. After milling or milling with annealing the ternary and quaternary alloys have the hexagonal Mg 2Ni crystal structure with crystallite sizes in the range of 5–15 nm, depending on the conditions of milling and annealing. The microstructure of the alloys obtained by long time milling is much finer compared to that of the shorter time milled samples, both subjected to annealing after milling. The grain size of the final nanostructures increases slightly during heating to above 400 °C. The nanocrystalline Mg 2Ni-based alloys prepared by extended milling show higher thermal stability than the short time milled alloys.