Effect of Vibration Milling Time on Structure, Chemical Composition and Fragmentation–Agglomeration Processes in Powders Produced from Melt-Spun Ni–Mn–Ga Ribbons

Abstract

Ni–Mn–Ga alloy ribbons were produced by melt spinning and subsequently processed by vibration milling for 15, 30, 60 and 240 minutes. The influence of milling time on chemical composition, phase structure and microstructural parameters was investigated using laser diffraction, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Chemical analysis revealed a gradual decrease in Ga content accompanied by a relative increase in Ni and Mn, leading to a systematic increase in the valence electron concentration (e/a). XRD results showed a milling-time-dependent transition from the ordered L2₁ structure in the as-spun ribbon to 14M martensite in the milled powders. Particle size analysis indicated a reduction in characteristic particle diameters with milling time, along with the formation of a secondary fine fraction originating from the ribbon microstructure. Williamson-Hall analysis revealed a decrease in crystallite size and an increase in microstrain in the parent phase. In contrast, the martensite exhibited finer, more uniform crystallite sizes and relatively low microstrain.