Magnetic and Microstructural Properties of Nanostructured/Amorphous NiTi Prepared by Mechanical Alloying

Abstract

This study aims to examine the effects of milling time on the morphological, structural, and magnetic properties of nanostructured Ni₅₀Ti₅₀ powders prepared by high-energy mechanical alloying using a Fritsch Pulverisette 7 planetary ball mill. Scanning electron microscopy and electron dispersive X-ray spectroscopy, results revealed a novel particle folding phenomenon during high-energy milling, significantly diverging from conventional welding and fracture processes. With increasing milling time, it was observed reduced particle size, and enhanced spherical equiaxial morphology, alongside a mixture of the amorphous phase, NiTi-martensite (Ms), NiTi-austenite (As), and solid solution phases (SS). Rietveld refinements of X-ray diffraction patterns and magnetic measurements highlighted the critical role of the amorphous phase in determining the Ms and Mr values of synthesized Ni₅₀Ti₅₀ powders. After 72 h of milling, the coercive field increased to 285.8 Oe, and the martensitic phase proportion reached 21.58%.