Structural, Microstructural, and Magnetic Property Dependence of Nanostructured Ti50Ni43Cu7 Powder Prepared by High-Energy Mechanical Alloying

Abstract

In the current study, Ti-Ni-Cu alloy powders were prepared by mechanical alloying using high-energy planetary ball mill under argon atmosphere. The effects of milling time on the evolution of structure, microstructure, and magnetic properties were analysed. Morphological observations indicated a narrow particle size distribution and homogeneous shape. According to the Rietveld analysis, during early milling stage (1–6 h), the milled powder consists of Ti-based solid solution [HCP-Ti(Ni,Cu)], Ni-based solid solution [FCC-Ni(Ti,Cu)], Cu-based solid solution [FCC-Cu(Ti,Ni)], and amorphous phase (28.52 wt%). For prolonged milling time, the NiTiCu (β19) was achieved from the pre-formed phases. Moreover, microstructural parameters varied considerably with milling time; the crystallite size was found to decrease to the nanoscale range, Ti (41), Ni (21 nm), Cu (16 nm), and β19 (29 nm), while the microstrain 1/2 increased due to the deformations and defects induced during the milling process. Magnetic measurements indicated that all powders exhibited a ferromagnetic behaviour irrespective of milling time whereas the corresponding magnetic parameters were found very sensitive to the milling time. This was associated with particle size refinement in addition to the phase composition and the amount of the amorphous phase; the higher the percentage of the amorphous phase was, the lower the values of Ms and Mr.