Mechanical alloying behavior of Nb–Ti–Si-based alloy made from elemental powders by ball milling process

Nb–Ti–Si-based alloy powders were prepared by mechanical alloying (MA) of elemental particles. The evolutions of morphology, size, phase constituents, crystallite size, lattice strain, composition and internal microstructure, etc., of the alloy powders were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), laser particle size analyzer and transmission electron microscope (TEM) analyses. The alloy particles are gradually refined and their shapes become globular with the increase in milling time. The diffraction peaks of Nb solid solution (Nbss) phase shift toward lower 2θ angles during ball milling from 2 to 5 h, and after that Nbss diffraction peaks shift toward higher 2θ angles with the increase in milling time from 5 to 70 h, which is mainly attributed to the alteration of the lattice parameter of Nbss powders due to the solution of the alloying element atoms into Nb lattice to form Nbss. During ball milling process, the decrease in crystallite size and increase in lattice strain of Nbss powders lead to continuous broadening of their diffraction peaks. A typical lamellar microstructure is formed inside the powder particles after ball milling for 5 h and becomes more refined and homogenized with the increase in milling time. After 40-h-ball milling, the typical lamellar microstructure disappears and a very homogeneous microstructure is formed instead. This homogeneous microstructure is proved to be composed of only supersaturated Nbss phase.