Phase transformations in a NiTiGe system induced by high energy milling

Abstract

A ternary mixture of Ni, Ti and Ge was submitted to high energy ball milling. Milling-induced phase transformations were investigated using ex situ X-ray diffraction. The changes in the unit cell parameters and the crystallites mean size as well as the crystalline and amorphous phase content were followed by Rietveld analysis. A rapid nucleation of the orthorhombic NiTiGe with small quantities of germanium-based binary alloys (Ti5Ge3, NiGe, Ni2.74Ge2) was observed. The milling process promoted the nanometrization of NiTiGe followed by a partial amorphization. The germanium intermetallic phases generated cubic NiTi and Ti3Ni4 phases. The continuity of the milling process induced a NiTi polymorphism and the amorphous phase promoted re-nucleation of the germanium binary alloys. After approximately 70 h, the nucleation of a nanostructured rutile TiO2 was observed.