Structural and thermodynamic aspects of glass formation in CuTiH: role of hydrogen in mechanical alloying

Abstract

The results of experiments of milling elemental powders of Cu and Ti in the presence of hydrogenated Ti are reported. A mixture of an amorphous phase and TiH 2 was obtained by grinding γ-CuTi under H 2. Ball milling was performed on ternary mixtures of Cu, Ti and TiH 2 under Ar. Complete amorphization occurred at low concentrations of TiH 2; otherwise, an amorphous phase coexisting with unreacted hydride was obtained. The structure of the powders was checked at steps during milling by correlating X-ray diffraction and thermal analysis data. The free energy of formation of the alloys, estimated at 300 K along a section of the CuTiH phase diagram, shows a driving force for amorphization at low hydrogen content. All ternary CuTiH hydrides, both crystalline and amorphous, are metastable with respect to a mixture of TiH 2 and CuTi intermetallics and the possibility of a phase separation in the amorphous hydrogenated alloy is outlined.