Inverse melting in the Ti-Cr system.

Abstract

Investigations of metastable phase transformations demonstrate that a polymorphous transformation from a crystal to a glass, the so-called inverse melting, is possible in the Ti-Cr system, however at different Cr concentrations compared to earlier reports. Single-phase, metastable bcc \ensuremath{\beta}-TiCr alloys with Cr concentrations between 40 and 65 at. % are prepared by mechanical alloying. A subsequent heat treatment results in a transformation into an amorphous phase. Complete amorphization is observed only in a narrow range around 55 at. % Cr, while two-phase equilibria between the bcc and the amorphous phase are found for other compositions. The experiments are in good agreement with the metastable phase diagram which is obtained from the free energy curves determined by the calculation-of-phase-diagram (CALPHAD) method.