Mechanical alloying of the Al–Ti system

Abstract

We have investigated the possibility of an amorphization reaction by mechanical alloying for two compositions of the Al–Ti binary system. While the Al-rich composition Al₇₅Ti₂₅ appears to give, after milling for 21 h, an Al(Ti) highly cubic phase, the Ti-rich composition Al₂₅Ti₇₅ does amorphize using various milling conditions.

The progress of the amorphization as a function of time of milling was monitored by X-ray diffraction. At first, Al atoms diffuse into the host lattice of hexagonal Ti; subsequently, the milling accumulates a critical density of disorder that causes the Ti(Al) crystalline phase to collapse into an amorphous phase.

The formation of amorphous alloys is discussed on the basis of thermodynamic models. The Miedema model is compared with a calculation of phase diagrams approach which has been modified to account for dependence of thermodynamic properties of the liquid upon temperature. T ₀ curves are presented, showing a glass-forming range in agreement with experiments.