Phase transformations in Al-rich Al-W alloys rapidly quenched from the melt

Al-W alloys with a W content from 4.3 to 11.7 wt% were rapidly quenched, using the two-piston quenching method. X-ray examination showed that in as-quenched alloys two kinds of samples appeared; multiphase samples and single-phase samples. Multiphase samples contained supersaturated Al-W solid solutions (-Al), Al₄W and two unknown phases, all of which were metastable. In single-phase samples -Al was present as the only phase. In these samples -Al began to decompose at temperatures as low as 100° C. During the decomposition of these solid solutions two other new phases were observed, the unit cell constants of which were determined. Experiments with isochronal and isothermal annealing showed that the presence of metastable phases in as-quenched alloys highly increases the resistance to decomposition of Al-W solid solutions. The possible reason for this behaviour is discussed.