Formation of new metastable bcc phases by crystallization of amorphous Al 92La 8 and Al 92Ce 8 alloys

Abstract

In the crystallization process of Al 92La 8 and Al 92Ce 8 amorphous alloys, new metastable phases were found to form as a primary crystalline phase. The Al 92La 8 and Al 92Ce 8 alloys were rapidly solidified into amorphous ribbons with a thickness of about 25 μm by a single roller method. As annealing temperature increases, the rapidly solidified Al 92La 8 amorphous alloy first changes into a metastable body-centered cubic (bcc) phase with a lattice parameter of a=0.6653 nm at 473 K, and then decomposes into α-Al and orthorhombic Al 11La 3 phases at 550 K. When the amorphous Al 92Ce 8 alloy is annealed at 473 K, the amorphous phase also changes into a metastable bcc phase with a lattice parameter of a= 1.3871 nm. With increasing temperature to 565 K, the metastable phase decomposes into α-Al and orthorhombic Al 11Ce 3 phases. The metastable bcc phases have high Vickers hardness numbers (≈ 300) which are about twice as high as those (≈ 168) for the amorphous single phase. The new metastable phases seem to be important for subsequent understanding of the amorphous structure for these alloys and the high strength of the crystallized mixed phase alloys.