Novel Heating-Induced Reversion during Crystallization of Al-based Glassy Alloys.

Thermal stability and crystallization of three multicomponent glassy alloys, Al86 Y7 Ni5 Co1 Fe0.5 Pd0.5 , Al85 Y8 Ni5 Co1 Fe0.5 Pd0.5 and Al84 Y9 Ni4 Co1.5 Fe0.5 Pd1 , were examined to assess the ability to form the mixture of amorphous (am) and fcc-aluminum (α-Al) phases. On heating, the glass transition into the supercooled liquid is shown by the 85Al and 84Al glasses. The crystallization sequences are [am] → [am + α-Al] → [α-Al + compounds] for the 86Al and 85Al alloys, and [am] → [am + α-Al + cubic Alx My (M = Y, Ni, Co, Fe, Pd)] → [am + α-Al] → [α-Al + Al3 Y + Al9 (Co, Ni)2  + unknown phase] for the 84Al alloy. The glass transition appears even for the 85Al alloy where the primary phase is α-Al. The heating-induced reversion from [am + α-Al + multicomponent Alx My ] to [am + α-Al] for the 84Al alloy is abnormal, not previously observed in crystallization of glassy alloys, and seems to originate from instability of the metastable Alx My compound, in which significant inhomogeneous strain is caused by the mixture of solute elements. This novel reversion phenomenon is encouraging for obtaining the [am + α-Al] mixture over a wide range of high temperature effective for the formation of Al-based high-strength nanostructured bulk alloys by warm working.