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

Thermal stability and crystallization of three multicomponent glassy alloys, Al(86)Y(7)Ni(5)Co(1)Fe(0.5)Pd(0.5), Al(85)Y(8)Ni(5)Co(1)Fe(0.5)Pd(0.5) and Al(84)Y(9)Ni(4)Co(1.5)Fe(0.5)Pd(1), 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 Al(x)M(y) (M = Y, Ni, Co, Fe, Pd)] → [am + α-Al] → [α-Al + Al(3)Y + Al(9)(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 Al(x)M(y)] 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 Al(x)M(y) 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.