Nanostructured Al 86Gd 6Ni 6Co 2 bulk alloy produced by twist extrusion of amorphous melt-spun ribbons

Abstract

Amorphous Al 86Gd 6Ni 6Co 2 ribbons produced by melt-spinning were consolidated using twist extrusion (TE). Transition of the amorphous alloy ribbon into the crystalline state at 5 K/min occurs via three stages in the temperature range from 473 to 673 K. Formation of fcc Al nanocrystals is the dominant process in the first and second stages, which leads to increasing microhardness of ribbons from 360 to 620 kgf/mm 2. From one to five TE passes were performed on chopped ribbon in several experimental runs at temperatures between 458 and 573 K and applied pressures between 1150 and 1700 MPa. Full consolidation of the ribbons was achieved at TE temperatures ≥523 K. The maximum microhardness (550 kgf/mm 2) was reached in bulk materials consolidated at 513 K with a nanocomposite microstructure consisting of about 57 vol.% of Al-crystals with a size of about 13 nm embedded in the residual amorphous phase. Extrusion at 573 K resulted in full crystallization of the amorphous phase via precipitation of equilibrium intermetallics and lowering of the microhardness to 380 kgf/mm 2.