Fabrication of consolidated layered samples by high-pressure torsion processing of rapidly solidified Al-based ribbons with amorphous and crystalline structures

Abstract

The fully consolidated bilayer (consisting of two amorphous Al86Ni9Gd5 ribbons) and trilayer (composed by the Al95.1Cr2.5Mo1.4Ti0.4Zr0.3V0.3 crystalline melt-spun ribbon placed between two amorphous ribbons) disks of 5 mm in diameter were fabricated by unconstrained high pressure torsion (HPT) processing up to four turns at applied stress of 2 GPA. The structure of the cross sections of the trilayer disk was analyzed by scanning electron microscopy and the critical strains required for partial and full mixing of the amorphous and crystalline ribbons were estimated. HPT processing of amorphous ribbons resulted in formation of Al nanocrystals about 8–9 nm in size and essential enhancement in microhardness from 2.7 to 4.1 GPa after one turn. The averaged surface microhardness of the firstly consolidated trilayer amorphous/crystalline disks increased from 2.3 to 4.7 GPa with increasing of up to 4 turns. The strain-hardening of these disks was caused by a simultaneous increase of the volume fraction of Al nanocrystals up to 0.41 and a decrease in their sizes from 41 to 14 nm. The internal structure of the HPT processed trilayer disks was strongly inhomogeneous and its microhardness varied in the range from 2.86 GPa in the central part to 6.45 GPa in the zone of partial mixing which was an exceptionally high value for Al-based alloys.