Restoration of the structure of amorphous and partially crystalline alloys using cryogenic thermocycling

Abstract

Creation of the new technologies includes the development of the materials, among which composite amorphous-nanocrystalline materials, characterized by a unique combination of the magnetic and mechanical properties (high strength, hardness, wear resistance, etc.) hold a specific position. However, their potential application is limited due to the loss of plasticity (embrittlement) which occurs relatively soon even at room temperature and cannot be restored by heat treatment of the amorphous phase. The plasticity can be restored when thermocycling is carried out in a temperature range between the temperature of liquid nitrogen (77 K) and room (295 K) temperature. This process dubbed «rejuvenation» turned out to be acceptable only for bulk samples obtained in the form of rods etc. and appeared to be entirely unsuited for ribbon samples with a thickness of 20 – 50 μm (i.e., the thickness of the absolute majority of amorphous alloys currently obtained). We present a modernized method for processing thin samples of amorphous and partially crystalline alloys using cryogenic thermocycling, which provides restoration of the amorphous structure and ductility of the samples. X-ray diffraction patterns of tape samples of Al₈₇Ni₈Gd₅ alloy annealed at 170°C with a fraction of the nanocrystalline phase not exceeding 10% before and after several successive cooling-heating cycles show that with an increase in the number of cycles up to two hundred the amorphous structure of the initial sample can be completely restored.