Influence of Annealing at Various Temperatures on the Structure and Hardness of Amorphous Ribbons of the Al85Y8Ni5Co2 Alloy

Abstract

Aluminum-based metal glasses are a promising new family of materials. However, the influence of thermal treatment on the structure and properties of amorphous alloys of the Al–Y–Ni–Co system is still not studied in detail. In this work, amorphous ribbons of the Al85Y8Ni5Co2 alloy are formed by quenching on a rotating copper disc. The influence of annealing in vacuum at temperatures from 100 to 500°C for 30 min on the structure and hardness of these ribbons is investigated. To investigate the variations occurring in their structure after thermal treatment, scanning electron microscopy, X-ray structural analysis, and differential scanning calorimetry are used. To investigate the influence of annealing on mechanical properties of ribbons, the Vickers microhardness is measured. Conclusions on the variation in hardness depending on the structure of ribbons of the Al85Y8Ni5Co2 alloy are made based on these results. It is established that their microhardness increases with an increase in temperature, reaching the maximal value of 575 ± 7 HV after annealing at 350°C, and then decreases with a further increase in the thermal-treatment temperature. It is shown that ribbons of the Al85Y8Ni5Co2 alloy remain totally amorphous after annealing at t ≤ 250°C for 30 min, and crystalline phases are absent in the structure. An abrupt increase in hardness after annealing at 350°C is associated with the formation of nanocrystals of the aluminum solid solution 10–30 nm in size in an amorphous matrix surrounded by the residual amorphous matrix, while its further decrease is caused by an increase in the size of these crystals and the appearance of Al3Yand Al19Ni5Y3 intermetallic compounds in the structure.