Abnormal crystallization in Al86Ni6Y4.5Co2La1.5 metallic glass induced by spark plasma sintering

Abnormal crystallization was observed in Al86Ni6Y4.5Co2La1.5 metallic glass powder at about 20 °C below its glass transition temperature (Tg, 271.5 °C) during spark plasma sintering (SPS). The crystallization product, identified to be a hexagonal-structured Al5Co2 phase, was not detected in the same powder when annealed in a differential scanning calorimeter (DSC). Nor was it detected in other Al-based metallic glasses of similar compositions which were annealed around their Tg temperatures by conventional heating. SPS is effective to introduce a unique nanometric intermetallic phase in the amorphous matrix. The abnormal crystallization is attributed to the high applied pressure and non-thermal effects of SPS.