Devitrification Behavior and Interface Microstructure of Ni-based Amorphous Foils During Spark Plasma Sintering

We present a detailed study of the devitrification behavior of five Ni-based amorphous metal foils of different compositions, consolidated using spark plasma sintering (SPS) or pressureless sintering. Samples of approximately 5 mm thickness and 20 mm in diameter were prepared by stacking layers of amorphous foil on top of each other. The sintering temperatures were based on the crystallization temperatures (Tx) for each sample as determined from differential scanning calorimetry (DSC). Through detailed X-ray diffraction (XRD) analysis, full-width-half-maximum (FWHM) measurements and DSC analysis, we observed that the width of the 100% diffraction peak decreased with increasing temperature. The changes in FWHM with temperature correspond to similar exothermic crystallization reaction stages observed in DSC analysis. In addition, differences in crystallization kinetics were noticed for samples sintered by SPS versus samples sintered in ambient atmosphere using an external heat source (free sintering). Microstructure analysis of the samples by scanning electron microscopy shows the extent of sintering between the foil layers and bonding mechanisms with different sintering methods. Unique morphologies with positive effect on foil bonding were observed when consolidating foils using SPS.