Microstructure characterization of Al-Cr-Fe quasicrystals sintered using spark plasma sintering

In this study, Al-Cr-Fe powders were consolidated using spark plasma sintering at different temperatures (650 °C, 700 °C, 750 °C and 800 °C). The sintered samples were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The porosity of the pellets is very sensitive to the sintering temperature: it reduces sharply from around 29.3% to around 3.1% when the sintering temperature increases from 650 °C to 700 °C probably due to the softening of quasicrystals at elevated temperatures. Metastable icosahedral Al-Cr-Fe transforms to stable decagonal Al-Cr-Fe in sintering process. Stable icosahedral Al-Cr-Fe forms in the samples sintered at 700 °C, 750 °C and 800 °C. Both stable quasicrystalline phases form through the nucleation and growth process in the sintering process. Selected area electron diffraction (SAED) analysis shows that the icosahedral phase and the decagonal phase formed in the sintering process have a quasilattice constant of about 0.45 nm and 1.2 nm, respectively.