Study of spark plasma sintered nanostructured ferritic steel alloy with silicon carbide addition

Pure nanostructured ferritic steel alloy (NFA) and NFA–silicon carbide (SiC) composites with different compositions (97.5 vol% NFA-2.5 vol% SiC and 95 vol% NFA-5 vol% SiC) have been sintered by spark plasma sintering (SPS) and systematically investigated based on XRD, SEM, density, Vickers hardness, and nano-hardness. Minor γ-Fe phase formation from the main α-Fe matrix occurs in pure NFA between the sintering temperature of 950 °C and 1000 °C. However, this is hindered in the NFA-SiC composite sintering. Densities for both the pure NFA and the NFA-SiC composites increase with the sintering temperature but decrease with the SiC content. The NFA-SiC composites have higher porosity than pure NFA under the same sintering condition. All the samples have the average grain sizes between 6 µm and 8 µm. Vickers hardness of the pure NFA and NFA-SiC composites is related to density and phase composition. By estimation, the 97.5 vol% NFA-2.5 vol% SiC composite sample has the maximum yield strength of 3.14±0.18 GPa. Nano-hardness of the NFA-SiC composite is degraded by diffusion and reaction between NFA and SiC. The addition of SiC decreases the elastic modulus of the NFA-SiC composites.