Hardness variation in nanocrystalline SiC irradiated with heavy ions

Abstract

This study reports on the hardness of nanocrystalline silicon carbide (nc-SiC) with different grain sizes using nanoindentation technique. Both amorphous SiC (am-SiC) and single-crystal SiC (sc-SiC) are also investigated for a comparison study. Irradiation experiments were performed for the different types of SiC using Kr and Xe ions at elevated temperatures. It is found that the hardness of the am-SiC increases after Kr ion irradiation at 550 K, which is attributed to the irradiation-induced densification of the amorphous network structure. At higher temperatures (≥700 K), irradiation leads to crystallization of spherical nanograins in the am-SiC. The hardness values of the resulting nc-SiC with average grain sizes of ∼7 and 10.5 nm from the Kr and Xe ion irradiations, respectively, are found to be similar (∼40 GPa) and comparable to that of sc-SiC (38 GPa). In contrast, as-deposited SiC with a nano-columnar texture full of stacking faults (SFs) and twins exhibits super high hardness of 52.7 GPa, likely due to the suppression of the formation and propagation of indentation-induced dislocations in SiC. After Xe ion irradiation at 700 K, the hardness of the nano-columnar SiC decreases to 41.8 GPa, although the SF structure within the grains is well retained after irradiation. This is attributed to generation of radiation defects (such as invisible defect clusters) in the nano-columns, which could cause the hardness to decrease.