Abstract
The microstructure and nanoindentation hardness of unirradiated, irradiated, annealed and corroded SiC coatings were characterized. Irradiation of 400 keV C+ and 200 keV He+ with approximately 10 dpa did not cause obvious amorphous transformation to nanocrystal SiC coatings and induced helium bubbles with 2–3 nm dimension distributed uniformly in the SiC matrix. High temperature annealing resulted in the transformation of SiC nanocrystals into columnar crystals in the irradiated region. Line-shaped bubble bands formed at the columnar crystal boundaries and their stacking fault planes and made the formation of microcracks of hundreds of nanometers in length. Meanwhile, some isolated helium bubbles distributed in SiC grains still maintained a size of 2–3 nm, despite annealing at 1200 °C for 5 h. The SiC coating showed excellent corrosion resistance under high-temperature, high-pressure water. The weight of the sample decreased with the increase of corrosion time. The nanoindentation hardness and the elastic modulus increased significantly with C+ and He+ irradiation, while their values decreased with high-temperature annealing. An increase in the annealing temperature led to an increased reduction in the values. Corrosion caused the decrease of nanoindentation hardness and the elastic modulus in the whole test depth range, whether the samples were irradiated or unirradiated.
Highlights
Zr-based materials have very impressive properties under normal operating conditions [1] and are always used to manufacture fuel claddings in commercial light water reactors (LWRs) [2]
The selected area electron diffraction (SAED) pattern taken from the region labeled letter “C” in Figure 4a was shown in Figure 4e, which displayed a typical single thermal effect, SiC nanocrystals were transformed into columnar crystals, and a large number of stacking faults were formed in the columnar crystals, which made helium atoms gather and grow in the columnar crystal boundaries and stacking fault planes
Some isolated helium bubbles distributed in SiC grains still maintained the size of 2–3 nanometers, despite annealing at 1200 ◦ C for 5 h
Summary
Zr-based materials have very impressive properties under normal operating conditions [1] and are always used to manufacture fuel claddings in commercial light water reactors (LWRs) [2]. Based on the requirements of ATF claddings, many kinds of surface coatings are being designed: metal coatings including pure Cr [20,21], CrAl [22], CrNi [23], FeCrAl [24], and other high entropy alloys [25]; ceramic coatings including SiC [26], ZrO2 [27,28], and ZrN [29]; MAX-phase coatings including Ti2 AlC [30], TiAlN [31], and TiAlCrN [32]. Under the bombardment of high-energy neutrons, a lot of He atoms are produced by transmutation in the fuels and claddings The implantation of He always causes irradiation swelling and has an effect on the mechanical properties of materials [43,44]. The nanoindentation hardness was a test for the SiC coatings under different experimental conditions
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