Significant Improvement of Mechanical Properties of SiC-Nanowire-Reinforced SiCf/SiC Composites via Atomic Deposition of Ni Catalysts.

This study aimed to study the effects of different catalyst introduction methods on the distribution of SiC nanowires (SiCNWs) and the mechanical properties of SiCf/SiC composites. Two different catalyst-introduction methods (electroplating (EP) vs. atomic deposition (AD)) have been used to catalyze the growth of SiC nanowires in SiCf preforms. The morphology, structure and phase composition were systematically investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The SiCNWs-reinforced SiCf/SiC composited was densified by CVI. The compressive strength of the SiCNWs-reinforced SiCf/SiC composites was evaluated by radial crushing test. Compared with EP, atomic Ni catalysts fabricated by AD have higher diffusivity for better diffusion into the SiCf preform. The yield of SiCNWs is effectively increased in the internal pores of the SiCf preform, and a denser network forms. Therefore, the mechanical properties of SiCNW-containing SiCf/SiC composites are significantly improved. Compared with the EP-composites and SiCf/SiC composites, the compressive strength of AD-composites is increased by 51.1% and 56.0%, respectively. The results demonstrate that the use of AD method to grow SiCNWs is promising for enhancing the mechanical properties of SiCf/SiC composites.

Investigation of Microstructure and Nanoindentation Hardness of C+ & He+ Irradiated Nanocrystal SiC Coatings during Annealing and Corrosion.

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.