Download or read book Radiation Effects on Mechanical Properties of Thin 3c-sic Investigated by in Situ Nanoindentation Via Transmission Electron Microscopy written by Xuying Liu (Ph.D.) and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In situ nanoindentation tests on thin 3C-SiC in a transmission electron microscope show small but non-negligible plastic deformation at room temperature. SiC is brittle in macroscopic studies but it can be become ductile when deformation occurs in small volumes. Here, we report such a brittle to ductile transition of 3C-SiC during nanoindentation of thin films (150-270 nm thick), and we reveal mechanisms of plastic deformation in situ. We find that plasticity in 3C-SiC is driven by dislocations, and that there is a pronounced plastic strain recovery at these length scales. We suggest that plastic deformation recovery arises from annihilation of transient dislocation extension driven by retracted external stress. In addition, we demonstrate that when the sample thickness is less than 90 nm, 3C-SiC becomes brittle again, and therefore the thickness of the films is important in determining whether the sample is brittle or ductile. In situ TEM nanoindentation tests on thin 3C-SiC irradiated at different radiation conditions indicate different mechanical behavior that is related to different microstructures. Samples irradiated at 600 [degrees]C 0.3 dpa and 600 2̐ʻC 3 dpa are easier to fracture under applied force than as-synthesized 3C-SiC. Long, straight, and simple crack paths are characteristic features for 600 [degrees]C 3 dpa samples, which is an evidence of easier fracture than 600 [degrees]C 0.3 dpa. However, 900 [degrees]C 3 dpa samples do not exhibit noticeable brittleness. Instead, they exhibit plastic deformation under applied force, which is the same as as-synthesized samples. Based on the microstructure of the irradiated samples, increasing the density of black spot defects that form at 600 [degrees]C degrades resistance to cracking, but the change of defect type to dislocation loops at 900 [degrees]C restores the plastic behavior. The results from this study are not consistent with macroscale analysis of fracture and cracking in irradiated SiC, which suggest different behavior and the microscale in irradiated as well as unirradiated SiC. These results therefore provide useful insights into the microscale properties of 3C-SiC which are important to multiscale simulation of 3C-SiC to predict mechanical performance of microelectromechanical systems, coatings, and next-generation fission reactor fuels.