Basal Plane Dislocation Analysis of 4H-SiC Using Multi Directional STEM Observation

A peculiar surface defect on a silicon carbide (SiC) epitaxial wafer, found to be associated a basal plane dislocation (BPD), was studied using a low energy scanning electron microscope (LESEM), and a novel method we are calling multi directional scanning transmission electron microscopy (MD-STEM). We have confirmed that an etch pit with double cores neighboring a peculiar surface defect is derived from the extended BPD. The BPD consisted of two partial dislocations with a stacking fault width of about 100 nm. Observation of only one viewing direction in a previous study missed the extended dislocation but through the use of the MD-STEM method in the current study, the dislocation has been confirmed to be extended into a stacking fault.

Modeling of Orientation Dependence of Critical Resolved Shear Stress and Deformation Mechanisms on Yield Point of Austenitic Stainless Steels Hardened by Interstitial and Substitution Atoms

The proposed dislocation model describes the orientation dependence of the critical resolved shear stress (CRSS) and deformation mechanisms on the yield point in single crystals of austenitic stainless steel with nitrogen impurities. The model takes into account the following: the change of the interstitial atom position in the lattice from octahedral interstice to tetrahedral site owing to passage of a leading Shockley’s partial dislocation; the change in the separation width between two partial dislocation in external stress field; the relationship between the width of the extended dislocation and the elastic interaction of the extended dislocation with the impurity atoms.

A Molecular Dynamics Simulation of Fracture in Nanocrystalline Copper

A large-scale molecular dynamics simulation was used to investigate the propagation of cracks in three dimensional samples of nanocrystalline copper, with average grain sizes ranging from 5.34 to 14.8 nm and temperatures ranging from 1K to 500 K. It was shown that intragranular fracture can proceed inside the grain at low temperature, and plastic deformation around the tip of the crack is accommodated by dislocation nucleation/emission; indeed, both fully extended dislocation and deformation twinning were visible around the tip of the crack during fracture. In addition, due to a higher concentration of stress in front of the crack at a relative lower temperature, it was found that twinning deformation is easier to nucleate from the tip of the crack. These results also showed that the decreasing grain size below a critical value exhibits a reverse Hall-Petch relationship due to the enhancing grain boundary mediation, and high temperature is better for propagating ductile cracks.

Experimental Study on Formation Characteristics and Laws of Dislocation and Stacking Fault during Cutting of Titanium Alloy

Formation characteristics and laws of dislocation and stacking fault during cutting of titanium alloy were investigated by TEM. Several crucial aspects of experiment, such as sample cutting, mechanical reduction of thickness, dimpling, and ion reduction of thickness, were carefully designed and implemented. Further, electron diffraction pattern, diffraction contrast image, and high resolution electron photomicrograph ofαphase andβphase were observed and analyzed. Following those analyses, the formation characteristics and laws of dislocation and stacking fault were made clear. Research results show that the edge dislocations exist commonly in the diffraction contrast images and high resolution electron photomicrographs ofαphase andβphase. The stacking fault energy is higher inβphase than inαphase. In addition, the extended dislocation is difficult to be seen inβphase, but it is easier to be produced inαphase.