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Title: Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (β) Silicon Carbide

Abstract

Along with other desirable properties, the ability of silicon carbide (SiC) to retain high strength after elevated temperature exposures to neutron irradiation renders it potentially applicable in fusion and advanced fission reactors. However, properties of the material such as room temperature fracture toughness must be thoroughly characterized prior to such practical applications. The objective of this work is to investigate the dependence of fracture toughness on crystallographic orientation for single-crystalline β-SiC. X-ray diffraction was first performed on the samples to determine the orientation of the crystal. Nanoindentation was used to determine a hardness of 39.1 and 35.2 GPa and elastic modulus of 474 and 446 GPa for the single-crystalline and polycrystalline samples, respectively. Additionally, crack lengths and indentation diagonals were measured via a Vickers micro-hardness indenter under a load of 100 gf for different crystallographic orientations with indentation diagonals aligned along fundamental cleavage planes. Upon examination of propagation direction of cracks, the cracks usually did not initiate and propagate from the corners of the indentation where the stresses are concentrated but instead from the indentation sides. Such cracks clearly moved along the {1 1 0} family of planes (previously determined to be preferred cleavage plane), demonstrating that the fracture toughnessmore » of SiC is comparatively so much lower along this set of planes that the lower energy required to cleave along this plane overpowers the stress-concentration at indentation corners. Additionally, fracture toughness in the <1 1 0> direction was 1.84 MPa·m1/2, lower than the 3.46 MPa·m1/2 measured for polycrystalline SiC (which can serve as an average of a spectrum of orientations), further demonstrating that single-crystalline β-SiC has a strong fracture toughness anisotropy.« less

Authors:
; ;
Publication Date:
Research Org.:
DOESC (USDOE Office of Science (SC) (United States))
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1051803
Resource Type:
Journal Article
Journal Name:
Journal of Undergraduate Research
Additional Journal Information:
Journal Volume: 6
Country of Publication:
United States
Language:
English

Citation Formats

Pharr, M, Katoh, Y, and Bei, H. Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (β) Silicon Carbide. United States: N. p., 2006. Web.
Pharr, M, Katoh, Y, & Bei, H. Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (β) Silicon Carbide. United States.
Pharr, M, Katoh, Y, and Bei, H. Sun . "Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (β) Silicon Carbide". United States. https://www.osti.gov/servlets/purl/1051803.
@article{osti_1051803,
title = {Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (β) Silicon Carbide},
author = {Pharr, M and Katoh, Y and Bei, H},
abstractNote = {Along with other desirable properties, the ability of silicon carbide (SiC) to retain high strength after elevated temperature exposures to neutron irradiation renders it potentially applicable in fusion and advanced fission reactors. However, properties of the material such as room temperature fracture toughness must be thoroughly characterized prior to such practical applications. The objective of this work is to investigate the dependence of fracture toughness on crystallographic orientation for single-crystalline β-SiC. X-ray diffraction was first performed on the samples to determine the orientation of the crystal. Nanoindentation was used to determine a hardness of 39.1 and 35.2 GPa and elastic modulus of 474 and 446 GPa for the single-crystalline and polycrystalline samples, respectively. Additionally, crack lengths and indentation diagonals were measured via a Vickers micro-hardness indenter under a load of 100 gf for different crystallographic orientations with indentation diagonals aligned along fundamental cleavage planes. Upon examination of propagation direction of cracks, the cracks usually did not initiate and propagate from the corners of the indentation where the stresses are concentrated but instead from the indentation sides. Such cracks clearly moved along the {1 1 0} family of planes (previously determined to be preferred cleavage plane), demonstrating that the fracture toughness of SiC is comparatively so much lower along this set of planes that the lower energy required to cleave along this plane overpowers the stress-concentration at indentation corners. Additionally, fracture toughness in the <1 1 0> direction was 1.84 MPa·m1/2, lower than the 3.46 MPa·m1/2 measured for polycrystalline SiC (which can serve as an average of a spectrum of orientations), further demonstrating that single-crystalline β-SiC has a strong fracture toughness anisotropy.},
doi = {},
url = {https://www.osti.gov/biblio/1051803}, journal = {Journal of Undergraduate Research},
number = ,
volume = 6,
place = {United States},
year = {2006},
month = {1}
}