Onset Plastic Deformation and Cracking Behavior of Silicon Carbide under Contact Load at Room Temperature

Abstract

The room temperature onset plastic deformation and crack behavior of 3C-SiC under contact load were investigated using nanoindentation and transmission electron microscopy (TEM). During loading, abrupt bursts or pop-in in the load-displacement curves was observed at a depth of~60 nm. The 3C-SiC deforms elastically before the pop-in depth, but exhibits a plastic-elastic behavior after that. TEM observations reveal that the shear slip is the predominant deformation mechanism in 3C-SiC during indentation. The cracks usually initiate at the intersection of shear bands or grain boundary. In addition, theoretical analysis confirms that the pop-in event is associated with the onset plasticity of 3C-SiC.

Incipient plasticity in 4H-SiC during quasistatic nanoindentation

“…This analysis is based on evaluation of the maximum shear stress and maximum tensile strength underneath the indenter during the process of nanoindentation. The maximum shear stress underneath the indenter can be found out using the following equation [14]:…”

“…The tensile stresses and cleavage strength of 4H-SiC were obtained using the following equation [14]:…”

“…In the past, experimental trials have been reported on polycrystalline 3C-SiC (CVD-SiC) [13][14], single crystal 6H-SiC [15][16][17], polycrystalline 6H-SiC (reaction bonded SiC) [18] and single crystal 4H-SiC [19][20]. These studies were focussed on exploring the ductile-regime machining of SiC and have shown that single crystal 6H-SiC exhibits a ductile to brittle transition (DBT) depth of only 70 nm [21] whereas DBT depth in CVD 3C-SiC (polycrystalline) was found to be 550 nm [22].…”

Comparison study of silicon carbide coatings produced at different deposition conditions with use of high temperature nanoindentation

“…In nanoindentation, the elastic response of a material is assessed within a small measurement volume that is subject to an extreme hydrostatic stress. Thus, this approach differs substantially from macroscopic bending testing techniques, since shear bands with associated dislocations and microcracks form to accommodate the plastic deformation [27,28,45]. With an increasing concentration of such defects in the volume beneath the indenter at higher temperatures the materials' elastic response is likely to be affected.…”

“…Earlier studies have shown that even at room temperature, the initial plastic deformation in SiC during nanoindentation is related to dislocation activity [27]. With the small curvature radius of the indenter tip a strong hydrostatic stress field is induced in which the critical shear strength is exceeded before the tensile stresses reach the cleavage strength [28]. Considering that subsequent SEM imaging showed cracking around the indent imprints regardless of the measurement temperature, it could be concluded that for the temperature range investigated here nanoindentation measurements induced plastic deformation by dislocation activity as well as fracture.…”