Mechanical Properties and Deformation of Cubic Silicon Carbide Micropillars in Compression at Room Temperature

Abstract

We performed microcompression tests on silicon carbide (SiC) pillars with diameters ranging from 4.7 down to 0.65 μm at room temperature. The SiC micropillars were fabricated from a polycrystalline 3C‐SiC plate using lithography and plasma etching. The pillars exhibited elastic loading behavior until a catastrophic brittle fracture occurred. The compressive fracture strength was found to increase with a decrease in pillar diameter. This scale dependency can be attributed to the flaw sensitivity of brittle materials, and cracking seems to start at the grain boundaries. Ductile plasticity occurred in micropillars with a diameter of 0.65 μm. Cross‐sectional transmission electron microscopy observation of the plastically deformed pillars showed that a slip occurred on the {111} planes. The critical resolved shear stress for a {111}<110> slip system was evaluated to be 4.9–7.3 GPa, which is consistent with the values obtained from numerical and theoretical studies in the literature.

Sample size induced brittle-to-ductile transition of single-crystal aluminum nitride

“…Fig. 8a shows the comparison of the maximum plastic strain and ultimate strength of AlN with other highstrength single crystals and amorphous alloys tested by micro-compression with pillar diameters ranging from $500 nm to 5 lm [22,25,[27][28][29][40][41][42][43][44]. The general trend from these data, regardless of deformation mechanisms, is that the higher strength of materials typically accompany with lower plasticity.…”

“…Recent microcompression experiments show that brittle ceramics could be plastically deformed by dislocations at small length scale [25,27,30]. For AlN, both single-crystal and polycrystalline samples at a macroscopic length scale always fails in a brittle manner at room temperature prior to plastic yielding although hydrostatic stress state introduced by mechanical confinements can significantly suppress the brittle failure and gives rise to dislocation plasticity [11][12][13].…”

“…Nevertheless, different from other ultra-high strength materials, the single-crystal AlN, especially (0 0 0 1) single crystals, shows an extraordinary combination of high strength and plasticity. Fig 8b summarizes the sample size effect on normalized strength of single crystals at a small length scale [22,25,[27][28][29][40][41][42], in which the shear strength (s) is normalized by the shear modulus (G) and fitted by a power law equation of sample diameters (d):…”

“…However, for strong and relatively brittle ceramics, the size dependence of their strength and ductility has not been well explored [4,[22][23][24]. Recently, the size induced plasticity has been observed in covalent and ionic crystals, such as sapphire [25], GaAs [26], SiC [27] and MgO [28], during room-temperature microcompression. These studies indicate that decreasing sample sizes to the order of micrometer scale can suppress cracking and leads to the change in the deformation behavior from brittle to ductile [29,30].…”

In situ investigation of MgO nanocube deformation at room temperature

“…This size effect involves also the plastic deformation regime for whom few theories based on the single-arm dislocation source model or the dislocation nucleation/starvation model [10,11] still try to provide a unique description of the now well-known principle "smaller is stronger". Nevertheless, most of these studies are carried on metals, especially face-centered cubic (fcc), and only few works have been dedicated to ceramics [12][13][14][15]. Calvie and collaborators have recently reported in situ compression tests in the TEM of a c-alumina Al 2 O 3 nanospheres [14].…”