Micro-scale fracture toughness of textured alumina ceramics

The effect of crystal anisotropy on fracture toughness and strength of ZrB2 microcantilevers

“…In the case of notched specimens, the milling started with the making of notches and was followed by three consecutive steps, as described in Ref. [22]. The long sharp notch was FIB-milled at a desired location with a length of about 10 µm using a low current of 50 pA for about 30 s, which resulted in a depth of about α = 300-600 nm.…”

“…For further details on microcantilever bending and surface characterization, the reader is referred to our recent works. 20,22…”

“…the varying stress field and sample geometry is considered to be comprised in the 𝑌( α) shape factor determined by FEM similar to that was done in our earlier work. 22 Finally, the shape factor as a function of normalized notch length was determined by a fourth-order polynomial fit as shown also in Figure 4B. 𝑌 ( α) = 1.121 − 1.171 α + 5.439 α2 − 8.185 α3 + 8.660 α4 (11) It is important to note that the shape factor function fits well with our recent result that was carried out on a more compliant Al 2 O 3 model (E = 380 GPa), 22 implying that 𝑌( α) depends only on the geometry but not on Young's modulus of the model within the isotropic approximation.…”

“…22 Finally, the shape factor as a function of normalized notch length was determined by a fourth-order polynomial fit as shown also in Figure 4B. 𝑌 ( α) = 1.121 − 1.171 α + 5.439 α2 − 8.185 α3 + 8.660 α4 (11) It is important to note that the shape factor function fits well with our recent result that was carried out on a more compliant Al 2 O 3 model (E = 380 GPa), 22 implying that 𝑌( α) depends only on the geometry but not on Young's modulus of the model within the isotropic approximation. Finally, it is worth emphasizing that the analytical solutions derived for the determination of fracture strength and fracture toughness (Equations 3, 8, and 11) are valid for other brittle and hard materials with the model geometry described above, not just for ZrB 2 .…”

“…However, the literature on microcantilever bending testing of refractory or UHTCs is quite scarce with only a couple of studies published [16][17][18][19] besides the works of the present authors. [20][21][22] To the best of our knowledge, the anisotropic fracture behavior of ZrB 2 gains has not been studied under tensile stress conditions previously. Thus, the aim of the present work is to study the effect of crystal anisotropy on the fracture toughness and strength in grains of a polycrystalline zirconium diboride specimen during microcantilever bending experiments.…”