Local Fracture Toughness of Si₃N₄ Ceramics Measured using Single‐Edge Notched Microcantilever Beam Specimens

Abstract

Local fracture toughness gives us useful and important information to understand and improve mechanical properties of bulk ceramics. In this study, the local fracture toughness of silicon nitride (Si3N4) ceramics was directly measured using single‐edge notched microcantilever beam specimens prepared by the focused ion beam technique. The measured fracture toughness of grain boundary of the Si3N4 ceramics is higher than the fracture toughness of SiAlON glass, which exists in the grain boundaries of Si3N4 ceramics. It is also shown that the fracture toughness of grain boundary depends on the rare earth oxide added as a sintering aid, which is expected in terms of the difference in the grain‐boundary structure. The fracture toughness of a single β‐Si3N4 grains is higher than the grain‐boundary fracture toughness. It was also higher than the value estimated from ab initio calculations and surface energy, which means that any dissipative energy should be included in the fracture toughness of a grain in spite of the brittle fracture in Si3N4. The fracture toughness of polycrystals of Si3N4 ceramics measured using single‐edge notched microcantilever beam specimens is intermediate between those of grains and grain boundaries, and it agrees with the estimated initial value of the Rcurve, KI0, in Si3N4 ceramics.

Microcantilever investigation of fracture toughness and subcritical crack growth on the scale of the microstructure in Al 2 O 3

“…These conclusions contrast with recent results on silicon, which appear to show no effect of residual stress or other beam damage effects [6,7]. This suggests that the effect of ion implantation may be material-dependent.…”

“…Very recently, Tatami et al [7] have used similar procedures to measure the fracture toughness of grains and grain boundaries in liquid phase sintered Si3N4. The elongated -Si3N4 grains in such microstructures enabled straight notches to be machined across a single grain or grain boundary spanning the beam width.…”

Large increase in fracture resistance of stishovite with crack extension less than one micrometer

“…We propose a method to investigate R-curve behavior by using micro-cantilever beam, which has been originally used to measure fracture toughness of amorphous/glass 10 , thin films 11 , single crystals 12 , and grain boundaries 13 . The micro-cantilever beam technique is applied to study the microscopic crack shielding mechanisms of nanocrystalline stishovite ceramics, which exhibit a large fracture toughness due to fracture-induced amorphization 14 15 .…”

Small-Scale Mechanical Testing of Cemented Carbides from the Micro- to the Nano-Level: A Review

“…Micro-and nanomechanical testing of brittle materials, such as advanced ceramics and hardmetals, have undergone rapid development over the last decade, providing access to the mechanical properties and performance of materials on length scales from a micrometer down to tenths of a nanometer [52][53][54][55][56][57][58][59][60][61][62][63]. The non-elastic mechanical behavior of ceramics, which are inherently brittle, is difficult to measure at room temperature due to their very limited ductility.…”