Fracture and Subcritical Crack‐Growth Behavior of Y‐Si‐Al‐O‐N Glasses and Si₃N₄ Ceramics

Abstract

Fracture and environmentally assisted subcritical crackgrowth processes are examined in bulk Y-Si-Al-O-N oxynitride glasses with compositions typical of the grain boundary phase of silicon nitride ceramics. Both long-crack (in compact tension specimens) as well as short-crack behavior (using indentation techniques) were investigated to establish a reliable fracture toughness and to elucidate the anomalous densification behavior of the oxynitride glass. Environmentally assisted subcritical crack-growth processes were studied in inert, moist, and wet environments under both cyclic and static loading conditions. Behavior is discussed in terms of the interaction of the environment with the crack tip. Likely mechanisms for environmentally assisted crack growth are discussed and related to the subcritical crack-growth behavior of silicon nitride ceramics.

The indentation fracture toughness (KC) and its parameters: the case of silica-rich glasses

“…Nitrogen enhances this trend: the YSiAlON glass is more resistant than its oxide counterpart. This was already suggested in a previous study [17], which showed that the tightening effect of the trivalent nitrogen on the vitreous network improves the chemical durability. The silica-rich glasses are less sensitive to indentation fatigue than WG1, WG3 and WG4 glasses, which means that glass fatigue is a function of both the modifier oxide content and the modifier type present in the glass composition.…”

“…In a previous study of sub-critical crack growth behavior of an YSiAlON glasses [17], it was concluded that the oxynitride glass investigated, which exhibited overestimated indentation fracture toughness K C , behaved in a rather anomalous way (flow densification). Since we did not observe the characteristic features of flow densification in the presently studied oxynitride glass, it is suspected that different glass synthesis routes result in different glass structures at the micro or nanometer scale.…”

“…In fact, the experimental procedure used to obtain glasses in Ref. [17] (slow melt cooling) is likely to lead to the formation of nano-crystallized areas strengthening the materials against crack propagation. No evidence for flow densification was observed in the CaSiAlO glass, nor in the YSiAlO(N) glasses by the present authors, consistently with the fact that these glasses exhibit relatively high network compactnesses: the WG4 and YsiAlON glasses are characterized by compactness values of 0.36 and 0.41 respectively, where the compactness parameter reflects the free volume content and thus the susceptibility of a glass to densification (see [18] for details).…”

Crack profiles under a Vickers indent in silicon nitride ceramics with various microstructures

“…The fracture surface was observed with the optical microscope. Environmental slow crack growth during the test was not expected since the red dye was nonwater-based solution and Si 3 N 4 is unsusceptible to the slow crack growth [20,21]. The possible disadvantage of the method is that the crack extension may be slightly underestimated due to the insufficient infiltration of the dye into the crack tips.…”

Ceramics and ceramic coatings in orthopaedics

“…Results obviously vary by material, but can also differ due to test conditions and applied stress ratios. Furthermore, the data shown in the Table are inclusive of various environmental conditionsparticularly the presence of moisture [211,212,[343][344][345][346][347][348][349][350][351][352][353][354][355]. Stress corrosion cracking is a common problem for all polycrystalline ceramics due in part to the presence of grain boundary impurities.…”