Mechanical Properties of Hot‐Pressed Silicon Nitride with Different Grain Structures

Abstract

During hot-pressing of a-Si3N, powders, the equiaxed a microstructure gradually transforms into a structure characterized by needle-shaped prkmatic grains which are closely entangled and linked together. With increasing amounts of the p fraction, the bend strength, fracture toughness, and work of fracture increase significantly, then decrease as grain growth occurs.The K,, improves by a factor of >2 and the change in yF by a factor of >4. The crack resistance to achieve the same crack velocity in materials of different / 3 contents shows a similar trend. The dependence of the mechanical properties on the microstructure is explained by linking and pullout of the /3 crystals and by grain coarsening.

Effect of microstructure and slow crack growth on lifetime prediction of monolithic silicon carbide

“…It is suggested that the oxide complexions along the grain boundaries make the LP-SiC materials prone to stress corrosion [30], because slow crack growth occurs as a result of a chemical reaction between water molecules and the metal-oxide (M-O bonds) [31]. It is also noticeable that the materials with coarse grains exhibit higher n values in contrast to materials with fine grains, which is in agreement with work done on alumina and silicon nitride ceramics [29,32,33]. The maximum allowable stress as a function of the desired lifetime is shown in Figure 3.…”

Thermodynamic Analysis of Grain Aspect Ratio in Fibrous Microstructures of Silicon Nitride

“…5,6 Furthermore, the fibrous microstructure reduces the sensitivity of the fracture strength to the grain size of silicon nitride. More recent work suggests that both the grain size and the grain aspect ratio must be controlled to optimize the mean value and the Weibull modulus of the fracture strength of silicon nitride.…”

Influence of low indentation load on Young's modulus and hardness of 4mol% Y2O3–ZrO2 by nanoindentation

“…In particular, Young's modulus and hardness are two of the most important properties for application of this material. Young's modulus has been measured for ceramics by a variety of common techniques, including strain gage bend bars [1], ultrasonic time of flight [2], and resonance techniques [3].…”