Degradation of structural ceramics by erosion
Materials wastage by solid-particle erosion can be severe and limit lifetimes. This paper will review the theoretical description of solid-particle erosion in brittle materials, which is well-developed for monolithic ceramics. The models can usually account for effects from the principal projectile properties: size, impact velocity, and impact angle. Materials parameters such as fracture toughness and hardness can be included. Steady-state erosion measurements on a wide variety of ceramics, ranging from Si single crystals to SiC-whisker-reinforced A12O3 are reviewed and compared to the models. It is believed thatR-curve behavior and/or particle fragmentation is responsible for discrepancies between the theory and experimental results for composite ceramics. Additionally, the theories make no attempt to describe threshold or incubation effects.
Particle size distribution effects on the solid particle erosion of brittle materials
Abstract The effects of distributions of projectile size and velocity on the erosion of brittle materials were assessed. Strong dependences of the steady state erosion rate on the width of the particle size distribution and on the velocity characteristics of the erosion equipment were predicted. The predictions were confirmed by experiment. The results indicate that careful design of controlled erosion experiments is essential in order to avoid misleading predictions of in-service erosion rates. The implications of the analysis for the interpretation of threshold effects and for experiments designed to verify erosion theories are also discussed.
The crack-initiation threshold in ceramic materials subject to elastic/plastic indentation
The threshold for indentation cracking is established for a range of ceramic materials, using the techniques of scanning electron microscopy and acoustic emission. It is found that by taking into account indentation plasticity, currant theories may be successfully combined to predict threshold indentation loads and crack sizes. Threshold cracking is seen to relate to radial rather than median cracking.