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.
Effect of erodent properties on the erosion of alumina
The effect of erodent particle properties for solid particle erosion in a series of alumina ceramics was investigated using alumina and SiC erodents. Using a new model analysis, the results were interpreted in terms of particle fragmentation effects and related erodent-target properties. An increase in the erosion rate with increase in the particle-target hardness ratio reported in the literature is related to these effects but is not actually a direct consequence of hardness. Changes in the velocity exponents for erosion were observed and can be explained by blunting due to crushing and fragmentation of larger erodent particles. The quasi-static model for erosion predicts a reduction in the velocity exponent as the particle-tip blunting increases. In steady state, SEM observations show that lateral crack controlled erosion mechanisms operate in all cases but, for certain combinations of erodent and target properties, damage accumulation by plastic punching occurs.
Effect of indentation load on fragmentation of erosion particle tips
Abstract Erosion studies on alumina of varying hardnesses impacted by Al 2 O 3 and SiC erodent particles suggest that particle fragmentation may significantly affect the erosion behavior of ceramics. The effect of load on the fragmentation of impacting particles has been systematically studied here using indentations of individual particles on sapphire. Replicas of particle tip geometry were made by indenting a diamond-turned copper sample. Scanning electron microscopy of such indentations at varying loads reveals a threshold load at which fragmentation occurs. The threshold load depends on the material properties of the individual particles, and it appears that softer particles fragment at lower loads than harder particles do. The crushing of impacting particles can lead to the blunting of particle tips and thus alter the erosion mechanism of hard targets impacted with softer erodents.