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Four “engineering” ceramics were subjected to impact (single particle) and erosion (multiple impacts) under conditions which simulate a natural dust environment in the subsonic velocity regime. The target materials are hot-pressed silicon nitride (Si3N4), reaction-bonded Si3N4, a glass-bonded aluminum oxide (Al2O3), and hot-pressed magnesium fluoride (MgF2). Tests were performed with six narrow size ranges of natural quartz between 10 and 385 μm average, and five velocities for each particle size. Hot-pressed Si3N4 was also impacted with silicon carbide (SiC) under the same particle size-velocity conditions.
The results are discussed in terms of current erosion and impact models by considering particle size-velocity dependencies, appearance of the impact damage, and the basic properties and structure of the targets.
Under these erosion conditions, the four target materials exhibited widely different behavior not only in absolute amount of material removed, but also in mechanism of removal. The systems hot-pressed Si3N4-SiC particles and MgF2-quartz particles were characterized by a highly deformed, permanent surface crater with associated lateral and radial crack formation, and erosion loss was proportional to particle mass and velocity, both to the fourth power. Erosion of hot-pressed Si3N impacted with quartz particles was proportional to the third power of particle size and the first power of velocity, and loss occurred by minor chipping with no secondary crack formation. Erosion of glass-bonded A12O3 and reaction-bonded Si3N did not show a consistent particle size-velocity dependence. The variation is related to the two-phase structure of these materials. It was found that strength is not necessarily reduced for erosion conditions which produce appreciable material removal.
impact, erosion, ceramics, bend strength, silicon nitride, aluminum oxide, magnesium flouride, mechanical properties, microscopy, quartz sand, silicon carbide particles
Senior research engineer, Solar Turbines International, an Operating Group Group of International Harvesters, San Diego, Calif.