ME 4763 Chapter : Fall 2009
Document Summary
Medium: corrosive environment: anhydrous ammonia, aqueous fluorides, steam, polythionic acid. External conditions: imperfections at the surface, tensile stress, crack-promoting environment. Crack growth features: branching perpendicular to the applied stress. Influence of sensitization: formation of chromium carbides along grain boundaries. Prevention: change the environment, oxidizing potential, protective coating, or applied/residual stress levels. Where and when does it occur, mechanism of its occurrence, two main requirements, what role corrosion plays, how is it prevented. When/where: on the surface of materials that come into contact with high velocity fluids subject to changes in pressure. Mechanism: formation and collapse of vapor bubbles in a liquid against a metal surface. Requirements: high velocity liquids and formation of bubbles. Role: allows for reformation of protect films, thus creating cavities and allowing for more cavitation. Prevention: minimize hydrodynamic pressure differences, use harder more corrosion resistant materials, smooth surfaces, coatings with rubber or plastic. Ii) answer any one of the following two questions: (15 pts. )
