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COBEF 2017
Congresso Brasileiro de Engenharia de Fabricação
EROSION AND CORROSION BY MICRO-JETS AND HIGH TEMPERATURE CAVITY IMPACTION ON METAL SURFACES
Submission Author:
Auzany Freitas Barbosa Junior , SC
Co-Authors:
Gil Bazanini, Nicodemus Lima
Presenter: Gil Bazanini
doi://10.26678/ABCM.COBEF2017.COF2017-1525
Abstract
Present work examines material surface damage by cavitation erosion of metals or the wear phenomenon owing to water bubbles collapse near the metallic surface. Material surface damage by cavitation erosion is due to wear mechanisms of hot liquid micro-jets impingement and impaction. To explain these erosion mechanisms based on water flow and mechanical properties of tested materials, experimental cavitation in tap water was investigated, using acompact rotating disk equipment. In this rig, a rotating disk with cavitation inducers and specimens fixed on it run in tap water to provide cavitating flow similar to service conditions in pumps and propellers. Cast iron, carbon steel and bronze specimens were tested in this test rig. The cavitation damage mechanisms were observed by scanning electron microscope after each 5 hours working under cavitating conditions. The specimens surfaces were worn out by cavitation erosion mechanisms, resulting in pitting formation or mass loss. All specimens presented surface damage. Pit diameter size was about to 50 m. Calculations of the temperature of the cavity contents in its final stage of the collapse resulted in great value for the temperature (of about 2,500 K) of the vapor and gas trapped inside it. The damages on the specimens are analyzed showing pits and approximate circular regions on their surfaces. An explanation is presented here based in temperature calculations and images of the specimens after the collapses. The pits are made by liquid micro-jets impingement while its surrounding approximate circular regions, showing some aspect of heating and craters are credited to the high temperature impaction of the bubble contents in the final stages of its collapse. The influence of heat by conduction rejected by the cavity is also studied here. Materials analyzed are commonly used in manufacturing of rotors of feed-water pumps.
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