CAVITATION EROSION OF LASER-MELTED DUCTILE IRON

The influence of laser processing on the cavitation erosion of ductile iron? a material employed extensively for components in marine applications? including diesel-engine cylinder liners, valves and pumps, is addressed here. Pearlitic ductile iron has only modest resistance to cavitation erosion; the mean depth of penetration rate (MDPR) was 10-12 mu m h(-1) in distilled water. Ferritic ductile iron had consistantly better resistance to erosion than pearlitic iron, particularly in corrosive media. The cavitation erosion rates in an aqueous slurry of 35 wt%. 220 grit SiC, Synthetic sea water (3.4 wt%) and centinormal dilute H2SO4 were 24, 40 and 86 mu m h(-1) respectively, whilst the corresponding rates were reduced to 3, 6 and 12 mu m h(-1) for laser-melted samples. The synergistic effect of corrosion and cavitation erosion was more pronounced in the dilute acid than in the salt water. The cavitation erosion rates decreased linearly with increase in the pH value of the cavitation bath. Laser treatment was very effective in bringing about a nearly seven-fold enhancement of the erosion resistance of ductile iron in mild corrosive media. This has enabled the delineation of the mechanism of cavitation erosion of ductile iron before and after laser processing, particularly in corrosive baths. A comprehensive review of published technical literature concerning the influence of laser surface treatment on the cavitation erosion of selected steels and cast irons in different baths is included.