Laser surface processing and the cavitation erosion of a 16 wt.% Cr white cast iron

Abstract

The cavitation erosion of a 16 wt.% Cr white cast iron in distilled and 0.02% and 3.0% NaCl water at 50 °C has been investigated using a 15 μm amplitude 20 kHz ultrasonic facility, and the corrosion behaviour during erosion in the 3.0% salt solution measured electrochemically. The effects of prolonged annealing, laser surface melting, laser surface hardening and plasma nitriding of the cast iron were also investigated. Salt in the water increased the erosion rate considerably, and only 0.02% salt increased the rate by over three times. Prolonged annealing at 1040 °C reduced the erosion rate in distilled water but had a negligible effect on the erosion rate in salt waters. Laser processing reduced the rate considerably. For laser surface melting, the reduction in the erosion rate in distilled and 3.0% salt water was by factors of 0.07 and 0.2 respectively. Nitriding did not reduce the erosion rate of the cast material, and it eliminated the beneficial effects of laser melting. Corrosion currents obtained under static and cavitating conditions allowed the contributions of erosion, of corrosion-enhanced erosion and of corrosion to the total cavitation damage to be estimated. For each material, corrosion-enhanced erosion was the major component of damage in 3% salt water. The results of detailed metallographic examination of the erosion damage are also presented, and the mechanism of cavitation erosion is discussed.