INFLUENCE OF SURFACE HARDENING DEPTH ON THE CAVITATION EROSION RESISTANCE OF A LOW ALLOY STEEL

摘要

In this paper, the influence of surface hardening depth promoted by plasma nitriding and Cr-AI-N coating deposition on the cavitation erosion resistance of a low alloy steel was investigated. 2 and 4 hours plasma nitrided samples were produced and coated with 1 and 2 urn Cr-AI-N coatings deposited by PAPVD. The characterization was carried out by X-ray diffraction (θ-2θ and glancing angle configurations), scanning electron microscopy, Rockwell C adhesion test and 3D profilometry. Knoop microhardness tests were also performed. Cavitation erosion tests were carried out according to ASTM G32-03 Standard. The cavitation erosion rate and incubation period were determined. Coating deposition had a major influence on the incubation period, in which a higher coating thickness resulted in a longer time. Plasma nitriding treatment was more effective on reducing the average erosion rate in the accelerated period. The plasma nitriding treatment and Cr-AI-N coating in conjunction led to a decrease in both incubation period and erosion rate. The hardened systems presented mass loss up to 11 times lower than the non hardened steel for the same time. It was concluded that as ticker is the coating and as deeper is the nitrided layer better is the cavitation erosion resistance.