Influence of surface hardening depth on the cavitation erosion resistance of a low alloy steel

In this paper, the influence of surface hardening depth promoted by plasma nitriding and Cr-Al-N coating deposition on the cavitation erosion resistance of a low alloy steel was investigated. Samples that were plasma nitrided for 2 and 4 h were produced and coated with 1 and 2 μm Cr-Al-N coatings deposited by plasma assisted physical vapor deposition. The characterization was carried out by X-ray diffraction (θ-2 θ and glancing angle configurations), scanning electron microscopy, Rockwell C adhesion test, and three dimensional (3D) profilometry. Knoop microhardness tests were also performed. Cavitation erosion tests were carried out according to ASTM G32-03 Standard. The incubation period and cavitation erosion rate were determined. Coating deposition had a major influence on the incubation period, with thicker coatings resulting in longer times. Plasma nitriding treatment was more effective on reducing the average erosion rate. The plasma nitriding treatment and Cr-Al-N coating deposition 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 nonhardened steel for the same time. It was concluded that the surface hardening was effective to improve the cavitation erosion resistance of a low alloy steel and the wear rate decreased with the increase of the hardening depth.