Influence of low temperature plasma carbonitriding on cavitation erosion resistance of the Stellite 250 alloy – A preliminary evaluation

• Published in: Wear 2021-07, Vol.476, p.203653, Article 203653
• Main Authors: Oliveira, D.B., Franco, A.R., Bozzi, A.C.
• Format: Article
• Language: English
• Subjects: Alloys; Carbonitriding; Cavitation; Cavitation erosion; Cavitation resistance; Cobalt base alloys; Cobalt superalloy; Corrosion resistance; Depth profiling; Erosion mechanisms; Erosion resistance; Gas mixtures; Glow discharges; Low temperature; Low temperature resistance; Optical emission spectroscopy; Plasma carbonitriding; S-phase; Superalloys; Surface treatment; Tribology; Vibration tests; Wear mechanisms
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2021.203653

Superalloys are a potential material class for selection in some tribological systems, particularly those subjected to wear. When subject to cavitation erosion, the cobalt-based alloys are often applied. Surface treatments have been employed to improve the tribological resistance without loss of corrosion performance for several class of materials. In this context, the thermochemical treatment of low temperature plasma carbonitriding was carried out in a superalloy of the Co-Cr-Fe system in order to improve cavitation erosion resistance. The carbonitriding treatments were performed at temperature of 380 °C over a period of 3, 9 and 15 h. The gas mixture was composed of 72.5% H2, 25% N2 and 2.5% CH4. After the thermochemical treatment, phases formation was identified by X-ray diffraction and the glow discharge optical emission spectroscopy was used for mass concentration depth profiling of carbon and nitrogen. Cavitation erosion resistance of specimens were evaluated by a vibratory test. Mass losses were periodically measured as a function of exposure time during test. Specimens were evaluated in terms of mean depth of erosion, incubation time and mass loss. In addition, the cavitation erosion mechanism was investigated by scanning electron microscopy observation of damaged surfaces. S-phase formation was observed for all treatments. Results showed that low temperature plasma carbonitriding and the formation of expanded phase are effective to increase cavitation erosion resistance of the studied cobalt-based alloy when treatment was carried out during 3 and 9 h. •Cavitation erosion resistance of the plasma carbonitrided Stellite 250 alloy was studied.•S-phase dual layer was formed after low-temperature plasma carbonitriding.•The thermochemical treatment improves the hardness of Stellite 250 alloy.•Low-temperature plasma carbonitriding performed at 380 °C during 3 and 9 h provided higher cavitation erosion resistance.