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Wear mechanisms and in-service surface modifications of a Stellite 6B Co–Cr alloy

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Title: Wear mechanisms and in-service surface modifications of a Stellite 6B Co–Cr alloy
Authors: Sebastiani, M. marco.sebastiani@stm.uniroma3.it, Mangione, V.1, De Felicis, D.1, Bemporad, E.1, Carassiti, F.1
Source: Wear. 6/30/2012, Vol. 290/291, p10-17. 8p.
Subjects: Fracture mechanics, Cobalt alloys, Surfaces (Technology), Microstructure, Focused ion beams, Transmission electron microscopy, Indentation (Materials science)
Abstract: Abstract: In the present paper, the in-service wear mechanisms and cross-sectional microstructural evolution of a Stellite 6B cobalt-based alloy subjected to sliding contact conditions were analysed by focused ion beam (FIB), transmission electron microscopy (TEM) and nanoindentation techniques. Samples under investigation consisted of a lip-seal adopted in a tunnel boring machine (TBM). In the working conditions, the lip-seal is in sliding contact with a rubber seal in a pressurised oil environment. In this specific case, an unexpected low wear resistance was observed during service, and a long machine downtime was necessary to remove the component. Results of FIB-SEM/EDS characterisation showed deep grooving due to sand (SiO2) particles embedded in the rubber seal inside the contact area, while three-body abrasive wear is observed immediately outside it. Microstructural evaluation of Stellite 6 B Co-based alloy of the cross-section also showed the presence of a nano-crystalline hardened layer with diffuse presence of stacking faults. The presence of a tribo-film with a complex structure was also clearly observed. It is concluded that wear resistance of such components could be significantly enhanced either by a proper control of abrasive contaminant particles in the lubricant oil or by introducing surface microstructural modifications of the component (e.g. a nanostructured thick coating). [Copyright &y& Elsevier]
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Database: Engineering Source
Description
Abstract:Abstract: In the present paper, the in-service wear mechanisms and cross-sectional microstructural evolution of a Stellite 6B cobalt-based alloy subjected to sliding contact conditions were analysed by focused ion beam (FIB), transmission electron microscopy (TEM) and nanoindentation techniques. Samples under investigation consisted of a lip-seal adopted in a tunnel boring machine (TBM). In the working conditions, the lip-seal is in sliding contact with a rubber seal in a pressurised oil environment. In this specific case, an unexpected low wear resistance was observed during service, and a long machine downtime was necessary to remove the component. Results of FIB-SEM/EDS characterisation showed deep grooving due to sand (SiO2) particles embedded in the rubber seal inside the contact area, while three-body abrasive wear is observed immediately outside it. Microstructural evaluation of Stellite 6 B Co-based alloy of the cross-section also showed the presence of a nano-crystalline hardened layer with diffuse presence of stacking faults. The presence of a tribo-film with a complex structure was also clearly observed. It is concluded that wear resistance of such components could be significantly enhanced either by a proper control of abrasive contaminant particles in the lubricant oil or by introducing surface microstructural modifications of the component (e.g. a nanostructured thick coating). [Copyright &y& Elsevier]
ISSN:00431648
DOI:10.1016/j.wear.2012.05.027