Duplex surface treatment of sintered iron by plasma nitriding and plasma carburizing at low temperature

The aim of this study is to investigate the combination of plasma nitriding and plasma carburizing at low temperature. Samples of sintered pure iron were nitrided at 500 °C for 3 h under three different atmospheres: (1% N2 + 99% H2), (10% N2 + 90% H2), and (90% N2 + 9% H2 + 1% CH4), all followed by...

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Bibliographic Details
Published in:Surface & coatings technology 2019-10, Vol.375, p.911-919
Main Authors: Lamim, T.S., Bernardelli, E.A., Bendo, T., Mello, C.H., Binder, C., Klein, A.N.
Format: Article
Language:English
Subjects:
Case depth
Cementite
Chemical analysis
Diamond pyramid hardness
Duplex treatments
Ion nitriding
Iron
Low temperature
Mechanical properties
Methane
Morphology
Nanohardness
Nitrides
Organic chemistry
Phase composition
Plasma carburizing
Plasma nitriding
Sintering
Surface hardness
Surface treatment
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Summary:The aim of this study is to investigate the combination of plasma nitriding and plasma carburizing at low temperature. Samples of sintered pure iron were nitrided at 500 °C for 3 h under three different atmospheres: (1% N2 + 99% H2), (10% N2 + 90% H2), and (90% N2 + 9% H2 + 1% CH4), all followed by plasma carburizing at 500 °C for 3 h under a mixed atmosphere of 2% CH4 + 98% H2. Microstructural characterization and chemical analysis of the layers were performed by scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. Phase identification was carried out by grazing incidence X-ray diffraction. The layer hardness was verified by nanohardness and the case depth by Vickers microhardness. The results show that the post-carburizing treatment promotes the formation of a thin outermost cementite layer over the nitride layers, leading to a nitrided–carburized layer on the surface. The morphology and phase composition of the nitride layer influence the structural and mechanical properties of the nitrided–carburized layers. The best surface hardness improvement, approximately 72%, was achieved by the duplex treatment of nitriding with 1% N2 content followed by a plasma carburizing at low temperature. Moreover, duplex nitriding–carburizing leads to deeper hardening depths when compared to simply nitrided samples. •Duplex treatments of sintered iron combining plasma nitriding and plasma carburizing at 500 °C were investigated.•Low-temperature plasma postcarburizing develops a thin cementite layer over the iron nitrided surfaces.•Morphology and phase composition of the nitrided layer influence the properties of the nitrided–carburized layers.•Duplex treatments of nitriding-carburizing promote higher H/E when compared to the nitrided-only samples.•The postcarburizing thermal cycle induces an annealing effect on the nitride compound layer and the diffusion zone.
ISSN:0257-8972
1879-3347
DOI:10.1016/j.surfcoat.2019.07.068