Investigations to the mechanisms of the layer formation using gas nitriding on remelted ledeburitic surfaces of unalloyed cast irons
Metallurgical, Thermal and Thermomechanical Treatment of Materials
Final Report Abstract
As part of the second continuation project (UmNiGu-III), investigations were conducted into the depth-dependent wear and corrosion behavior of combined-treated cast iron surface layers. Based on the insights into the specific nitriding mechanism, suitable alloy compositions and nitriding parameters were selected to deliberately vary the phase composition and distribution of the compound layers. The following target layers/boundary conditions were generated: I. εrich; II. γ′-rich; III. ε/γ′ in a lateral arrangement; IV. γ′/ε in a horizontal arrangement. After an in-depth examination of the properties of these target layers, the depth-dependent tribological behavior was investigated using a ball-on-plate model wear test, and the corrosive behavior was studied via potentiodynamic polarization measurements in 5% NaCl solution (using material removal methods). Four removal planes were located within the compound layer, and one at approximately half the diffusion layer thickness. The wear and corrosion behavior of the first removal plane, that is, the near-surface compound layer, is mainly determined by the porosity. Larger pore accumulations lead to a deterioration of wear and corrosion resistance and should be removed by polishing the surface after nitriding. Within the compound layer, the stress behavior is significantly influenced by the proportions and types of nitrides. Single-phase ε-nitride layers exhibit the best properties under corrosive stress. To achieve optimal friction and wear properties in the abrasive ball-on-plate wear test, a homogeneous hardness distribution within the compound layer has proven advantageous. This is present in a compound layer of ε/γ′ in a lateral arrangement. As a result, for each prevailing load case, a suitable layer structure was identified, and practical guidelines for the alloy design of the cast iron material, the nitriding process, and the posttreatment were derived.
Publications
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Potenziale und Grenzen kombinierter Randschichtbehandlungstechnologien in Verbindung mit einer Fest-/Flüssigphasen-Randschichtbehandlung mittels energiereicher Strahlverfahren für Gusseisenwerkstoffe. Habilitation. TU Bergakademie Freiberg. In: Freiberger Forschungshefte, B390 Werkstoffwissenschaft, 1. Aufl., ISBN 978-3-86012-655-4.
Buchwalder, Anja
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Effect of a surface treatment consisting of electron beam remelting and gas nitriding on the corrosion resistance of cast iron. Materials and Corrosion, 75(3), 386-397.
Holst, Anja; Biermann, Horst & Buchwalder, Anja
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Untersuchungen zum Schichtbildungsmechanismus beim Gasnitrieren von umgeschmolzenen ledeburitischen Randschichten auf unlegierten Gusseisenwerkstoffen. In: Festschrift 50 Jahre Institut und Studienrichtung Werkstofftechnik, S. 20-21.
Holst, Anja; Biermann, Horst & Buchwalder, Anja
