Browsing by Author "Lindner, Thomas"

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Citation - WoS: 22
Citation - Scopus: 22
Boriding of Laser-Clad Inconel 718 Coatings for Enhanced Wear Resistance
(Mdpi, 2021) Lindner, Thomas; Günen, Ali; Toeberling, Gerd; Vogt, Sabrina; Karakaş, Mustafa Serdar; Loebel, Martin; Lampke, Thomas
Nickel-based superalloys are particularly suitable for applications under corrosive conditions. Economic advantages can be achieved by limiting the use of materials to the surface region. Furthermore, the tribological property profile can be significantly improved by surface hardening. In the present study, the possibility of a process combination comprising a coating and a surface hardening technology was investigated. For this purpose, Inconel 718 coatings were applied to austenitic stainless steel by laser cladding. Subsequently, a thermochemical surface hardening by boriding was carried out. Scanning electron microscopic (SEM) examinations were performed to evaluate the microstructure. The phase composition was determined by means of X-ray diffraction (XRD) for the different states of the coating system. The influence of thermochemical hardening was investigated for different wear conditions. The increase in microhardness and wear resistance clearly demonstrates the utilization potential of the presented process combination.
Effect of Vibratory Peening Pretreatment on Boriding Kinetics of Hadfield Steel by Taylor Expansion Model
(Elsevier Science S.A., 2025) Gunen, Ali; Lindner, Thomas; Karakas, Mustafa Serdar; Unal, Okan; Keddam, Mourad; Malachowska, Aleksandra; Lampke, Thomas
X120Mn12 high-manganese steel is widely used for its excellent toughness, yet its limited wear resistance under low-impact conditions necessitates surface enhancement. While boronizing improves surface hardness, the role of vibratory peening pretreatment (VPP) in influencing boride layer growth remains underexplored. In this study, the influence of VPP on the boronizing kinetics of X120Mn12 austenitic manganese steel was systematically evaluated. VPP was conducted at 50 Hz with a 5 mm amplitude, using 3 mm diameter AISI 52100 bearing balls (approximate to 58 HRC) for 2 h. Subsequent pack boronizing was performed at temperatures of 1023 K, 1173 K, and 1323 K for durations of 1, 3, and 5 h. Microstructural analysis revealed that peening induced significant near-surface plastic deformation to a depth of approximately 150 mu m, resulting in a 12 % reduction in grain size and a two-fold increase in surface hardness. The boride layer thickness ranged from 13.63 to 193.15 mu m, with microhardness values ranging from 984 to 1741 HV0.1 in peened specimens, compared to 11.89-180.89 mu m and 898-1720 HV0.1 in the as-cast counterparts. Enhanced dislocation density and vacancy formation decreased the boron activation energy, which was determined using a Taylor-expansion diffusion model, yielding values of 150.53 kJ center dot mol- 1 for the peened samples and 155.72 kJ center dot mol- 1 for the as-cast samples. These findings demonstrate that VPP effectively refines the microstructure and accelerates boron diffusion by generating high-density defect structures.