Browsing by Author "Günen, Ali"

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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.
Citation - WoS: 37
Citation - Scopus: 38
Characteristics and High Temperature Wear Behavior of Chrome Vanadium Carbide Composite Coatings Produced by Thermo-Reactive Diffusion
(ELSEVIER SCIENCE SA, 2020) Günen, Ali; Kalkandelen, Müge; Gök, Mustafa Sabri; Kanca, Erdoğan; Kurt, Bülent; Karakaş, Mustafa Serdar; Çetin, Melik
In this study, Cr-V-C composite carbide layers were grown on the surface of a GGG-80 ductile iron using thermoreactive diffusion (TRD). The TRD process was carried out at temperatures of 900, 1000, and 1100 degrees C for 1 h using nano-sized Fe-V and Fe-Cr powders. The coatings were characterized by X-ray diffractometry (XRD), 2D profilometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), microhardness measurements, nanoindentation, and wear tests. The wear tests were performed on untreated and coated samples using a ball-on-disc type wear tester under 10 N load at four different temperatures (25 degrees C, 250 degrees C, 500 degrees C and 750 degrees C) against a 6-mm WC ball. Metallographic investigations revealed that the graphite nodules near the surface were dissolved as a result of the TRD process. Depending on the TRD process temperature, a coating with a thickness of 12-36 mu m, hardness of 24.14-31.38 GPa, and elastic modulus of 198-233 GPa was obtained. An increase in process temperature increased the thickness, hardness, and elastic modulus of the obtained Cr-V-C layers, which resulted in low friction coefficient values and decreased wear rates. Although all coated samples showed improved wear resistance in all wear test conditions, the wear rates were significantly increased at 750 degrees C due to flaking.
Citation - WoS: 54
Citation - Scopus: 59
Effect of the Boriding Environment on the Wear Response of Laser-Clad Alcocrfeni High Entropy Alloy Coatings
(Elsevier Science Sa, 2022) Günen, Ali; Lindner, T.; Karakas, M. S.; Kanca, E.; Toberling, G.; Vogt, S.; Lampke, T.
Laser-clad AlCrFeCoNi high entropy alloy (HEA) coatings, produced on the surface of AISI 316 L stainless steel, were pack-borided at 1000 ?C for 4 h in open air, high-purity Ar and vacuum environments. The HEA, which had an initial hardness of 6.14 +/- 2.06 GPa, formed a complex boride layer consisting of (CoFe)B-2, (CrFe)B(2 )and Cr(2)Ni(3)B(6 )phases on its surface, with hardness ranging from 15.95 +/- 0.7 to 20.15 +/- 4.50 GPa as a result of the boriding process. While the greatest boride layer thickness was obtained in the sample borided in vacuum, the highest surface hardness was obtained in the sample borided in air. The borided coatings showed improved wear resistance and lower friction values compared to the untreated control samples, both at 25 ?C and 650 ?C. The borided coatings also showed reduced coefficients of friction at 650 ?C. The wear losses at 650 ?C significantly exceeded those at 25 ?C.
Citation - WoS: 23
Citation - Scopus: 22
Effect of Thermal Degradation on the Properties and Wear Behavior of Cr-V Composite Coatings Grown on Ductile Iron
(ELSEVIER SCIENCE SA, 2021) Günen, Ali; Kanca, Erdoğan; Karakaş, Mustafa Serdar; Gök, Mustafa Sabri; Kalkandelen, Müge; Kurt, Bülent; Karahan, İsmail Hakkı
The thermal fatigue behavior of chromium vanadium carbide (Cr - V - C) coatings and the wear of the coatings after thermal fatigue cycling was studied. The Cr - V - C coatings were grown on the surface of a ductile iron using thermo-reactive diffusion (TRD) and subjected to thermal fatigue in the temperature range of 25 to 750 degrees C for up to 500 cycles. Characterizations were made using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, microhardness measurements and wear tests. The Cr - V - C coated samples displayed superior thermal fatigue and wear resistance compared to the untreated ductile iron, mainly due to the dissolution of graphite nodules in the vicinity of the surface during TRD. The dissolution of graphite reduced the possibility of failure initiating from graphite nodules and graphite-matrix interfaces. Increasing the number of cycles resulted in increased flaking and decreased wear resistance in both the Cr - V - C coatings as well as the untreated ductile iron. Although much of the Cr V C coating was lost (due to flaking) after thermal cycling, the absence of graphite near the surface still provided improved resistance to wear in the TRD-treated samples. The results of this study indicate that TRD coatings hold great promise for use in the industrial applications.
Citation - WoS: 47
Citation - Scopus: 49
Microstructural, Wear and Corrosion Characteristics of Boronized Aisi 904l Superaustenitic Stainless Steel
(PERGAMON-ELSEVIER SCIENCE LTD, 2021) Çetin, Melik; Günen, Ali; Kalkandelen, Müge; Karakaş, Mustafa Serdar
AISI 900 series stainless steels are considered as low-cost alternatives to nickel-based superalloys used for highly corrosive environments. However, in terms of mechanical properties, they have average strength and hardness similar to other austenitic stainless steel grades and this often limits their use. If a 900 series alloy were to be used under tribocorrosive conditions, its surface properties would have to be improved by a wear and corrosion resistant coating. In this study, AISI 904L steel was pack boronized in a solid medium at temperatures of 900, 1000 and 1100 ?C for 2, 4 and 6 h with nano-sized boronizing powders. The grown boride layers were evaluated using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometry, 2D profilometry, microhardness measurements, ball-on-disk type wear tests and electrochemical corrosion tests. Characterization studies revealed a complex boride layer consisting of FeB, Fe2B, CrB, Cr3B4, Ni3B and Mo2B phases with 2366?2396 HV hardness. Wear tests showed that the abrasive wear resistance of the AISI 904L steel was improved by up to 40 times. The corrosion resistance of boronized AISI 904L was inferior to untreated AISI 904L in 3.5% NaCl, but comparable to AISI 316L.
Citation - WoS: 47
Citation - Scopus: 51
Microstructure, Some Mechanical Properties and Tribocorrosion Wear Behavior of Boronized Al(0.07)co(1.26)cr(1.80)fe(1.42)mn1.35ni1.10 High Entropy Alloy
(ELSEVIER SCIENCE SA, 2021) Karakaş, Mustafa Serdar; Günen, Ali; Çarboğa, Cemal; Karaca, Yusuf; Demir, Mehmet; Altınay, Yasemin; Erdoğan, Azmi
High-entropy alloys (HEAs) with face-centered cubic (FCC) structures exhibit high toughness and corrosion resistance, but their average strengths and relatively low wear resistance can limit their engineering ap-plications. In this study, FCC Al0.07Co1.26Cr1.80Fe1.42Mn1.35Ni1.10 HEAs were boronized for 4 h at temperatures of 900, 950, and 1000 degrees C to form hard, protective metal borides on their surfaces. The microstructural characteristics of the borides formed were examined using X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mechanical properties of the boride layers were studied by nanoindentation measurements, and the tribological performances of the layers were evaluated by ball-on -disk type wear tests in air, 3.5% NaCl and 5% H2SO4. Irrespective of the boronizing temperature, (Fe0.4Mn0.6) B, (Cr0.4Mn0.6)B, (CoFe)B2 and Cr2Ni3B6 phases were detected in the surfaces of the boronized samples. The surface hardnesses of the boronized samples reached nearly ten times the hardness of the as-cast HEA. The borides were effective in reducing friction as well as wear. Increasing the boronizing temperature increased the thicknesses of the coatings and further improved wear characteristics. Wear rates in 5% H2SO4 were generally higher than the wear rates in 3.5% NaCl, but the highest wear rates were observed in air. (c) 2021 Elsevier B.V. All rights reserved.
Citation - WoS: 18
Citation - Scopus: 17
Pack-Boriding of Monel 400: Microstructural Characterization and Boriding Kinetics
(KOREAN INST METALS MATERIALS, 2022) Günen, Ali; Keddam, Mourad; Erdoğan, Azmi; Karakaş, Mustafa Serdar
Monel 400 was pack-borided in the temperature range of 1173-1273 K for exposure times of 2-6 h. The boride layers produced on the surface of the alloy were examined by scanning electron microscopy and phase identification was carried out by X-ray diffraction. The topmost layer on the borided Monel 400 was compact and contained the Ni2B phase while the diffusion zone contained grain boundary precipitates of borides. Boride layers of 35-290 mu m thickness and 1002-1476 HV0.025 hardness were obtained. SEM observations revealed a smooth interface between the boride layer and the diffusion zone. A kinetic model based on the integral method was applied to investigate the kinetics of Ni2B layer. The boron activation energy in the Ni2B layer was estimated as equal to 300.7 kJ mol(-1). An experimental validation of the model was made by comparing the experimental layer thicknesses obtained, after boriding at 1198 K for 1 and 3 h, with predicted values. [GRAPHICS] .
Citation - WoS: 28
Citation - Scopus: 31
Properties and Corrosion Behavior of Chromium and Vanadium Carbide Composite Coatings Produced on Ductile Cast Iron by Thermoreactive Diffusion Technique
(ASME, 2020) Günen, Ali; Kalkandelen, Müge; Karahan, İsmail Hakkı; Kurt, Bülent; Kanca, Erdoğan; Gök, Mustafa Sabri; Karakaş, Mustafa Serdar
Ductile iron (DI) owes many of its attractive mechanical properties to the graphite nodules in its structure. However, since galvanic coupling can occur between the graphite nodules and the matrix in aggressive environments, these nodules can, at the same time, reduce its corrosion resistance. In this study, composite carbide coatings were grown on the surface of GGG-80 using the thermoreactive diffusion (TRD) process. The process was carried out at 900, 1000, and 1100 degrees C for 1 h using nanosized Fe-V and Fe-Cr powders. The coatings were characterized by X-ray diffractometry (XRD), two-dimensional profilometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and microhardness tests. The corrosion behavior of the coatings were evaluated in three different solutions (3.5 wt% NaCl, 5 wt% H2SO4, and 5 wt% HNO3) using electrochemical open-circuit potential (OCP) and potentiodynamic polarization measurements. Microstructures and hardness tests showed that the nodular graphite in the surface was dissolved at the TRD process temperatures and that a coating of 12-36 mu m thickness and 2461-3200 HV0.05 hardness was obtained. The corrosion resistance of the composite coating was up to 10, 33.5, and 75 times higher than the uncoated GGG-80 in NaCl, H2SO4, and HNO3, respectively. The improvement in corrosion resistance was a direct result of the formation of complex carbides and the elimination of graphite nodules in the surface of the alloy.
Citation - WoS: 40
Citation - Scopus: 45
Properties and Corrosion Resistance of Aisi H13 Hot-Work Tool Steel With Borided B4c Powders
(KOREAN INST METALS MATERIALS, 2020) Günen, Ali; Karahan, İsmail Hakkı; Karakaş, Mustafa Serdar; Kurt, Bülent; Kanca, Yusuf; Çay, Vedat Veli; Yıldız, Murat
In this study, the surface of AISI H13 steel was borided with powder blends of B4C and NaBF(4)using the powder-pack method at 800, 900 and 1000 degrees C for 2, 4 and 6 h. The structural and mechanical characteristics of the boride layers formed on the surface were characterized using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, 2D surface profilometry, microhardness and electrochemical corrosion (3.5 wt% NaCl) tests. The boride layer exhibited a single phase structure (Fe2B) in samples coated at 800 degrees C and a dual-phase structure (FeB + Fe2B) at higher boriding temperatures (900 and 1000 degrees C). The boride layers were compact and crack-free in all boriding conditions. Depending on boriding parameters, the thickness, hardness and average surface roughness (R-a) of the coatings were found to range between 5.81 and 102.46 mu m, 1635-1915 HV and 0.315-0.650 mu m, respectively. The borided AISI H13 steel displayed up to 33.5 times and 2.4 times higher corrosion resistance than untreated AISI H13 steel and martensitic AISI 431 steel, respectively. This suggests potential use of borided AISI H13 steel in the steam turbines and marine applications as an alternative to the more costly martensitic and duplex stainless steel grades. The corrosion resistance depended on the phase structure (single- or dual-layer), density, thickness and surface roughness of the boride coatings. Graphic
Citation - WoS: 44
Citation - Scopus: 45
Wedm Machining of Monbtatizr Refractory High Entropy Alloy
(Elsevier, 2022) Günen, Ali; Ceritbinmez, Ferhat; Patel, Kunjal; Akhtar, Mst Alpona; Mukherjee, Sundeep; Kanca, Erdoğan; Karakaş, Mustafa Serdar
Refractory high entropy alloys (RHEAs) have shown great promise for a multitude of advanced engineering applications due to their high mechanical stability from cryogenic temperatures to 1600 degrees C. However, the low ductility they exhibit at room temperature limits their machinability when traditional machining techniques are used. Studies on the nontraditional machining of RHEAs, on the other hand, are very limited. In the present work, MoNbTaTiZr RHEAs subjected to wire electrical discharge machining (WEDM) were examined using electron microscopy, contact profilometry, and nanoindentation. Voids, microcracks, and recast material were observed on the machined surfaces. A transition from roughing to finishing decreased the amount of recast material, but the density of observable voids and microcracks on the surface increased. Optimal results were obtained by finishing, where the surface quality was improved by the removal of recast material remaining from prior passes. The brass wire electrode provided a smoother surface while the copper-core electrode provided minor heat-affected zone in the MoNbTaTiZr samples. In the roughing cuts, a 7.00% improvement in surface roughness was achieved using the copper-core electrode compared to the brass electrode. In the semi-finishing and finishing cuts, the brass wire electrode provided improvements of 13.68% and 22.68%, respectively, compared to the copper-core electrode. On the other hand, the wear of the brass electrode was as much as 20.98% higher than that of the copper-core electrode.(c) 2022 CIRP.