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    Characteristics and high temperature wear behavior of chrome vanadium carbide composite coatings produced by thermo-reactive diffusion
    (Elsevier Science Sa, 2020) Gunen, Ali; Kalkandelen, Muge; Gok, Mustafa Sabri; Kanca, Erdogan; Kurt, Bulent; Karakas, Mustafa Serdar; Karahan, Ismail Hakki
    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.
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    Corrosion behaviour of borided AISI 304 austenitic stainless steel
    (Emerald Group Publishing Ltd, 2014) Gunen, Ali; Karakas, Mustafa Serdar; Kurt, Bulent; Calik, Adnan
    Purpose - The paper aims to clarify the effect of bonding on the corrosion behavior and mechanical properties of AISI 304 austenitic stainless steel. Design/methodology/approach - The commercially available steel was subjected to a bonding treatment with Ekabor III powders at temperatures of 1,223-1,273 K with bonding durations of 2-4 h. Microstructural characterization of the steel was carried out with optical microscopy, scanning electron microscopy and X-ray diffraction analyses. Static immersion corrosion tests were made using a 10 percent H2SO4 acid solution and salt spray tests were carried out in accord with the ASTM B-117 standard. Findings - Grain boundary precipitation of carbides was observed in the transition zone beneath the boride layers. The corrosion resistance of the steel against the acid solution increased to about seven times its untreated value with the bonding treatment. Research limitations/implications - The boride coating improved the corrosion resistance of the AISI 304 stainless steel against acidic media, but suffered from spalling in the salt spray test. Future work will focus on improving the adhesion between the coating and the substrate by changing the parameters for the bonding process. Practical implications - Pack bonding is a simple, environmentally friendly coating process and can be recommended for use in small and medium enterprises. The boride coatings deposited have potential in further improving the wear and corrosion resistance of stainless steels. Originality/value - The outcome of the research is of great importance for the industry using wear- and corrosion-resistant coatings.
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    The effect of process conditions in heat-assisted boronizing treatment on the tensile and bending strength characteristics of the AISI-304 austenitic stainless steel
    (Maik Nauka/Interperiodica/Springer, 2015) Gunen, Ali; Kurt, Bulent; Somunkiran, Ilyas; Kanca, Erdogan; Orhan, Nuri
    In this study, AISI 304 austenitic stainless steel surface was boronized with nanoboron and ekabor-III powders at 950 and 1000A degrees C for 2 and 4 hours period by solid-state box boronizing method. Then, behaviors of the boronized specimen in the microstructure, three-point bending, and tensile strength characteristics were investigated. As a result of the boriding process, the boride layer thickness in the range of 23-67 A mu m and microhardness value in the range of 1020-2200 HV have been obtained according to the increase in processing time and temperature and to the particle size of the boron source (0, 1). The coating layer on boronized specimens did not exhibit any sign of reaction caused by the tensile strength applied until the yield point was in both tests. Although the particle size of the boron agents was more effective on the boronized specimen's bending and tensile strength behaviors, it was observed that processing temperature and its duration are effective as well.
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    Effect of thermal degradation on the properties and wear behavior of Cr-V-C composite coatings grown on ductile iron
    (Elsevier Science Sa, 2021) Gunen, Ali; Kanca, Erdogan; Karakas, Mustafa Serdar; Gok, Mustafa Sabri; Kalkandelen, Muge; Kurt, Bulent; Cetin, Melik
    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.
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    The investigation of corrosion behavior of borided AISI 304 austenitic stainless steel with nanoboron powder
    (Maik Nauka/Interperiodica/Springer, 2014) Gunen, Ali; Kurt, Bulent; Orhan, Nuri; Kanca, Erdogan
    In this study, corrosion behavior and mechanical properties of AISI 304 austenitic stainless steel, which was borided with Nanoboron powder, was investigated. The commercially available steel was subjected to a boriding treatment with a size of 10-50 nm Nanoboron powders, at the temperatures of 1223 K to 1273 K with boriding durations of 2 to 4 h. Microstructure characterization of the steel was carried out with optical microscopy, scanning electron microscopy, microhardness and X-ray diffraction analyses. Corrosion tests were made by static immersion into a 10% H2SO4 acid solution and weight loss calculations as well as salt spray tests were carried out in accord with the ASTM B-117 standard. Boriding thermal treatment, increased the corrosion resistance of the steel against the acid solution, up to about 4.3 times while in the salt spray tests, weight loss corrosion resistance increased up to tier 2. However, anti-corrosion resistance decreased by 40%, its untreated value.
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    Properties and Corrosion Behavior of Chromium and Vanadium Carbide Composite Coatings Produced on Ductile Cast Iron by Thermoreactive Diffusion Technique
    (Asme, 2020) Gunen, Ali; Kalkandelen, Muge; Karahan, Ismail Hakki; Kurt, Bulent; Kanca, Erdogan; Gok, Mustafa Sabri; Karakas, 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.
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    Properties and Corrosion Resistance of AISI H13 Hot-Work Tool Steel with Borided B4C Powders
    (Korean Inst Metals Materials, 2020) Gunen, Ali; Karahan, Ismail Hakki; Karakas, Mustafa Serdar; Kurt, Bulent; Kanca, Yusuf; Cay, Vedat Veli; Yildiz, 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