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    Characterizations and Kinetics of Refractory Niobium Carbide Coatings on AISI D3 Steel
    (Springer, 2023) Gunen, Ali; Acikgoz, Hasan Huseyin; Keddam, Mourad; Karahan, Ismail Hakki
    Niobium carbide (NbC) coatings were carried out by means of the thermo-reactive diffusion (TRD) on AISI D3 cold work tool steel, in the powder mixture composed of 25 wt.% ferro-niobium, 70 wt.% alumina and 7.5 wt.% ammonium chloride at 1173, 1273 and 1373 K for 2, 4 and 6 h. NbC coatings were inspected with scanning electron microscopy, x-ray diffractometer, Vickers micro-hardness testing. Homogeneous, crack-free and uniform NbC coatings with 8.75-17.10 mu m thickness and 1586-2263 HV0.025 hardness were obtained on AISI D3 steel by TRD process. The integral method-based model was used for studying the carbon diffusion by forming NbC coatings. The value of 45.93 kJ mol(-1) was determined as the necessary activation energy required for the niobizing process of AISI D3 steel.
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    Niobium Carbide Coatings Grown on Cold Work Tool Steel AISI D3 by Thermomechanical Processing: Characterization, Wear and Corrosion Behaviors
    (Maik Nauka/Interperiodica/Springer, 2023) Gunen, Ali; Acikgoz, Hasan Huseyin; Karahan, Ismail Hakki
    In this study, niobium carbide (NbC) coatings were grown on AISI D3 cold work tool steel via thermoreactive diffusion (TRD) at 900, 1000 and 1100 degrees C for 2, 4, and 6 h. The microstructures and phase formed, the surface roughnesses, the microhardness and fracture toughness values, and the wear and electrochemical corrosion behavior of the NbC coatings were investigated. Compact, smooth and crack-free NbC layers with 8.75-17.10 mu m thickness and 1558-2286 HV0.1 hardness were obtained on the surface of the AISI D3 steel. Depending on the TRD temperature and duration, the NbC coatings improved the wear resistance by up to 5 times and corrosion resistance up to 14 times compared to the untreated alloy. With increasing temperature and duration, the thickness and microhardness values of NbC coatings increased. However, significant changes in wear and corrosion resistance was observed depending on Nb, C, O and Fe contents of NbC coatings rather than thickness and microhardness. The wear resistance was found to depend on fracture toughness as well as hardness. Corrosion resistance depended mostly on the surface roughness and the defects (especially microcracks) present on the surface.
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    A RESPONSE SURFACE STUDY ON THE GROWN BEHAVIOR AND SOME MECHANICAL PROPERTIES OF NIOBIUM CARBIDE COATINGS
    (World Scientific Publ Co Pte Ltd, 2023) Gunen, Ali; Acikgoz, Hasan Huseyin; Cavdar, Faruk; Karahan, Ismail Hakki
    In this study, response surface methodology was used to examine the effects of temperature and time on the development of niobium carbide coatings on AISI D3 steel. The effect of niobizing temperature (900-1100(& LCIRC;)C) and period (2-6 hours) on coating thickness, hardness, fracture toughness, coefficient of friction and wear rates was investigated. ANOVA was conducted to analyze the experimental data, and it was observed that the coating thickness and microhardness increased with temperature and time. The response surfaces developed for fracture toughness, coefficient of friction and wear rates were found to exhibit a complex structure that is significantly influenced by temperature, time and their interactions. The correlation coefficients of the developed regression models range between 0.82 and 0.99. Using the empirical formulas obtained with these mathematical models, it is predicted that niobium carbide coatings can be obtained with the targeted properties more economically and practically with the thermochemical method.