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Öğe A comparative study on the effects of different thermochemical coating techniques on corrosion resistance of STKM-13A steel(Springer Boston, 2018) Günen, Ali; Kanca, Yusuf; Karahan, İsmail Hakkı; Karakaş, Mustafa Serdar; Gök, Mustafa Sabri; Kanca, Erdoğan; Çürük, AhmetThe corrosion resistances of three different thermochemical coatings (grown using titanizing, boriding, and borotitanizing treatments) applied to STKM-13A steel surfaces were investigated. The coatings were characterized using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, 2D profilometry, and microhardness experiments. The corrosion tests were conducted using both electrochemical and static immersion methods, in 3.5 pct NaCl and 40 pct HF acid solutions, respectively. The corrosion resistance of STKM-13A steel was enhanced after the coating process. The specimens were exposed to more corrosion in the HF solution than in the NaCl solution. The best corrosion resistance was obtained in the borotitanized and borided specimens immersed in the NaCl and HF solutions, respectively. The borided STKM-13A steel sample showed even less cumulative weight loss than Inconel 625 in the static immersion HF acid solution test. This suggests potential use of the borided STKM-13A steel in the uranium production units of nuclear power plants as an alternative to more costly alternatives such as Monel, Inconel, and Hastelloy. © 2018, The Minerals, Metals & Materials Society and ASM International.Öğe Frequency and voltage dependence of electric and dielectric properties of Au/TiO2/n-4H-SiC (metal-insulator-semiconductor) type Schottky barrier diodes(Institute of Physics Publishing, 2015) Erbilen Tanrıkulu, Esra; Yıldız, Dilber Esra; Günen, Ali; Altındal, ŞemsettinThe main electrical and dielectric properties of Au/TiO2/n-4H-SiC (MIS) type Schottky barrier diodes (SBDs) have been investigated as functions of frequency and applied bias voltage. We believe that the use of high dielectric interfacial layer between metal and semiconductor can improve the performance of Schottky diodes. From the experimental data, both electrical and dielectric parameters were found as strong function of frequency and applied bias voltage. The Fermi energy level (EF), the concentration of doping donor atoms (P), barrier height (?B) and series resistance (Rs) values were obtained from reverse and forward bias C-V characteristics. The changes in EF and ND with frequency are considerably low. Therefore, their values were taken at about constant. The real and imaginary parts of dielectric constant (??, ??), tangent loss (tan?), ac electrical conductivity (?ac), and real and imaginary parts of electric modulus (M? and M?) values were also obtained from reverse and forward bias C-V and G/?-V characteristics. In addition, the voltage dependent profiles of all these electrical and dielectric parameters were drawn for each frequency. These results confirmed that both electrical and dielectric properties of Au/TiO2/n-4H-SiC (MIS) type SBD are quite sensitive to both the frequency and applied bias voltage due to surface polarization, density distribution of interface traps (Dit), and interfacial layer. © 2015 The Royal Swedish Academy of Sciences.Öğe High temperature wear behavior of the surface-modified externally cooled rolls(Elsevier B.V., 2018) Günen, Ali; Kanca, Erdoğan; Karakaş, Mustafa Serdar; Koç, Vahdettin; Gök, Mustafa Sabri; Kanca, Yusuf; Çürük, Ahmet; Demir, MehmetExternally cooled rolls of a steel plant were coated using three different surface modification techniques, namely titanizing, boronizing and borotitanizing. The grown coatings were examined using optical microscopy, scanning electron microscopy, microhardness measurements, X-ray diffraction and Raman analysis. Depending on the coating technique, a wide range of coating thicknesses and microhardness values were obtained; the highest microhardness was obtained in the titanized sample, while the greatest coating thickness was obtained in the borotitanized sample. Wear tests were performed on the untreated and coated specimens using a ball-on-disc wear tester under two different loads (1 N, 3 N) at three different temperatures (25 °C, 250 °C, 450 °C). The average friction coefficient values decreased at elevated temperatures, and increased under increased load. Temperature had a significant effect on the wear mechanism. At room temperature the effective wear mechanism was delamination, while at 250 °C and 450 °C oxidative wear was observed. All of the surface modification treatments improved the wear resistance. The highest wear resistance was observed in the borotitanized sample. © 2018 Elsevier B.V.Öğe Properties and tribologic behavior of titanium carbide coatings on AISI D2 steel deposited by thermoreactive diffusion(Minerals, Metals and Materials Society, 2018) Kurt, Bülent; Günen, Ali; Kanca, Yusuf; Koç, Vahdettin; Gök, Mustafa Sabri; Kırar, Ersan; Askerov, KhangardashIn the present study, the metallographic, mechanical and tribologic behaviors of AISI D2 steel specimens coated with TiC through the titanizing process were investigated. The titanizing treatment was performed at the temperatures of 900°C, 1000°C or 1100°C for 1 h, 2 h or 3 h using a solid-state box thermoreactive diffusion technique. In all cases, the predominant phase in the coating was TiC, but the mechanical properties of the coating varied with treatment condition. The wear resistance of the coated samples against a linear reciprocating Al2O3 ball improved as the hardness and thickness of the coating increased. The effective wear mechanism of samples that had been treated at 900°C, 1000°C and 1100°C were severe plastic deformation, delamination and polishing type wear, respectively. The wear performance was affected by coating layer’s thickness and uniformity as well as its surface hardness, elastic modulus and toughness. © 2018, The Minerals, Metals & Materials Society.
