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    Diffusion welding of stainless steel 304L/Monel K-500 composite materials produced with different methods
    (SAGE Publications Ltd, 2020) Kejanli, Haluk
    The stainless steel 304L (commercially supplied) and Monel K-500 that was prepared through cold pressing of metal matrix composite materials powder mixtures were joined by diffusion welding. Welding was performed under uniaxial compression using the 50 µm-thick nickel (Ni) and aluminum (Al) 2024 interlayers under 3 MPa at 950–980°C for 60 min in an argon gas atmosphere. After welding, the diffusion and intermediate zones of the samples were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive spectrometry analysis. As evaluating the diffusion zone with interlayer, it was determined that different interlayers expanded due to increasing temperature of the diffusion area. Interlayers expanded more on the K-500 side and relatively less on the 304L side. On the other hand, when samples with Ni interlayers were examined, high amount of Ni contained by both base material (304L) and interlayer led to the formation of rich Ni phases in the diffusion side. The brittle FeNi, Fe3Ni2, CuNi, Cu9Si, Cu0,81Ni0,19, Fe0,64Ni0,36, CrNi, Cr2Ni3, FeNi3, FeCu4, and Al0.71Cr0.3Fe17.65, which were identified to form irregularity in the diffusion zone. These intermetallic phases increased the hardness and significantly decreased the ductility of different material couples joined by diffusion welding. As a result, the microhardness and lap shear tests were applied to specimens to characterize the mechanical properties of the joint zones. The maximum hardness and maximum lap shear values were obtained at joint that made with the Al interlayer at 980°C as 432.8 HV and 165 MPa.
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    Effects on Mechanical and Physical Properties of Ta Element Addition to Ti-6Al-7Nb Alloy
    (Springer, 2024) Caligulu, Ugur; Durmus, Hulya; Kejanli, Haluk; Keskinkilic, Ali Riza; Balci, Esra
    Ti and its alloys play a leading role in biomedical applications within the field of materials science. In this study, different amounts of Ta were added to the TiAlNb alloy. Various analyses were carried out to determine the physical and chemical properties of the produced samples. DSC (differential scanning calorimetry), and XRD (X-ray diffraction) analyses were conducted to determine the phase transformations and crystal structure of the alloys, respectively. SEM-EDX (scanning electron microscopy) and OM (optical microscopy) images were taken to analyze the chemical structure of the samples and to examine their microstructures in more detail. Microhardness and wear resistance tests were performed to determine some mechanical properties of the produced samples. It was observed that increasing the tantalum content increased both hardness and wear resistance. These findings suggest that the addition of tantalum to the Ti-6Al-7Nb alloy could be an effective strategy to improve biomaterial performance.
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    Interface characterization of CO2 laser welded austenitic stainless steel and low carbon steel couple
    (Emerald Group Publishing Ltd, 2012) Caligulu, Ugur; Taskin, Mustafa; Kejanli, Haluk; Orhan, Ayhan
    Purpose - The purpose of this paper is to investigate interface characterization of CO2 laser welded AISI 304 austenitic stainless steel and AISI 1010 low carbon steel couple. Laser welding experiments were carried under argon and helium atmospheres at 2000, 2250 and 2500 W heat inputs and 200-300 cm/min welding speeds. Design/methodology/approach - The microstructures of the welded joints and the heat affected zones (HAZ) were examined by optical microscopy, SEM, EDS and X-Ray analysis. The tensile strength of the welded joints was measured. Findings - The result of this study indicated that the width of welding zone and HAZ became much thinner depending on the increased welding speed. On the other hand, this width widened depending on the increased heat input. Tensile strength values also confirmed this result. The best properties were observed at the specimens welded under helium atmosphere, at 2500 W heat input and at 200 cm/min welding speed. Originality/value - There are many reports which deal with the shape and solidification structure of the fusion zone of laser beam welds in relation to different laser parameters. However, the effect of all influencing factors of laser welding has up to now not been extensively researched. Much work is required for understanding the combined effect of laser parameters on the shape and microstructure of the fusion zone. This paper, therefore, is concerned with laser power, welding speed, defocusing distance and type of shielding gas and their effects on the fusion zone shape and final solidification structure of some stainless steels.
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    AN INTRODUCTION TO RADIOGRAPHY EXAMINATION METHOD IN THE INSTRUCTION ON WELDING
    (Int Council Materials Education, 2020) Kejanli, Haluk; Gur, Ali Kaya; Turkmen, Mustafa; Caligulu, Ugur
    The radiography examination method is used to detect defects both inside and on the surface in the weld seams in metals and alloys. We describe the radiography examination method for instructional purposes. We provide an example of radiographic testing of AISI 1010 steel + copper materials welded by friction welding in a direct-drive type friction-welding machine. The subsequent radiographic testing shows that such a pair can be welded with adequate strength via the friction welding technique. The amount of flash increases in all specimens with increasing rotational speed, friction pressure, and forging pressure. On the other hand, as friction time increased, the amount of flash decreases.
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    Surface morphology and optical properties of Ca and Mn doped TiO2 nano-structured thin films
    (Elsevier B.V., 2021) Çalıgülü, Uǧur; Darcan, Nida; Kejanli, Haluk
    This study was conducted to investigate the impact of Calcium (Ca) and Manganese (Mn) dopants on the optical and surface properties of Titanium dioxide (TiO2) nanomaterial. Ca and Mn doped TiO2 thin films were fabricated by sol–gel spin-coating method. By keeping the doping ratio of Ca constant, Mn was doped at the ratios of 1, 3, and 5%. The morphological, structural and optical properties of the fabricated samples were taken by Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM), Energy Dispersive X-Ray Analysis (EDX), X-Ray Diffraction Method (XRD) and UV–VIS spectroscopy. AFM and SEM analysis revealed that the morphological properties of TiO2 changed depending on the increase in doping ratio of Mn. XRD values obtained from the samples showed that the increases of crystallite size with manganese ions doping into the TiO2 the optical band gap of the samples increased with Ca and Mn dopants. As a result of the investigations, it was determined that Mn doping has significant effects on the morphological and optical properties of TiO2 films and the produced samples can be used in transparent conductive electrode applications, optoelectronic devices, and sensor production.
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    Transient liquid phase (tlp) diffusion bonding of Ti45Ni49Cu6 P/M components using Cu interlayer
    (Springer London Ltd, 2009) Kejanli, Haluk; Taskin, Mustafa; Kolukisa, Sedat; Topuz, Polat
    In this study, transient liquid phase diffusion bonding parameters of Ti45Ni49Cu6 P/M components using copper interlayer were experimentally investigated in a protective (argon) atmosphere. Bonding processes of sintered Ti45Ni49Cu6 P/M compacts were carried out at various temperatures and bonding periods while bonding pressure was kept unchanged. The process pressure, 20 MPa, was selected just below those which would cause macro deformations. Optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy were employed for microstructure examinations. Shear strength and hardness (HB) of bonded specimens were measured at bond interface and parent materials for mechanical property evaluations. Along the bond interface, copper, titanium, and nickel atom mutual migration was observed. Structural tests, metallographic analysis have shown the integrity of the diffusion bonded hardware, bonded between 940 and 970A degrees C process temperatures, for 40-60-min bonding periods.