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    Aging Effect on Microstructure and Machinability of Corrax Steel
    (Eos Assoc, 2020) Guldibi, Ahmet Serdar; Demir, Halil
    In this paper, the influence of the aging process on the microstructure and machinability of Corrax Steel was investigated for four samples: a solution heat-treated (A0) and three samples aged at 400 degrees C (A4), 525 degrees C (A5.25) and 600 degrees C (A6) for four hours. The effect of aging temperature on hardness was examined. Machining tests were carried out using a CNC lathe with a multi-layer coated PVD (AlTiN) cutting tool, at various cutting speeds (50, 100, 150, 200, 250, 300, 350m/min) with constant feed rate (0.1mm/rev) and 1mm constant cutting depth. The microstructure was investigated using an optical microscope and EDS attached SEM. The effect of aging on reverted austenite formation was also evaluated. In order to understand the changes in surface topology, cutting forces and vibrations were measured. With increasing aging temperature, the lath martensite was transformed to plate martensite because of the formation of precipitates and reverted austenite. Aging at different temperatures increased hardness up to 58%, cutting forces up to 117% and surface roughness up to 450%. The results describe the effect of the aging treatment on cutting forces, surface topology, tool wear and vibrations.
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    A comparative study on the machinability of ?-type novel Ti29Nb13Ta4.6Zr (TNTZ) biomedical alloys under micro-milling operation
    (Elsevier Sci Ltd, 2023) Aslantas, Kubilay; Demir, Bilge; Guldibi, Ahmet Serdar; Niinomi, Mitsuo; Dikici, Burak
    beta-type Ti29Nb13Ta4.6Zr (TNTZ) alloy is a new-generation alloy that does not contain toxic/allergic elements. The alloys have low Young's modulus (-60 GPa) close to the cortical bone, providing excellent biocompatibility over familiar commercial CP Ti or Ti6Al4V ELI. Different macro/micro-machining methods can be used to obtain the final shape of Ti alloys and impact on the implant's bio ecosystem and performance. This study compared the micro-mill machining performance of the TNTZ alloys with commercial CP Ti and Ti6Al4V ELI. Machining ex-periments were performed under similar and different cutting speeds and constant feed rate conditions. In the study, cutting forces, surface roughness, burr size and tool wear were obtained. The results showed that the Fx cutting forces for TNTZ are about 3 and 2 times higher than for CP Ti and Ti6Al4V alloys, respectively. Depending on the increasing cutting distance, the surface roughness of CP Ti and Ti6Al4V materials followed a similar trend. However, the surface roughness values for TNTZ alloy are higher and decrease with increasing cutting distance. Burr widths for CP Ti and Ti6Al4V are similar, but the milling direction at which maximum burr occurs varies. In the TNTZ alloy, the burr width is about 3 times higher, and the burr occurred inside the slot, not at the edge of the machined slot. The predominant type of damage in milling Ti6Al4V and CP Ti materials is abrasive and adhesive. The dominant damage type in TNTZ alloy is chipping. Increasing the number of revolutions in TNTZ causes the cutting forces and burr width to increase.
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    Effects of compaction pressure on microstructure, mechanical properties, and machining characteristics of sintered AISI 316L steel
    (Walter De Gruyter Gmbh, 2024) Erden, Mehmet Akif; Koklu, Ugur; Guldibi, Ahmet Serdar; Elitas, Muhammed
    In this study, the effect of compaction pressure on the properties of AISI 316L and its machining performance was evaluated. AISI 316L powders were subjected to three different compaction pressures (550, 650, and 750 MPa). Subsequently, the samples were sintered in an argon atmosphere at a constant temperature of 1523.15 K. The microstructure, hardness, and mechanical properties of the materials were investigated. To examine the effect of compaction pressure on drilling characteristics (thrust force, torque, surface roughness, chip formation, and burr formation), the samples were subjected to dry drilling at different feed rates and cutting speeds. It was observed that increasing the compaction pressure resulted in smaller grain sizes in the microstructure, increased hardness, and higher tensile strength. Higher compaction pressure led to higher thrust force and torque, whereas lower compaction pressure resulted in improved hole surface quality and shorter chips. Additionally, at higher cutting speeds, the color of the chips changed due to the elevated temperatures associated with increased cutting speeds.