Browsing by Author "Keleş, Ali"

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Effect of Aging Time on Phase Transformation, Microstructure and Hardness of Co-Cr Alloys
(2019) Yıldırım, Mehmet Serdar; Keleş, Ali; Bb, Aa,
The effect of heat-treatment on phase relationships, microstructures and hardness of CoCr-Mo alloys were investigated in detail. The samples were produced by investment casting techniqueand subsequently solutionized (1240 °C for 4 h) and aged (720 °C for 2, 4, 8 and 16 h). Phase analysis ofthe samples were performed via X-ray diffraction analysis, microstructural examination were done bylight optical and scanning electron microscopy. The microstructures of as-cast and short-time (2 and 4 h)aged samples were composed of FCC ?-Co matrix phase and fine M23C6 (where M= Co, Cr and Mo)precipitates. Increasing the aging time to 8 and 16 h led to partial transformation of FCC ?-Co matrixphase into HCP ?-Co phase. The volume fraction of ?-Co phase increased with increasing aging time.Moreover, hardness of the Co-Cr-Mo samples were significantly enhanced with formation of ?-Co phase.
Citation - WoS: 2
Effect of Alloying Elements and Technological Parameters of Austempering on the Structure and Mechanical Properties of Ductile Cast Iron (adi)
(SPRINGER, 2023) Keleş, Ali; Cengiz, Rabia; Yıldırım, Mehmet
The effect of additions of alloying elements (Mo and Ni), austempering time and thickness of the product section on the mechanical properties of industrial ductile iron of grade GGG-70 (EN-GJS-700-2) is studied. Standard keel blocks and crankshafts have been produced by static sand casting from unalloyed, alloyed with 0.2% Mo and 0.2% Mo + 0.6% Ni ductile iron. Austempering is carried out at 350 & DEG;C for 90, 120, 150, and 180 min in a salt bath. It is shown that the alloying has a significant effect on the ability of cast iron to austempering and its mechanical properties after heat treatment. Alloyed cast iron has the best combination of ultrahigh yield and tensile strength with high ductility. After austempering, crankshafts alloyed with 0.2% Mo + 0.6% Ni have a typical ductile iron ADI structure even in the thickest sections (58-mm-thick main bearing center) with a uniform hardness distribution.
Citation - WoS: 12
Citation - Scopus: 18
Improvement of Mechanical Properties by Means of Titanium Alloying To Steel Teeth Used in the Excavator
(ELSEVIER - DIVISION REED ELSEVIER INDIA PVT LTD, 2020) Keleş, Ali; Yıldırım, Mehmet
The effect of Ti addition (0.15 and 0.20 wt%) on mechanical properties and wear resistance of steel excavator bucket teeth was investigated. Teeth were produced by commercial sand casting technique. After production normalizing, hardening, and tempering heat treatment procedures were applied to the teeth. Lath martensitic microstructure was observed and small amount of carbide particles were present in the microstructures of Ti containing ones. In addition, small amount of hard and brittle TiN particles were observed in the microstructure of 0.20 wt% Ti containing teeth. The best mechanical properties were obtained for 0.15 wt% Ti containing teeth with considerably high abrasive wear resistance. However, 0.20 wt% Ti containing teeth exhibited worst abrasive wear resistance and limited ductility due to the formation of TiN particles. (c) 2019 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).