Browsing by Author "Akcay, Serhatcan Berk"

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The Effect of Milling Time and Hot-Pressing on the Structural Properties and Wear Behavior of CoCrFeMnNi High-Entropy Alloys Fabricated by Mechanical Alloying
(Springer, 2024) Bulut, Caner; Yildiz, Fatih; Varol, Temel; Akcay, Serhatcan Berk; Erguder, Tevfik Oguzhan
In this work, CoCrFeMnNi high-entropy alloys (HEAs) were fabricated by mechanical alloying and hot-pressing-assisted powder metallurgy method. For HEA powders, the effect of milling time on the morphology, particle size, crystallite structure and oxidation resistance of the HEA particles was studied. For sintered HEAs, effects of milling time and hot-pressing on the microstructure evolution, density, hardness, friction coefficient, wear rate and surface roughness of CoCrFeMnNi HEAs were investigated. Milling the particles for 5 h resulted in further cold welding of the initial particles and the formation of many coarse and cold-welded particles. The particle-size distribution obtained after 5 h of milling was single peaked and had a relatively narrow distribution range. An increase in oxidation resistance with increasing milling time was observed due to the embedding of hard and highly oxidation-resistant particles such as Co, Cr and Ni into ductile Fe particles. The CoCrFeMnNi alloy produced with 5 h of milling and at 650 MPa pressure had the highest relative density with 86.29%, while the sample fabricated with 0.5 h of milling and 550 MPa pressure showed the lowest relative density with 77.34%. The lowest wear rate was obtained in the sample produced with 5 h of milling and at 650 MPa. At the same time, the lowest average coefficient of friction was obtained as approximately 0.28 for the sample produced under these conditions.
The Effect of Selective Laser Melting Process on the Microstructure, Density, and Electrical Conductivity of Silver-Coated Copper Cores
(Springer, 2021) Varol, Temel; Hacisalihoglu, Ilyas; Kaya, Gurkan; Guler, Onur; Yildiz, Fatih; Aksa, Huseyin Can; Akcay, Serhatcan Berk
In this study, compact materials were fabricated by selective laser melting (SLM) method using copper-silver core-shell particles obtained by electroless coating method. The effect of SLM parameters such as laser power, scanning speed and hatch spacing on the important properties such as microstructure, density and electrical conductivity of compacts produced from core-shell particles was investigated. This study significantly contributes to the fact that the parameters used in the fabrication of copper-silver-based materials with the SLM method directly affect the properties of the compacts. The results showed that the silver shell thickness obtained on the core of copper powders by electroless plating method varied between 1 and 3 mu m and was distributed homogeneously. It was also found that the highest apparent density value among all samples was obtained above about 99% from the sample where 100 W power, 250 mm/s scanning speed and 45% hatch spacing values were used. In addition the highest electrical conductivity value was obtained for these conditions.
Effects of Fabrication Parameters and Post-Processing Treatments on the Mechanical and Tribological Behavior of Surface-Enhanced Copper Based Materials by Selective Laser Melting
(Elsevier Science Sa, 2022) Aksa, Huseyin Can; Hacisalihoglu, Ilyas; Yildiz, Fatih; Varol, Temel; Guler, Onur; Kaya, Gurkan; Akcay, Serhatcan Berk
Selective laser melting (SLM), which is an advanced manufacturing method developed in recent years, produces parts with complex shapes and critical dimensions using metallic powder and laser beam. In this study, copper based conductive materials with silver networks were fabricated by electroless silver coating and SLM. The effects of laser power, scanning speed, hatch spacing, build orientation and post treatments on the mechanical and tribological properties of SLM compacts manufactured from core-shell particles were investigated. After the mechanical tests, higher stress and elongation values were obtained in the sample positioned horizontally on the build platform with a laser power of 100 W, scanning speed of 250 mm/s and hatch spacing value of 45%. After that SLM process, the post-processes were applied to the samples and the physical and mechanical properties improved significantly. The highest density value was obtained by the rolling process at 900 ?, and an increase of approximately 35.6% was obtained compared to the sample without post-processing. The lowest wear rate among all samples was obtained in the hot-pressing process at 750 ?.
Influence of Post Processing on the Mechanical Properties and Wear Behavior of Selective Laser Melted Co-Cr Alloys
(Elsevier Sci Ltd, 2024) Varol, Temel; Aksa, Huseyin Can; Yildiz, Fatih; Akcay, Serhatcan Berk; Kaya, Gurkan; Beder, Murat
In the study, the effect of laser energy density and post-processes (sintering, cold rolling, and hot rolling) on the properties of Co-Cr-Mo-W alloys fabricated by selective laser melting (SLM) are investigated. The samples are fabricated at 83, 125, and 167 J/mm3 of laser energy density to compare their properties. XRD results show that the samples in which epsilon-Co martensitic phase dominates gamma-Co phase are the samples exposed to hot rolling. The highest hardness values obtained with the hot rolling applied after SLM. The hardness for SLM1hr, SLM2hr and SLM3hr is 489.2, 500.4 and 509.8 HV, respectively. The lowest wear rate values are also obtained after the hot rolling post-process, where the highest hardness values and lowest average COFs were obtained.