Browsing by Author "Varol, Temel"

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Development of Cutting Tools with Selective Laser Melting from Electroless Nickel-Coated Tungsten Carbide Powder Material
(Elsevier Sci Ltd, 2025) Erguder, Tevfik Oguzhan; Yildiz, Fatih; Guler, Onur; Sevim, Murat Ibrahim; Varol, Temel
This study was on whether cemented carbide tools could be produced using cheaper and more readily available Ni binder instead of expensive Co binder using selective laser melting, which is a new generation production method that can be easily produced in the desired design without losing scrap. The study determined the optimum laser manufacturing parameters for the production of Ni coated WC powder by electroless deposition using the selective laser melting (SLM) method and produced turning inserts with those parameters. Production of SLM-based turning inserts, including Ni-coated WC powder (WC-Ni), encountered some problems due to lack of binder. Pure Ni powders were added to Ni-coated WC powders (WC-Ni + Ni) to improve bonding which increased relative density, reduced surface roughness and resulted in similar to 95 % reduced wear rate. For optimum SLM conditions, the microhardness value was measured as 1879 +/- 130 HV0.3. The surfaces of the turning inserts produced by SLM were then ground. TiN coating was applied and the microhardness after coating was as 2002 +/- 174 HV0.3. After turning, the TiN-coated SLM insert had the lowest surface wear and performed very close to the conventionally manufactured insert.
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.
Effect of Titanium on the Structural, Mechanical and Surface Properties of CoCrFeMnNiTi High Entropy Alloy Fabricated by Selective Laser Melting
(Elsevier Science Ltd, 2024) Bulut, Caner; Yildiz, Fatih; Varol, Temel; Ergueder, Tevfik Oguzhan
In this study, the effect of titanium (Ti) on the microstructure, mechanical properties, wear resistance and corrosion behavior of CoCrFeMnNi high -entropy alloy (HEA) was examined. The selective laser melting (SLM) method was used to produce HEAs without Ti addition (HEA-1) and with Ti additions of 3 and 5 wt% (HEA-2 and HEA-3, respectively). While the HEA-1 sample exhibited a single-phase face -centered cubic (FCC) structure, the HEA-2 and HEA-3 samples exhibited intermetallic phase structures (Sigma and Laves) along with FCC. The addition of Ti and the presence of intermetallic phases in the HEA-2 sample revealed an improvement in mechanical properties without reducing the ductility value of the structure. However, in parallel with the increasing Ti ratio, the formation of more brittle intermetallic phases in the microstructure of the HEA-3 alloy caused a significant increase in strength but a decrease in ductility. Microstructural examinations revealed that all alloys had a cellular/dendritic structure and the relative densities of the samples were above 99%. While the ultimate tensile stress (UTS) of the HEA-1 sample was 548 MPa and the UTS of the HEA-3 alloy was 832.1 MPa, elongation values were obtained as 48% and 2%, respectively. HEA-2 sample exhibited more ideal results with an elongation value of approximately 22% and UTS values of 760.8 MPa. It was observed that the addition of Ti significantly increased the wear resistance in sliding conditions due to the increase in the hardness of the alloy. The highest hardness and lowest wear rate were obtained with HEA-3 coded samples. The HEA-1 sample exhibited the best corrosion rate, with higher corrosion potential (E corr ) and lower corrosion current density (I corr ) values. The highest corrosion rate was observed in the HEA-3 sample.
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 ?.
Effects of Selective Laser Melting Process Parameters on Structural, Mechanical, Tribological and Corrosion Properties of CoCrFeMnNi High Entropy Alloy
(Korean Institute of Metals and Materials, 2024) Bulut, Caner; Yildiz, Fatih; Varol, Temel; Kaya, Gurkan; Erguder, Tevfik Oguzhan
The structural, tribological, mechanical, corrosion, and other properties of materials produced by laser-based powder bed fusion additive manufacturing methods are significantly affected by production parameters and strategies. Therefore, understanding and controlling the effects of the parameters used in the manufacturing process on the material properties is extremely important for determining optimum production conditions and for saving time and materials. This study aimed to determine the optimal laser parameter values for CoCrFeMnNi high-entropy alloy powders using the selective laser melting (SLM) method. The layer thickness was kept constant during experimentation. 5 different laser powers and 10 varying laser scanning speeds were tested, with hatch spacing from 30 to 90%. After determining the optimal laser parameters for SLM, prismatic samples were fabricated in different build orientations (0 degrees, 45 degrees, and 90 degrees), and subsequently, their structural, mechanical, tribological, and corrosion properties were compared. Melt pool morphology could not be obtained at 20-40 and 60W laser powers and at all laser scanning speeds used at these laser powers. At 100 W laser power, 600 mm/s laser scanning speed, and 70% hatch spacing parameters, an ultimate tensile stress of 550 MPa and elongation of 48% were obtained. Among the samples produced in different build orientations, the sample produced with a 0 degrees build orientation exhibited the highest relative density (99.94%), the highest microhardness (201.2 HV0.1), the lowest friction coefficient (0.7025), and the lowest wear and corrosion rates (0.7875 mpy). Additionally, SLM parameters were evaluated to have a significant impact on the performance of all properties of the samples.
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.
Influence of Ti on Structure, Tribology, and Corrosion of Cocrfemnnitix High-Entropy Alloy
(Springer, 2026) Bulut, Caner; Yildiz, Fatih; Varol, Temel; Akcay, Serhat Berk; Erguder, Tevfik Oguzhan
In this study, high purity Co-Cr-Fe-Mn-Ni-Ti powders were produced by mechanical alloying, hot pressed at 650 MPa, and then sintered at 1000 degrees C for 2 h. The microstructural, mechanical, tribological, and corrosion properties of Ti-free (HEA-Ti-0-B), 3% Ti-added (HEA-Ti-3-B), and 5% Ti-added (HEA-Ti-5-B) high-entropy alloys (HEAs) were systematically investigated. The changes in the mass of the alloy powder materials were evaluated as a function of temperature and time using thermogravimetric analysis (TGA). At 850 degrees C, the HEA-Ti-0-P powders exhibited a mass gain of approximately 15.82%, while HEA-Ti-3-P and HEA-Ti-5-P showed increases of 26.83 and 28.55%, respectively. As confirmed by TGA, the increasing Ti content in the alloy powders led to a decrease in oxidation resistance. Microstructural analysis revealed that HEA-Ti-0-B exhibited a single-phase FCC structure, whereas Ti-containing alloys formed intermetallic phases. Porosity increased with Ti content, reaching 13.97% in HEA-Ti-5-B. Ti addition significantly enhanced mechanical performance, with HEA-Ti-5-B exhibiting the highest hardness (348.82 HB), a 32.2% improvement over HEA-Ti-0-B, alongside a 15.93% lower wear rate and 43.1% reduction in friction coefficient. However, in 3.5% NaCl medium, corrosion resistance decreased with increasing Ti addition and corrosion rates increased from 23.21 mpy (HEA-Ti-0-B) to 37.27 mpy (HEA-Ti-5-B). These findings highlight the trade-off between mechanical strength and electrochemical stability in Ti-containing HEAs.
Microstructure and Wear Characterization of Al2O3 Reinforced Silver Coated Copper Matrix Composites by Electroless Plating and Hot Pressing Methods
(Elsevier, 2021) Guler, Onur; Varol, Temel; Alver, Umit; Kaya, Gurkan; Yildiz, Fatih
Copper-based composites are frequently used in areas such as contacts, contactors, switches etc. where electrical conductivity and tribological properties play a critical. In this work, the microstructure, electrical and wear properties of silver plated copper powder matrix and Al2O3 reinforced composites fabricated by electroless silver plating (ESP) and hot pressing were investigated. Copper powders with different morphologies fabricated by mechanical milling (MM) were used as matrix while different Al2O3 contents (0.5 %, 1 %, 2 %, 3 % and 5 wt. %) were used as reinforcement materials for the production of composites. The results showed that the ESP layer on milled copper powders for 2 h was quite uniform and the Al2O3 distribution was better in these composites than others. The highest hardness value (similar to 125 HB) and the lowest wear rate (1.5E-04 mm(3)/Nm) were observed in composites including silver plated copper matrix powders and Al2O3 (3 wt. %). Although the electrical conductivity values decrease with increasing Al2O3 ratio for all composites, the decrease in electrical conductivity was only up to about 86 %IACS in composites where the highest hardness value was obtained. Besides, the dominant wear mechanism was abrasive wear with grooves and scratches while the lowest wear scar width (about 557 mu m) was observed in these composites.