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https://hdl.handle.net/20.500.12587/8840

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A single step synthesis by mechanical alloying and characterization of nanostructured Fe2B of high magnetic moment
(Elsevier Sci Ltd, 2021) Şimşek, Telem; Avar, Barış; Şimşek, Tuncay; Yıldız, Büşra; Chattopadhyay, Arun K.; Özcan, Şadan
This paper delineates a single-step production method of nanostructured diiron boride (Fe2B) and its structural, magnetic and magnetothermal properties. Structurally Fe2B resembles the tetragonal copper aluminide, CuAl2. The samples of nanostructured Fe2B were synthesized by milling Fe and B powders without any pre-treatment. Single phase Fe2B nanoparticles were successfully produced with the crystallite sizes of 68 and 46 nm after milling the powders for 10 h and 20 h, respectively. The saturation magnetization of the samples was found to decrease with increased milling time indicating that the surface spin disorder plays a crucial role in the magnetic properties. The highest saturation magnetization (Ms) of 141 emu/g with low coercivity (Hc) of 48 Oe was obtained for the 10 h milled sample of Fe2B, whereas the 20 h milled sample exhibited Ms and Hc as 129 emu/g and 149 Oe. This paper also presents a detailed information on the total and atom projected densities of state functions as well as the magnetic moment contribution of the individual atoms of Fe and B in Fe2B explaining the strong room temperature ferromagnetic properties contributed by the large number of unpaired 3 d electrons in Fe. The magnetothermal properties of the as-made Fe2B nanocrystals of high magnetic moment were investigated by measuring the rise in temperature as a function of time in the presence of AC magnetic fields. The magnetic Fe2B nanocrystals show significant thermal response with the high specific absorption rate of 172 W/g, demonstrating the advantages of using Fe2B nanocrystals for the application in magnetic fluid therapy for hyperthermia.
A critical review of the refractory high-entropy materials: RHEA alloys, composites, ceramics, additively manufactured RHEA alloys
(Elsevier, 2025) Güler, Seval Hale; Yakın, Alican; Güler, Ömer; Chattopadhyay, Arun K.; Şimşek, Tuncay
In this study, the traits, production methods, and applications of refractory high-entropy materials-including refractory high-entropy alloys (RHEAs), refractory high-entropy composites (RHE-Cs), and refractory high- entropy ceramics (RHE-Ce)-which are part of the broader category of refractory high-entropy materials with a wide range of applications, have been thoroughly examined and discussed. RHEAs have emerged as materials that exhibit superior properties, such as high melting temperatures, excellent temperature resistance, and high wear and corrosion resilience, in addition to high mechanical and fatigue strength. These attributes have made them extensively studied materials in recent times. The properties of RHEAs suggest their safe operation in challenging environments such as nuclear reactors, gas turbines, aerospace, and energy production. Among refractory materials, RHE-Cs stand out for their high strength and low density, showing significant potential for use in the automotive, aerospace, and space industries. Another group with a wide range of applications, RHE-Ce materials, is distinguished by their high-temperature resilience, high hardness, and low thermal conductivity, making them suitable for high-temperature environments. Refractory materials are generally fabricated using traditional techniques such as arc melting, powder metallurgy, and magnetron sputtering. In this study, along with traditional production methods, additive manufacturing techniques which have revolutionized the manufacturing field are discussed concerning their applications in refractory material production. Additive manufacturing methods enable the achievement of high temperatures and the production of homogeneous, single-phase solid solutions, making them suitable for fabricating refractory materials with high melting points.
A comparison of magnetic, structural and thermal properties of NiFeCoMo high entropy alloy produced by sequential mechanical alloying versus the alloy produced by conventional mechanical alloying
(Elsevier, 2021) Şimşek, Tuncay; Akgül, Şaban; Güler, Ömer; Özkul, İskender; Avar, Barış; Chattopadhyay, Arun K.; Canbay, Canan A.
The soft ferromagnetic materials are of great industrial importance for their applications in magnetic cores for transformers, electric motors, inductors, and generators. In recent years, the trend has been to use magnetic high entropy alloys (HEAs) owing to their superior magnetic properties compared to the conventional magnetic materials. In this study, the traditional magnetic materials, (NiFeCo)(95)Mo-5 and (NiFeCo)(90)Mo-10 produced by conventional mechanical alloying method, were compared with the NiFeCoMo high entropy alloy produced by the sequential mechanical alloying method. Unlike conventional mechanical alloying, NiFeCoMo HEA was produced by mechanical alloying using sequential additions of Co and Mo to the preformed Fe-Ni alloy. Besides its magnetic properties, the effect of Co and Mo on the overall characteristics of the alloy was also investigated. In 60 h milled samples of the (NiFeCo)(95)Mo-5 and (NiFeCo)(90)Mo-10 alloys, the crystallite sizes were estimated as 10.5 and 10.8 nm respectively, whereas the crystallite size for the NiFeCoMo HEA was 15 nm. The presence of Mo in the alloy induced the formation of lamellar or layered structures of the particles. During the sequential milling to form NiFeCoMo HEA, it was noticed that the addition of Co into the preformed Fe-Ni alloy increased the magnetic saturation value due to the formation of FeCoNi alloy phase. However, further addition of Mo into the FeCoNi alloy phase reduced the magnetic saturation value of NiFeCoMo alloy significantly. After 60 h of milling the magnetic saturation value was dropped from 102.48 emu/g for the NiFeCo alloy to 60.52 emu/g for the NiFeCoMo alloy.
Prediction of Surface Roughness considering Cutting Parameters and Humidity Condition in End Milling of Polyamide Materials
(Hindawi Ltd, 2018) Bozdemir, Mustafa
To know the impact of processing parameters of PA6G under different humidity conditions is important as it is vulnerable to humidity up to 7 %. This study investigated the effect of cutting parameters to surface roughness quality in wet and dry conditions. Artificial Neural Network (ANN) modeling is also developed with the obtained results from the experiments. Humidity condition, tool type, cutting speed, cutting rate, and depth of cutting parameters were used as input and average surface roughness value were used as output of the ANN model. Testing results showed that ANN can be used for prediction of average surface roughness.
The Effects of Humidity on Cast PA6G during Turning and Milling Machining
(Hindawi Ltd, 2017) Bozdemir, Mustafa
We compared the foundry PA6G samples in several dry and humid but different storage environments by processing them under the same cutting conditions such as progress rate (100, 120, 140, and 160 mm/min), cutting rate (90, 110, and 130 m/min), and cutting depth (1, 1.5, 2, 2.5, and 3 mm), in terms of formation of average surface roughness values. An improvement of 10.4% in average surface roughness was observed in the measurements performed after the milling process on the humid material and then the process was carried out under a dry condition. Degradation of about 14% in the average surface roughness was observed. The measurement was carried out after the samples were used inmilling measurement which was performed on the dry PA6G material that was kept in a humid environment. An improvement of 6.4% in average surface roughness was observed. The measurements were performed after CNC machines process was applied on humid and dried PA6G material. This difference between milling and turning procedures is caused by the workpiece losing its humidity in the turning machine due to the turning effect. It was noted that the processes performed on the CNC turning stand were less affected by the humidity factor.
Application of Genetic Algorithms (GA) for the Optimization of Riveted Joints
(Carl Hanser Verlag, 2013) Baskal, Tamer; Nursoy, Mustafa; Esme, Ugur; Kulekci, Mustafa Kemal
Genetic algorithms have an effective search technique in a predefined research space based on natural selection theory. They use the same combination of selection, recombination, and mutation to evolve a solution to a problem. In this study, it has been demonstrated how to determine the optimal diameter, sheet thickness, and sheet width in riveted joints by means of genetic algorithms (GA). In this study the optimization of objective function for the variables in predetermined limit ranges was applied. Since the algorithms developed by this way are based on a principle to find out the best within a range like genetic process, it is becoming possible to predict the most suitable values for riveted junction dimensions in the defined limit range. The algorithms were restrained considering rivet diameter, thickness and width of the sheet, shear strength, tensile strength, and tear hazard of the sheet.
Application of Genetic Algorithm (GA) for Optimum Design of Module, Shaft Diameter and Bearing for Bevel Gearbox
(Carl Hanser Verlag, 2012) Mendi, Faruk; Baskal, Tamer; Kulekci, Mustafa Kemal
In this study selection of optimum module, shaft diameter and rolling bearing for conical gear has been done using genetic algorithm (GA). GA, is a novel stochastic method of optimization. GAs are based on the principles of natural selection and evolutionary theory. Objective function was optimized for the design variables between determined boundary values. The GA was constrained by taking into account the power, moment, velocity, wall thickness and bearing distances. Tooth strength and surface crush were considered to be design constraints for module optimization. The other algorithm constraints are maximum bending and torsion moments for shaft optimization, and working life for bearing optimization.

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