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    The Effect of Mn and Ti Ratio on Microstructure and Mechanical and Machinability Properties of 316 L Stainless Steel Used in Biomedical Applications
    (Mdpi, 2023) Turkmen, Mustafa; Tanouz, Alla Muhammed; Akgun, Mahir; Erden, Mehmet Akif
    In this study, titanium (Ti) and manganese (Mn) element powders in determined amounts (0.35-0.75 and 1.5 wt %) were added into the 316 L stainless steel matrix by means of powder metallurgy (PM) technology, either individually or in pairs, and the desired composition was obtained as a powder mixture. The powders used in the study were cold-pressed tensile sample molds prepared in ASTM E8M standards, unidirectionally cold-pressed under 750 MPa compression pressure and formed into blocks. After pressing, the raw strength samples were sintered in an atmosphere-controlled tube furnace at 1250 degrees C for two hours in an argon atmosphere. The microstructure and mechanical properties of the produced PM steels were characterized using an optical microscope, SEM, EDS, tensile test, and hardness test. The results showed that the stainless steel samples with 0.35 (Ti and Mn) added to 316 L stainless steel had the highest yield strength, tensile strengths, and hardness strengths. However, with the addition of 0.75-1.5 Ti, 0.75-1.5 Mn and 0.75-1.5 (Ti and Mn) to 316 L stainless steel, a decrease was observed in the mechanical properties. Moreover, the stainless steel sample with 0.35 (Ti and Mn) added to 316 L stainless steel is better than other samples in terms of surface quality.
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    Effect of Mo addition on microstructure, mechanical and machinability properties of Cr-PM steels
    (Sage Publications Ltd, 2022) Erden, Mehmet A.; Akgun, Mahir
    In this work, it was investigated the effect of molybdenum (Mo) addition on machinability, mechanical properties, and microstructure of Cr steels produced by using powder metallurgy method. Tensile and hardness experiments were applied to define the mechanical properties of the produced Cr-PM steels. The machining experiments have been also performed without coolant on a CNC vertical machining center at three different cutting speeds (150, 210, and 270 m/min), two different feed rates (0.4 and 0.8 mm/tooth), and constant depth of cut (0.5 mm). The machinability of the alloys was evaluated in regard to surface roughness (Ra) and tool wear (Vb). The results indicated that that Cr-PM steel with 5% Mo addition by weight had the highest yield, tensile strength, and hardness, and the best surface quality was obtained in this sample in terms of surface roughness. However, according to Vb measurement results, the cutting performance of the cutting inserts wasnegative affected by MoC(N), CrC(N), and MoCrC(N) precipitates formed in the microstructure of PM steel.
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    Evaluation of the effect of hot forging and cooling conditions on the microstructure, hardness and machinability of medium carbon DIN 41Cr4 steel
    (Gazi Univ, Fac Engineering Architecture, 2023) Ozlu, Baris; Akgun, Mahir; Demir, Halil
    This work DIN 41Cr4 tempered steel of hot forging applied focuses on the investigation of machinability of samples obtained by cooling in sand and air. The machinability evaluation has made in terms of main cutting force (Fc) and surface roughness (Ra). DIN 41Cr4 original material (OM), sand (SC) and air cooling (AC) samples has investigate microstructure and hardness changes. Turning experiments carried out at five different cutting speeds, four different feed rates and depth of cut. As a result, it has seen that the cooling environment of the samples after hot forging has a significant effect on the hardness and microstructure. The lowest main Fc was 131.54 N in the OM, while the highest Fc was 337.49 N in the AC sample in the turning of the samples. Evaluated in terms of Ra, the lowest Ra was obtained as 0.505 mu m in the AC sample, while the highest Ra was obtained as OM 1.793 mu m. It has been observed that the main Fc increases, while the Ra somewhat decreases depending on the increase in hardness and decrease in grain size. In general, SEM examinations, it has been seen that built-up edge (BUE) and breaks occurred in the cutting tools.
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    Evaluation of the mechanical properties and machinability of chromium and molybdenum-added powder metallurgy steels
    (Sage Publications Ltd, 2024) Vassouf, Abdul Rahman; Akgun, Mahir; Erden, Mehmet Akif
    The present study focuses on the microstructure, mechanical properties, and machining aspects of powder metallurgy (PM) steel containing different rates of chromium (Cr) and molybdenum (Mo). PM steel alloys were pressed at 700 MPa and sintered at 1400 degrees C in a mixture of nitrogen and hydrogen atmosphere for 1 hour. While the precipitates and fracture surfaces of the samples obtained were examined by scanning electron microscope (SEM) and EDS analyzes, the grain size and phase distributions were also examined with an optical microscope. Moreover, tensile and hardness measurement tests were carried out to determine the mechanical properties of the samples with different ratios of Cr and Mo content. The milling experiments were also performed without using coolant in a CNC milling machine at different cutting parameters. The surface roughness (Ra), tool wear (Vb), and wear mechanism were investigated under these conditions. The outcomes of this study reveal that the yield and tensile strength values of the samples with the addition of Cr and Mo increased but the elongation value decreased. The results also stated that the most effective process parameter for both Vb and Ra was the workpiece material and the regression models developed to estimate the output parameters (Vb and Ra) give successful results with high determination coefficients (R-2) of 98.05% and 98.11%, respectively.
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    Influence of Ti and Nb addition on the microstructure, mechanical, and machinability properties of 316L stainless steel fabricated by powder metallurgy
    (Walter De Gruyter Gmbh, 2023) Erden, Mehmet Akif; Uzun, Fatma Gul; Akgun, Mahir; Gokce, Hasan
    In this study, titanium and niobium element powders in determined amounts (0.25 and 0.5wt%) were added into the 316L stainless steel matrix by means of powder metallurgy (PM) technology, either singly or in pairs, and the desired composition was obtained as a powder mixture. The powders used in the study were cold pressed tensile sample molds prepared in ASTM 8 M standards, unidirectionally cold pressed under 700 MPa compression pressure and formed into blocks. After pressing, the raw strength samples were sintered in an atmosphere-controlled tube furnace at 1325 degrees C for 2 h in an argon atmosphere. The microstructure and mechanical properties of the produced PM steels were characterized by optical microscope, SEM, EDS, and tensile test. The results showed that the stainless-steel samples with 0.25(Ti-Nb) added composition to 316L stainless steel had the highest yield strength and tensile strengths. However, with the addition of 0.5Ti, 0.5Nb, and 0.5(Ti-Nb) to 316L stainless steel, a decrease was observed in the mechanical properties. Moreover, the MQL machining is better on the machining output such as surface roughness and cutting temperature than dry machining in terms of a sustainable machining process.
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    Optimization and Finite Element Modelling of Tool Wear in Milling of Inconel 625 Superalloy
    (Gazi Univ, 2021) Akgun, Mahir; Demir, Halil
    This study focuses on optimization of cutting conditions and numerical analysis of flank wear in milling of Inconel 625 superalloy using PVD AlTiN and CVD TiCN/Al2O3/TiN-coated carbide inserts. The milling experiments have been performed in CNC vertical machining centre according to Taguchi L18 orthogonal array. Finite element modelling of tool wear was performed using Deform 3D software. Analysis of variance was utilized to define the influences of the milling conditions on Vb. The results showed that the feed rate (with 41.5% contribution rate) is the most important parameter affecting Vb. The linear and quadratic regression analyses were used to estimate the results of the test. The regression analysis results showed that the estimated Vb values achieved by the quadratic regression model were more effective compared to the linear regression model. Statistical results revealed that the Taguchi method was successful to define optimum cutting parameters in the milling of Inconel 625.
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    Optimization of Cutting Parameters Affecting Surface Roughness in Turning of Inconel 625 Superalloy by Cryogenically Treated Tungsten Carbide Inserts
    (Springer International Publishing Ag, 2021) Akgun, Mahir; Demir, Halil
    This work focuses on developing the mathematical model of surface roughness (Ra) in the turning of Inconel 625 superalloy with cryogenically treated tungsten carbide inserts. The influence of cryogenic treated on the microstructure and hardness of tungsten carbide tools was also investigated for the as-received inserts and deep cryogenic treatment at - 196 degrees C for 12, 24, and 36 h conditions. Turning experiments have been performed according to an orthogonal array L16 with three parameters (cutting tool, feed rate, cutting speed) at different levels with a 1 mm depth of cut. The ideal cutting tool and cutting parameters were evaluated in terms of the surface roughness (Ra). Analysis of Variance has been applied to determine the percentage of each cutting factor. It has been observed that the cutting speed has a maximum with 66.28% contribution on Ra. The best optimal turning parameters are obtained as A3B3C1 according to S/N ration. The mathematical model of Ra has been developed by regression analysis. The developed model is tested with verification experiments and found to be in good agreement with the experimental results.
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    Optimization of Surface Roughness in Turning Mg2Si Particle Reinforced Magnesium
    (Gazi Univ, 2018) Akgun, Mahir; Demir, Halil; Ciftci, Ibrahim
    In this study, Mg2Si reinforced Mg alloy material was produced by adding 10 % Al12Si alloy ingot to Mg matrix by conventional casting method and then the melt was poured into a metal mould in cylindrical form. Machining tests were carried out on these cast alloys through single point turning method. Optimum machining conditions was aimed to be determined by investigating the effects of cutting parameters on surface roughness. For this purpose, the machining tests were performed without coolant on a CNC turning centre at four different cutting speeds (250, 350, 450 and 550 m/min), two different feed rates (0.1 and 0.2 mm/rev) and two different tool tip radii (0.4 mm ve 0.8 mm). The experimental design was conducted according to Taguchi's L8 orthogonal array. Machining experiments were carried out on CNC lathe under dry cutting conditions. ANOVA was used to determine the effect of cutting parameters on the surface roughness. According to the obtained analysis results, it was seen that the most influential parameters on surface roughness was feed rate by 57.6 %.