Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Investigations on the Effect of Secondary Treatments on Ti48Al2Cr2Nb Alloy Manufactured by Electron Beam Powder Bed Fusion Method(Elsevier Sci Ltd, 2025) Bilgin, Guney Mert; Ozer, Seren; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.As-built Ti48Al2Cr2Nb alloy samples produced by electron beam powder bed fusion (PBF-EB) exhibited notable brittleness. The low ductility was attributed to coarse gamma bands aligned perpendicular to the building and tensile direction. Additionally, variations in aluminum content and hardness between the coarse colonies and fine gamma/alpha(2) lamellae contribute to this phenomenon. Electron backscattered diffraction (EBSD) studies revealed a higher amount of dislocation density and inherent strain after PBF-EB manufacturing. Hence, usage of Ti48Al2Cr2Nb alloy in the as-built condition in aviation applications with high loads and demanding environments is not found to be viable. To eliminate these negative aspects and make PBF-EB produced Ti48Al2Cr2Nb alloy available for demanding applications, two distinct post-processing heat treatments; namely, hot isostatic pressing (HIP) and annealing heat treatment (HT) were employed at 1200 degrees C. A comprehensive characterization covering microstructure analysis, EBSD, fracture surface examination, as well as room and high-temperature tensile tests allowed determination of the effect of post-processes. HIPing altered the banded structure observed in the as-built samples by increasing the amount of alpha(2) phase and grain size. On the other hand, HT made the banded structure more pronounced without significantly increasing the amount of alpha(2) phase. HT also strengthened the <001> texture, while HIPing introduced randomization of grains. On the other hand, complete recrystallization is achieved as a result of HT at 1200 degrees C for 2 h, whereas HIPing at the same temperature for 2 h induced only 80.5 % recrystallization. In both post-processes, dislocation density and inherent strain were reduced. Room temperature and high-temperature tensile tests demonstrated that both HIPing and HT eliminated the extreme brittleness of the as-built samples.Article The Johnson and Cook Damage and Flow Stress Model Parameters of a Rolled Stainless Steel 304 Alloy(Elsevier, 2026) Akdogan, Ibrahim Berk; Davut, Kemal; Gueden, Mustafa; Erten, Hacer Irem; Tasdemirci, Alper; Maleki, Farshid Khosravi; Gok, Mustafa SabriPrevious studies on stainless steel 304 alloy (SS 304) have mostly focused on the stress-strain behavior as function of the volume fraction of deformation induced martensite and the applied strain and strain rate. Although equally important, the failure/fracture of this alloy has not been thoroughly investigated so far. In the present study, the Johnson and Cook (JC) damage model parameters of a rolled-SS 304 alloy, valid at a high strain rate (2900 s-1), were experimentally determined and numerically validated along with the JC flow stress parameters. The tensile failure strain of the alloy decreased as the strain rate increased from 10-3 to 10-1 s-1 and to 2900 s-1. Experimentally lower flow stresses at 2900 s-1 than at 1x10-3 s-1 were also found at the strains above 0.2, which was attributed to the adiabatic heating that declined the extend of the martensitic transformation at increasing strains. The determined damage and flow stress model parameters were further calibrated with the results of the numerical models of the quasi-static and high strain rate tension tests. Microscopic analyses and the hardness measurements on the untested and tested specimens confirmed the martensitic transformation and the highest hardness values were found in the specimens tested at 1x10-3 s-1. The martensite volume fraction as function strain rate until about necking strain (homogeneous deformation) was calculated and also microscopically determined using the electron back-scatter diffraction (EBSD) for the specimens tested at different strain rates. The results indicated the highest martensite volume fraction in the specimens tested at 10-3 s-1 (0.55-0.6) and the lowest in the specimens tested at the high strain rate (0.27-0.30). An agreement between the calculated and the EBSD determined martensite volume fractions was shown for the studied alloy.Article Citation - WoS: 3Citation - Scopus: 3Influence of Oscillating Fiber Laser Welding Process Parameters on the Fatigue Response and Mechanical Performance of Butt-Jointed Twip980 Steels(Walter de Gruyter Gmbh, 2025) Cavusoglu, Oktay; Aydin, Hakan; Eroglu, Mehmet; Davut, KemalIn this study, the effect of laser power, welding speed, linear heat inputs on the mechanical performance of TWIP980 steels joined by oscillating fiber laser welding in butt welding configuration was investigated. Oscillating fiber laser welding were changed: laser power from 1.2 to 1.6 kW, welding speed from 20 to 30 mm s-1, linear heat input from 40 to 80 J mm-1. The tensile, hardness and fatigue tests were carried out to determine mechanical performance. A significant improvement in weld penetration, fatigue performance and mechanical properties was detected at linear heat inputs above 53.33 J mm-1. The best mechanical properties were obtained at 1.6 kW laser power and 25 mm s-1 welding speed. The study reveals that linear heat inputs, laser power, and welding speed have significant effects on mechanical performance and weld geometry. Furthermore, the results demonstrate that oscillating fiber laser welding enables good weldability even at low laser power.Article Citation - WoS: 6Citation - Scopus: 10Influence of the Heat Treatment on the Microstructure, Mechanical and High-Temperature Oxidation Behavior of Hastelloy X Alloy Fabricated Via Laser Powder Bed Fusion(Elsevier Science Sa, 2025) Ozer, Seren; Yalcin, Mustafa Alp; Bilgin, Gueney Mert; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.The effect of building direction and heat treatment on the microstructure, mechanical properties, and high- temperature oxidation behavior of Hastelloy X (HX) alloy fabricated by the laser powder bed fusion (L-PBF) method was studied. Electron backscatter diffraction analyses revealed that the development of textured columnar grains with varying average grain sizes, boundary fractions, and dislocation densities induced the mechanical anisotropy observed in both horizontally and vertically fabricated samples. The yield strength (YS) values of the horizontally and vertically as-fabricated samples were determined as 605.7 +/- 15.9 MPa and 552.3 +/- 8.5 MPa, respectively. The post-processing heat treatment increased the ductility remarkably and reduced YS value down to similar to 445 MPa for all samples by the elimination of microstructural anisotropy and increased grain size subsequent to recrystallization. Oxidation tests conducted at 900 degrees C up to 100 h on as- fabricated samples exhibited severe intergranular oxidation, which was accompanied by the formation of large voids and microcracks as well as spallation of the oxide layer. In contrast, the heat-treatment improved the oxidation resistance of the alloy possibly due to the formation of uniform and dense Cr2O3 layer on the substrate surface.Article Citation - WoS: 2Citation - Scopus: 2The Spheroidization Behavior of Low Alloy White Cast Iron and Its Effect on Impact Toughness and Wear Resistance(Elsevier Science Sa, 2025) Camkerten, Ruziye; Davut, Kemal; Yilmaz, Tolga; Nalcaci, Burak; Erdogan, MehmetThe effect of spheroidization on impact toughness and wear resistance, together with the spheroidization kinetics of a low alloy white cast iron (LAWCI) have been studied. Spheroidization process was carried out using two different routes; intercritical annealing and subcritical annealing both of which were followed by furnace cooling to room temperature. Both routes involve a process window, which is determined by holding time and temperature. For the intercritical annealing the spheroidization window is significantly shorter (0.5-3 h) than the conventional subcritical spheroidization (6 - 12 h); and that process window narrows with increasing intercritical annealing temperature. The intercritical spheroidization involves 3 distinct stages; (i) partial, followed by (ii) fully spheroidization of lamellar pearlitic matrix by divorced eutectoid transformation (DET); and (iii) partially spheroidization by pearlitic structure formation in previous fully spheroidized region. The end of third stage produces almost fully pearlitic matrix, which is coarser than the as-cast condition. In case of subcritical spheroidization, the process window opens after about 6 hours and the size of spherical carbides gets larger with time. The as-cast LAWCI having a microstructure composed of eutectic carbide network and pearlite matrix exhibits and impact toughness of 4.6 J. Spheroidization process not only changes the lamellar pearlitic structure into spheroidized carbides but also slightly reduces the amount of eutectic carbides. Those microstructural changes greatly improve the impact toughness of LAWCI up to 11.8 J; whereas some decrease in the wear resistance. For spheroidized LAWCI, mean diameter of carbides (D), interparticle spacing of carbides (s), and number of carbides per area (n) seems to be important microstructural variations to determine the impact toughness and wear properties. Taking properties of the current material into consideration, spheroidized white cast irons may be a viable alternative material for industrial applications, offering a trade-off between wear resistance and toughness.Article Citation - WoS: 8Citation - Scopus: 8A Comprehensive Study of the Effect of Scanning Strategy on In939 Fabricated by Powder Bed Fusion-Laser Beam(Elsevier, 2024) Dogu, Merve Nur; Ozer, Seren; Yalcin, Mustafa Alp; Davut, Kemal; Obeidi, Muhannad Ahmed; Simsir, Caner; Brabazon, DermotThis study provides a comprehensive investigation into the effects of different scanning strategies on the material properties of IN939 fabricated using the PBF-LB process. The scanning strategies examined included alternating bi-directional scanning with rotation angles of 0 degrees, 45 degrees, 67 degrees, and 90 degrees between adjacent layers (named as shown), as well as alternating chessboard scanning with rotation angles of 67 degrees and 90 degrees (named as Q67 degrees and Q90 degrees). The results revealed that the 45 degrees and 67 degrees samples had the highest relative density, while the 0 degrees and Q67 degrees samples showed the highest average porosity. Moreover, various types of cracks, including solidification, solid-state, and oxide-induced cracks, were observed. Among the bi-directional scan samples, the 0 degrees sample displayed the most extensive cracking and the highest sigma max residual stress values in both XZ and XY planes. Conversely, the 45 degrees and 67 degrees samples exhibited fewer cracks. Notably, the lowest sigma max residual stress in the XZ planes among the bidirectional scan samples was observed in the 67 degrees sample. Additionally, microstructural analyses indicated differences in grain size and morphology, among the samples. Texture analysis indicated that the 0 degrees and 90 degrees samples exhibited strong cube textures, whereas the texture intensity weakened for the 45 degrees and 67 degrees samples. Moreover, the alternating chessboard scanning strategy led to rougher surfaces (higher Sa and Sz values) compared to the alternating bi-directional scanning strategy, regardless of the rotation angles. Furthermore, the microhardness values among the samples showed minimal variance, ranging between 321 + 14 HV and 356+ 7 HV.Article Citation - WoS: 13Citation - Scopus: 11Effect of Aging Treatment on the Microstructure, Cracking Type and Crystallographic Texture of In939 Fabricated by Powder Bed Fusion-Laser Beam(Elsevier, 2024) Ozer, Seren; Dogu, Merve Nur; Ozdemirel, Ceren; Bilgin, Guney Mert; Gunes, Mert; Davut, Kemal; Brabazon, DermotThis study aimed to provide a comprehensive understanding of how aging treatments (namely, HT1 and HT2) affect the microstructure, cracking behavior, and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam (PBF-LB) method. Although both aged samples demonstrated similar grain structure and recrystallization behavior according to the electron backscatter diffraction (EBSD) analysis, as well as the precipitation of bimodal gamma ' phase and MC- and M23C6-type carbides, notable differences were observed in the size and morphology, particularly the gamma ' phase. The HT1 sample displayed coarsened primary gamma ' phase, with sizes reaching up to 2 mu m and exhibiting varied morphologies, including irregular and cuboidal shapes. Additionally, this treatment led to the formation of some gamma '-gamma eutectic regions and plate-like eta phase, along with the decomposition of MC-type carbides into M23C6-type carbides. In contrast, the HT2 sample displayed uniformly distributed spherical primary gamma ' phase with sizes ranging from 70 to 120 nm, accompanied by very fine secondary gamma ' phase. Furthermore, it was found that changes in both aged sample microstructures could result in the formation of strain-age cracks due to the gamma ' phase formation and liquation cracks due to the partial remelting of lower melting point phases. The findings also revealed that with the application of aging treatments, the hardness of the as-fabricated sample (339.8 +/- 3.4 HV) increased to 440.2 +/- 5.6 HV and 508.1 +/- 4.8 HV for the heat treatment of HT1 and HT2, respectively.Article Citation - WoS: 11Citation - Scopus: 11A Comprehensive Characterization of the Effect of Spatter Powder on In939 Parts Fabricated by Laser Powder Bed Fusion(ELSEVIER SCI LTD, 2023) Dogu, Merve Nur; Mussatto, Andre; Yalçın, Mustafa Alp; Özer, Seren; Davut, Kemal; Obeidi, Muhannad Ahmed; Kumar, AjayThis study is focused on a comprehensive characterization of virgin and spatter IN939 powders and the effects of a certain amount of spatter powder on the part quality of IN939 fabricated by the L-PBF process. A brown tint coloration formed Al2O3 oxide, pores, a 124.4% increase in the average particle size, a 10.2% decrease in the powder circularity, and a 7.5% decrease in the powder aspect ratio were observed in the spatter powder. Additionally, higher average grain size and lower nanohardness were obtained for the spatter powder. In order to understand the effect of a certain amount of spatter powder on the part quality, 10 wt% spatter powder was mixed with the virgin powder. This addition was found to decrease the flowability of the powder. Moreover, this addition decreased relative density by around 0.3% and increased surface roughness by around 80.8% in the fabricated samples (termed as V and SV). On the other hand, there was no considerable microstructural, texture, microhardness, and nanohardness difference between V and SV samples, although the spatter powder addition caused a 30.2% increase in the average grain size of SV. The overall texture for both V and SV samples exhibit (00 1)//BD.Article Citation - WoS: 5Citation - Scopus: 4Influence of Partitioning Treatment on Microstructure and Mechanical Properties of an Alloyed Ductile Iron Austempered at Different Temperatures(Walter de Gruyter GmbH, 2023) Neite, Maximilian; Münstermann, Sebastian; Nalçacı, Burak; Davut, Kemal; Erdoğan, MehmetThe present study was conducted to uncover effects of partitioning treatment on Cu-Ni-Mo alloyed ductile iron (DI) austempered at different temperatures. For this purpose, the DI samples, produced via sand casting, were austenitized at 900 °C for 60 min, followed by austempering at the temperatures of 275-325-375 °C for 120 min and afterwards a partitioning treatment was applied at 200 °C for 15 min. In the characterization studies, dilatometer, image analysis, JMat-Pro, mechanical tests, XRD, optical microscope, and scanning electron microscope (SEM) equipped with EBSD detector were utilized. Characterization studies showed that the effects of partitioning treatment were directly correlated with austempering temperature and high carbon austenite volume fraction changed in the range of 19.48-35.45%. That redistribution of carbon (C) between bainitic ferrite and high carbon austenite occurred, in turn, the carbon content of high carbon austenite increased with the partitioning treatment irrespective of austempering temperature were uncovered. Furthermore, the partitioning treatment considerably changed the grain morphologies of both high carbon austenite and banitic ferrite. As a consequence of these microstructural differences, the highest tensile strength of 1489.2 MPa was established in the sample austempered at 275 °C and partitioned at 200 °C, whereas the highest ductility of 5.61% acquired at the austempering temperature of 375 °C. © 2023 Walter de Gruyter GmbH, Berlin/Boston.Article Citation - WoS: 22Citation - Scopus: 25Effect of Solution Heat Treatment on the Microstructure and Crystallographic Texture of In939 Fabricated by Powder Bed Fusion-Laser Beam(Elsevier, 2023) Doğu, Merve Nur; Özer, Seren; Yalçın, Mustafa Alp; Davut, Kemal; Bilgin, Guney Mert; Obeidi, Muhannad Ahmed; Brodin, Hakan; Gu, Hengfeng; Brabazon, DermotThe effect of various solution heat treatment temperatures (i.e., 1120, 1160, 1200 and 1240 & DEG;C) on the microstructure, grain morphology and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam (PBF-LB) was investigated. Microstructural analyses showed that the high-temperature gradient and rapid solidification of the PBF-LB processing caused different resulting microstructures compared to conventionally pro-duced counterparts. The melt pool morphologies and laser scanning paths were examined in the as-fabricated samples in the XZ-and XY-planes, respectively. After the application of solution heat treatment at 1120 & DEG;C, the as-fabricated PBF-LB initial microstructure was still apparent. For solution heat treatments of 1200 & DEG;C and above, the melt pool and scanning path morphologies disappeared and converted into a mixture of columnar grains in the XZ-plane and equiaxed grains in the XY-plane. On the other hand, large equiaxed grains were observed when the samples were solutionized at 1240 & DEG;C. Additionally, g' phase precipitated within the matrix after all solution heat treatment conditions, which led to increase in the microhardness values. According to electron backscatter diffraction (EBSD) analyses, both as-fabricated and solution heat-treated samples had intense texture with {001} plane normal parallel to the building direction. The first recrystallized grains began to appear when the samples were subjected to the solution heat treatment at 1160 & DEG;C and the fraction of the recrystallized grains increased with increasing temperature, as supported by kernel average misorientation (KAM) and grain spread orientation (GOS) analyses.& COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).