Browsing by Author "Özer, Seren"

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Citation Count: 2
A 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; Yalcin, Mustafa Alp; Ozer, Seren; Davut, Kemal; Obeidi, Muhannad Ahmed; Brabazon, Dermot; Metallurgical and Materials Engineering; Department of Metallurgical and Materials Engineering
This 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.
Citation Count: 0
Effect 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, Dermot; Metallurgical and Materials Engineering; Department of Metallurgical and Materials Engineering
This 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.
Citation Count: 15
Effect of post fabrication aging treatment on the microstructure, crystallographic texture and elevated temperature mechanical properties of IN718 alloy fabricated by selective laser melting
(Elsevier Science Sa, 2022) Ozer, Seren; Bilgin, Guney Mert; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.; Metallurgical and Materials Engineering; Department of Metallurgical and Materials Engineering
The effect of building direction and post fabrication aging treatment on the microstructure, crystallographic texture and high temperature mechanical properties of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) method was investigated. After aging, arc-shaped structures seen in as-fabricated samples dis-appeared and converted into a mixture of columnar and equiaxed grains. Nano-sized gamma '' and/or gamma' precipitates were formed upon aging; however, MC type carbides and Laves phase encountered in as-fabricated samples were not dissolved completely after aging. Moreover, aging did not alter the texture ((001)//building direction (BD)) of as-fabricated samples. Mechanical properties of the alloys under tension were influenced by the build direction, aging time and test temperature. As-fabricated samples produced in vertical direction exhibited higher room temperature strengths with lower ductility due to orientation of overlapped prior melt pools. Room temperature tensile test results revealed that peak aging caused a significant improvement in ultimate tensile strength (UTS), from 1066.5 MPa and 998.4 MPa to 1408.5 MPa and 1330.4 MPa whereas elongation values decreased from 27.5% and 32.2% to 19.6% and 23.7% in vertically and horizontally built samples, respectively. Peak-aged samples (aged at 700 degrees C for 8 h) tested at 600 degrees C displayed serrated regions in their stress-strain curves due to dynamic strain aging (DSA). Although strength values of the samples displayed an expected decrease by temperature, ductility of the samples reduced to minimum at temperatures around 700-800 degrees C, which was attributed to intermediate temperature embrittlement.
Citation Count: 5
Effect of solution heat treatment on the microstructure and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam
(Elsevier, 2023) Dogu, Merve Nur; Ozer, Seren; Yalcin, Mustafa Alp; Davut, Kemal; Bilgin, Guney Mert; Obeidi, Muhannad Ahmed; Brabazon, Dermot; Metallurgical and Materials Engineering; Department of Metallurgical and Materials Engineering
The 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/).