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Davut, Kemal
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Davut, K.
K.,Davut
K., Davut
Davut,K.
D., Kemal
Davut, Kemal
D.,Kemal
Kemal, Davut
K.,Davut
K., Davut
Davut,K.
D., Kemal
Davut, Kemal
D.,Kemal
Kemal, Davut
Job Title
Doktor Öğretim Üyesi
Email Address
kemal.davut@atilim.edu.tr
Main Affiliation
Department of Metallurgical and Materials Engineering
Status
Former Staff
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Scholarly Output
26
Articles
17
Citation Count
201
Supervised Theses
3
25 results
Scholarly Output Search Results
Now showing 1 - 10 of 25
Article Citation - WoS: 5Citation - Scopus: 5Effect 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 EngineeringThis 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: 9Citation - Scopus: 9A 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 EngineeringThis 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: 40Citation - Scopus: 41Recrystallization and Grain Growth Kinetics of In718 Manufactured by Laser Powder Bed Fusion(Elsevier, 2022) Dogu, Merve Nur; Davut, Kemal; Obeidi, Muhannad Ahmed; Yalcin, Mustafa Alp; Gu, Hengfeng; Low, Thaddeus Song En; Brabazon, Dermot; Department of Metallurgical and Materials EngineeringThe recrystallization and grain growth behaviour of IN718 alloy additively manufactured by laser powder bed fusion (L-PBF) is presented herein. The effects of three different temperatures (1050, 1150 and 1250 degrees C) and holding times (15, 45 and 90 min) were investigated. The texture evolution of the samples was recorded via electron backscatter diffraction (EBSD). The as-built sample is composed of bowl-shaped melt pools, a chessboard-like grain pattern and has a cube texture {100}<001>. Recrystallized grains were observed in the samples treated at 1150 degrees C for 15 min, as well as the samples treated for longer periods and at higher temperatures. Recrystallization was observed to start from high dislocation density regions, including the overlapping melt pools and the borders of the chessboard-like pattern. The initial cube texture transforms into a first-generation cube-twin texture {122}<212> via a twinning-assisted recrystallization mechanism. Then, those recrystallization nuclei sweep through the high defect density matrix; during which almost no new twins are formed. The samples treated at 1250 degrees C are almost completely recrystallized, which forms a weaker cube texture and a stronger P-orientation {011}<112>. However, the growth of recrystallized grains is very limited due to the presence of non-coherent precipitates. (C) 2022 The Author(s). Published by Elsevier B.V.Article Citation - WoS: 16Citation - Scopus: 19Effect 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 EngineeringThe 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/).Conference Object Citation - WoS: 5Citation - Scopus: 5Influence of Cu and Ni Alloying on the Microstructure and Mechanical Properties of Austempered Ductile Iron Castings(Polish Acad Sciences inst Physics, 2019) Yalcin, M. A.; Cetin, B.; Davut, K.; Department of Metallurgical and Materials EngineeringAustempered ductile cast iron (ADI) offers a good combination of high tensile and fatigue strength, good ductility, toughness, wear resistance and damping characteristics, lower density in an economical way. This excellent combination of properties is due to the specific microstructure of ADI; which is composed of spheroidal graphite particles on an ausferritic matrix. The ausferrite consists of acicular ferrite and high carbon retained austenite; which is produced via austempering heat treatment after casting. The alloying additions of Cu or Cu + Ni increases austemperability, which means completely ausferritic structures can be produced on larger cross-sections. In the present study the effect of the alloying additions of Cu and Cu + Ni on mechanical properties and microstructure of ADI was studied. For that purpose, Y-block specimens having a lean composition, 0.8% Cu and 0.8% Cu + 0.4% Ni alloying additions were cast. After austempering treatment, mechanical tests, fractographic and metallographic examinations were performed. The results show that the Cu + Ni alloyed specimen has higher strength and elongation. The lean alloy on the other hand, has the highest nodularity and matrix hardness but the lowest strength and ductility. Those differences in mechanical properties were attributed to the fraction and morphology of the retained austenite regions of the matrix.Article Strain Hardening Behavior Characterization of Dual Phase Steels(2018) Davut, Kemal; Şimşir, Caner; Çetin, Bariş; Manufacturing Engineering; Department of Metallurgical and Materials EngineeringThe requirements for higher passenger safety, improved fuel economy and weight reductionin automobile industry necessitates the usage of advanced high strength steel (AHSS)grades. Dual phase (DP) steels are the most widely used one among AHSS. DP steels becomeincreasingly popular, since they provide a combination of sufficient formability at room temperatureand tensile strength over 1000 MPa. The current standards for DP steels only specifiesyield and tensile strength. Steels from various producers have considerably different compositionand microstructure; however they still have the same grade name. Combined withthe inherited heterogeneous microstructure, those steels exhibit different strain hardeningbehavior. The aim of this study is to evaluate the strain hardening behavior of DP800 steels,obtained from different vendors and thus having different compositions and microstructures.The strain hardening behavior was characterized with tensile tests performed along rollingand transverse directions. The microstructure has been characterized with optical andscanning electron microscopes. The martensite fraction, grain size of ferrite and chemicalcomposition has been correlated to the strain hardening behavior. The results show thatthe steel with more micro-alloying addition has finer ferritic grain size, which cause higherinitial strain hardening rate. The steel with higher Mn and Cr has higher martensite fraction,which cause strain hardening rate to be higher at higher strain levels.Article Citation - WoS: 9Citation - Scopus: 9Elektrik Direnç Punta Kaynağı ile Birleştirilen %15 Deforme Edilmiş Twıp Çeliğinde Kaynak Akımının Mikroyapı ve Mekanik Özellikler Üzerindeki Etkisi(Gazi Univ, Fac Engineering Architecture, 2020) Aydın, Hakan; Tutar, Mümin; Davut, Kemal; Bayram, Ali; Department of Metallurgical and Materials Engineering; Industrial EngineeringÇalışmada, %15 deforme edilmiş TWIP saclarının elektrik direnç punta kaynağıyla birleştirmelerindekaynak akımının mikroyapı ve mekanik özellikler üzerindeki etkisi incelenmiştir. Mikroyapıkarakterizasyonunda optik mikroskop, taramalı elektron mikroskobu (SEM), SEM/Enerji dağılımlı X-ışınıSpektroskopisi (SEM-EDS) ve SEM/Elektron Geri Saçılım Kırınımı (SEM-EBSD) teknikleri kullanılmıştır.Mekanik özelliklerin belirlenmesinde, mikrosertlik ölçümleri ve çekme testleri yapılmıştır. Kaynak akımıartışı ile erime bölgesindeki kaynak boşlukları azalırken, çekirdek çapı, çökme miktarı ve ısı tesiri altındakibölge (ITAB) genişliği yaklaşık lineer bir şekilde artmıştır. Kaynak bölgesinde deformasyon ikizleri ortadankalkarken, ITAB’da iri tavlama ikizleri ortaya çıkmıştır. Ayrıca, kaynak akımı artışıyla ITAB’daki taneirileşmesi ve ikiz kalınlıkları artmıştır. Ancak, kaynak işlemi kaynak bölgesinde herhangi bir fazdönüşümüne neden olmamıştır. Bu sebeple, kaynak bölgesi sertlik değerleri temel malzemenin sertlikdeğerlerinden oldukça düşük kalmıştır. Genel itibariyle, en düşük sertlikler ITAB’da gözlenmiştir. Kaynakakımı ile kaynak bölgesi sertlik değerleri arasında herhangi bir korelasyon elde edilmemiştir. Kopma yükükaynak akımı ile artmıştır: En yüksek kopma yükü 10 kA kaynak akımında elde edilmiştir. Düşük kaynakakımlarında aryüzey tipi kırılma meydana gelirken yüksek kaynak akımlarında buton çekirdek tipi kırılmalarortaya çıkmıştır. Kırılma karakteristikleri genel itibariyle gevrek-sünek karışımıdır. Daha yüksekmukavemete sahip numunelerde gevrek-sünek kırılma bölgesinde sünek kırılma, gevrek kırılma bölgesindeise trans-granular kırılma karakteristikleri artış göstermiştir.Conference Object Citation - WoS: 4Citation - Scopus: 4A Material Perspective on Consequence of Deformation Heating During Stamping of Dp Steels(Iop Publishing Ltd, 2017) Simsir, C.; Cetin, B.; Efe, M.; Davut, K.; Bayramin, B.; Department of Metallurgical and Materials Engineering; Manufacturing EngineeringRecent studies showed that, during stamping of high strength steels at industrially relevant production rates, local temperature in the blank may rise up to 200 degrees C - 300 degrees C due to deformation heating. Moreover, die temperature may also rise up to 100 degrees C - 150 degrees C for progressive stamping dies. Based on the common assumption that the blank softens as the temperature increases, thermal softening creates a margin in Forming Limit Diagram (FLD) and therefore the FLD determined at room temperature can safely be used for those cases. In this article, the validity of this assumption on DP590 steel is questioned by high temperature tensile tests (RT - 300 degrees C) at various strain rates (10(-3) s(-1) - 1 s(-1)). The results indicated a decrease both in uniform and total elongation in 200 degrees C - 300 degrees C range together with several other symptoms of Dynamic Strain Aging (DSA) at all strain rates. Concurrent with the DSA, the simulated FLD confirms the lower formability at high temperature and strain rates. Thus, it is concluded FLD determined at RT may not be valid for the investigated steels.Master Thesis Sementasyon ve Takip Eden Su-verme İşlemlerinin Süreç Tasarımı ve Kalite Değerlendirmesine Yönelik Malzeme Karakterizasyon Çalışmaları(2017) Yıldız, Seçil; Davut, Kemal; Şimşir, Caner; Department of Metallurgical and Materials EngineeringSementasyon ve su-verme ısıl işlemi; aşınma ve yorulma dayancı özelliklerini iyileştirmek için düşük karbonlu çelik parçalara uygulanan bir yüzey sertleştirme işlemidir. Çarpılma, çatlak, sertlik veya sertlik derinliğinde yetersizlik bu işleme bağlı olarak en sık karşılaşılan sorunlardır. Son yirmi yılda, bu sorunları tahmin etmek ve engellemek için, analitik ve deneme-yanılma gibi geleneksel yöntemler yerine bilgisayar simülasyonları daha popüler hale gelmiştir. Bilgisayar destekli ısıl işlem simülasyonları sorunları çözmenin dışında istenilen mikroyapı ve kalıntı gerilme dağılımını sağlayan en uygun proses parametrelerinin belirlenmesini ve bu sayede parça performansının artırılmasını sağlamaktadır. Bu çalışmanın birinci amacı, DIN 22NiCrMo2-2 (SAE 8620H) çeliğine uygulanan sementasyon ve su-verme işlemlerinin simülasyonu için gerekli malzeme veri setinin geliştirilerek hesaplamalı malzeme mühendisliği yöntemlerini tamamlamaktır. Bu amaçla öncelikle, hesaplama tekniklerine gerekli girdiyi sağlamak için, kimyasal ve mikroyapısal olarak ham malzeme karakterizasyonu yapılmıştır. Ardından, su-verme aşamasında faz dönüşümleri üzerinde önemli derecede etkisi olan östenit büyüme kinetiği araştırılmıştır. Son olarak, kritik sıcaklıklar ve dönüşüm kinetiği belirlenerek, TTT ve CCT diyagramları şeklinde sunulmuştur. Ham malzeme karakterizasyon çalışmalarıyla kütüklerin makro segregasyon içermediği, eşeksenli ferritik/perlitik bantlaşmış ve homojen dağılımlı tane yapısına sahip olduğu ve bu nedenlerle proses ve doğrulama çalışmaları için uygun olduğu tespit edilmiştir. Ayrıca, deneysel ve hesaplamalı yöntemlerle belirlenen CCT diyagramlarının birbirleriyle uyumlu olduğu görülmektedir. Deneysel ve hesaplamalı yöntemlerle belirlenen TTT diyagramları arasındaki en büyük farklılık, yerel kimyasal kompozisyon ve yerel östenit tanesi boyutu gibi kontrol edilmesi zor olan faktörlere karşı daha hassas olan beynitik faz dönüşümünde gözlenmektedir. Bu çalışmanın ikinci amacı, aynı proje kapsamında yürütülen tamamlayıcı bilgisayar simülasyonları çalışmalarının geçerliliğinin belirlenmesi ve sementasyon ısıl işleminin kalite değerlendirmesi için içyapı incelemeleri yapmaktır. Bahsi geçen tamamlayıcı çalışmaların birinde, endüstriyel prosesteki değişkenliği en aza indirgemek için DIN 22NiCrMo2-2 ve DIN 16MnCr5 çeliklerinden imal edilen miller üzerinde Taguchi metodu kullanılarak Deney Tasarımı (DoE) yapılarak endüstriyel koşullarda sementasyon deneyleri yapılmıştır. Diğer tamamlayıcı çalışmada ise, aynı Deney Tasarımı (DoE) bilgisayar simülasyonu çalışmalarıyla incelenmiştir. Bu tez çalışmasında ise, içyapı ve sertlik dağılımlarının belirlenmesiyle belirtilen diğer çalışmalar tamamlanmaktadır. Elde edilen sonuçlar bilgisayar simülasyonları ve deneysel sonuçların birbirine uyumlu olduğunu göstermektedir. Sonuçların uyumu beynit dönüşüm kinetiğinin gerilim, yerel tane boyutu ve yerel kimyasal kompozisyona bağlılığını da dahil eden daha iyi karakterizasyon çalışmalarıyla iyileştirilebilir.Article Citation - WoS: 31Citation - Scopus: 32Friction Stir Processing of Dual Phase Steel: Microstructural Evolution and Mechanical Properties(Elsevier Science inc, 2019) Aktarer, S. M.; Kucukomeroglu, T.; Davut, K.; Department of Metallurgical and Materials EngineeringThe influence of friction stir processing (FSP) on the microstructure and mechanical properties of a DP 600 steel has been studied. The microstructure evolution during the FSP has been characterized using electron back scatter diffraction (EBSD) technique and scanning and transmission electron microscopes. Standard tension and hardness tests were used to characterize the mechanical properties. The results show that the FSP produced a refined microstructure composed of ferrite, bainite, martensite, and tempered martensite which in turn increased the hardness and strength magnitudes by a factor of 1.5. The initially 2.83 mu m average grain size of ferrite has decreased to 0.79 mu m in the pin effected zone of (PE-SZ-I) of the processed region. Both EBSD and TEM observations showed regions with high dislocation density and sub-structures region in the processed zone. The grain size became coarser, the density of both dislocations and low-angle grain boundaries decrease, away from the processed zone. Moreover, phase fractions and hardness values were predicted using CALPHAD thermodynamic based software based on commercial material properties. Although the prediction does not take into consideration the influence of severe plastic deformation, the results were within 10% uncertainties of the experimental findings. The present study demonstrates that an ultra-fine grained structure can be obtained through the thickness of a 1.5 mm thick D P600 steel sheet via FSP. FSP can produce a range of different hardness and strength values; which can also be predicted successfully by inputting the composition and local temperatures reached during the FSP.
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