Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Microstructure-Based Prediction of Mechanical Properties of Austempered Ductile Iron Using Multiple Linear Regression Analysis(Springer int Publ Ag, 2025) Yalcin, M. Alp; Davut, KemalMultiple linear regression analysis (MLRA) was used to predict the mechanical properties of austempered ductile iron (ADI) including yield and tensile strength, uniform elongation, hardening exponent, as well as fracture energy by building a model that uses characteristic features of microstructural constituents as input parameters. The complex multi-scale microstructure of ADI, which is composed of spherical graphite particles over 10 mu m diameter; and an ausferritic matrix with sub-micron sized features, makes it ideal for prediction of mechanical properties. For that purpose, low alloyed ductile iron samples austempered between 300 and 400 degrees C for 45-180 min were tensile tested, and also multi-scale microstructural characterization were carried out using optical microscope, SEM, and EBSD technique. Moreover, a sensitivity analysis was performed to determine which microstructural parameter(s) each mechanical property is most sensitive to. The results show that tensile and yield strength are most sensitive to size and morphology of matrix phases. Moreover, the size and aspect ratio of acicular ferrite correlate well with those of high-carbon austenite; since both form during transformation of parent austenite into ausferrite during austempering treatment. Equiaxed parent austenite grains transform into ausferrite with acicular morphology during the austempering treatment; and presence of equiaxed austenite grains in the austempered samples indicates untransformed regions during austempering treatment. Ductility was found to be more sensitive to nodularity of graphite particles, and this sensitivity was attributed to the size difference between graphite particles and grain size of matrix phases.Article Citation - WoS: 2Citation - Scopus: 2Microstructural Evolution and Mechanical Performance of Dual-Phase Steels Under Fiber Laser Welding: Effects of Heat Input and Weld Penetration(Springer, 2025) Tuncel, Oguz; Davut, Kemal; Aydin, HakanThis study investigates the effects of fiber laser welding (FLW) parameters on the microstructural evolution and mechanical properties of DP800, DP1000, and DP1200 dual-phase steels, focusing on the role of heat input. Welding was performed using laser powers ranging from 1500 to 3000 W and welding speeds between 20 and 100 mm/s, resulting in heat inputs from 18 to 120 J/mm. Optimal welding conditions were identified as 55 J/mm for DP800, 120 J/mm for DP1000, and 53 J/mm for DP1200, which ensured full penetration and minimized HAZ softening. Detailed microstructural analysis using SEM and EBSD revealed significant transformations in the heat-affected zone (HAZ), including martensite degradation, grain coarsening, and tempered martensite formation, particularly in DP1200 steel, where hardness reductions reached up to 29%. Tensile tests demonstrated that while DP800 and DP1000 joints primarily failed within the base material (BM) with ductile fracture characteristics, DP1200 joints fractured within the HAZ due to a combination of brittle cleavage and ductile dimples caused by martensite breakdown and carbide precipitation. The findings underscore the necessity of optimizing welding parameters to control HAZ softening and preserve mechanical performance. By systematically analyzing the interplay between heat input, microstructure, and mechanical properties across different DP steel grades, this research provides a comprehensive understanding of how FLW conditions influence joint integrity, offering valuable guidance for designing robust welding strategies in advanced engineering applications.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.