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Article Citation - WoS: 8Citation - Scopus: 11Influence 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 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.
