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527 results on '"Petrov, Roumen"'

2. Microstructure evolution and mechanical behavior of Fe-Mn-Al-C low-density steel upon aging

Author

Banis, Alexandros, Gomez, Andrea, Bliznuk, Vitaliy, Dutta, Aniruddha, Sabirov, Ilchat, and Petrov, Roumen H.

Subjects
Condensed Matter - Materials Science
Abstract

This study focuses on the microstructure's evolution upon different aging conditions of a high-strength low-density steel with a composition of Fe-28Mn-9Al-1C. The steel is hot-rolled, subsequently quenched without any solution treatment, and then aged under different conditions. The microstructure of the samples was studied by means of Scanning Electron Microscopy, Electron Backscatter Diffraction, and Transmission Electron Microscopy. The aging treatment leads to the formation of an ordered face-centered cubic L12 phase named k-carbide. This study aims to characterize the formation and growth of these k-carbides qualitatively and quantitatively under different aging conditions. Then, an effort is made to relate the fraction and size of this phase with the tensile properties of the steel to determine the optimal aging conditions that will lead to a good combination of strength and ductility. It has been found that the k-carbides start to form intragranularly through concentration fluctuations of aluminum and manganese inside the austenite grain. Then, with the process of spinodal decomposition, they grow in size coherently with the matrix. During this process, the strength and hardness of the steel increase while maintaining a relatively high elongation. The best combination of high strength and ductility was achieved at the aging condition of 8 h at 550 degrees Celsius with an ultimate tensile strength up to 1157 MPa and total elongation of 51%. Increasing the aging temperature and time, k-carbides start to form intergranularly, lose their coherency with the matrix and severely compromise the hardness and strength. The shearing of the carbides during deformation is also studied., Comment: 34 pages, 10 figures

Published
2023
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49. Time-Dependent Evolution of Volume Fraction and Stability of Retained Austenite in a Hot-Rolled and Intercritically Annealed Al-Alloyed Medium-Mn Steel

Author

Silesian University of Technology, Skowronek, A., Grajcar, A., García Mateo, Carlos, Jiménez, José Antonio, Petrov, Roumen, Silesian University of Technology, Skowronek, A., Grajcar, A., García Mateo, Carlos, Jiménez, José Antonio, and Petrov, Roumen

Abstract

The development of superior mechanical properties in medium-Mn requires the optimization of microstructural parameters such as retained austenite (RA) stability, volume fraction, and morphology. The present work explores the possibility of using a continuous annealing approach instead of conventional batch annealing to perform an intercritical annealing (IA) treatment in a hot-rolled strip of an Al-alloyed 5Mn steel. Dilatometric studies were performed at a temperature of 680 ºC with soaking times ranging from 1 to 300 min to follow the microstructural changes as a function of time. The microstructures thus obtained were thoroughly characterized by means of X-ray diffraction, SEM and TEM, TEM-EDS microanalysis and EBSD phase and orientation maps. It was observed that with increasing soaking times, the volume fraction of retained austenite gradually increases, albeit at the cost of its stability. The comparison of martensite start temperatures (M) based on the chemical composition of austenite at 680 ºC with that experimentally obtained at higher process temperature revealed the effect of the grain size on the reduction of RA stability for longer process times. Accordingly, mechanical tests results showed that the yield stress, tensile strength and hardness decrease with an increase in the IA soaking time.

Published
2023

50. Correlation between microstructural inhomogeneity and architectural design in additively manufactured NiTi shape memory alloys.

Author

Yan, Zhaorui, Zhu, Jia-Ning, Hartl, Darren, Riemslag, Ton, Scott, Sean Paul, Petrov, Roumen, Hermans, Marcel, Jovanova, Jovana, and Popovich, Vera

Abstract

Additively manufactured Nitinol (NiTi) architectured materials, designed with unit cell architectures, hold promise for customisable applications. However, the common assumption of homogeneity in modeling and additive manufacturing of these architectured materials needs further investigation because geometric-dependent melt pool behaviour results in inhomogeneous microstructure and thermomechanical properties. This study shows that property inhomogeneity at the mesoscale is one reason for pseudo-linear response and partial superelasticity of the fabricated NiTi body-centered cubic (BCC) architectured materials. We modeled using a phenomenological constitutive relation and additively manufactured NiTi architectured materials with varying relative densities. These fabricated samples showed distinct microstructural textures and compositions that affected their local recoverability. The edge effects and laser turn regions were identified as the causes underlying the observed microstructural inhomogeneity. The dimensionless Fourier number is used to describe the transition of printing modes. This study provides valuable information on rigorous experimental/computational consistency in future work. [ABSTRACT FROM AUTHOR]

Published
2024
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