Hierarchical Fatigue Damage M F. Yoshinaka 1 1 Research Center for Structural Materials, National Institute for Materials Science (NIMS) Fatigue is a major cause of failure in mechanical structures, and prevention of fatigue is crucial to ensure their safety. Fatigue failure results from fatigue crack initiation and propagation on a macroscopic level, but plastic deformation at the crack initiation site or crack tip region drives the crack initiation and propagation on a microscopic level. In other words, metallic fatigue is a phenomenon that spans dislocations, plastic deformation, and cracks, and necessitates comprehension at all level of the hierarchy. Thus, we are undertaking research to clarify the fatigue mechanism by examining the factors affecting fatigue properties on a multi-scale using various types of microscopes and synchrotron radiation techniques, mainly for alloys characterized by variety of plastic deformation mechanisms. Based on the findings of multi-scale characterization of fatigue deformation and fracture, we are developing new fatigue-resistant alloys. The research indicated that the fatigue durability can be improved by increasing the deformation reversibility, and bidirectional martensitic transformation could be an effective deformation mechanism to achieve high reversibility. The bidirectional transformation-induced plasticity (B-TRIP) steel developed showed a fatigue life 20 times longer than general steels. On the Three-dimensional Atomic Scale Characterisation of Nano-Scale B2 Phase in Ni-Alloyed Fe-Mn Mainak Saha 1, M.B. Ponnuchamy1 Correlative Microscopy Laboratory, Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai, 600036, India. 2 National Facility for Atom Probe Tomography, Indian Institute of Technology Madras, Chennai, 600036, India. The enhanced mechanical properties of Al-alloyed Fe-Mn-C based multi-component steels are primarily derived from the different phases present in them in addition to their size, distribution, morphology, volume fraction and stability. Here we report on the thermal stability and the associated phase evolution sequence especially that of nanoscale precipitates in a hot-rolled 5Ni-alloyed Fe-16Mn-9Al-0.9C (wt.%) low-density steel. Systematic heat treatment studies were performed in the temperature range of 600-1200 °C. Bulk phase analysis using X-ray diffraction indicates the presence of three phases, ' structured κ and BCC phases in as-rolled condition which is in good namely FCC structured γ, L12agreement with the thermodynamic phase stability estimates. Combined microscopic analysis involving three-dimensional atom probe tomography reveals the presence of nano-scale κ and B2 precipitates, highly localized within the majority γ and banded BCC phase regions respectively. This presentation, therefore will focus on the temporal evolution of B2 nanoprecipitates and their localisation within the banded BCC phase regions along with their stability as a function of varied thermal treatments. Poster Presentation ｜NIMS Award Symposium 2023 1, M. Sadhasivam1 and K.G. Pradeep 1,2 echanism and Development of Fatigue-resistant Alloy -Al-C Low-density Steel P2 ｜ CharacterizationPP22--0033 PP22--0044 45
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