ME Seminar - Exploring avenues for modulating hierarchical architectures in high-temperature structural materials

Guest Speaker: Prof. Florian Vogel

School of Mechanical and Automotive Engineering
South China University of Technology

Florian Vogel is a German materials scientist and currently an Associate Professor at South China University of Technology (SCUT). His research focuses on atomic-scale phase transformation physics and the role of interfacial energetics in complex alloy systems. He specializes in advanced microscopy and microanalysis, including atom probe tomography (APT), TEM, FIB/SEM, EBSD, combined with thermodynamic modeling to study multicomponent high-temperature alloys and high-entropy alloys. Prof. Vogel has published extensively, including papers in Nature Communications, Acta Materialia, JMST, and Materials & Design, with 18 first- or corresponding-author publications. He has led 11 national and provincial research projects, including the NSFC Foreign Young and Excellent Young Scientist programs. Before joining SCUT, he held faculty positions at Hainan University and Jinan University, and previously served as head of the Atom Probe Laboratory at TU Berlin. He also conducted postdoctoral research at the University of Alabama and TU Berlin. His current work aims to unravel hierarchical microstructure evolution and interfacial segregation mechanisms in high-temperature alloys and to develop compositionally efficient alloy-design strategies for next-generation structural materials. He is also engaged in the standardization and reproducibility of atom probe tomography representing APT as the China delegate in ISO/TC 201/SC 6 (Surface Chemical Analysis) and is an active member of the International Field Emission Society (IFES) and contributor to the Committee on APT Standards, member of the Chinese Committee on Ion and Atom Probe Professional Committee within the Chinese Society for Measurement, and the Committee on Three-Dimensional Atom Probe Tomography within the Chinese Society of Metrology.

The performance of Ni-based high-temperature structural materials for critical components in jet engines and gas turbines, is defined by the alloys’ high-temperature properties and microstructural stability. Performance, service life and sustainability of such alloys are critically intertwined and controlled by microstructure and phase chemistry. Ni-based superalloys comprise a  matrix (A1) with cube-shaped ’ precipitates (L12), a hierarchical microstructure is created when additional nanoscale  particles emerge within ’ precipitates. Such hierarchical microstructures show a prominent impact on mechanical and high-temperature creep properties of Ni-based superalloys [1,2]. However, research has identified two metastability pathways: The  particles either emerge as spheres and then transform to plates which further grow and split ’ precipitates, or they grow and then gradually dissolve within ’ precipitates. Both scenarios result in a loss of the strengthening effect. Such behavior is determined by phase chemistry and intrinsically linked to thermodynamics, i.e. enthalpy of mixing of ’, elastic energy and interface energy, and kinetics controlled by diffusivity. Here, we explore the impact of adding  forming elements to Ni_86.1-nAl_8.5Ti_5.4X_n with X = Cr, Co, Mo, Ru, W, Hf or Re and n = 1–4 at.%, on formation and thermal phase stability of hierarchical microstructures. We show that phase targeted alloy design by adding  forming species enables to specifically trigger partitioning to the hierarchical  particles, and thereby to control their morphology and thermal stability. We utilized transmission electron microscopy (TEM), atom probe tomography (APT) and ThermoCalc to ascertain the fundamental mechanisms underpinning the formation and thermal stability of hierarchical microstructures in the context of thermodynamics and kinetics. We compare our experimental phase chemistry data to predictions made by ThermoCalc. Our work demonstrates avenues for modulating the thermal stability of hierarchical architectures via phase targeted alloy design.