Focus Seminar on hard metals

This event consists of four short seminars on hard metals, given by four distinguished scientists within the field of ab initio modeling and experimental investigation of cemented carbides.

Professor Göran Wahnström
First-principles derived “interfacial phase diagrams” for phase boundaries in doped cemented carbides

PhD RuiwenXie
Quantum mechanics basis of quality control in hard metals

Professor Klaus Leifer
Towards atomic resolution electron magnetic circular dichroism

PhD Song Lu
Stacking fault energy and deformation mechanism of binder phase

For questions please contact: hillertmodelinglab@kth.se

Welcome!

More information about the topics and the speakers below.

Seminars

Seminar A

First-principles derived “interfacial phase diagrams” for phase boundaries in doped cemented carbides

Professor Göran Wahnström

The macroscopic properties of polycrystalline materials, such as hard metals, may be equally influenced by the thermodynamic and mechanical properties of its internal interfaces as by the properties of the constituent bulk phases. Therefore, being able to understand and predict the properties of interfaces of polycrystalline materials becomes important.

We have developed a methodology based on a combination of DFT calculations and Thermo-Calc evaluations to determine the properties of interfaces in WC/Co based cemented carbides, doped with secondary transition metal carbides. The material is produced under liquid phase sintering conditions and the doping is used to mitigate the WC grain growth to obtain a harder material. It is known that the dopants may segregate to phase boundaries in the material and produce complex interfacial structures. We use our developed technique to derive “interfacial phase diagrams”, which depict regions of stability for different interface structures as function of temperature and chemical potentials.

Lecturer

Professor Göran Wahnström was awarded a PhD degree in Theoretical Physics at Chalmers University of Technology in 1985. After graduating, he moved to University of California, Santa Barbara for a two-year postdoctoral stay. He then moved back to Chalmers University of Technology and in 2001 he became Professor in Physics at the same university.

His research interest is electronic and atomic scale modeling in materials science. He has studied various kinetic processes using both classical and quantum mechanics. Slow relaxation phenomena in disordered materials have been revealed using simple generic models. Diffusion of hydrogen in metals and on metal surfaces has been investigated including quantum and non-adiabatic effects. Interfaces in hard metals have been studied and a type of defect phase diagrams has been derived using a first-principles based approach. Various properties of proton diffusion in oxides have been investigated as well as more generic properties of perovskite structured oxides.

Seminar B

Quantum mechanics basis of quality control in hard metals

PhD Ruiwen Xie

Non-destructive and reliable quality control methods are a key aspect to designing, developing and manufacturing new materials for industrial applications and new technologies. The measurement of the magnetic saturation is one of such methods and it is conventionally employed in the cemented carbides industry. We present a general quantum-mechanics-based relation between the magnetic saturation and the components of the binder phase (85Ni15Fe) of cemented carbides, which can be directly employed as a quality control. The excellent agreement between calculated and measured magnetization saturation demonstrates the applicability of our method to any binder phase, which allows us to explore new materials for alternative binder phases efficiently.

Lecturer

Dr. Ruiwen Xie is a postdoctoral researcher affiliated with the Technical University of Darmstadt, where she is actively engaged in research on the magnetic properties of rare-earth-based and high-entropy intermetallicsusing advanced ab initio computational methods. Prior to her current role, she completed her Ph.D. in Materials Science and Engineering from KTH Royal Institute of Technology, with her doctoral research focusing on DFT-based study of defects in austenitic steels and hard metals. She has also developed additional interests in applying machine learning techniques to facilitate and accelerate material design.

Seminar C

Towards atomic resolution electron magnetic circular dichroism

Professor Klaus Leifer

To date, the transmission electron microscope is in many domains of science the only instrument that allows the analysis of bulk properties with down to sub-atomic resolution. Magnetic measurements in the TEM approach sub-nanometer to atomic resolution nowadays using techniques such as electron holography, electron magnetic circular dichroism (EMCD) and Lorentz microscopy. The hitherto best resolutionswere reported using the technique of (EMCD). The phenomenon of EMCD observed has stimulated many experiments since the proposal of the method by P. Schattschneider[1]. The technique has demonstrated atomic plane resolution of the core loss edge of the ferromagnetic elements. Thus, this technique might also enable the analysis of a magnetic sample at atomic resolution. Here, we show that an improvement of signal/noise ratio and orientation control of the sample leads to a strong enhancement of the EMCD signal whereas the use of highly convergent electron beams yields an EMCD signal inside the convergent beam diffraction disk. The use of custom-made multi-hole apertures inside the energy filter finally allows us to demonstrate an EMCD signal on the zone axis orientation at convergence angles corresponding to atomic resolution conditions. In a collaboration with SandvikCoromant, we have started to apply this technique for the analysis of magnetic phases in hard materials.

[1] Schattschneider,etal. (2006). Nat. 441(7092): 486. Ruszet al. (2016). Nat. Comm., 7: 12672; Wang et al. (2018). Nat. Mat. 17: 221. Ali et al. (2020).
[2] Negi et al. (2019). Phys.Rev.Lett. 122: 037201.

Lecturer

Professor Klaus Leifer studied physics at the RWTH Aachen, Germany. In his PhD work at the EPFL in Lausanne, Switzerland, he analysed quantum nanostructures and the impact interfacial atomic scale structure and chemical composition on properties of metallic thin films using mainly transmission electron microscopy.

In 2005, he started to work as a professor on “Experimental Physics and Analytical Electron Microscopy” at Uppsala University. With his group of electron microscopy and nano-engineering, ELMIN, he developed and applied several TEM techniques such as spectroscopic electron tomography, soft materials TEM and interfacial analysis mainly in energy and hard materials. Through modification and functionalization of molecular electronics materials as well as 2D materials, the group could modify electronic properties leading to band-gap opening, novel mechanical properties as well as nano-sensors. Developing the technique of Electron Magnetic Circular Dichroism Spectroscopy allowed the group to analyse magnetic materials with close to atomic scale resolution.

Seminar D

Stacking fault energy and deformation mechanism of binder phase

PhD Song Lu

Stacking fault energy (SFE) plays an important role in deformation mechanisms and mechanical properties of face-centered cubic (fcc) metals and alloys. This is also true for Co as the binder phase in hard metals. Here, I will discuss the experimental and theoretical methods for determining the SFE and the correlations between SFEs and deformation mechanisms. I will discuss the underlying dislocation mechanisms underpinning twinning and martensitic transformation in metastable fccmetals. The atomistic scale simulations of Co binder phase (solid solution) for understanding the thermodynamicalproperties and deformation behaviors will facilitate our design of Co-free new binder phases.

Lecturer

Dr. Song Lu has been working with applying advanced first-principles density functional theory (DFT) methods for studying the mechanical properties of metallic materials for many years. His research interest focuses on studying the properties of various defects (e.g., interfaces, grain boundaries, twin, stacking fault, etc.) and their impacts on mechanical properties of engineering alloys including stainless steels, and high entropy alloys. He has performed systematic simulations for planar defects in alloys over 10 years, exploring the effects of composition, magnetism and temperature on their properties. He is interested in applying multiscale simulation methods in designing new TWIP (transformation-induced plasticity) and TRIP (transformation-induced plasticity) alloys.