Tao Zhou

Tao Zhou did his master study in materials science and engineering at university of science and technology Beijing (USTB), followed by PhD study (2015-2019) in materials science at KTH. Thereafter, He have been working as a postdoc and now senior researcher at KTH, with the current roles as follows:

- Senior researcher at the Department of Materials Science and Engineering, working on the Composition-Process-Structure-Property-Performance/Recycling relationships of sustainable metals through advanced characterization and computational tools.

- Developer at the Center for X-rays in Swedish Materials Science (CeXS), focusing on the application and development of synchrotron X-rays based techniques, mainly WAXS and SAXS, under different sample environments.

- Project leader at the center NEXT (Neutron and X-ray science for industrial technology transitions), focusing on high-throughput in situ experiments.

- Team leader for Micro-/Nano-structure Characterization at the Unit Hultgren Laboratory for materials characterization, focusing on electron microscopy and atom probe tomography.

Research interests

- Precipitation in different alloy systems, including steels, Ni-based alloys, Al-based alloys, etc.

- Martensitic microstructure and martensitic phase transformation.

- Development of hydrogen-tolerant and scrap-tolerant steels.

- Computational materials design of high-performance steels.

- Microscopy and microanalysis, including SEM, TEM, APT, etc.

- Application of computational thermodynamics and kinetics.

Research cases

- Computational materials design framework for Cu precipitation-strengthened maraging stainless steels.    Cu, through forming Cu-rich precipitates in bcc-Fe matrix, is an effective alloying element for developing high-performance steels with combination of high-strength and good toughness (the Cu precipitation strengthening allows the reduction of carbon content to obtain same strength). An computational framework including bothor Cu precipitation kinetics using the Langer-Schwartz-Kampmann-Wagner approach coupled with CALPHAD thermodynamic and kinetic databases, quantitative characterization of Cu precipitates including structure, size, volume fraction, number density and chemical composition were performed for different aging conditions using TEM, APT and in situ SANS. Except for precipitation, other microstructure characteristics like effective grain size and dislocation density were also modelled using semi-empirical models, after being calibrated by experiments, where the dislocation density was quantified using the modified Williamson-Hall and Warren-Averbach method through analyzing the peak broadening of XRD data. Further on, yield strength of the material as a function of aging treatment was modelled using semi-empirical models; the Cu precipitation contribution to the stress-strain curves were modelled using an analytical flow stress model based on strain gradient plasticity theory; The stress-strain curves of the martensite matrix were modelled using a dislocation density-based crystal plasticity model.

- Carbides precipitation engineering for high-performance tool steels.   Cr, Mo, and V are widely used as alloying elements for carbon steels, especially tool steels and heat resistant steels, to increase hardenability, hardness, thermal stability,etc. They can potentially form carbide phases of V-rich MC, Mo-rich M2C and M6C, Cr-rich M7C3 and M23C6, etc., except for Fe-rich metastable carbides, depending on the chemical composition and process conditions. Firstly, Mulitple carbides precipitation and mechanical properties of a high-performance tool steel were investigated, and it was found that coarse types of carbides were the dominant secondary phases at the tempering conditions, which is not ideal for the optimal performance. Thereafter, some efforts were put to tailor the carbides precipitation using computational thermodynamics and kinetics to achieve the precipitation of high number density of merely fine types of precipitates, as we know from open literature that the fine carbides precipitation has the merits of high precipitation strengthening, weak effects on toughness (also allowing the reduction in carbon content to improve toughness), H trapping for improved resistance to hydrogen embrittlement, higher thermal stability, increasing creep performance,etc.

- Overview of TEM on precipitation analyiss in metallic materials TEM, a versatile technique for precipitation characterization, has historically been facilitating the understanding of precipitation and precipitation hardening, and over the past decades TEM has also stimulated the optimization of performance of metallic materials through precipitation engineering. The recent advancements in TEM-based techniques, sample preparation methodologies and algorithms for data analysis have significantly strengthened the capability of the premier TEMs. Incorporated with recently developed aberration-corrected techniques, TEM provides an irreplaceable and indispensable instrumentation for precipitation-related research in metallic materials, combining morphological (imaging), chemical (spectroscopy), structural (diffraction), three-dimensional (tomography), environmental (in situ) analyses down to the Ångström scale. (Click here to access to this work)

-Wire-arc additive manufacturing of 17-4 PH stainless steelThe solidification and microstructural evolution during deposition, as well as the structural evolution during post heat treatment, determine the mechanical properties of wire-arc additively manufactured maraging stainless steel. In the present work, we tune the austenite reversion and nanoscale precipitation during post heat treatment and achieve an excellent combination of strength and ductility. The structural evolution is studied through computational thermodynamics, electron microscopy, in situ SANS, and synchrotron XRD. The as-built microstructure is composed of mainly martensite and retained austenite together with a minor fraction of δ-ferrite, M23C6, Nb(C, N), spherical and ellipsoidal Cu precipitates and some inclusions. The presence of these phases cannot be fully predicted by the Scheil-Gulliver model due to the complicated thermal history and non-homogenous elemental distribution. The reverted austenite formed during the post heat treatments has high stability and fine grain size (~1 µm), which contributes to the excellent ductility, while the nanoscale precipitation hardening contributes to the achieved high strength. (Clink here to access to the work)

-CeXS streamlining report series    The CeXS Technical Report Series aims to provide researchers with information and protocols in order make it more straightforward to use the PETRA III Swedish Materials Science beamline. The current three published reports are: 1) Streamlining in-situ SAXS/WAXS heat treatment experiments at the PETRA III Swedish Materials Science beamline; 2) Overview of sample environments for research use at the PETRA III Swedish Materials Science beamline; 3) Inventory of data reduction and analysis software used in high-energy X-ray research at PETRA III. (Clink here to access to the reports)