Research Project #18: MAX phases and SMART tungsten materials: understanding the high-temperature performance at a nanoscale
New renewable energy sources, including concentrated solar power (CSP) stations, strongly demand novel advanced materials capable to operate at higher temperature than the current used metallic compounds in order to increase their efficiency. However, the aggressive operating conditions – temperatures above 1000 °C, humid and chemically reactive environment, thermal and mechanical stresses, etc. – have limited the number of potential candidates. This problem has been tackled in our institutes in the last years with the development of the two most promising materials for novel energy sources under aggressive environments: MAX phases at IEK-1 and Self-passivating Metal Alloys with Reduced Thermo-oxidation (SMART) at IEK-4. Both materials have been already processed and developed, positioning us as pioneers in the material science field [1, 2], but now is the time to transfer this knowledge to the real final application. To fully achieve this task, the PhD candidate will focus on the performance and evolution of both materials under the aggressive environmental conditions expected for the solar receiver of a CSP station.
Self-passivating Metal Alloys with Reduced Thermo-oxidation (SMART), which are based on tungsten with additions of chromium and yttrium, are under development for future fusion power plants. SMART materials demonstrate good performance in plasma under planned operation conditions and ensure safety under assumed accidental scenarios due to their high oxidation resistance in humid air . The innovative MAX phases, in this specific case Cr2AlC, are a new family of materials (more than 70 different compositions) that bridge the gap between metals and ceramics, featuring exceptional chemical inertness, thermal stability at temperatures exceeding 1000oC along with electrical conductance, easy machinability and exceptional damage tolerance . These features make them prime candidates for use in a number of modern energy systems including turbines, heat exchangers and catalyst supports.
Due to their remarkable high temperatures properties, SMART and MAX materials appear as the perspective candidates for the advanced solar receivers in CSP plants as well. The performance of both material classes is controlled by their microstructure, rendering their further improvement critically dependent on the fundamental understanding of processes occurring in the materials down to the nanoscale level. The project addresses the questions of phase formation and stability, high-temperature oxidation behavior and microstructural evolution of the materials with a particular focus on advanced microstructural characterization techniques such as Atom Probe Tomography (extensive knowledge at ZEA-3 institute). These methods will be used to deliver the crucial experimental input for predictive modelling of material properties  and eventually optimize the alloy design strategy. Based on this study, the feasibility of employing the SMART and MAX materials for CSP receiver will be assessed. The project assumes a close collaboration with several research groups possessing high expertise in materials synthesis, advanced characterization, performance testing and modeling.
The following scientific tasks will be addressed in the framework of the proposed Ph.D. thesis:
- Characterization of the microstructure of W-Cr-Y, W-Cr-Zr (SMART) and Cr2AlC (MAX Phase) base materials with the focus on electron microscopy and atom probe tomography analyses.
- Analysis of their microstructural evolution (segregation, phase formation and diffusion under temperatures of ³ 1000oC) and its effect on the CSP-relevant properties.
- Controlled oxidation testing (dry and wet air) and characterization of surface oxide scales.
- Providing experimental input for predictive modeling of the properties and assessment of its accuracy.
 A. Dash, R. Vaßen, O. Guillon, J. Gonzalez-Julian, “Molten Salt Shielded Synthesis of Oxidation Prone Materials in Air,” Nature Materials, 18 (2019) 465.
 A. Litnovsky, F. Klein, J. Schmitz, T. Wegener et al., „Smart first wall materials for intrisic safety of a fusion power plant,“ 136 (2018) 878.
 A Litnovsky, T Wegener, F Klein et al., "New oxidation-resistant tungsten alloys for use in the nuclear fusion reactors", Phys. Scr. T170 (2017) 014012.
 J. Gonzalez-Julian, S. Onrubia, M. Bram, C. Broeckmann et al., “High-temperature oxidation and compressive strength of Cr2AlC MAX phase foams with controlled porosity”, J. Am. Ceram. Soc. 101 (2018) 542.
 D. Nguyen-Manh, M. Muzyk, K.J. Kurzudlowski, N. Baluk et al., “First principles modeling of tungsten-based alloys for fusion power plant applications”, Key Engineering Materials 465 (2011) 15.
M.Sc. degree in Materials Science, Physics, Mechanical Engineering; (experience) in-depth understanding of material characterization and modeling.
Dr. A. Litnovsky
tel.: +49 2461 61-5142
Dr. I. Povstugar
tel.: +49 2461 61-9582
Prof. Dr. J. Gonzalez-Julian
tel.: +49 2461 61-96761