High-performance Ferritic (HiperFer) steels represent a promising materials innovation for next-generation thermal energy conversion systems, particularly in cyclically operating applications like concentrating solar thermal plants and heat storage power plants (Carnot batteries), where current market adoption is hindered by the lack of cost-effective, high-performance materials. HiperFer steels demonstrate superior fatigue resistance, creep strength, and corrosion resistance compared to conventional ferritic-martensitic 9-12 Cr steels and some austenitic stainless steels, making them potentially transformative for future energy technologies. This paper examines the microstructural mechanisms underlying HiperFer’s enhanced fatigue resistance in both short and long crack propagation, while also presenting current findings on salt corrosion properties and exploring potential alloying improvements for fusion reactor applications, highlighting the broad technical relevance of these innovative materials.

Future, flexible thermal energy conversion systems require new, demand-optimized high-performance materials. In order to provide a basis for the targeted development of fatigue-resistant, cost-effective steel grades, the microstructural damage to materials and the failure of conventional and novel steels were investigated in thermo-mechanical fatigue and fatigue crack propagation experiments. Based on the results, improved, ferritic “HiperFer” (High performance Ferrite) steels were designed, produced and characterized. A brief description of the current state of development is given.

More efficient, sustainable, flexible and cost-effective energy technologies are strongly needed to fulfil the new challenges of the German “Energiewende”. For a reduction of consumed primary resources higher efficiency steam cycles with increased operating parameters, pressure and temperature, are mandatory. Hence, advanced materials are needed. The present study focuses on stainless, high strength, ferritic (non-martensitic) steel grades, regarding thermal treatment effects on particle evolution. The heat treatment includes variations, e.g. a two phase pre heat treatment. Effects of the treatment were analysed and connected to creep performance. Experiments at differently heat treated materials show promising improvement of creep performance. These results can be linked to the stability and evolution of strengthening Laves phase particles.

High chromium HiperFer (High performance ferritic) materials present a promising concept for the development of high temperature creep and corrosion resistant steels. The institute for Microstructure and Properties of Materials (IEK-2) at Forschungszentrum Jülich GmbH, Germany develops high strength, Laves phase forming, fully ferritic steels which feature excellent resistance to steam oxidation and better creep life than state of the art 9-12 Cr steels. Mechanical strength properties of these steels depend not only on chemical composition, but can be adapted to various applications by specialized thermo(mechanical) treatment. The paper will outline the sensitivity of tensile, creep, stress relaxation and impact properties on processing and heat treatment. Furthermore an outlook on future development potentials will be derived.

In the present study a creep resistant, ferritic steel, based on the chemical composition of Crofer 22 H, was analysed regarding microstructure and particle evolution. Because of the preceding hot-rolling process formation of sub-grain structures was observed, which disappears over time. Additionally formation of particle-free zones close to high angle grain boundaries was observed. These zones are considered to be responsible for long-term material failure by lacking particle hardening and thus a concentration of deformation. Therefore in-depth analyses by transmission and scanning electron microscopy were performed to investigate dislocation behaviour in these areas

Characteristics of atmospheric plasma spraying based on single-cathode-anode-systems like the F4 gun with convergent-cylindrical nozzle designs, are voltage fluctuations caused by periodically changes of the arc length. As a result continuous varying plasma flow properties lead to inhomogeneities during energy transfer to injected powder particles and variations of coating quality and process efficiency. With an adjusted convergent-divergent nozzle design and optimized high energy plasma parameters it is proven that process efficiency and stability could be significantly increased, also due to the reduced arc movement. A drawback in this case is the increased anode wear which needs to be optimized to secure industrial usage. Aim of this work was to minimize the anode wear of contoured convergent-divergent nozzles by using high efficient plasma parameters. Therefore arc characteristics in different nozzle designs were analyzed and the influence of the geometry to arc anode attachment was investigated. Consequently a stepwise optimization of anode wear by keeping the plasma fluid dynamic properties almost constant could be achieved. The results contribute to understanding of the arc characteristics in atmospheric plasma spraying. Also a new concept of a ”three-zone anode geometry“, convergent-inlet-section, cone-shaped arc movement section and a divergent plasma fluid shape section was developed.

Constricted steam oxidation resistance and finite microstructural stability limits the use of 9 - 12 wt.-% chromium ferritic-martensitic steels to steam temperatures of about 620 °C. Newly developed 12 wt.-% Cr steels are prone to Z-phase precipitation, which occurs at the expense of the strengthening precipitates, and therefore suffer an accelerated decline in strength during longterm operation. While the concept of ferritic-martensitic chromium steels thus seems to hit technological limitations, further improvement in steam power plant efficiency necessitates a further increase of steam pressure and temperature. Furthermore increasing integration of intermitting renewable energy technologies in electrical power generation poses a great challenge for supply security, which has to be ensured on the basis of conventional power plant processes. Besides improved efficiency for resource preservation, load flexibility, thermal cycling capability and downtime corrosion resistance will play key roles in the design of tailored materials for future energy technology. Under these preconditions a paradigm shift in alloy development towards improvement of cyclic steam oxidation and downtime corrosion resistance in combination with adequate creep and thermomechanical fatigue strength seems to be mandatory. The steam oxidation, mechanical and thermomechanical properties of fully ferritic 18 - 24 wt.-% chromium model alloys, strengthened by the precipitation of intermetallic (Fe,Cr,Si)2(Nb,W) Laves phase particles, indicate the potential of this type of alloys as candidate materials for application in highly efficient and highly flexible future supercritical steam power plants.

Hot electron induced beta degradation has been observed from fiber optic transistors after multiple parametric testing. Beta degradation originated from increasing base leakage current due to the multiple testing. Base leakage current increases were directly related to the hot electron phenomenon at Si-SiO2 interface layer. The hot electron effect broke down the trivalent silicon and its hydrogen compounds (SisH) at the interface layer, which created mobile interstitial hydrogen atoms (Hi) and trivalent silicon atoms Si* (interface trap charges) at the same time. Typically, the SisH forms during the post metallization anneal. This paper will outline the following topics: 1.) The generation of mobile hydrogen atoms and trap charges at the Si-SiO2 interface due to the hot electron phenomenon and its relationship to transistor beta degradation. 2.) A quantitative analysis of hydrogen atoms measured by Secondary Ion Mass Spectrometry (SIMS), and a direct relationship model between beta degradation and hydrogen profiles at the interface layer. 3.) Experimental result showing transistor beta recovery as well as the repopulation of the hydrogen atoms at the interface layer after low temperature annealing (150 °C to 200 °C bake).