Development of materials concepts and in situ alloying methods for joining and coating components used in the combustion, storage and transport of hydrogen-based energy carriers

Project description

Welded joints are particularly critical in the transport, storage and combustion of hydrogen and its derivatives, where process-related defects, residual stresses and martensitic microstructures further increase the tendency toward embrittlement. In the direct combustion of hydrogen in large engines, higher temperatures and increased corrosion are additional factors. Existing solutions such as austenitic stainless steels, nickel-based alloys and thin-film barriers are either too expensive, cannot be repaired or are unsuitable for large and complex components subjected to high stresses. There is a need for specifically developed, industrially viable materials and processing concepts for welded joints and coatings in hydrogen technology.

EWIG is pursuing a transformative approach: The materials concept of high-entropy and complex alloys (HEA and CCA) is advancing so that mechanical and corrosion properties in welds and coatings can be specifically and locally adjusted in situ, that is, directly during the manufacturing process. The desired alloy composition is created only during welding or coating - flexibly, gradable and with cost-effective on-the-fly alloying. A digital materials design tool combines atomistic and thermodynamic simulations with experimental process and materials data and, using machine learning, enables rapid predictions of phase formation and properties. Practical feasibility is demonstrated using two demonstrators at TRL 5 to 6: a welded pressure vessel component with a graded weld (hydrogen-resistant root, tough middle section, corrosion-resistant cover layer) and a build-up welded valve seat for large engines. Advanced testing methods for materials in hydrogen-containing atmospheres and an evaluation concept for the design of welded joints under hydrogen stress further enhance the approach. 

Fraunhofer IWM Work Packages:

Fraunhofer IWM performs atomistic calculations based on density functional theory (DFT) to predict phase stability in high-entropy and complex alloy systems - including the influence of hydrogen on phase formation. In parallel, thermodynamic simulations based on the CALPHAD (CALculation of PHASE Diagrams) method with systematic element variation are performed to efficiently narrow down the vast composition space of HEAs and CCAs and to calculate melting intervals and heat treatment parameters. From these results, Fraunhofer IWM derives specific alloy compositions for experimental high-throughput screening (in collaboration with IWS). Fraunhofer IWM’s particular strength lies in its automated, combinatorial high-throughput methodology. This has led to the development of the material design tool - a Streamlit-based web tool that clearly presents simulation data, experimental materials and process data and ML-based predictions (e.g., regarding chemical composition based on wire feed, phase formation and properties of materials) and makes them accessible to all partners.

Fraunhofer IWM is responsible for the structural and mechanical characterization of all produced layers and welded joints. This includes microstructure analyses (scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD)), advanced diffraction methods (strain-stress analysis by X-ray diffraction (STRAP)) and pair distribution function (PDF) analyses to elucidate the local atomic order in the complex alloys. A key contribution lies in materials testing in hydrogen atmospheres: Using a micro-tensile testing apparatus developed at Fraunhofer IWM, researchers can determine local mechanical properties of individual weld zones even under hydrogen pressure. Within the project, the testing methodology is being expanded to include mixed gases (hydrogen with various additives), elevated temperatures and preloaded specimens.

Fraunhofer IWM tests the welded pressure vessel components under conditions close to those in service (mechanical loading in a hydrogen atmosphere, corrosion) and is establishing a tribological test sequence for valve linings to evaluate their wear behavior under hydrogen exposure. In addition, Fraunhofer IWM is developing an evaluation concept for welds in hydrogen: Building on fractographic analyses, existing design concepts (Fatigue Assessment Techniques (FAT) classes according to the International Institute of Welding (IIW) guideline, Fachkreis Metall (FKM) guideline) are being applied for the first time to samples tested in hydrogen, and concepts for expanding these guidelines are being developed.