Microstructure-specific Hardening of Ferritic-Martensitic Steels pre and post 15 dpa Neutron Irradiation at 330°C: A Dislocation Dynamics Study

In this work, we used Dislocation Dynamics (DD) simulations to investigate the role of the hierarchical defects microstructure of ferritic-martensitic steel Eurofer97 in determining its hardening behavior. A Representative Volume Element (RVE) for DD simulation is identified based on the typical martensitic lath size. Material properties for DD simulations in b.c.c Eurofer97 are determined, including the dislocation mobility parameters. The dependence of material parameters on temperature is fitted to experimental yield strength measurements carried out at room temperature and 330 °C, respectively. Voids and precipitates observed in the microstructure, such as M23C6 and Tantalum-rich MX, are considered in our DD simulations as inclusions with realistic size distribution and volume density, while 〈1 1 1〉 -and 〈1 0 0〉 -type irradiation loops are included directly in the DD simulations. The lath structure, together with its typical precipitates arrangement and the different crystallographic orientation of the martensitic blocks can also be captured in the simulations. DD simulations are used to extract microstructure-specific hardening parameters, which can be used to simulate the properties of Eurofer97 at the engineering scale

Review and critical assessment of dislocation loop analyses on EUROFER97

The understanding of microstructural defects behavior after neutron irradiation is crucial for assessing the applicability of reduced activation ferritic/martensitic (RAFM) steel EUROFER 97 in future fusion reactors. Formation and evolution of dislocation loops is believed to play the major role in material's hardening under neutron irradiation. In this work, transmission electron microscopy (TEM) data on dislocation loop size distribution is provided after different irradiation campaigns to determine the role of neutron dose on the dislocation loop evolution. A comparison of investigations on dislocation loop behavior and appearance yield considerable differences. For a conclusive interpretation, this work reviews available data, and possible reasons for the observed differences are discussed. Recommendation for future TEM investigation are given. Keywords: TEM, Microstructural defects, Neutron irradiation, Fusion, Reduced activation ferritic/martensitic RAFM steel

Thermomechanical design rules for photovoltaic modules

We present a set of thermomechanical design rules to support and accelerate future (PV) module developments. The design rules are derived from a comprehensive parameter sensitivity study of different PV module layers and material properties by finite element method simulations. We develop a three dimensional finite element method (FEM) model, which models the PV module geometry in detail from busbar and ribbons up to the frame including the adhesive. The FEM simulation covers soldering, lamination, and mechanical load at various temperatures. The FEM model is validated by mechanical load tests on three 60-cell PV modules. Here, for the first time, stress within a solar cell is measured directly using stress sensors integrated in solar cells (SenSoCells®). The results show good accordance with the simulations. The parameter sensitivity study reveals that there are two critical interactions within a PV module: (1) between ribbon and solar cell and (2) between front/back cover and interconnected solar cells. Here, the encapsulant plays a crucial role in how the single layers interact with each other. Therefore, its mechanical properties are essential, and four design rules are derived regarding the encapsulant. Also four design rules concern front and back sides, and three address the solar cells. Finally, two design rules each deal with module size and frame, respectively. Altogether we derive a set of 15 thermomechanical design rules. As a rule of thumb of how well a bill of material will work from a thermomechanical point of view, we introduce the concept of specific thermal expansion stiffness ${\hat{E}}_{\alpha }=E\cdotp \alpha \cdotp {A}_{\mathrm{j}}\cdotp h$ as the product of Young\u27s modulus E, coefficient of thermal expansion $\alpha$, joint area A$_{j}$, and materials height h. The difference between two materials is a measure of how much thermal strain one material can induce in another. A strong difference means that the material with the larger value will induce thermal strain in the other

Mechanical properties and quality of plasma sprayed, functionally graded tungsten/steel coatings after process upscaling

The First Wall of a fusion reactor needs to withstand high heat flux as well as particle bombardment. For this, a First Wall made of steel requires a protective coating with a material that may still transfer heat for conversion to energy, such as tungsten. Its thermal expansion mismatch towards steel is overcome by vacuum plasma spraying of a functionally graded material onto the steel wall, followed by a tungsten top coat. This process was recently transferred to industry for upscaling, to develop a coating technology that can cover the large dimensions of First Wall components without deteriorating the substrate steel\u27s properties by overheating. This work represents an instrumented indentation study of the achieved coating quality and properties, combined with microstructural analysis. Hardness profiles within coating and substrate indicate successful establishment of a linearly functionally graded material and only minor substrate overheating. The latter observation is supported by electron backscatter diffraction showing no change in the substrate\u27s microstructure. The substrate hardness was investigated on several positions of coated plates sizing up to 500 × 250 mm2. The results indicate faster cooldown in the plate corners. Cooling channel bores that were pre-fabricated in the plates had no effect on plate hardness after coating. The elastic modulus of the coating\u27s interlayers, determined by instrumented indentation, was found lower than predicted from bulk properties. This is attributed to the heterogeneous microstructure of the thermally sprayed coating