Methods

Neutron imaging is a powerful non-destructive technique used in materials science to visualize the internal structure of materials. Unlike X-rays, neutrons are highly sensitive to light elements such as hydrogen, making them particularly useful for studying materials containing these elements. This sensitivity allows researchers to investigate a wide range of materials, including metals, ceramics, polymers, and biological samples.

One of the key capabilities of neutron imaging is its ability to penetrate deeply into materials without causing significant damage, providing detailed insights into their internal features. This makes it ideal for examining complex structures, detecting defects, and analyzing the distribution of different phases within a material. Additionally, neutron imaging can be used to study dynamic processes in real-time, such as fluid flow, phase transitions, and mechanical deformation.

Advanced techniques like energy-selective imaging and neutron tomography further enhance the capabilities of neutron imaging. Energy-selective imaging allows for the differentiation of elements and isotopes within a sample, while neutron tomography provides three-dimensional reconstructions of the internal structure. These capabilities make neutron imaging an invaluable tool for advancing our understanding of material properties and behaviors, leading to innovations in various fields, including engineering, chemistry, and biology.

From the cell membrane to the surface of electrodes or at the contact between moving parts in a motor, interfaces play a crucial role in many systems and processes.

Reflectometry is a method of choice to investigate such systems: [just as observing the reflexion of the sun on the surface of a lake tells us about .....] The exact way our sample's surface reflects neutrons provides detailed information about its structure at the microscopic scales.

This method is most often used to identify and describe how the density and composition of a thin film changes along its normal. (image? ref??) The thickness of individual layers can be measured, diffuse interfaces can be detected and quantitatively characterized.

In some cases, it might also be interesting to investigate how the material is organized laterally inside the layers: this is particularly relevant for nanostructured systems. That can be accomplished using off-specular reflectometry, that is, by analyzing how neutrons are reflected in directions which differ from that expected for an ideally flat surface.

Understanding the microstructural origins of specific material properties is central to cutting-edge research in advanced materials, such as modern engineering alloys and superalloys, battery cathodes and anodes, solid-state hydrogen storage systems, and plasma-facing materials for fusion reactors. These materials, despite their diversity, share one important feature: they are characterized by hierarchical structures, where length scales ranging from atomic distances to the nanoscale influence both their structural and functional properties. Many of these materials also exhibit partial crystallization, with certain sub-phases contributing to their overall behaviour.

By investigating the nano-structural properties—such as precipitation size, morphology, and volume fraction—and combining this information with data from other scattering techniques (e.g., neutron diffraction), we can gain a deeper understanding of how these factors contribute to material functionality. Insights into properties like phase fraction, space group, crystal quality, and correlation lengths are crucial to advancing material performance and design.

The SANS technique is ideal for probing structural inhomogeneities at the mesoscopic scale (roughly 10–3000 Å) within bulk materials. It is widely applied to polymers, disordered and porous materials, colloidal systems, ceramics, biological structures, and metallic alloys, including precipitates in composites. SANS data can provide valuable bulk information about the size, composition, and volume fraction of crystalline or amorphous precipitates, which are essential for understanding a material’s properties. These measurements can also be taken in situ to study size evolution during temperature treatments, offering real-time insights into material behaviour.

Moreover, SANS takes advantage of the neutron’s spin degree of freedom, allowing for a unique sensitivity to magnetic materials and nanoscale magnetic correlations. This makes SANS an invaluable tool for studying a wide range of magnetic systems, from soft magnetic Fe-based nanocomposites to hard magnetic NdFeB permanent magnets, magnetic steels, ferrofluids, nanoparticles, magnetic oxides, and more. It also offers new opportunities for investigating fundamental condensed matter phenomena, such as skyrmionic spin textures, non-collinear magnetic structures, magnetic/electronic phase separations, and vortex lattices in type-II superconductors.

Neutron diffraction is a powerful technique for measuring residual stresses (RSs) and crystallographic texture in materials. Due to the deep penetration of neutrons is in ~ cm range in most engineering materials (e.g., steels, aluminium, nickel), it is particularly useful for bulk residual stress analysis and texture characterization.

RSs are internal stresses that remain in a material after external loads or thermal gradients are removed. Neutron diffraction measures these stresses by analysing changes in the crystal lattice spacing (d-spacing) within the material. Principle is that the atomic planes within the crystal lattice extension or contract when a material is under stress, causing a change in the d-spacing. Using Bragg’s Law neutron diffraction measures the diffraction angle (θ) of neutrons scattered by the crystal lattice. By comparing the measured d-spacing with a stress-free reference (e.g., a stress-free sample or powder), the strain (ϵ) can be calculated. The residual stress (σ) can be then determined using Hooke's Law and the material's elastic constants.

Texture refers to the preferred orientation of crystallites (grains) in a polycrystalline material with respect to the sample coordinator. Neutron diffraction is used to measure so-called pole figures by analysing the intensity distribution of diffraction peaks as a function of sample orientation. High quality complete pole figures with good grain statistics are obtained.

For both measurements, most important is that the neutron diffractometers take the most advantages for precise gauge volume definition which can be realized by high flexible optics systems such as slit or collimators at both incoming and outgoing beams. Moreover, with the help of modern robotic system, RSs and texture measurements can be automatically performed.

Dilatometry measures the change in length of a sample when heated, which is the thermal expansion coefficient (TEC) of the material. In addition, these measurements can also provide information on phase and structural transformations at high temperature. A set of different measurements can be performed for constructing time-temperature transformation (TTT) and continuous cooling transformation (CCT) diagrams. TTT diagrams provide critical information about the phase transformations and microstructural evolution that occur during the heat treatments at a constant temperature as a function of time. CCT diagrams are used to represent which types of phase changes occur in a material as it is cooled at different rates. Knowledge of the TTT or CCT diagrams of materials is an important factor in the thermo- mechanical processing of those materials.

With our system it is also possible to perform specimen deformation at different temperatures by compression and by tension. This provides additional information about the materials under investigation, such as true stress/strain curves (which reveal properties of a material such as the Young's modulus, the yield strength and the ultimate tensile strength), time-temperature-transformation diagrams after deformation (DTTT), creep and relaxation processes. In addition, tensile and compression tests can be alternated to emulate mill processing. The dilatometer can also be used to induce microstructural transformations, such as high temperature texturing of alloys, phase transformations and in situ hot pressing of composite materials, among others.