Johan Hektor

Johan Hektor
Malmö University | mah · Department of Materials Science and Applied Mathematics (IMP)

Doctor of Philosophy

About

18
Publications
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140
Citations

Publications

Publications (18)
Article
Full-text available
Nakhlite meteorites are igneous rocks from Mars that were aqueously altered ~630 million years ago. Hydrothermal systems on Earth are known to provide microhabitats; knowledge of the extent and duration of these systems is crucial to establish whether they could sustain life elsewhere in the Solar System. Here, we explore the three-dimensional dist...
Article
Full-text available
The formation of stacking faults and dislocations in individual austenite (fcc) grains embedded in a polycrystalline bulk Fe-18Cr-10.5Ni (wt.%) steel was investigated by non-destructive high-energy diffraction microscopy (HEDM) and line profile analysis. The broadening and position of intensity, diffracted from individual grains, were followed duri...
Article
Full-text available
The bone tissue formed at the contact interface with metallic implants, particularly its 3D microstructure, plays a pivotal role for the structural integrity of implant fixation. X-ray tomography is the classical imaging technique used for accessing microstructural information from bone tissue. However, neutron tomography has shown promise for visu...
Article
Full-text available
Braze clad on aluminum (Al) sheets has enabled fast and convenient brazing assembly of complex heat exchangers. However, there are details in the brazing process that are not fully understood. In this work we have employed three-dimensional X-ray diffraction (3DXRD) to investigate the grain position, size, and orientation before and after controlle...
Article
Full-text available
Currently, in the era of big data and 5 G communication technology, electromigration has become a serious reliability issue for the miniaturized solder joints used in microelectronic devices. Since the effective charge number (Z*) is considered as the driving force for electromigration, the lack of accurate experimental values for Z* poses severe c...
Article
Full-text available
In Pb-free solder alloys used in solder balls of diameter of 50 μm or small, larger proportion of Cu6Sn5 intermetallics formation is a major reliability concern, and this is aggravated in presence of external thermal gradient. A complete understanding of mechanism of intermetallics compound (IMC) growth under thermomigration is essential for devisi...
Article
Full-text available
Two methods for reconstructing intragranular strain fields are developed for scanning three-dimensional X-ray diffraction (3DXRD). The methods are compared with a third approach where voxels are reconstructed independently of their neighbours [Hayashi, Setoyama & Seno (2017). Mater. Sci. Forum , 905 , 157–164]. The 3D strain field of a tin grain, l...
Article
Full-text available
High-energy synchrotron radiation has been demonstrated to be a powerful tool for materials characterization. The development of novel methodologies is still ongoing, driven by major technological advances regarding the available source brilliance and efficient large area detectors. The Swedish Materials Science beamline at PETRA III is dedicated t...
Preprint
Full-text available
High-energy synchrotron radiation has been demonstrated to be a powerful tool for materials characterization. The development of novel methodologies is still ongoing, driven by major technological advances regarding the available source brilliance and efficient large area detectors. The Swedish Materials Science beamline at PETRA III is dedicated t...
Article
Full-text available
Scanning Laue microdiffraction was used to study the evolution of the microstructure and the stress field around two tin whiskers during ageing for up to 21 months. In the heterogeneous stress fields obtained, localised ridges of high compressive stress leading to the root of the whiskers were found. Due to the evolution of the intermetallic compou...
Article
Full-text available
The 3D microstructure around a tin whisker, and its evolution during heat treatment were studied using scanning 3DXRD. The shape of each grain in the sample was reconstructed using a filtered-back-projection algorithm. The local lattice parameters and grain orientations could then be refined, using forward modelling of the diffraction data, with a...
Article
Full-text available
We have used Differential Aperture X-ray Microscopy (DAXM) to measure grain orientations and deviatoric elastic strains in 3D around a tin whisker. The results show strain gradients through the depth of the tin coating, revealing a higher strain deeper in the Sn layer. These higher strains are explained by the volume change occurring during growth...
Chapter
Towards the improvement of the understanding of force/stress distribution in granular media under load, a new experimental approach is suggested. Neutron diffraction, a non-conventional experimental technique, has been successfully used to map the evolution of intragranular strains in sand specimens loaded in a novel plane-strain apparatus. Represe...
Poster
Full-text available
Neutron diffraction scanning has been successfully used to infer force/stress distribution from ”grain strains”; i.e., the d-spacing changes in the crystal lattices of grains. This work involves the development of a new plane-strain loading apparatus to perform neutron diffraction based experiments on granular geomaterials. New results are presente...
Article
Full-text available
A coupled diffusion-deformation, multiphase field model for elastoplastic materials is presented. The equations governing the evolution of the phase fields and the molar concentration field are derived in a thermodynamically consistent way using microforce balance laws. As an example of its capabilities, the model is used to study the growth of the...

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