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The present study focuses on the weldability of hot-rolled Fe–Mn–Al–Ni shape memory alloy sheets by vacuum electron beam welding. Tailored process-specific welding parameters, such as preheating with electron beam or beam oscillation during welding, allowed defect-free joining with very thin weld seams and heat-affected zones. By applying a post-weld cyclic heat treatment, abnormal grain growth can be promoted across the weld seams. However, regardless of the selected welding parameters, some specimens are characterized by the formation of smaller grains within the former fusion zone. In situ incremental strain tests reveal that the former fusion zone has only a minor influence on the functional properties and is not responsible for structural failure. Thus, electron beam welding is a promising welding technology for joining Fe–Mn–Al–Ni shape memory alloys.

The effect of cooling rate after annealing at 900 °C on the microstructure and hardness of high entropy alloys was investigated using two typical samples with the chemical composition of Co16Cr14.5Fe29Mn11.5Ni29 and Co11.5Cr7Fe27Mn27Ni27(Nb0.08C0.5) (at%). The microstructural characterisation and hardness measurements were carried out by optical microscopy, scanning electron microscopy, wavelength-dispersive X-ray spectroscopy, electron back scattered diffraction, X-ray diffraction technique and Vickers hardness testing. A face centred cubic crystal structure matrix was observed in both alloys before and after annealing and regardless of cooling conditions. SEM analyses revealed an extensive precipitation in Co11.5Cr7Fe27Mn27Ni27(Nb0.08C0.5) alloy after annealing. It was also found that air/furnace cooling can enhance grain growth-coarsening just in Co16Cr14.5Fe29Mn11.5Ni29. However, the hardness results generally showed insignificant hardness variations in both alloys after water-quenching, air-cooling and furnace-cooling. The results suggested that the hardness is mainly controlled by solid solution strengthening.

Welding and joining of hybrid components consisting of additively manufactured (AM) parts and conventionally processed parts offer new opportunities in structural design. In the present study, AlSi10Mg specimens were fabricated using two different manufacturing processes, i.e., laser-based powder-bed fusion of metals (PBF-LB/M) and casting, and welded by means of friction stir welding (FSW). Material strength of dissimilar welded joints was found to be governed by the as-cast material, which is characterized by a very coarse microstructure resulting in inferior hardness and tensile properties. During fatigue testing, cast-cast specimens performed slightly better than their hybrid AM-cast counterparts with respect to lifetime, being rationalized by most pronounced strain inhomogeneities in the AM-cast specimens. With the aim of cost reduction, FSW can be employed to fabricate graded large parts as long as the AM as-built material is placed in the region demanding superior cyclic load-bearing capacity. Graphical abstract

Shape memory alloys (SMAs), such as Ni–Ti, are promising candidates for actuation and damping applications. Although processing of Ni–Ti bulk materials is challenging, well-established processing routes (i.e. casting, forging, wire drawing, laser cutting) enabled application in several niche applications, e.g. in the medical sector. Additive manufacturing, also referred to as 4D-printing in this case, is known to be highly interesting for the fabrication of SMAs in order to produce near-net-shaped actuators and dampers. The present study investigated the impact of electron beam powder bed fusion (PBF-EB/M) on the functional properties of C-rich Ni50.9Ti49.1 alloy. The results revealed a significant loss of Ni during PBF-EB/M processing. Process microstructure property relationships are discussed in view of the applied master alloy and powder processing route, i.e. vacuum induction-melting inert gas atomization (VIGA). Relatively high amounts of TiC, being already present in the master alloy and powder feedstock, are finely dispersed in the matrix upon PBF-EB/M. This leads to a local change in the chemical composition (depletion of Ti) and a pronounced shift of the transformation temperatures. Despite the high TiC content, superelastic testing revealed a good shape recovery and, thus, a negligible degradation in both, the as-built and the heat-treated state.

Iron-based shape memory alloys came into focus as promising candidate materials for large-scale structural applications owing to their cost-efficiency. In the present work, the superelastic properties of a recently introduced Fe-Ni-Co-Al-Ti-Nb shape memory alloy are investigated. For 〈001〉-oriented single-crystalline material in aged condition (650 °C/6 h), an incremental strain test reveals excellent superelasticity at −130 °C with fully reversible strains up to about 6%. Under cycling loading at different test temperatures, however, the alloy system investigated suffers limited functional stability.

Heusler-type Co–Ni–Ga shape memory alloys attracted significant scientific attention owing to excellent superelasticity in single-crystalline state. However, due to pronounced anisotropy, polycrystalline Co–Ni–Ga suffers from transformation-induced constraints at grain boundaries and, thus, premature failure upon thermo-mechanical loading. The present study reports on a novel thermo-mechanical processing route. Hot rolling followed by solution-annealing promotes abnormal grain growth, eventually leading to high-performance single-crystalline structures. The procedure proposed offers great potential for a direct microstructure design.

Co-Ni-Ga shape memory alloys attracted scientific attention as promising candidate materials for damping applications at elevated temperatures, owing to excellent superelastic properties featuring a fully reversible stress-strain response up to temperatures as high as 500 °C. In the present work, the effect of aging treatments conducted in a wide range of aging temperatures and times, i.e. at 300–400 °C for 0.25–8.5 h, was investigated. It is shown that critical features of the martensitic transformation are strongly affected by the heat treatments. In particular, the formation of densely dispersed γ’-nanoparticles has a strong influence on the martensite variant selection and the morphology of martensite during stress-induced martensitic transformation. Relatively large, elongated particles promote irreversibility. In contrast, small spheroidal particles are associated with excellent functional stability during cyclic compression loading of 〈001〉-oriented single crystals. In addition to mechanical experiments, a detailed microstructural analysis was performed using in situ optical microscopy and neutron diffraction. Fundamental differences in microstructural evolution between various material states are documented and the relations between thermal treatment, microstructure and functional properties are explored and rationalized.

A synchrotron X-ray diffraction study of high-temperature (HT) shape memory alloy 49Co–21Ni–30Ga (in at. pct.) was performed. The volume fraction, cell parameter and temperature evolution of the different secondary phases were analyzed. This study reports reliable experimental data on these parameters to be used as a future reference to adjust the composition of the material.

Corrigendum to T. Wegener, A. Liehr, A. Bolender, S. Degener, F. Wittich, A. Kroll, T. Niendorf: Calibration and Validation of Micromagnetic Data for Non-Destructive Analysis of Near-Surface Properties after Hard Turning. HTM J. Heat Treatm. Mat. 77 (2022) 2, pp. 156-172, DOI:10.1515/htm-2021-0023.

Most techniques employed for powder bed additive manufacturing (AM) only can handle a single material. However, additional functionality of the structures built, e.g., local insulation, is desirable for more sophisticated applications. In the present work, a multi-material process allowing for realization of a ceramic coating on a steel substrate and a novel sandwich system are introduced. Both were manufactured by selective laser melting (SLM). As a first step, the microstructure of a bulk zirconia–alumina ceramic, directly manufactured by SLM, was examined and its tensile strength determined. Afterwards, the ceramic was manufactured directly on the as-built surface of a tool steel processed by SLM. For this compound, the adhesive strength was determined. Finally, an open porous structure, made of the same tool steel, was built on top of the ceramic layer. The results clearly prove that the SLM process can be used for direct manufacturing of a multi-material sandwich structure made from metal and ceramic, providing an important step towards complex structures functionalized for electric insulation.

Results are presented reporting on the martensite domain variant selection and stress-induced martensite morphology in [001]-oriented superelastic Co49Ni21Ga30 shape memory alloy (SMA) single crystals under tensile load. In situ neutron diffraction, as well as in situ optical- and confocal laser scanning microscopy were conducted focusing on three differently treated samples, i.e. in the as-grown, solution-annealed and aged condition. An aging treatment performed at 350 °C promotes the precipitation of nanoprecipitates. These second phase precipitates contribute to an increase of the number of habit plane interfaces, while reducing lamellar martensite plate thickness compared to the as-grown and solution-annealed (precipitate free) samples. During tensile loading, all samples show a stress-induced formation of martensite, characterized by one single domain variant (“detwinned”) and one set of parallel habit planes in a shear band. The results clearly show that γ’ nanoprecipitates do not necessarily promote multi-variant interaction during tensile loading. Thus, reduced recoverability in Co-Ni-Ga SMAs upon aging cannot be solely attributed to this kind of interaction as has been proposed in literature so far.

A heat treatable TiB2/Al-3.5Cu-1.5Mg-1Si composite was successfully fabricated by selective laser melting (SLM). The results show that the Q phase forms in the matrix of the as-fabricated TiB2/Al-3.5Cu-1.5Mg-1Si composite. After T6 heat treatment, the Q phase disappears and the AlxMny, Mg2Si and Al2Cu(Mg) phases are formed. The same results can be observed before and after heat treatment in the unreinforced Al-Cu-Mg-Si alloy. EBSD and TEM analyses indicate that the addition of the TiB2 particles results in a remarkable grain refinement, leading to enhanced strength of the TiB2/Al-Cu-Mg-Si composite in comparison to the unreinforced Al-Cu-Mg-Si alloy in both the as-fabricated and heat-treated conditions. Both grain refinement and Orowan strengthening contribute to the high strength of the heat treated TiB2/Al-Cu-Mg-Si composite.

The value of diffusion-weighted magnet resonance imaging (DWI-MRI) has been demonstrated for an ever growing range of clinical indications. DWI is sensitive to the diffusion of water molecules and probes their random displacement within tissue. DWI provides both qualitative and quantitative information on tissue characteristics, e.g. tissue cellularity. This review provides an overview of diffusion-weighted imaging and its emerging applications in ophthalmology. The basic physics and technical foundations of DWI are introduced. The emerging applications of DWI are surveyed, particularly in diseases of the eye, orbit and optical nerve.

This review documents technical progress in ophthalmic magnetic resonance imaging (MRI) at ultrahigh fields (UHF, B(0) ≥ 7.0 T). The review surveys frontier applications of UHF-MRI tailored for high spatial resolution in vivo imaging of the eye, orbit and optic nerve. Early examples of clinical ophthalmic UHF-MRI including the assessment of melanoma of the choroid membrane and the characterisation of intraocular masses are demonstrated. A concluding section ventures a glance beyond the horizon and explores research promises along with future directions of ophthalmic UHF-MRI.

MR microscopy using an ultra high-field MR system is a novel non-invasive imaging technique to explore the human eye without optical distortions. This review aims to provide an insight into the technique. Normal MR microscopic anatomy of the human eye in vivo is demonstrated and clinical applications of MR microscopy are discussed.

Ultrahigh field magnetic resonance imaging (UHF-MRI) has recently gained substantial scientific interest. At field strengths of 7 Tesla (T) and higher UHF-MRI provides unprecedented spatial resolution due to an increased signal-to-noise ratio (SNR). The UHF-MRI method has been successfully applied in various neurological disorders. In neuroinflammatory diseases UHF-MRI has already provided a detailed insight into individual pathological disease processes and elucidated differential diagnoses of several disease entities, e.g. multiple sclerosis (MS), neuromyelitis optica (NMO) and Susac's syndrome. The excellent depiction of normal blood vessels, vessel abnormalities and infarct morphology by UHF-MRI can be utilized in vascular diseases. Detailed imaging of the hippocampus in Alzheimer's disease and the substantia nigra in Parkinson's disease as well as sensitivity to iron depositions could be valuable in neurodegenerative diseases. Current UHF-MRI studies still suffer from small sample sizes, selection bias or propensity to image artefacts. In addition, the increasing clinical relevance of 3T-MRI has not been sufficiently appreciated in previous studies. Although UHF-MRI is only available at a small number of medical research centers it could provide a high-end diagnostic tool for healthcare optimization in the foreseeable future. The potential of UHF-MRI still has to be carefully validated by profound prospective research to define its place in future medicine.

This involves high spatial resolution cardiac imaging with ultrahigh magnetic fields (7 T) and clinically acceptable image quality.Cardiovascular magnetic resonance imaging (MRI) at a field strength of 1.5 T using a spatial resolution of (2 × 2 × 6-8) mm(3).Cardiac MRI at ultrahigh field strength makes use of multitransmit/receive radiofrequency (RF) technology and development of novel technology that utilizes the traits of ultrahigh field MRI.Enhanced spatial resolution which is superior by a factor of 6-10 to what can be achieved by current clinical cardiac MRI. The relative spatial resolution (pixels per anatomical structure) comes close to what can be accomplished by current cardiac MRI in small rodents.Feasibility studies demonstrate the gain in spatial resolution at 7.0 T due to the sensitivity advantage inherent to ultrahigh magnetic fields.Please stay tuned and please put further weight behind the solution of the remaining technical problems of cardiac MRI at 7.0 T.

To compare highly accelerated parallel MRI of the bowel with conventional balanced FFE sequences in children with inflammatory bowel disease (IBD).20 children with suspected or proven IBD underwent MRI using a 1.5 T scanner after oral administration of 700 -1000 ml of a Mannitol solution and an additional enema. The examination started with a 4-channel receiver coil and a conventional balanced FFE sequence in axial (2.5 s/slice) and coronal (4.7 s/slice) planes. Afterwards highly accelerated (R = 5) balanced FFE sequences in axial (0.5 s/slice) and coronal (0.9 s/slice) were performed using a 32-channel receiver coil and parallel imaging (SENSE). Both receiver coils achieved a resolution of 0.88 x 0.88 mm with a slice thickness of 5 mm (coronal) and 6 mm (axial) respectively. Using the conventional imaging technique, 4 - 8 breathholds were needed to cover the whole abdomen, while parallel imaging shortened the acquisition time down to a single breathhold. Two blinded radiologists did a consensus reading of the images regarding pathological findings, image quality, susceptibility to artifacts and bowel distension. The results for both coil systems were compared using the kappa-(kappa)-coefficient, differences in the susceptibility to artifacts were checked with the Wilcoxon signed rank test. Statistical significance was assumed for p = 0.05.13 of the 20 children had inflammatory bowel wall changes at the time of the examination, which could be correctly diagnosed with both coil systems in 12 of 13 cases (92 %). The comparison of both coil systems showed a good agreement for pathological findings (kappa = 0.74 - 1.0) and the image quality. Using parallel imaging significantly more artifacts could be observed (kappa = 0.47) without impairing the diagnostic impact. The comparison of the bowel distension showed no significant differences.The highly accelerated parallel MRI using the SENSE technique and a 32-channel surface coil enables the examination of the entire bowel in a single breathhold without relevant restrictions in image quality and diagnostic impact.

Cardiovascular Magnetic Resonance (CVMR) imaging has proven to be of clinical value for non-invasive diagnostic imaging of cardiovascular diseases. CVMR requires rapid imaging; however, the speed of conventional MRI is fundamentally limited due to its sequential approach to image acquisition, in which data points are collected one after the other in the presence of sequentially-applied magnetic field gradients and radiofrequency pulses. Parallel MRI uses arrays of radiofrequency coils to acquire multiple data points simultaneously, and thereby to increase imaging speed and efficiency beyond the limits of purely gradient-based approaches. The resulting improvements in imaging speed can be used in various ways, including shortening long examinations, improving spatial resolution and anatomic coverage, improving temporal resolution, enhancing image quality, overcoming physiological constraints, detecting and correcting for physiologic motion, and streamlining work flow. Examples of these strategies will be provided in this review, after some of the fundamentals of parallel imaging methods now in use for cardiovascular MRI are outlined. The emphasis will rest upon basic principles and clinical state-of-the art cardiovascular MRI applications. In addition, practical aspects such as signal-to-noise ratio considerations, tailored parallel imaging protocols and potential artifacts will be discussed, and current trends and future directions will be explored.

Intrastriatal injection of the excitotoxin N-methyl-D-aspartate (NMDA) in neonatal rat brain resulted in an acute ipsilateral decrease of the apparent diffusion coefficient (ADC) of brain tissue water, as measured with diffusion-weighted MRI. The early diffusion changes were accompanied by only mild changes in the overall metabolic status as measured by in vivo 1H MRS and 31P MRS and metabolic imaging of brain sections. Minimal decreases in the high-energy phosphate levels and a small hemispheric acidosis were observed in the first 6 h after NMDA administration. In addition, there was very modest lactate accumulation. Twenty-four hours after the induction of the excitotoxic injury the tissue energy status was still only moderately affected, whereas an overall decrease of 1H MRS-detected brain metabolites was found. Treatment with the non-competitive NMDA-antagonist MK-801 given within 90 min after NMDA injection rapidly reversed the NMDA-induced changes in the entire ipsilateral hemisphere. The effect of the competitive NMDA-antagonist D-CPPene was restricted to the cortical areas and was accomplished on a slower time scale. Our results indicate that; (i) early excitotoxicity in the neonatal rat brain does not lead to profound changes in the metabolic status; and (ii) brain tissue water ADC changes are not necessarily associated with a metabolic energy failure.

13C-NMR spectroscopy of perchloric acid and lipid extracts of F98 glioma cells showed that volume-regulatory processes under anisosmotic conditions were accompanied by marked alterations in cellular metabolism. Production of alanine, glutamate, and glycine from [U-13C]-glucose is decreased under hypotonic stress and is oppositely increased under hypertonic stress. In contrast, degradation of these molecules is raised under hypotonic conditions and reduced under hypertonic conditions. Furthermore, phospholipid synthesis is decreased under hypertonic stress and increased under hypotonic stress. Obviously, glial metabolism is directed under hypertonic conditions to maintain a high level of small, osmotically active molecules, whereas under hypotonic conditions molecular fragments are increasingly incorporated into the phospholipids and so do not contribute to the osmotic pressure. The latter is evoked by the activation of membrane synthesis process to compensate for stretching and/or damaging of the membranes due to cell swelling.

Background: Magnetic resonance imaging (MRI) yields important information on the development and current status of many different diseases. Whole-body MRI was accordingly made a part of the multicenter, population-based NAKO Health Study. The present analysis concerns the feasibility of the baseline MRI examination and various aspects of quality assurance over the period 2014-2019., Methods: 32 252 participants in the NAKO Health Study, aged 20 to 74, who had no contraindication to MRI were invited to undergo scanning in one of five MRI study centers across Germany. The whole-body MRI scan took about one hour and consisted of sequences for the visualization of structural and functional features of the brain, musculoskeletal system, cardiovascular system, and thoracoabdominal system. A comprehensive quality-assurance assessment was carried out, with evaluation of adverse events, the completeness of the MRI protocols, the participants' subjective perceptions, and image quality., Results: 31 578 participants (97.9%) were successfully included in the MRI study. They reported a high level of comfort and suffered no severe adverse events; mild adverse events occurred in only four participants. Depending on the imaging sequence, the image quality was rated as excellent in 80.2% to 96.8% of cases. Quality assessment with respect to structural features of the brain revealed high consistency across study centers, as well as with regard to age-and sex-based differences in brain volume (men, 1203.81 ± 102.06 cm³; women, 1068.10 ± 86.69 cm³)., Conclusion: Whole-body MRI was successfully implemented in the NAKO baseline examination and was associated with high patient comfort and very good image quality. The imaging biomarkers of the brain confirmed previously observed differences based on age and sex, underscoring the feasibility of data pooling.