This study introduces a novel Al-2Fe-2Cr-1Mn-0.7Zr (wt.%) alloy designed for high-temperature applications. The design strategy leverages the alloy's near-eutectic composition to create a printable alloy with refined eutectic intermetallic reinforcements and to take advantage of the supersaturation of slow-diffusing elements (Mn, Zr, and Cr). The as-printed microstructure shows a homogeneous grain structure with coarse columnar grains. The distribution, nature, size and morphology of the intermetallic dispersoids is heterogeneous at the melt pool scale. Coarse facetted Cr-rich precipitates are only found near the melt pool boundaries while the melt pool interiors consist of a refined eutectic structure (interparticle spacing similar to 200 nm) with elongated, Fe-rich intermetallics (similar to 10% in area fraction). The composition of the solid solution is also heterogeneous with higher supersaturations in Mn, Zr, and Cr in the melt pool interiors than at the melt pool boundaries. The high-temperature tensile properties of the as-printed material are evaluated from 100 to 350 degrees C and over four orders of magnitude in strain rate. This alloy shows a very limited decrease in yield strength between 100 and 300 degrees C, nearly no strain rate sensitivity, and maintains a reasonable ductility (elongation to failure >= 5%) despite a reduction in ductility at low strain rate. The role of the refined eutectic structure to confine dislocation motion and mitigate dynamic recovery is emphasized. The role of supersaturation in climb-restricting solutes such as Fe, Mn and Zr is highlighted. A mechanism to rationalize the drop in ductility at elevated temperature and low strain rate is proposed.

The mechanical properties of additively manufactured aluminium alloys at room temperature are often optimized through post-fabrication heat treatment (peak ageing). However, at high temperatures, peak-ageing does not necessarily result in the best mechanical properties. This raises the question of whether there is an optimal microstructure depending on the operating temperature. Herein, we examine the influence of ageing in an Al-4Mn-3Ni-2Cu-1Zr (wt.%) alloy processed by laser powder bed fusion on the tensile yield strength from room temperature to 300 degrees C at 10(-2) and 10(-5) s(-1). In the stress-relieved conditions, the material shows a higher yield strength than in the peak-aged conditions at temperatures above 150 degrees C at 10(-2) s(-1) and as low as 100 degrees C at 10(-5) s(-1). This evolution was not expected since nanoscale L1(2)-Al3Zr thermally stable precipitates form in the peak-aged conditions. The microstructure evolutions upon ageing are characterized across all scales and provide insights to rationalize the evolution of the alloy strength with temperature. The role of different microstructural features such as grain size, intermetallic morphology, nanoscale precipitates and solid solution composition is discussed. While the nanoscale Zr-rich precipitates contribute greatly to the room-temperature yield strength, their effect at elevated temperatures, typically >150 degrees C, is minor. On the contrary, the supersaturation in Mn in the as-built material that is preserved after stress-relief is found to have a large impact on the tensile yield strength at elevated temperature. The globularisation of the elongated intermetallics observed in the stress-relieved microstructure is also identified to lower the elevated-temperature yield strength.

MAB phases are a class of layered ternary transition metal borides with large chemical and structural diversity. In this work, we used the Lewis acid etching method to topochemically convert MoAlB into Mo2AlB2 single crystals with a typical size of 0.5-1.5 mm. We comprehensively characterized the single crystals and confirmed the high quality and preferred orientation of the converted Mo2AlB2 crystals using X-ray diffraction, polarized Raman spectroscopy, and transmission electron microscopy. The converted Mo2AlB2 crystals are metallic and exhibit lower resistivity compared to the precursor phase, which is associated with the higher density of states at the Fermi energy of Mo2AlB2 as compared to MoAlB. We show that the chemical conversion is a pathway to produce M2AlB2 phases and this approach can be further extended to other members of M2A2B2 phases for conversion.

Understanding the morphology, composition and structural changes experienced by metallic glass powder particles upon laser powder bed fusion (LPBF) is the first step towards evaluating the impact of spatter generation on part quality and on feedstock degradation. This study presents the characterization of Zr-Cu-Al-Nb spatter particles by means of scanning and transmission electron microscopy with automated crystallographic orientation mapping and energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. The powder exposed to the LPBF environment exhibits an average surface composition similar to the original feedstock, but with a rougher morphology. The typical spatter encountered in the remaining lack-of-fusion is a vapour-entrained particle, which probably underwent partial melting leading to the formation of α-Zr(O) dendrites, and “big-cube” Cu2Zr4O nanocrystals in its heat affected zone. In the present work, spatter characteristics are discussed considering glass properties and their connection to lack-of-fusion defects is addressed.

Current societal challenges, such as climate change and resource depletion, highlight an unprecedented need for disruptive innovation in materials science. Significant breakthroughs are expected in multinary materials whose efficient exploration necessitates dedicated strategies. The exploration of a refractory high entropy alloy Nb-Ti-Zr-Cr-Mo is proposed here as test case for a new strategy. Based on the proven methodology of mixture design and on combinatorial thin film metallurgy, the composition space is explored by a limited number of chosen gradients to build an alloy library comprising hardness and ductility, two antagonistic properties. The workflow is showcased here by studying the properties of the as-grown graded film, which presents wide amorphous domains and contrasted mechanical properties. This experimental dataset then trains machine learning models to provide continuous predictions of the alloy properties over the entire composition space. We show that optimal alloy properties are expected close to the binary edges of the quinary.

Tungsten heavy alloys (Co-Ni-W) of different compositions were prepared by powder metallurgy (solid sintering), heat treated at 800 degrees C and 1000 degrees C and subsequently analyzed. The experimental phase identifications and composition measurements emphasized discrepancies compared to the isothermal ternary sections simulated with commercial thermodynamic databases. The isothermal sections at 800 degrees C and 1000 degrees C were found more complex than expected since a new intermetallic phase appeared to be stable (D0(a) structure-Cu3Ti prototype). Likewise, an interpretation of phase equilibria evolution with temperature was established to reach agreement with high temperature data. Formation enthalpies associated with the new phase were obtained through first-principles calculations and supported experimental results as they confirmed the stabilizing role of Ni addition for the D0(a) structure. (C) 2021 Elsevier B.V. All rights reserved.

Traditional high strength aluminum alloys such as the 2xxx or 7xxx series are prone to cracking when processed by additive manufacturing. Designing new aluminum alloys that can be processed crack-free by Laser Powder Bed Fusion (L-PBF) while exhibiting comparable or enhanced mechanical properties is a major target, which may be reached by including in the alloy design strategy specific features of this processing route such as the very high cooling rates. Here, we study a novel Al-4Mn-3Ni-2Cu-2Zr alloy processed by L-PBF, which shows some specific features in comparison to other Al-alloys developed for additive manufacturing. We establish the relationships between the processing conditions and the specific features of the microstructure inherited from L-PBF based on a multi-scale microstructural characterization approach from the melt pool scale up to the nanoscale using X-ray diffraction and electron microscopy with a special focus on Automated Crystal Orientation Mapping (ACOM) in transmission. At the melt pool scale, three regions have been identified: FEZ (Fine Equiaxed Zone), CZ (Columnar Zone) and CEZ (Coarse Equiaxed Zone) giving a hierarchical architecture to the microstructure. Each region has been thoroughly characterized by coupling ACOM and chemical mapping. Five different intermetallic phases have been identified in the as-built microstructure: Al3Zr, Al3Ni2, Al9Ni2, Al60 Mn 11Ni 14, and Al2Cu. The spatial distribution of these intermetallic phases has been found to vary within a given molten pool. The solidification sequence and the various mechanisms involved in the formation of this peculiar microstructure are discussed in the light of our multi-scale microstructural observations along with solidification thermodynamic calculations.

In-situ high energy X-Ray diffraction (HEXRD) was used on compositionally graded steels to study the effect of substitutional elements on ferrite growth kinetics in Fe–C–X and Fe–C–X–Y systems. Two systems were selected to illustrate the applicability of the combinatorial approach in studying such transformations, Fe–C–Mn and Fe–C–Mn–Mo. Comparison between the measured ferrite growth kinetics using HEXRD and the predicted ones using Para-Equilibrium (PE) and Local Equilibrium with Negligible Partitioning (LENP) models indicates that the fractions reached at the stasis of transformation are lower than the predicted ones. Experiments indicated a deviation of measured kinetics from both PE and LENP models when increasing Mn and decreasing Mo (in Fe–C–Mn–Mo system). The large amount of data that can be obtained using this approach can be used for validating existing models describing ferrite growth kinetics.

Non-filamentary and non-volatile reproducible resistive switching with a high memory window has been obtained for novel nanoionic memristors based on GdBaCo2O5+δ.

The deposition of epitaxial superconducting (Nb,Ti)N thin films is addressed with a new approach, using a chemical vapor deposition technique with in situ production of precursors. Both classic and reactive CVD process are optimized toward (i) the control of crystal structure of the deposited films and (ii) the control of stoichiometry and thus of superconducting properties. Films are chararcterized using thermodynamic, structural, and electrical characterization tools. Precession electron diffraction and electron backscatter diffraction techniques provide the phase and orientation mapping of the films down to the nanometer scale. We demonstrate that the cubic phase (structure with the most prominent superconducting properties) is the thermodynamically stable phase under classic CVD from 800 degrees C up to 1300 degrees C. The hexagonal (Nb,Ti)N is formed via a "nitridation like" process under reactive CVD, up to 1200 degrees C. The composition of the films is controlled by the chemistry of the gas phase, whereas the thickness is regulated down to less than 10 nm due to the low growth rate that can be achieved. This technique allows for the control of the superconducting properties of the films, through the control of Ti composition.

The effect of La[Formula: see text]Sr[Formula: see text]MnO[Formula: see text] (LSM) coating on SS446 steel on air oxidation at 800[Formula: see text]C was investigated by transmission electron microscopy. Dense and crack free thin LSM films were prepared by electrostatic spray deposition. The microstructural characterization was carried out on coated and uncoated interconnectors. A thin chromia scale at the alloy interface along with two spinel phases were observed after long term oxidation in both cases. Specimens exhibit, in addition, an SiO2 layer at the interface with steel due to the high content of Si in the steel. Significant changes in the thickness, morphology and composition occurred in the reaction layer for the LSM coated steel. These effects are explained on the basis of changes in the diffusive fluxes during exposure to the oxidation treatment. The implications of these effects for the degradation mechanism of LSM-based interconnects are discussed.

The complex microstructures developed during post-welding heat-treatment in the vicinity of the fusion line between a ferritic and austenitic steel were examined in the case of submerged arc welded 18MND5/309L dissimilar joints. Quantitative measurements of the carbon distribution in the as-welded and post-weld heat-treated conditions were performed by both wavelength dispersive spectrometry and secondary ion mass spectrometry. The extent of carbon diffusion was confirmed by hardness profiles performed by nanoindentation. On the low-alloy ferritic side, decarburization resulted in cementite dissolution allowing the evolution of the bainitic structure toward a large-grained ferritic region. In the weld metal, the carbon content reached unusually high levels and an intense precipitation of chromium-rich carbides was observed in both the interfacial martensitic layer and the austenitic weld metal. The evolution of the precipitation as a function of the distance from the interface was analyzed in terms of crystallography, chemistry, volume fractions, and size distributions. Automated crystal orientation mapping in a transmission electron microscope allowed identification of the precipitates extracted on carbon replicas from both the martensitic and austenitic matrices. A 3D reconstruction of the carbides population in the martensitic layer was performed by serial cutting with a focused ion beam: M7C3 and M23C6 were found to coexist in the two carburized regions, but displayed different sizes, compositions, and morphologies, depending on their location with respect to the fusion line. This evolution in terms of precipitation was analyzed taking into account the local microstructure and composition.

A TEM observation of a TiN inclusion associated to a spinel (MgAl2O4) and calcium sulfide germs is reported. It shows an orientation relationship between these three phases, indicating an epitaxial growth of the TiN over the spinel and CaS. This observation strengthens the hypothesis of a heterogeneous nucleation of TiN particles during the solidification of a maraging steel.

The effect of grain microstructure on the age-hardening behavior is investigated on recrystallized and un-recrystallized Al–Cu–Li alloys by combining electron-backscatter-diffraction and micro-hardness mapping. The spatial heterogeneity of micro-hardness is found to be strongly dependent on the grain microstructure. Controlled experiments are carried out to change the pre-strain before artificial ageing. These experiments lead to an evaluation of the range of local strain induced by pre-stretching as a function of the grain microstructure and results in heterogeneous formation of the hardening T1 precipitates.

We conducted an inter-laboratory study of a metallic glass whose main component is nickel. Two determinations of the mass fractions of the different elements present within the sample were asked to the participants: one at an acceleration voltage of 15 or 20kV and another one at 5kV. We compare the mass fractions obtained from wavelength dispersive (WDS) and energy dispersive spectrometries (EDS) and also try to find an influence of the kind of EDS detector and its entrance window, the background subtraction method, the use or not of standards as well as the quantification method. Both means of WDS and EDS mass fractions are close to the reference values. The dispersion of the results was larger at 5kV than at 15-20kV owing to the use of the L lines rather than K lines and to the lowest collected intensities. There is an exception with the case of boron because at the lowest voltage, the excitation condition is more favorable for the production of the K line. It appears that the dispersion of the results is larger with EDS than with WDS, but it was not possible to find a correlation between the large dispersion and one of the considered experimental parameters and quantification factors. Thus, one can think that electron microprobes are inherently better for the determination of mass fractions or that the implementation of quantitative analysis must be optimized for some cases, especially in scanning electron microscopes. Copyright (c) 2014 John Wiley & Sons, Ltd.

Controlling the polarity of ZnO nanowires in addition to the uniformity of their structural morphology in terms of position, vertical alignment, length, diameter, and period is still a technological and fundamental challenge for real-world device integration. In order to tackle this issue, we specifically combine the selective area growth on prepatterned polar c-plane ZnO single crystals using electron-beam lithography, with the chemical bath deposition. The formation of ZnO nanowires with a highly controlled structural morphology and a high optical quality is demonstrated over large surface areas on both polar c-plane ZnO single crystals. Importantly, the polarity of ZnO nanowires can be switched from O- to Zn-polar, depending on the polarity of prepatterned ZnO single crystals. This indicates that no fundamental limitations prevent ZnO nanowires from being O- or Zn-polar. In contrast to their catalyst-free growth by vapor-phase deposition techniques, the possibility to control the polarity of ZnO nanowires grown in solution is remarkable, further showing the strong interest in the chemical bath deposition and hydrothermal techniques. The single O- and Zn-polar ZnO nanowires additionally exhibit distinctive cathodoluminescence spectra. To a broader extent, these findings open the way to the ultimate fabrication of well-organized heterostructures made from ZnO nanowires, which can act as building blocks in a large number of electronic, optoelectronic, and photovoltaic devices.

This volume of IOP Conference Series: Materials Science and Engineering contains papers from the 12th Workshop of the European Microbeam Analysis Society (EMAS) on Modern Developments and Applications in Microbeam Analysis, which took place from the 15–19 May 2011 in the Angers Congress Centre, Angers, France.

Nickel sulphide inclusions are known to be responsible for delayed fracture in tempered glasses due to phase transformation within the inclusion. Microstructural identification of the phase transformation mechanisms in the Ni–S system close to the NiS composition were carried out on a series of partially transformed states. Observations allow to investigate the morphological evolution during transformation, the phase orientation relationships and the first stages of the transformation were investigated by optical microscopy, electron backscatter diffraction, and scanning and transmission electron microscopy. The transformation mechanisms change significantly with the change in sulphur content of the α-NiS phase. Massive transformation is observed for near-stoichiometric composition. For overstoichiometric composition, the transformation is controlled by a long-range diffusion mechanism. The influence of stoichiometry and impurities (Fe) on the microstructural evolution and transformation mechanisms has also been studied.

Abstract An AA 7075 aluminum alloy with Zr and Sc additions was subjected to 6 – 8 passes of equal-channel angular pressing at 120, 170, and 220 °C in order to study the effect of the pressing conditions on the microstructural characteristics and the consequences for high-temperature mechanical properties. Using the method of electron backscatter diffraction, a decrease in pressing temperature was found to lead to a more pronounced refinement of the microstructure and a higher fraction of high-angle grain boundaries, but at the same time compromised the ability of the Al3 (Zr, Sc) phase to stabilize the ultra-fine-grained microstructure at elevated temperatures. Optimum superplastic properties were therefore achieved after pressing at the intermediate temperature of 170 °C. The material exhibited high strain-rate superplasticity with a ductility of 650 % at an initial strain rate of 1 × 10 – 1 s – 1.