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High-temperature interaction of liquid Gd in contact with dense, polycrystalline TiO2 substrate, was investigated. Wettability and reactivity tests were carried out at two different temperatures (1362°C and 1412°C) in flowing gas (Ar, 850-900 hPa) using the sessile drop method and classical contact heating of the examined couple of materials. The procedure was combined with a drop pushing procedure. During high temperature studies, images of the Gd/ TiO2 couple were continuously recorded by a high-resolution CCD camera. The results of wettability tests of liquid gadolinium on titanium dioxide substrate show that the Gd/ TiO2 system is non-wettable at both test temperatures (in either case the final contact angle was 100°). The results of structure examinations on the cross-sectioned samples show the dissolution of the TiO2 substrate in liquid Gd and the presence of two sublayers at the drop/substrate interface: Gd2TiO5 (from the drop side) and Gd7Ti2O7 (from the substrate side). [ABSTRACT FROM AUTHOR]

The shear-band propagation in bulk metallic glasses (BMGs) during deformation plays a key role in determining their macroscopic ductility. In this work, the shear band propagation during plastic deformation was investigated in the Cu46Zr46Al8 BMG and its in situ or ex situ prepared BMG composites. Compared with the brittle BMG, both types of ductile BMG composites show a more stable shear banding behavior as revealed by a larger power-law scaling exponent obtained from statistical analysis of serrations recorded in compressive curves. A higher cut-off elastic energy density (δc) linked with the multiplication of shear bands is observed for the in situ prepared BMG composites. However, the ex situ fabricated BMG composites show an almost equivalent or slightly larger δc since the dominant shear band but not multiple shear bands mainly governs their deformation. Such observations imply that the shear banding stability of BMGs during deformation is enhanced not only by inducing multiple shear bands but also by obstructing the movement of the dominant shear band at its driven path. [ABSTRACT FROM AUTHOR]

The microstructures and mechanical properties of (Cu0.5Zr0.5)100-xZnx (x = 0, 1.5, 2.5, 4.5, 7, 10, and 14 at. %) bulk metallic glass (BMG) composites were studied. CuZr martensitic crystals together with minor B2 CuZr and amorphous phases dominate the microstructures of the as-quenched samples with low Zn additions (x = 0, 1.5, and 2.5 at. %), while B2 CuZr and amorphous phases being accompanied with minor martensitic crystals form at a higher Zn content (x = 4.5, 7, 10, and 14 at. %). The fabricated Cu-Zr-Zn BMG composites exhibit macroscopically appreciable compressive plastic strain and obvious work-hardening due to the formation of multiple shear bands and the deformation-induced martensitic transformation (MT) within B2 crystals. The present BMG composites could be a good candidate as high-performance structural materials. [ABSTRACT FROM AUTHOR]

The structure of (GeTe4)1-x(AgI)x (x = 0.15 and 0.25) glasses has been investigated by X-ray and neutron diffraction as well as extended X-ray absorption spectroscopy (EXAFS) and Raman spectroscopy. Large-scale structural models have been obtained by fitting simultaneously the experimental datasets in the framework of the reverse Monte Carlo simulation technique (RMC). Short-range order parameters have been calculated and compared with that of GeTe4. Doping with AgI affects the structure of the host GeTe4 matrix in two ways. First, while Te is essentially twofold coordinated in GeTe4, its coordination number is as high as ~2.9 ± 0.3 for x = 0.25. The change is mainly due to the increased fraction of Te-Te bonds. Second, Ge atoms remain fourfold coordinated but the tetrahedral symmetry is distorted due to the elongation of some Ge-Te bonds. The incorporation of AgI in the GeTe4-based host covalent matrix and the Te coordination increase explains the enhanced thermal stability of (GeTe4)1-x(AgI)x in the supercooled liquid-state hindering the crystallization of Te found in case of GeTe4 glass. [ABSTRACT FROM AUTHOR]

It is shown that ZrO2 nanoparticles essentially stimulate the heterogeneous nucleation of droplets from the minority phase in Al-Pb monotectic alloys, which results in a significant increase of the number of Pb particles and in a decrease of their size upon solidification. This is related to the contact angle between coexisting liquid phases and ZrO2 ceramic, which is 20-30 degrees in the Al35Pb65 alloy and 35-40 degrees in the Al29.4In70.6 alloy. In the Al34.5Bi65.5 alloy at 670°C, the contact angle at the (l-l) interface and ZrO2 ceramics shows a hysteresis between 37° and 115°. The contact angle between coexisting liquid phases and Al2O3 ceramic is close to zero in the Al34.5Bi65.5 alloy. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) have inspired considerable interest due to their attractive physical and mechanical properties. In this work, the microstructural evolution induced by different heat treatments on rapidly solidified hypoeutectic precursors of a Fe26.7Co26.7Ni26.7Si8.9B11 HEA is investigated and correlated with the corresponding mechanical properties. The microstructures of the rapidly solidified precursors are composed of primary fcc solid solution dendrites embedded in a eutectic matrix. When the samples are annealed at different temperatures after furnace cooling or quenching, respectively, the eutectic structure gradually decomposes into fcc, tetragonal (Fe,Co)2B, and hexagonal Ni31Si12 crystals with increasing annealing temperature, leading to a gradual increase of the content of the fcc crystals and both their aggregation and coarsening. Then the dominant structural framework gradually transforms from eutectic structures to fcc dendrites and ultimately the (Fe,Co)2B crystals become isolated as dominant reinforcement particles distributed in the interdendritic regions. This gradual microstructural transition from hypoeutectic to quasi-duplex structures leads to the change of the dominant deformation mechanism from crack-controlled to dislocation-dominated deformation, which allows to control both ductility and strength in a wide range. Hence, this study provides some guideline for how to tune the microstructure and mechanical properties of HEAs. [ABSTRACT FROM AUTHOR]

To understand the effect of aluminum addition on the non-equilibrium solidification of the equiatomic CoCrFeNi alloy, the Al 0.3 CoCrFeNi and AlCoCrFeNi high-entropy alloys (HEAs) have been investigated in situ using electromagnetic levitation and high-energy synchrotron X-ray diffraction (XRD). Because the five-component alloys could not be deeply undercooled, the studies were confined to the low undercooling regime. The in situ XRD revealed that a fcc single-phase solid solution is the primary crystalline phase nucleating in Al 0.3 CoCrFeNi melt undercooled up to 80 K. In contrast, the B2 ordered phase appears as the primary phase in the AlCoCrFeNi melt, at least at a low undercooling of about 30 K. These results correlate with the equilibrium phase diagrams available. Crystal growth velocities of the Al 0.3 CoCrFeNi alloy are shown to be smaller than for CrFeNi and CoCrNi equiatomic alloys; nonetheless, they are in the same order of magnitude. Spontaneous grain refinement was observed in the Al 0.3 CoCrFeNi alloy solidified at a low undercooling of Δ T = 70 K. [Display omitted] • In situ non-equilibrium solidification of high-entropy alloys is studied. • Al 0.3 CoCrFeNi alloy shows a sluggish crystal growth, compared to CoCrFeNi. • Spontaneous grain refinement is observed as undercooling of the Al 0.3 CoCrFeNi melt increases. • AlCoCrFeNi forms B2 phase at high temperature and bcc and B2 at room temperature. [ABSTRACT FROM AUTHOR]

Chalcogenide phase‐change materials combine a remarkable set of properties that makes them promising candidates for future non‐volatile memory applications. Binary data storage exploits the high contrast in electrical and optical properties between the covalent amorphous and metavalent crystalline phase. Here the authors perform an analysis of the liquid phase kinetics of the phase‐change material Ge3Sb6Te5, which is the key to ultrafast switching speeds. By employing four experimental techniques, the viscosity is measured over sixteen orders of magnitude despite its propensity for fast crystallization. These measurements reveal that the liquid undergoes a transition in viscosity–temperature dependence associated with a liquid–liquid phase transition. The system exhibits a shallow viscosity change with temperature near the glass transition which stabilizes the memory cells in the amorphous state and which limits the severity of relaxation processes. Meanwhile, when heated during the writing process, the fragility increases to more than double, causing the viscosity to drop rapidly enabling a nanosecond crystallization speed. This change in viscosity–temperature dependence is highly unusual among glass forming liquids and is reminiscent of the behavior of water. This viscosity transition is also key to the technological success of phase‐change materials for computer memory applications. [ABSTRACT FROM AUTHOR]

[Display omitted] The complex phase evolution sequence of a promising new high temperature structural alloy with composition Al 20 Cr 20 Fe 35 Ni 20 Ti 5 (at.%) has been studied in situ using an electromagnetic levitation (EML) setup combined with time-resolved high energy X-ray diffraction (XRD), as well by scanning transmission electron microscopy (STEM) observations during in situ heating. These experiments were supplemented by both scanning electron microscopy (SEM) and high resolution STEM observations of the as-cast alloy microstructure, as well as by energy dispersive X-ray spectroscopy (EDS) composition measurements. Differential scanning calorimetry (DSC) was used to identify liquidus, solidus, A2 ↔ B2, and B2 ↔ L2 1 transition temperatures. The results obtained by these complementary techniques indicate that the alloy forms primary dendrites of A2-structured body-centered cubic (bcc) phase initially from the melt, followed by ordered bcc of B2-structure in interdendritic regions once compositional segregation has sufficiently enriched the remaining liquid. Ordered B2 precipitates form within the primary A2-structured dendrites and the interdendritic B2 regions undergo a continuous decomposition reaction into a maze-like arrangement of A2 and B2/L2 1 phases below the solidus. Below approximately 1380 K, the B2 domains in both dendritic and interdendritic regions likely undergo a continuous ordering transition to the L2 1 phase. The experimental observations of Al 20 Cr 20 Fe 35 Ni 20 Ti 5 are found to be in good agreement with CALPHAD predictions but suggest that the solubility limits of the L2 1 -Heusler phase in the database should be relaxed to include greater Fe solubility for the Ni sublattice and to consider deviations in order parameter from stoichiometric ordering. [ABSTRACT FROM AUTHOR]

The martensitic transformation within B2 phase plays a critical role for the ductility of CuZr-based bulk metallic glass (BMG) composites, yet the underlying mechanism for the martensitic transformation process needs further investigations. Here, we found that the onset temperature of the thermally-activated martensitic transformation for CuZr-based BMG composites was reduced to 162.7 ± 2.5 K, which is far lower than those of polycrystalline samples, due to the stabilization of the austenitic phase induced by crystalline-amorphous interfaces. In situ high-energy X-ray diffraction measurements (HEXRD) further demonstrate that the thermally-activated martensitic transformation is governed by an extremely incomplete martensitic transformation from B2 to B19' and B33 phases without the decomposition of B2 phase which generally appears in polycrystalline samples. Due to unconfined stress states during the thermally-activated martensitic transformation, B33 phase forms more early during thermal process than deformation process. The present study provides a further understanding on the martensitic transformation behaviors of shape memory type CuZr-based BMG composites. Image 1 • In situ observations on thermally-activated martensitic transformation for BMG composites was conducted. • Martensitic transformation temperature is far below room temperature. • Extremely incomplete martensitic transformation was observed. • Decomposition of B2 phase does not appear during martensitic transformation. • B33 phase forms earlier during thermal process than deformation process. [ABSTRACT FROM AUTHOR]

Solidification and growth behavior of undercooled eutectic CoSi–CoSi 2 melts was observed using containerless levitation and in situ high-energy synchrotron X-ray diffraction techniques. Three metastable solidification pathways of eutectic CoSi–CoSi 2 were determined as a function of undercooling. Upon double recalescence at low undercoolings the primary and secondary phases are CoSi and CoSi 2 , while at high undercoolings the phase formation sequence is reversed. At intermediate undercoolings a single recalescence was observed and attributed to a crossover of the nucleation barriers for the two phases. Scanning electron microscopy combined with electron back-scattering diffraction measurements revealed changes of the morphological characteristics and orientation of CoSi and CoSi 2 phases for different solidification pathways. Image 1 [ABSTRACT FROM AUTHOR]

A density variation in shear bands visible by electron microscopy is correlated with compositionally altered locations measured by atom-probe tomography in plastically-deformed Al 85.6 Y 7.5 Fe 5.8 metallic-glass ribbons. Two compositionally distinct regions are identified along shear bands, one is Al-rich (~92 at.%), the other is Al-depleted (~82.5 at.%) and both regions show marginal concentration fluctuations of Y and Fe. The elemental re-distribution is observed within shear bands only, and no chemical exchange with the surrounding glassy matrix is observed. Unlabelled Image [ABSTRACT FROM AUTHOR]

The crystallization mechanism and solid-state phase transformations in Cu 46.5 Zr 48 Al 4 Nb 1.5 metallic glass upon isokinetic and isothermal annealing are studied by using conventional and fast-scanning differential calorimetry, electric current flash-annealing, electromagnetic levitation, and in-situ high-energy synchrotron X-ray diffraction. Continuous-heating-transformation and time-temperature-transformation diagrams mapping the formation and evolution of the Cu 10 Zr 7 , B2 CuZr, τ 3 Zr 51 Cu 28 Al 21 and τ 4 Cu 2 ZrAl phases in dependence on heating rate and temperature are constructed. Cu 46.5 Zr 48 Al 4 Nb 1.5 metallic glass shows an increased propensity for the Cu 10 Zr 7 phase formation compared to the parent Cu 47.5 Zr 47.5 Al 5 glass. • Crystallization of Cu 46.5 Zr 48 Al 4 Nb 1.5 metallic glass upon flash-annealing is studied. • Processing parameters for fabrication of glass-matrix composites are established. • Nb-microalloying enhances formation of Cu 10 Zr 7 phase upon annealing. • B2 CuZr is always primary phase by crystallization from undercooled liquid. [ABSTRACT FROM AUTHOR]

The constituent ratio merged into as-fabricated composites can directly influence the content of in-situ formed reinforcing phases, which is closely related to the mechanical performance of these composites. In this work, aluminum matrix composites reinforced with 10, 15, and 20 wt% (ZrC+TiC) ceramic fractions have been manufactured by laser powder bed fusion (LPBF) additive manufacturing. The effect of hybrid ceramic reinforcement content on laser absorption behavior, fabrication and fraction of micro-nanoscale reinforcing phases, mechanical performance of the as-fabricated aluminum matrix composites is studied. In the laser processing, TiC reacts with ZrC to synthesize interfacial layer on the unmolten ceramic particals and precipitate nano-particles. With the hybrid ceramic content raising from 10 to 20 wt%, the laser absorption behavior is enhanced, and the nano-particle fraction increases. The micro/nano hardness of the composites with 20 wt% ceramic content, reaches 120 HV 0.2 and 1.33 GPa, respectively. An elastic modulus of ∼94.4 GPa and tensile strength of ∼280 MPa are obtained for the 15 wt% (ZrC+TiC)/Al composites, much higher than those of the unreinforced Al matrix. This is attributed to the combination of formation of nano-precipitates and coherent bonding at the reinforcement/matrix interfaces in these composites. • (ZrC+TiC)/Al composites with different ceramic contents are fabricated by LPBF. • Spherical and acicular nano-reinforcements in-situ precipitate in the matrix. • A thin transition layer is formed at the unmelted ceramic/matrix interface. • The strengthening mechanism of the (ZrC+TiC)/Al composites is revealed. [ABSTRACT FROM AUTHOR]

Abstract: The influence of ball milling on the atomic structure and magnetic properties of the Co40Fe22Ta8B30 metallic glass with a high thermal stability and excellent soft magnetic properties has been investigated. After 14h of milling, the obtained powders were found to consist mainly of an amorphous phase and a small fraction of the (Co,Fe)21Ta2B6 nanocrystals. The changes in the reduced pair correlation functions suggest noticeable changes in the atomic structure of the amorphous upon ball milling. Furthermore, it has been shown that milling is accompanied by introduction of compressive and dilatational sites in the glassy phase and increasing the fluctuation of the atomic-level hydrostatic stress without affecting the coordination number of the nearest neighbors. Ball milling has decreased the thermal stability and significantly affected the magnetic properties through increasing the saturation magnetization, Curie temperature of the amorphous phase and coercivity. [Copyright &y& Elsevier]

Abstract: In this letter we report about a new melt-spun Co40Fe22Ta8B30 metallic glass with a wide supercooled liquid region of 74K. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) investigations confirmed that crystallization occurs with significantly longer incubation time during annealing above the glass transition, as compared to the well-known Co43Fe20Ta5.5B31.5 glassy alloy. The new alloy as a good soft magnetic material showed a very low coercivity of 0.8A/m and polarization of 0.5T. The origin of high thermal stability was attributed to the formation of Ta–Ta bonds in the microstructure and the absence or very low quantity of Ta-based units with the composition close to the stoichiometry of the (Co,Fe)21Ta2B6 crystalline phase. [Copyright &y& Elsevier]

Time- and temperature-resolved phase formation in the equiatomic NbTiVZr refractory high-entropy alloy has been studied in situ using high-energy synchrotron X-ray diffraction and high-speed video imaging during non-equilibrium solidification. Phase formation is shown to be dependent on the solidification conditions. When the melt is undercooled over 80 K it crystallizes as a bcc single-phase solid solution despite solute partitioning between dendrites and interdendritic regions. When the sample is for some time kept in the semisolid state, two additional bcc phases form in the interdendritic regions. The crystal growth velocity for the NbTiVZr alloy, as estimated from the high-speed videos, shows pronounced sluggish kinetics. [Display omitted] [ABSTRACT FROM AUTHOR]

The solidification behavior of the CoCrFeNi high-entropy alloy and the ternary CrFeNi and CoCrNi medium-entropy suballoys has been studied in situ using high-speed video and synchrotron X-ray diffraction on electromagnetically levitated samples. In all alloys, the formation of a primary metastable bcc phase was observed if the melt was sufficiently undercooled. The delay time for the onset of the nucleation of the stable fcc phase, occurring within bcc crystals, is inversely proportional to the melt undercooling. The experimental findings are corroborated by thermodynamic calculations of stable and metastable phase diagrams for the (CoCrNi)-Fe section. Crystal-growth velocities for the CrFeNi, CoCrNi, and CoCrFeNi medium- and high-entropy alloys extracted from the high-speed video sequences in the present study are comparable to the literature data for Fe-rich Fe-Ni and Fe-Cr-Ni alloys, evidencing the same crystallization kinetics. The effect of melt undercooling on the microstructure of solidified samples is analyzed and discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

Image, graphical abstract The relationship between remelting and undercooling in Co 38.2 Si 61.8 (at. %) eutectic alloys is investigated with in situ X-ray diffraction experiments and microstructural observations. High-energy in situ X-ray diffraction during uncoupled eutectic solidification of undercooled Co 38.2 Si 61.8 allows the phase fractions to be tracked through time and reveals remelting of primary solid coincident with the formation of secondary solid. Microstructure analysis suggests that remelting occurs at the supersaturated dendrite interior. The remelted solid fraction is quantified for a wide range of solidification conditions and found to be strongly correlated with the secondary undercooling of the melt, yet independent of convection and containerless processing technique. A remelting limit was observed in experiments with primary CoSi 2 , indicating that system-specific factors impose additional constraints. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) of Al-Cu alloys shows high susceptibility to cracking due to a wide solidification temperature range. In this work, 2024 alloys were manufactured by LPBF at different laser processing parameters. The effect of processing parameters on the densification behavior and mechanical properties of the LPBF-processed 2024 alloys was investigated. The results show that the porosity increases significantly with increasing laser power, while the number of cracks and lack-of-fusion defects increase distinctly with increasing scan speed. The solidification cracking susceptibility of the LPBF-processed 2024 alloys prepared at different processing parameters was analyzed based on a finite element model, which was accurately predicted by theoretical calculations. Dense and crack-free 2024 samples with a high densification of over 98.1% were manufactured at a low laser power of 200 W combined with a low laser scan speed of 100 mm/s. The LPBF-processed 2024 alloys show a high hardness of 110 ± 4 HV 0.2 , an ultimate tensile strength of 300 ± 15 MPa, and an elongation of ∼3%. This work can serve as reference for obtaining crack-free and high-performance Al-Cu alloys by LPBF., Competing Interests: The authors declare that they have no known competitive economic interests or personal relationships that could affect the work reported in this article., (Copyright 2024, Mary Ann Liebert, Inc., publishers.)

Metallic glasses exhibit unique mechanical properties. For metallic glass composites (MGC), composed of dispersed nanocrystalline phases in an amorphous matrix, these properties can be enhanced or deteriorated depending on the volume fraction and size distribution of the crystalline phases. Understanding the evolution of crystalline phases during devitrification of bulk metallic glasses upon heating is key to realizing the production of these composites. Here, results are presented from a combination of in situ small- and wide-angle X-ray scattering (SAXS and WAXS) measurements during heating of Zr-based metallic glass samples at rates ranging from 10 2 to 10 4 Ks -1 with a time resolution of 4ms. By combining a detailed analysis of scattering experiments with numerical simulations, for the first time, it is shown how the amount of oxygen impurities in the samples influences the early stages of devitrification and changes the dominant nucleation mechanism from homogeneous to heterogeneous. During melting, the oxygen rich phase becomes the dominant crystalline phase whereas the main phases dissolve. The approach used in this study is well suited for investigation of rapid phase evolution during devitrification, which is important for the development of MGC., (© 2024 The Authors. Advanced Science published by Wiley‐VCH GmbH.)

A combination of complementary high-energy X-ray diffraction, containerless solidification during electromagnetic levitation and transmission electron microscopy is used to map in situ the phase evolution in a prototype Cu-Zr-Al glass during flash-annealing imposed at a rate ranging from 10 2 to 10 3  K s -1 and during cooling from the liquid state. Such a combination of experimental techniques provides hitherto inaccessible insight into the phase-transformation mechanism and its kinetics with high temporal resolution over the entire temperature range of the existence of the supercooled liquid. On flash-annealing, most of the formed phases represent transient (metastable) states - they crystallographically conform to their equilibrium phases but the compositions, revealed by atom probe tomography, are different. It is only the B2 CuZr phase which is represented by its equilibrium composition, and its growth is facilitated by a kinetic mechanism of Al partitioning; Al-rich precipitates of less than 10 nm in a diameter are revealed. In this work, the kinetic and chemical conditions of the high propensity of the glass for the B2 phase formation are formulated, and the multi-technique approach can be applied to map phase transformations in other metallic-glass-forming systems.