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3D-printed conductive structures are highly attractive due to their great potential for customizable electronic devices. While the traditional 3D printing of metal requires high temperatures to sinter metal powders or polymer/metal composites, low or room temperature processes will be advantageous to enable multi-material deposition and integration of optoelectronic applications. Herein, digital light processing technology and inkjet printing are combined as an effective strategy to fabricate customized 3D conductive structures. In this approach, a 3D-printed nanoporous (NPo) polymeric material is used as a substrate onto which a nanoparticle-based Ag ink is printed. SEM and X-ray nano computed tomography (nanoCT) measurements show that the porous morphology of the pristine NPo is retained after deposition and annealing of the Ag ink. By optimizing the deposition conditions, conductive structures with sheet resistance

Despite remarkable advances, high-performance thermoelectric (TE) materials-based thermocouples (TCs) lack mechanical robustness and flexibility. Hence, conventional low Seebeck coefficient metals (Ni, Cu, Fe) wire-junction-based TCs are used for temperature sensor applications. However, not only the sensitivity of the metal-based TC sensor is low, but also it is very difficult to fabricate a pixelated sensor using the conventional approach. In this study, high-performance (SbBi)$_2$(TeSe)$_3$-based printed flexible TE materials are employed to fabricate two types of shape-conformable TC-based temperature sensor arrays with 25 pixels (TSA I and TSA II). Bi$_{0.5}$Sb$_{1.5}$Te$_3$-based p-type (p-BST) printed TE film and copper are used to fabricate TSA I, and the p-type film together with the Bi$_2$Te$_{2.7}$Se$_{0.3}$-based n-type (n-BT) film is used to fabricate TSA II. A high average sensitivity (S$_{exp}$) value of ≈124 µV °C$^{−1}$ for TSA I and ≈319 µV °C$^{−1}$ for TSA II is attained with high linearity.

The mechanical properties of superalloys are strongly governed by the resistance to shearing of ordered precipitates by dislocations. In the operating environments of superalloys, the stresses and temperatures present during thermomechanical loading influence the dislocation shearing dynamics, which involve diffusion and segregation processes that result in a diverse array of planar defects in the ordered L12γ′ precipitate phase. This review discusses the current understanding of high-temperature deformation mechanisms of γ′ precipitates in two-phase Ni-, Co-, and CoNi-base superalloys. The sensitivity of planar fault energies to chemical composition results in a variety of unique deformation mechanisms, and methods to determine fault energies are therefore reviewed. The degree of chemical segregation in the vicinity of planar defects reveals an apparent phase transformation within the parent γ′ phase. The kinetics of segregation to linear and planar defects play a significant role in high-temperature properties. Understanding and controlling fault energies and the associated dislocation dynamics provide a new pathway for the design of superalloys with exceptional properties.

We present a new approach for the quantitative study of high-temperature diffusion in compositionally complex superalloys on the nano-scale. As key element, the approach utilizes the γ/γ'-microstructure itself as intrinsic nano-diffusion-couple (NDC). By establishing equilibrium at one temperature followed by annealing at a different temperature, well-defined transient states are generated which are studied using STEM-EDXS. We demonstrate this approach for a multi-component superalloy of CMSX-4 type. The temporal evolution of element concentrations is consistently revealed for γ- and γ'-forming elements and is compared to diffusion simulations based on DICTRA. Excellent agreement is obtained for Ni, Co, and Cr whereas diffusion of Al and, in particular, Re lacks behind in experiment. Finally, it is demonstrated that transient states can also be captured by in situ TEM using chip-based heating devices. The NDC approach offers great opportunities for diffusion studies in compositionally complex superalloys and might be extended to other two-phase multi-component systems.

The possibility of designing multi-principal element alloys in the Ni-Co-Ru system is investigated by first-principles and experimental means. A high-throughput first-principles approach is employed to probe the effect of composition on planar fault energies. Of most interest, a FCC alloy, Ni40Co40Ru20, exhibits a high room temperature strength compared to existing nickel-containing solid solution FCC high entropy alloys. The presence of Ru imparts the alloy with unique properties. First, the low stacking fault energy provides a low critical resolved shear stress for twinning, allowing a TWIP effect. Second, the high lattice friction and the associated high yield strength enables the critical resolved shear stress for twinning to be reached at low strains at room temperature, resulting in the formation of a dense network of planar defects for increased work hardening. A TRIP effect is also observed at higher strains at room temperature.

It has been a substantial challenge to develop a printed thermoelectric (TE) material with a figure-of-merit

This work establishes carbon nanofibre-mediated patterning of metal oxide nanostructures, through the combination of electrospinning and vapor-phase transport growth. Electrospinning of a suitable precursor with subsequent carbonization results in the patterning of catalyst gold nanoparticles embedded within carbon nanofibres. During vapor-phase transport growth, these nanofibres allow preferential growth of one-dimensional metal oxide nanostructures, which grow radially outward from the nanofibril axis, yielding a hairy caterpillar-like morphology. The synthesis of metal oxide caterpillars is demonstrated using zinc oxide, indium oxide, and tin oxide. Source and substrate temperatures play the most crucial role in determining the morphology of the metal oxide caterpillars, whereas the distribution of the nanofibres also has a significant impact on the overall morphology. Introducing the current methodology with near-field electrospinning further facilitates user-defined custom patterning of metal oxide caterpillar-like structures.

The creep behavior of a multinary single crystal Co-base superalloy has been compared for uniaxial tension and compression of 400 MPa applied along [001] at 850 °C. Creep under tensile stress proceeds two times faster than creep under compression. A detailed TEM study shows that already after ∼0.3 % creep strain planar faults are formed in both samples. While extended a/2 ribbons with SISF loops embedded in APBs are observed in tension, extrinsic SFs are revealed in compression. At ∼5 % creep strain SISFs confined to the γ′ phase dominate in tension, whereas extrinsic SFs and microtwins extending across both phases are the prevalent planar faults in compression. In addition, dense networks of regular a/2 matrix dislocations develop at the γ/γ′ interfaces in both loading scenarios. In tensile creep and early compressive creep the direct contribution of planar faults to plastic deformation is minor and does not exceed 10 % of the measured plastic strain. In contrast, thickening of microtwins appears to become an efficient deformation channel in the later stages of compressive creep. A pronounced asymmetry regarding the rafting kinetics is observed resulting in a P-type rafted and topologically inverted microstructure after ∼5 % creep in tension while hardly any rafting has occurred under compression. The pronounced rafting and related recovery processes are likely responsible for the inferior creep behavior in tension. Finally, two novel diffusion-assisted degradation mechanisms related to microtwins are shown to be active: an expansion of the γ phase into γ′ precipitates along microtwins and the formation of γ phase nuclei at planar fault intersections inside γ′. Both phenomena are hypothesized to be triggered by segregation of γ formers like Co and Cr to planar faults.

The Heulser intermetallic ${\mathrm{MnAu}}_{2}\mathrm{Al}$ is shown to undergo a dramatic change in net magnetization in response to plastic deformation. A mechanism is proposed involving antiferromagnetic interactions in the otherwise ferromagnetic compound (when ordered) that arise due to chemical changes at the antiphase boundaries created by the deformation. The coupling between chemical and magnetic order across antiphase boundaries is likely to occur in other ordered magnetic systems and may provide an explanation for otherwise anomalous magnetic behavior across several systems, including other Heusler intermetallics.

Multiphasic intermetallic materials are attractive candidates for functional applications where the constituent phases alone do not meet the property targets. The interfaces at the phase boundaries in these materials are central to their macroscopic properties, with the details of the atomic structure underpinning local thermomechanical, electrical, and magnetic behavior. Here, we characterize the interface structure in the biphasic Nb-Co-Sn system consisting of $\mathrm{Nb}{\mathrm{Co}}_{2}\mathrm{Sn}$ full Heusler (FH) precipitates embedded in a NbCoSn half Heusler (HH) matrix, which exhibits semicoherent interfaces with a 3.3% lattice parameter misfit that determines the constitution of the FH/HH interface on the nanometer scale. We use detailed transmission electron microscopy (TEM) and atomistic calculations to precisely determine the dislocation content and structure at the semicoherent interface, which modulates the strain fields in a semiregular pattern. We find that the interface forms regularly spaced paired partial dislocations with a joint Burgers vector of $a/2\ensuremath{\langle}110\ensuremath{\rangle}$, favored by misfit energy relief and chemical ordering. The interface exhibits numerous interface steps (disconnections) which in turn determine the precipitate morphology. Overall, the two phases show full coherency except in the vicinity of the misfit dislocation cores located every 11 nm, leading to a modulated strain field parallel to the interface, and no long-range strain fields as the interfacial dislocations accommodate the misfit strain.

Flexibility in a printed thermoelectric (TE) material is vital for low-cost manufacturing of shape-conformable TE devices. In this work, a one-pot facile method was adapted to prepare a Cu-Se-based printable ink. The ink was printed on flexible substrates followed by sintering to let β-Cu2-δSe phase be formed. The film is found to be exceptionally flexible with a change in film resistance μ W with an open-circuit voltage VOC of 12 mV is demonstrated using a TE-generator (Flex-TEG) with two thermocouples made of the prepared material.

A study on the individual role of γ and γ′-phase during the scale formation on Co-9Al-9W (at.%) at 900 °C was conducted. High-accuracy thermogravimetric analysis was used to locate changes in the kinetics of scale growth. Compositions of three separated layers within the scale have been elucidated in detail. The results demonstrate the substantial impact of the two-phase microstructure on the initiation of oxidation for the appearance of the scale. Examination of STEM-EDX elemental mappings of the internal oxidation front during the early stages of scale growth can explain the origin of isolated Al2O3 precipitates instead of a closed protective layer.

The formation of a ternary μ-phase is documented for the system Co-Ti-W. The relevant compositional stability range is identified by high-throughput energy dispersive X-ray spectroscopy, electrical resistance and X-ray diffraction maps from a thin-film materials library (1 μm thickness). Bulk samples of the identified compositions were fabricated to allow for correlative film and bulk studies. Using analytical scanning and transmission electron microscopy, we demonstrate that in both, thin film and bulk samples, the D8 5 phase (μ-phase) coexists with the C36-phase and the A2-phase at comparable average chemical compositions. Young's moduli and hardness values of the μ-phase and the C36-phase were determined by nanoindentation. The trends of experimentally obtained elastic moduli are consistent with density functional theory (DFT) calculations. DFT analysis also supports the experimental findings, that the μ-phase can solve up to 18 at.% Ti. Based on the experimental and DFT results it is shown that CALPHAD modeling can be modified to account for the new findings.

We present a new approach for the quantitative study of high-temperature diffusion in compositionally complex superalloys on the nano-scale. As key element, the approach utilizes the γ/γ'-microstructure itself as intrinsic nano-diffusion-couple. By establishing equilibrium at one temperature followed by annealing at a different temperature, well-defined transient states are generated which are studied using analytical transmission electron microscopy (TEM). We demonstrate this approach for a high-performance multi-component superalloy. The temporal evolution of element concentrations is consistently revealed for γ- and γ'-forming elements and is compared to multi-component diffusion simulations. Excellent agreement is obtained for Ni, Co, and Cr whereas diffusion of Al and, in particular, Re lacks behind in the experiment. Finally, it is demonstrated that transient states can also be captured by in-situ TEM using chip-based heating devices. The nano-diffusion-couple approach offers great opportunities for diffusion studies in compositionally complex superalloys and might be extended to other two-phase multicomponent systems.

The great potential of Rapid Thermal Annealing (RTA), a widespread technique in semiconductor technology, for studying high-temperature properties of superalloys is demonstrated. As an application example, early stages of high-temperature oxidation of Co/Ni-base superalloys are investigated. Model alloys with different Co/Ni ratio are oxidized in synthetic dry air at 900 °C to understand the differences between the oxidation behavior of Ni- and Co-base alloys. Upon short exposure times (below 64 s), the two-phase γ/γ′ microstructure has a pronounced influence on both the morphology and growth kinetics of Al2O3 precipitates. Depending on the base element, Al2O3 nucleates in either the γ′ phase in the form of needles (Ni-base superalloy) or in the γ matrix as lath- and plate-like precipitates (Co-base superalloy) with the latter showing much slower formation kinetics. Observed differences in oxidation behavior can be directly correlated to changes in the partitioning of W, which acts as a γ former in Ni- and a γ′ former in Co-base superalloys. We propose that a significant amount of W in γ′ has an inhibitory effect on the diffusion of Al, suppressing the formation of Al2O3 in the γ′ phase of Co-base superalloys. Our approach proved to be very successful for oxidation studies and opens up new opportunities for superalloys research.

The system Co–Ti–Cr was recently identified as a very promising base for low mass-density Co-based superalloys. This study presents the influence of quaternary alloying additions on the thermophysical and mechanical properties of a Co–11Ti–15Cr model superalloy. Al, Ta, Re, and W were selected as a starting point for alloy development as they represent important alloying elements in both Ni-based and Co–Al–W-based superalloys. Microstructure analysis reveals that the addition of only 1 at.% of either of these elements causes the formation of different undesired intermetallic phases in addition to γ and γ′ phases, which is in agreement with thermodynamic calculations. However, a diffusion couple between the Co–Ti–Cr and a Co–Al–W–Ta alloy suggests that the tolerance for alloying elements without destabilizing the γ/γ′ two-phase microstructure is higher when they are present in a certain ratio. Energy-dispersive X-ray spectroscopy shows that Cr and Re are enriched in the γ phase, whereas Ti and W preferentially partition to γ′. All alloying elements increase the yield strength at room temperature, but are disadvantageous at 1000 °C. Re and W retain their strengthening effect up to 900 °C.

The structure and formation mechanism of extended planar defects in the γ/γ′ microstructure of creep deformed CoNi-base single crystal superalloys have been studied by conventional and advanced transmission electron microscopy (TEM). Planar defects in numerous isolated as well as contiguous γ′ precipitates on {111} planes reveal a characteristic configuration whereby superlattice intrinsic stacking faults (SISF) are fully embedded within antiphase boundaries (APB). Detailed analysis revealed that a leading 1/3[ 1 ¯ 1 ¯ 2] superpartial dislocation first creates an SISF. The SISF is then transformed into an APB by a trailing 1/6[ 1 ¯ 1 ¯ 2] partial dislocation. The partial is left inside the precipitate and remains as a dislocation loop. Thus, the entire shearing process constitutes a crystallographic slip of type 1/2[ 1 ¯ 1 ¯ 2]. A force balance analysis indicates that the initial APB energy exceeds the SISF energy. However, energy-dispersive X-ray spectroscopy (EDXS) indicates pronounced local reordering and diffusion processes near both types of planar defects. The APB qualitatively adopts the composition of the γ phase whereas the SISF locally changes its composition towards that of the Co3W–D019 phase. We propose that these atomic diffusion processes determine the formation and shrinkage of the loops. A post mortem in situ TEM heating experiment shows that with increasing temperature the APBs exhibit complete faceting into {100} planes followed by coarsening, eventually leading to disintegration of the γ′ precipitate. This indicates a detrimental impact of APBs as potential nuclei for fragmentation of the γ/γ′ microstructure in CoNi-base superalloys.

Precipitate shearing mechanisms during single-crystal tensile creep of L12-containing Co- and CoNi-base alloys have been investigated. Interrupted creep tests were conducted at 900 °C under vacuum at constant load, and stresses varied between 275 and 345 MPa. Transmission electron microscopy diffraction contrast analysis revealed superlattice intrinsic and extrinsic stacking faults in the γ′ precipitates in the Co-base alloys. However, in alloys containing significant additions of nickel (CoNi-base alloys), antiphase boundaries formed by shearing of a/2〈1 1 0〉 dislocations on octahedral planes. The shearing mechanisms in the Co- and CoNi-base γ′ phase are compared to commercial Ni-base alloys, and the relative fault energies inferred from these observations are discussed.

Creep-induced antiphase boundaries (APBs) in new Co-base single-crystal superalloys with coherent embedded L12-γ′ precipitates have been observed. APBs formed during single-crystal tensile creep tests performed at 900 °C under vacuum at stresses between 275 and 310 MPa. The alloys investigated contained 30–39 at.% Ni, which was added to the Co–Al–W ternary system to expand the γ–γ′ phase field and increase the γ′-solvus. Transmission electron microscopy (TEM) using two-beam conditions with fundamental and superlattice reflections was performed for defect characterization. The Burgers vector b of dislocations associated with the APBs was determined to be of type b = a0/2[011] and a0/2 [ 0 1 1 ¯ ] . The displacement vectors, R, of the APBs matched the dislocation Burgers vectors, with R = b = a0/2[011]. APBs were observed in nearly every precipitate beyond 0.5% creep strain for the compositions investigated. The implications for high-temperature properties are discussed.

Lightweighting of structural materials has proven indispensable in the energy economy, predicated on alloy design with high strength-to-weight ratios. Modern aluminum alloys have made great strides in ambient temperature performance and are amenable to advanced manufacturing routes such as additive manufacturing, but lack elevated temperature robustness where gains in efficiency can be obtained. Here, we demonstrate the intentional design of disorder at interfaces, a notion generally associated with thermal runaway in traditional materials, in a segregation-engineered ternary nanocrystalline Al–Ni–Ce alloy that exhibits exceptional thermal stability and elevated temperature strength. In-situ transmission electron microscopy in concert with ultrafast calorimetry and X-ray total scattering point to synergistic co-segregation of Ce and Ni driving the evolution of amorphous intergranular films separating sub-10 nm Al-rich grains, which gives rise to emergent thermal stability. We ascribe this intriguing behavior to near-equilibrium interface conditions followed by kinetically sluggish intermetallic precipitation in the confined disordered region. The resulting outstanding mechanical performance at high homologous temperatures lends credence to the efficacy of promoting disorder in alloy design and discovery.