Function Of Crystal Orientation Research Articles

Operative slip systems and their critical resolved shear stresses in η-Fe2Al5 investigated by micropillar compression at room temperature

The plastic deformation behavior of single crystals of orthorhombic η-Fe2Al5 has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. Plastic flow is observed even at room temperature by the operation of six slip systems; (001)<010>, (001)<110>, (001)<130>, {22¯3}<110>, {311}<1¯03> and {301}<1¯03>. The CRSS values for the five identified slip systems are very high all in the range of 1.1∼1.5 GPa and do not vary much with specimen size. In the middle of the stereographic projection, the (001)<010>, (001)<110>, (001)<130> and {22¯3}[110] slip systems operate according to the relative Schmid factors with the similar CRSS values in the range of 1.08∼1.23 GPa. In orientations close to [001], the {311}<1¯03> slip system as well as the {301}<1¯03> slip system operate with a much higher CRSS values around 1.5 GPa, producing wavy slip traces due to the occurrence of frequent cross-slip among these slip planes. In orientations close to the [100]-[110]-[010] symmetry line, on the other hand, premature failure occurs without the operation of any slip systems, although, the Schmidt factor-wise, the {311}<1¯03> and {301}<1¯03> slip systems could operate. The selection of slip systems, their CRSS values and the possible dislocation dissociation modes are discussed based on the overlapped atomic volume that occurs during shear along the slip direction on the slip plane, taking into account the partial occupancies of Al atoms in the linear atomic chain along the orthorhombic c-axis direction.

Broadband High-Precision Faraday Rotation Spectroscopy with Uniaxial Single Crystal CeF3 Modulator

We present a low-noise (&lt;10 µrad/Hz) broadband Faraday Rotation Spectroscopy method which is feasible for near-ultraviolet through near-infrared wavelengths. We demonstrate this in the context of a high-precision spectroscopy experiment using a heated Pb vapor cell and two different lasers, one in the UV (368 nm) and a second in the IR (1279 nm). A key element of the experimental technique is the use of a uniaxial single crystal CeF3 Faraday modulator with excellent transmission and optical rotation properties across the aforementioned wavelength range. Polarimeter performance is assessed as a function of crystal orientation and alignment, AC modulation amplitude, laser power, and laser wavelength. Crystal-induced distortion of the (6p2)3P0→(6p2)3P1 (1279 nm) and (6p2)3P1→(6p7s)3P0 (368 nm) spectral lines due to misalignment-induced birefringence is discussed and modeled using the Jones calculus.

On the inherent strength of Cr23C6 with the complex face-centered cubic D84 structure

The deformation behavior of single crystals of Cr23C6 with the complex D84 crystal structure based on the face-centered cubic lattice has been investigated by micropillar compression as a function of crystal orientation and specimen size at room temperature. For the first time, the {111}<1‾01> slip system is identified to be the only operative slip system. The 1/2<1‾01> dislocation dissociates into two partial dislocations with identical collinear Burgers vectors (b) as confirmed by transmission electron microscopy (TEM) and atomic-resolution scanning transmission electron microscopy (STEM). The energy of the stacking fault bounded by two coupled partial dislocations with the b = 1/4<1‾01> is evaluated from their separation distances to be 840 mJ/m2. The critical resolved shear stress (CRSS) for {111}<1‾01> slip increases with the decrease in the specimen size, following the inverse power-law relationship with a relatively low exponent of ∼ -0.19. The room-temperature bulk CRSS value evaluated by extrapolating this inverse relationship to the specimen size of 20∼30 μm is 0.79 ± 0.15 GPa. The exact position of the slip plane among many different parallel {111} atomic planes and possible dislocation dissociations on the relevant slip planes are discussed based on the calculated generalized stacking fault energy (GSFE) curves. The inter-block layer slip is deduced to occur for {111}<1‾01> slip based on the TEM/STEM observations and the result of GSFE calculations. Finally, plausible atomic structures for stacking faults on (111) and coherent twin boundaries are discussed.

Room-temperature deformation of single crystals of WC investigated by micropillar compression

The room temperature deformation behavior of single crystals of WC has been investigated as a function of crystal orientation and specimen size by micropillar compression tests. Plastic flow is successfully observed at room temperature by the operation of slip on {011¯0}〈21¯1¯3〉 when the specimen size is reduced to micrometer orders. This slip system is the only operative slip system in WC at room temperature, and thus plastic flow is not observed for crystal orientations close to the c-axis orientation. The bulk critical resolve shear stress (CRSS) is estimated to be 1.2 ± 0.3 GPa from the extrapolation of the size-dependent CRSS. The 1/3〈21¯1¯3〉 dislocation carrying slip on {011¯0} dissociates into two identical collinear partial dislocations separated by a stacking fault with the energy of 211∼264 mJ/m2. The preference of slip along 〈21¯1¯3〉 among possible directions (such as 〈21¯1¯0〉 and [0001]) on the {011¯0} prism plane is discussed in terms of dislocation self-energy based on anisotropic elasticity, stacking fault energy, dislocation dissociation and Peierls stress for dislocation motion. The lowest Peierls stress arising from the shorter Burgers vector (1/6〈21¯1¯3〉) of dislocations as a result of collinear dissociation of dislocations with b = 1/3〈21¯1¯3〉 on the {011¯0} slip plane is considered to be the main reason for the preference of the {011¯0}〈21¯1¯3〉 slip system.

Orientation anisotropy and strain localization during elevated temperature tensile deformation of single crystal and bi-crystal Ni-based GTD444 superalloy

The aspects of grain boundary character as well as orientation of constituent grains are important for high temperature applications of directionally solidified (DS) blades as they are expected to influence the overall mechanical behavior; however, there exist limited studies at critical test temperature. Single crystals (SX) with orientations [001] and [101] and their equivalent bi-crystals (BX) are used to understand the effects of crystal orientation and grain boundary misorientation on the deformation of Ni-based (GTD444) superalloy at 650 °C. The high temperature tensile tests are coupled with digital image correlation (DIC) to study plastic heterogeneity as a function of crystal orientations. Among the two SX samples, the [001] orientation had slightly higher yield stress than [101] orientation. On the other hand, the ductility of [101] orientation is 1.5 times of [001] orientation. DIC strain field maps and orientation imaging microscopy (OIM) showed extensive flow localization in one of the grains in BX samples. However, flow localization appeared to be insensitive to grain boundary misorientation. The measured lattice rotation by OIM is shown to be correlated with localized strain for all the samples. Selected transmission electron microscopy and detailed fractography analyses of the deformed samples were performed to understand the deformation mechanisms active in each of the orientations. It is found that there is greater strain localization within γ channels in [001] which leads to higher hardening. In contrast, shearing of γ' precipitates followed by increased dislocation activity in conjunction with higher lattice rotation lead to higher ductility in [101] orientation.

Room-temperature plastic deformation of single crystals of α-manganese - hard and brittle metallic element

The deformation behavior of single crystals of α-manganese has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. When the specimen size is reduced to the micrometer-range, single crystals of α-manganese are found to plastically deform by dislocation motion at room temperature for the first time, accompanied by very high yield stresses of the range of 4–6 GPa. Slip along [111] and [001] are identified to operate for compression axis orientations near [001] and near [011] and [1¯11], respectively. Any low-indexed planes cannot be designated as the slip plane for both slip along [111] and [001], because of the significantly wavy nature of slip lines caused by the occurrence of frequent cross-slip. Slip along [111] tends to prefer the slip plane of {112} rather than {110}. Slip along [001], on the other hand, tends to occur on the maximum resolved shear stress plane. The 1/2[111] dislocation carrying slip along [111] moves as a perfect dislocation without dissociating into partials and does not have any preferred orientation. The [001] dislocation carrying slip along [001] also moves as a perfect dislocation without dissociating into partials. Although the Peierls stress for the motion of these dislocations must be very high, there seems no deep Peierls valleys along particular directions, unlike the screw direction for the 1/2[111] dislocation in body-centered cubic metals.

In situ MOCVD growth and band offsets of Al2O3 dielectric on β-Ga2O3 and β-(AlxGa1−x)2O3 thin films

The in situ metalorganic chemical vapor deposition (MOCVD) growth of Al2O3 dielectrics on β-Ga2O3 and β-(AlxGa1−x)2O3 films is investigated as a function of crystal orientations and Al compositions of β-(AlxGa1−x)2O3 films. The interface and film qualities of Al2O3 dielectrics are evaluated by high-resolution x-ray diffraction and scanning transmission electron microscopy imaging, which indicate the growth of high-quality amorphous Al2O3 dielectrics with abrupt interfaces on (010), (100), and (2¯01) oriented β-(AlxGa1−x)2O3 films. The surface stoichiometries of Al2O3 deposited on all orientations of β-(AlxGa1−x)2O3 are found to be well maintained with a bandgap energy of 6.91 eV as evaluated by high-resolution x-ray photoelectron spectroscopy, which is consistent with the atomic layer deposited (ALD) Al2O3 dielectrics. The evolution of band offsets at both in situ MOCVD and ex situ ALD deposited Al2O3/β-(AlxGa1−x)2O3 is determined as a function of Al composition, indicating the influence of the deposition method, orientation, and Al composition of β-(AlxGa1−x)2O3 films on resulting band alignments. Type II band alignments are determined at the MOCVD grown Al2O3/β-(AlxGa1−x)2O3 interfaces for the (010) and (100) orientations, whereas type I band alignments with relatively low conduction band offsets are observed along the (2¯01) orientation. The results from this study on MOCVD growth and band offsets of amorphous Al2O3 deposited on differently oriented β-Ga2O3 and β-(AlxGa1−x)2O3 films will potentially contribute to the design and fabrication of future high-performance β-Ga2O3 and β-(AlxGa1−x)2O3 based transistors using MOCVD in situ deposited Al2O3 as a gate dielectric.

Integrated multi-scale modeling of variant selection during stress-induced martensite formation in metastable β Ti-alloys

Stress-induced martensite formation is the predominant mechanism during the deformation of various functional and structural Ti- alloys. To predict the performance of these alloys, stress-induced martensite formation was modeled as a function of crystal orientation and stress state. We present an integrated micromechanical modeling approach using finite element (FE) analysis and an elastic spectral solver based on Fast Fourier Transforms (EFFT), which allows direct correlation of the available work from martensite formation under complex stress-states in an in-situ characterized microstructure. The model is applied as a virtual analogue of an experimental 3-point bending test of a metastable β Ti–10V–2Fe–3Al alloy containing 5% α. The FE model incorporates the experimental β microstructure from electron backscattering diffraction (EBSD) with anisotropic elastic behavior. The EFFT solver uses strain fields in two local regions from the FE model to predict local stresses in experimental microstructures containing β and α phases. The stress and orientation data are used to predict the available work from stress-induced α″ martensite formation of the six different α″ variants. It was found that stress and available work concentrated around the tips of lamellar α, making these regions preferred nucleation sites for α″ formation, which is in excellent agreement with the in-situ experimental observations. This suggests that the local stress conditions in the β phase play a more important role in triggering α″ formation than the compositional inhomogeneity in the β phase at α-β interfaces. Using the integrated model, the first variants forming at low levels of deformation could be confidently predicted. However, the transformation behavior at elevated levels of deformation could not be properly captured. This indicates the need of further model improvement, including Dirichlet boundary conditions for the EFFT solver and accounting for the role of plasticity induced by phase transformation.

Plastic deformation of bulk and micropillar single crystals of Mo5Si3 with the tetragonal D8m structure

The plastic deformation behavior of single crystals of Mo5Si3 with the tetragonal D8m structure has been investigated in compression as a function of crystal orientation and temperature (1200–1500°C) in the bulk form and as a function of crystal orientation and specimen size at room temperature in the micropillar form. The slip system of {112¯}<111> is identified to be the only one that operates at high temperatures above 1200°C in bulk crystals, while any plastic flow is not detected at room temperature in micropillar crystals. The critical resolved shear stress (CRSS) for {112¯}<111> slip at room temperature estimated from the extrapolation of the temperature dependence of CRSS obtained for bulk crystals is considerably higher than fracture stresses obtained for micropillar crystals, indicating that the room-temperature brittleness is due in principle to the difficulty in dislocation motion arising from the very high CRSS value. The value of fracture toughness evaluated with a chevron-notched micro-beam specimen with a notch plane parallel to (001) is 1.54 MPa•m1/2, which is comparable to those reported for other transition-metal (TM) silicides of the TM5Si3-type. The selection of {112¯} slip plane and the dissociation of the 1/2<111> dislocation on the slip plane are discussed based on generalized stacking fault energy (GSFE) curves theoretically calculated by first-principles calculations.

RUScal: Software for the analysis of resonant ultrasound spectroscopy measurements.

Resonant ultrasound spectroscopy is used to nondestructively measure the elastic resonances of small solids to elucidate the material's elastic properties or other qualities like size, shape, or composition. Here, we introduce the software RUScal for the purpose of determining elastic properties by analyzing the eigenfrequencies of solid specimens with common shapes, such as rectangular parallelepipeds, cylinders (solid and hollow tube), ellipsoids, and octahedrons, as well as irregularly shaped ellipsoids that can be described analytically. All symmetry classes are supported, from isotropic to triclinic, along with the option to add or remove up to three orthogonal mirror planes as well as the ability to reorient the crystal axes with respect the sample edges via Euler angles. Additional features include tools to help find initial sets of elastic constants, including grid exploration and Monte Carlo methods, a tool to analyze frequencies as a function of sample length or crystal orientation, an error analysis tool to assess fit quality, and formatting of the input and output files for batch fitting, e.g., as a function of temperature. This software was validated with published resonant ultrasound spectroscopy data for various materials, shapes, and symmetries with noted improvements in calculation time compared to finite element methods.

Performance of in situ oxidized platinum/iridium alloy Schottky contacts on (001), (2¯01), and (010) β -Ga2O3

The performance of β-Ga2O3 Schottky contacts (SCs) fabricated using amorphous, intentionally oxidized platinum–iridium alloys was investigated as a function of alloy composition and β-Ga2O3 crystal orientation. PtyIr(1−y)Ox SCs with Pt fractions of y = 0.8, 0.5, and 0.3 were deposited on (001), (2¯01), and (010) single-crystal β-Ga2O3 substrates via the reactive rf and dc co-sputtering of Pt and Ir targets using oxygen–argon plasmas. In each case, the PtyIr(1−y)Ox SCs were highly rectifying with current rectification ratios (at ±3 V) of 11/10/9 orders of magnitude (at 300 K) for the (001)/(2¯01)/(010) β-Ga2O3 substrates. Current–voltage (I–V) and capacitance–voltage (C–V) measurements revealed that the Pt0.5Ir0.5Ox SCs contained the highest Schottky barriers on all β-Ga2O3 crystal faces, with the best contacts having ideality factors of 1.05 and image-force-corrected I–V and C–V determined barrier heights of 2.10 and 2.20 eV, respectively. These were consistently higher by ∼0.2 eV than the corresponding barriers for the Pt0.8Ir0.2Ox and Pt0.3Ir0.7Ox SCs, with the Pt0.5Ir0.5Ox SCs also having significantly lower reverse leakage currents (in the 0 to −100 V range). In comparison, the barrier heights of the best unoxidized plain-metal Pt0.5Ir0.5 SCs were only ∼1.2 eV, illustrating the effectiveness of in situ oxidation in improving the performance of PtIr SCs. All PtyIr(1−y)Ox SCs on (2¯01) β-Ga2O3 showed excellent high-temperature performance with rectification ratios (at ±3 V) of 109 at 300 °C and of 106 at 500 °C.

Mechanistic fatigue in Ni-based superalloy single crystals: A study of crack paths and growth rates

The mechanistic basis of microstructurally short crack paths and growth rates is investigated in Ni-based superalloy single crystals using Crystal Plasticity (CP) and eXtended Finite Element (XFEM) analyses of experimental edge-cracked samples over a range of crystal orientations. Crack paths are determined to be those along crystallographic slip systems within which the slip is highest. Crack growth rates are determined by the crack tip critical stored energy density. Experimental observations of tortuous crack paths and their dependence on crystal orientation are reasonably well captured by the mechanistic model. Key features of alternating and straight crack paths are reproduced. The experimentally measured crack growth rates as a function of crystal orientation are also captured by the mechanistic model and controlled by the crack tip critical stored energy density which was found to be 385 Jm−2 in the Ni-based superalloy single crystals analysed. A new methodology for determination of critical stored energy density and mechanistic quantification of short crack growth rates is presented.

Room-temperature deformation of single crystals of ZrB2 and TiB2 with the hexagonal AlB2 structure investigated by micropillar compression

The plastic deformation behavior of single crystals of two transition-metal diborides, ZrB2 and TiB2 with the AlB2 structure has been investigated at room temperature as a function of crystal orientation and specimen size by micropillar compression tests. Although plastic flow is not observed at all for their bulk single crystals at room temperature, plastic flow is successfully observed at room temperature by the operation of slip on {1{bar{1}}00}<11{bar{2}}3> in ZrB2 and by the operation of slip on {1{bar{1}}00}<0001> and {1{bar{1}}00}<11{bar{2}}0> in TiB2. Critical resolve shear stress values at room temperature are very high, exceeding 1 GPa for all observed slip systems; 3.01 GPa for {1{bar{1}}00}<11{bar{2}}3> slip in ZrB2 and 1.72 GPa and 5.17 GPa, respectively for {1{bar{1}}00}<0001> and {1{bar{1}}00}<11{bar{2}}0> slip in TiB2. The identified operative slip systems and their CRSS values are discussed in comparison with those identified in the corresponding bulk single crystals at high temperatures and those inferred from micro-hardness anisotropy in the early studies.

Deep learning model to predict fracture mechanisms of graphene

Understanding fracture is critical to the design of resilient nanomaterials. Molecular dynamics offers a way to study fracture at an atomistic level, but is computationally expensive with limitations of scalability. In this work, we build upon machine-learning approaches for predicting nanoscopic fracture mechanisms including crack instabilities and branching as a function of crystal orientation. We focus on a particular technologically relevant material system, graphene, and apply a deep learning method to the study of such nanomaterials and explore the parameter space necessary for calibrating machine-learning predictions to meaningful results. Our results validate the ability of deep learning methods to quantitatively capture graphene fracture behavior, including its fractal dimension as a function of crystal orientation, and provide promise toward the wider application of deep learning to materials design, opening the potential for other 2D materials.

Plastic deformation of single crystals of CrB2, TiB2 and ZrB2 with the hexagonal AlB2 structure

The plastic deformation behavior of single crystals of three transition-metal diborides with the AlB2 structure, CrB2, TiB2 and ZrB2 has been investigated as a function of crystal orientation in the temperature range from room temperature to 1500 °C. Plastic flow is observed above 800 °C by the operation of slip on {11¯00}<112¯3> in CrB2, while in ZrB2, the onset temperature for slip on {11¯00}<112¯3> is 700 °C and that for slip on (0001)<112¯0> is 800 °C. In contrast, any appreciable plastic flow is not observed in TiB2 at 1500 °C and below. The critical resolved shear stress (CRSS) for slip on {11¯00}<112¯3> in CrB2 monotonously decreases with increasing temperature up to 1500 °C. On the other hand, the CRSS for slip on {11¯00}<112¯3> in ZrB2 decreases with increasing temperature up to 1000 °C and then increases anomalously with increasing temperature. Similarly, the CRSS for slip on (0001)<112¯0> in ZrB2 decreases with increasing temperature up to 1200 °C and then increases anomalously with increasing temperature, followed again by the decrease above 1400 °C. Generalized stacking fault (GSF) energy calculations well explain slip direction on the relevant slip plane, dislocation dissociation scheme and relative ease of slip among the three transition-metal diborides. The existence of planar growth faults on prism planes in CrB2 and TiB2 significantly affects the plastic deformation behavior so that the high onset temperature for plastic flow for these two diborides cannot be predicted solely by GSF energy calculations.

Crystal rotations and alignment in spatially varying magma flows: 2-D examples of common subvolcanic flow geometries

Summary Elongate inclusions immersed in a viscous fluid generally rotate at a rate that is different from the local angular velocity of the flow. Often, a net alignment of the inclusions develops, and the resulting shape preferred orientation of the particle ensemble can then be used as a strain marker that allows reconstruction of the fluid’s velocity field. Much of the previous work on the dynamics of flow-induced particle rotations has focused on spatially homogeneous flows with large-scale tectonic deformations as the main application. Recently, the theory has been extended to spatially varying flows, such as magma with embedded crystals moving through a volcanic plumbing system. Additionally, an evolution equation has been introduced for the probability density function of crystal orientations. Here, we apply this new theory to a number of simple, 2-D flow geometries commonly encountered in magmatic intrusions, such as flow from a dyke into a reservoir or from a reservoir into a dyke, flow inside an inflating or deflating reservoir, flow in a dyke with a sharp bend, and thermal convection in a magma chamber. The main purpose is to provide a guide for interpreting field observations and for setting up more complex flow models with embedded crystals. As a general rule, we find that a larger aspect ratio of the embedded crystals causes a more coherent alignment of the crystals, while it has only a minor effect on the geometry of the alignment pattern. Due to various perturbations in the crystal rotation equations that are expected in natural systems, we show that the time-periodic behaviour found in idealized systems is probably short-lived in nature, and the crystal alignment is well described by the time-averaged solution. We also confirm some earlier findings. For example, near channel walls, fluid flow often follows the bounding surface and the resulting simple shear flow causes preferred crystal orientations that are approximately parallel to the boundary. Where pure shear deformation dominates, there is a tendency for crystals to orient themselves in the direction of the greatest tensile strain rate. Where flow impinges on a boundary, for example in an inflating magma chamber or as part of a thermal convection pattern, the stretching component of pure shear aligns with the boundary, and the crystals orient themselves in that direction. In the field, this local pattern may be difficult to distinguish from a boundary-parallel simple shear flow. Pure shear also dominates along the walls of a deflating magma chamber and in places where the flow turns away from the reservoir walls, but in these locations, the preferred crystal orientation is perpendicular to the wall. Overall, we find that our calculated patterns of crystal orientations agree well with results from analogue experiments where similar geometries are available.

Micropillar compression deformation of single crystals of Fe3Ge with the L12 structure

The plastic deformation behavior of single crystals of Fe3Ge with the L12 structure has been investigated at room temperature as a function of crystal orientation by micropillar compression tests. In addition to slip on (010), slip on (111) is observed to occur in Fe3Ge for the first time. The CRSS (critical resolved shear stress) for (111)[101¯] slip, estimated by extrapolating the size-dependent strength variation to the ‘bulk’ size, is ~240 MPa, which is almost 6 times that (~40 MPa) for (010)[101¯] slip similarly estimated. The dissociation scheme for the superlattice dislocation with b=[101¯] is confirmed to be of the APB (anti-phase boundary)-type both on (010) and on (111), in contrast to the previous prediction for the SISF (superlattice intrinsic stacking fault) scheme on (111) because of the expected APB instability. While superlattice dislocations do not have any preferential directions to align when gliding on (010) (indicative of low frictional stress at room temperature), the alignment of superlattice dislocations along their screw orientation is observed when gliding on (111). This is proved to be due to thermally-activated cross-slip to form Kear-Wilsdorf locks, indicative of the occurrence of yield stress anomaly that is observed in many other L12 compounds such as Ni3Al. Some important deformation characteristics expected to occur in Fe3Ge (such as the absence of SISF-couple dissociation and the occurrence of yield stress anomaly) will be discussed in the light of the experimental results obtained (APB energies on (111) and (010) and CRSS values for slip on (111) and (010)).

Micropillar Compression Deformation of Single Crystals of Fe &lt;sub&gt;3&lt;/sub&gt;Ge with the L1 &lt;sub&gt;2&lt;/sub&gt; Structure

The plastic deformation behavior of single crystals of Fe3Ge with the L12 structure has been investigated at room temperature as a function of crystal orientation by micropillar compression tests. In addition to slip on (010), slip on (111) is observed to occur in Fe3Ge for the first time. The CRSS (critical resolved shear stress) for (111)[10‾1] slip, estimated by extrapolating the size-dependent strength variation to the ‘bulk’ size, is ~240 MPa, which is almost 6 times that (~40 MPa) for (010)[101] slip similarly estimated. The dissociation scheme for the superlattice dislocation with b=[10‾1] is confirmed to be of the APB (anti-phase boundary)-type both on (010) and on (111), in contrast to the previous prediction for the SISF (superlattice intrinsic stacking fault) scheme on (111) because of the expected APB instability. While superlattice dislocations do not have any preferential directions to align when gliding on (010) (indicative of low frictional stress at room temperature), the alignment of superlattice dislocations along their screw orientation is observed when gliding on (111). This is proved to be due to thermally-activated cross-slip to form Kear-Wilsdorf locks, indicative of the occurrence of yield stress anomaly that is observed in many other L12 compounds such as Ni3Al. Some important deformation characteristics expected to occur in Fe3Ge (such as the absence of SISF-couple dissociation and the occurrence of yield stress anomaly) will be discussed in the light of the experimental results obtained (APB energies on (111) and (010) and CRSS values for slip on (111) and (010)).

Anisotropic Cathodic Corrosion of Gold Electrodes in the Absence and Presence of Carbon Monoxide

In this work, we investigate gold surface dissolution under cathodic potentials as a function of crystal orientation using cyclic voltammetry, scanning electron microscopy, and atomic force microscopy to determine to what extent cathodic corrosion is anisotropic in nature. Additional experiments were performed to gain insights into the effect of the presence of CO on cathodic corrosion. Carbon monoxide experiments were conducted to investigate the effect of more realistic reaction conditions on cathodic corrosion as they might be found in gold-driven CO2 electrolyzers, although the effects of the presence of CO2 (reactant) and carbonate salts (typically present in the reaction medium) were excluded from this study. It was found that cathodic corrosion of gold is strongly anisotropic, with stepped surfaces and the {110} plane being most susceptible to dissolution, whereas the {111} and {100} planes were much more resilient to dissolution. On these more stable surfaces, nanocrystallite growth was observed instead, which we hypothesize originates from redeposition of the gold that dissolves from the more corrosive, more open, and/or defective facets. Finally, the presence of carbon monoxide was found to slightly enhance the rate of surface change, as evidenced by increases in charge in cyclic voltammograms after corrosion and an earlier onset of crystallite growth on the {111} and {100} planes, which we ascribe to enhanced gold mobility due to the strong bond formed between CO and gold in alkaline media.

Plastic deformation of single crystals of the equiatomic Cr−Mn−Fe−Co−Ni high-entropy alloy in tension and compression from 10 K to 1273 K

The plastic deformation behavior of single crystals of the quinary, equiatomic Cr−Mn−Fe−Co−Ni high-entropy alloy (HEA) with the face-centered cubic structure has been investigated in tension and compression as a function of crystal orientation and temperature from 10 K to 1373 K. The critical resolved shear stress (CRSS) for {111}<110> slip at room temperature is 42−45 MPa. It does not depend much on crystal orientation (i.e., the Schmid law holds true) and the sense (tension vs. compression) of the applied load. The CRSS for {111}<110> slip increases with the decrease in temperature, without showing any significant inertia effects at cryogenic temperatures below 77 K. Extrapolation from the measured yield stresses down to 10 K yields a CRSS value at 0 K of 168 MPa. At cryogenic temperatures, the measured strain-rate sensitivity of flow stress is consistent with a very small activation volume. The concept of stress equivalence holds true both for the temperature dependence of CRSS and the stress dependence of activation volume, indicating that solid-solution hardening is the major strengthening mechanism. Deformation twinning occurs at 77 K but not at room temperature, resulting in higher tensile elongation to failure at 77 K than at room temperature. Deformation twinning at 77 K occurs at a shear stress of 378 MPa on conjugate (1¯1¯1) planes in the form of Lüders deformation after large plastic strain (about 85%) achieved by the stage I (easy glide) and stage II (linear work-hardening) deformation.