Deformation Of Single Crystals Research Articles

Anisotropy and symmetry in the elastoplastic deformation of single crystals under scratching: Unravelling the microscopic deformation mechanisms

The nanoscratch test, as an established technique for assessing material tribological properties has received significant attention. However, the symmetry and anisotropy in scratching performances as well as the quantitative correlation between the orientation-dependent deformation and inherent microscopic deformation mechanism remain unexplored. Herein, crystal plasticity simulations can quantitatively capture scratching forces, elastic recovery, and surface pile-ups, as well as accurately describe inner deformation fields and lattice rotation patterns, as confirmed by experimental results. The simulation results reveal that surface pile-up and elastic recovery mappings on (001)-, (011)-, and (111)-oriented samples exhibit eight-fold, four-fold, and six-fold symmetries, respectively. The orientation-dependent location and intension of both slip activities and lattice rotation, determine the features of macroscopic elastoplastic deformation under scratching.

Study on the influence of rolling process parameters on the microscopic plastic deformation of nickel-based superalloy single crystal at atomic scale

Nickel-based superalloy workpieces strengthened by rolling process are widely used in the aviation field. However, there remains a need for further investigation into the influence of rolling parameters on the micro-plastic deformation of nickel-based superalloys. In this study, we establish micro-rolling and analysis models to investigate the impact of rolling parameters on nickel-based superalloy single crystals. We delve into the micro-effects of rolling depth, rolling speed, roller rotation speed, and roller radius. The micro-analysis model elucidates the influence mechanism of rolling parameters on nickel-based superalloy single crystals. The research methods and findings offer a novel microscopic perspective and approach for studying the strengthening of nickel-based superalloys through rolling. Additionally, they provide a microscopic theoretical foundation for optimizing rolling parameters.

Analysis of the temperature-dependent plastic deformation of single crystals of quinary, quaternary and ternary equiatomic high- and medium-entropy alloys of the Cr-Mn-Fe-Co-Ni system

ABSTRACT Temperature-dependent plastic deformation behaviors of single crystals of quaternary and ternary equiatomic medium-entropy alloys (MEAs) belonging to the Cr-Mn-Fe-Co-Ni system were investigated in compression at temperatures in the range 9 K to 1373 K. Their critical resolved shear stresses (CRSSs) increase with decreasing temperature below room temperature. There is also a dulling of the temperature dependence of CRSS below 77 K due to dislocation inertial effects that we attribute to a decrease in the phonon drag coefficient. These behaviors were compared with those of previously investigated single crystals of the equiatomic Cr-Co-Ni and Cr-Fe-Co-Ni MEAs, and the equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy (HEA). The temperature dependence of CRSS and the apparent activation volumes below room temperature can be well described by conventional thermal activation theories of face-centered cubic (FCC) alloys. Above 673 K, there is a small increase in CRSS, which we believe is due to elastic interactions between solutes and mobile dislocations, the so-called Portevin-Le Chatelier (PL) effect. The CRSS at 0 K was obtained by extrapolation of fitted CRSS vs. temperature curves and compared with predictions from solid solution strengthening models of HEA and MEAs.

Development of Microstructure in Aluminum Single Crystal During Complex Shearing of Extruded Tube

The development of the microstructure during severe plastic deformation of an aluminum single crystal by complex shearing of the extruded tube (CSET) was studied in this paper. The research has demonstrated that even in a single crystal, an ultrafine-grained microstructure can be obtained during this one-step process. The size of the grains gradually changes and reaches the minimum size on the level of 1 μm at the inner surface of the resulting tube. Simultaneously, preferential orientations in individual parts of the deformed sample change in a complex way. The main mechanism affecting the final microstructure is continuous dynamic recrystallization. The microhardness also exhibits a gradient character with higher values at the inner surface of the tube compared to its center.Graphical

Plastic deformation of magnesium single crystal: a crystal plasticity coupled twinning phase field simulation

Plastic deformation of magnesium single crystal: a crystal plasticity coupled twinning phase field simulation

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.

Determining the fundamental failure modes in Ni-rich lithium ion battery cathodes

Challenges associated with in-service mechanical degradation of Li-ion battery cathodes has prompted a transition from polycrystalline to single crystal cathode materials. Whilst for single crystal materials, dislocation-assisted crack formation is assumed to be the dominating failure mechanism throughout battery life, there is little direct information about their mechanical behaviour, and mechanistic understanding remains elusive. Here, we demonstrated, using in situ micromechanical testing, direct measurement of local mechanical properties within LiNi0.8Mn0.1Co0.1O2 single crystalline domains. We elucidated the dislocation slip systems, their critical stresses, and how slip facilitate cracking. We then compared single crystal and polycrystal deformation behaviour. Our findings answer two fundamental questions critical to understanding cathode degradation: What dislocation slip systems operate in Ni-rich cathode materials? And how does slip cause fracture? This knowledge unlocks our ability to develop tools for lifetime prediction and failure risk assessment, as well as in designing novel cathode materials with increased toughness in-service.

Plastic deformation of single crystals of the equiatomic Cr-Fe-Co-Ni medium entropy alloy – A comparison with Cr-Mn-Fe-Co-Ni and Cr-Co-Ni alloys

The plastic deformation behavior of single crystals of the equiatomic Cr-Fe-Co-Ni medium-entropy alloy was investigated in compression and tension from 9 K to 1373 K. The critical resolved shear stress (CRSS) for {111}<11¯0> slip is 44–45 MPa at room temperature and does not exhibit significant tension-compression asymmetry. It increases rapidly with decreasing temperature but exhibits a dulling of the temperature dependence below 77 K due to the inertia effect. The 0 K CRSS was determined to be 200 MPa by extrapolating the temperature dependence of CRSS from above 77 K to lower temperatures. This CRSS value is higher than that of the equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy, 174 MPa, but lower than that of the equiatomic Cr-Co-Ni medium-entropy alloy, 225 MPa. The rank of CRSS at 0 K of the three equiatomic alloys is consistent with the prediction of some solid solution strengthening models. The stacking fault energy (SFE) of the Cr-Fe-Co-Ni is about 20 mJ/m2, which falls between those of the Cr-Mn-Fe-Co-Ni and Cr-Co-Ni alloys. Deformation twinning in the Cr-Fe-Co-Ni MEA occurs at a shear stress of 249 MPa on conjugate (1¯1¯1) planes in the form of Lüders deformation at 77 K. The relationship between twinning stress and SFE is not monotonic as previously believed, but displays a concave with a minimum twinning stress at an intermediate SFE value.

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 deformation of single crystals of the sigma-phase compound FeCr with the tetragonal D8b structure investigated by micropillar compression

Room-temperature deformation of single crystals of the sigma-phase compound FeCr with the tetragonal D8b structure investigated by micropillar compression

Insights into fracture behavior of Ni-based superalloy single crystals: An atomistic investigation

Comprehending the plastic deformation and failure mechanisms in Ni-based superalloys is vital to enhance their intrinsic ductility. In view of this, the present work intends to illustrate the complex deformation mechanisms ensued during tensile deformation of pre-cracked Ni-Ni3Al single crystals using atomistic simulations. Simulations of fracture, thermodynamic continuum treatments of crack initiation and detailed calculations of crack propagation toughness are performed synergistically to analyze the competition between dislocation emission and cleavage. This competition is evaluated under Mode-I loading for 18 different pre-cracked configurations (three different crack lengths, three phase orientations and two phases) in totality. Our results demonstrate that dislocation as well as twin plasticity eventuate and the competition between the two plastic modes depends on the crystallographic orientation of the abutting phases. Higher initial crack lengths can otherwise lead to cleavage like propagation in the material; however this does not imply inferior ductility of the system as long as the phase boundary lies in the path of advancing crack. Changes in configurations in terms of pre-cracked phase or initial crack lengths can engender appreciable differences in the elementary crack tip phenomena. The numerical computations of crack propagation toughness are compared favorably well with the available experiments in the literature. The calculated variations in overall toughness of the material are discussed and analyzed in light of the observed deformation landscapes.

Deformation and Fracture of Single Crystals of Nickel-Base Superalloys CMSX-4 and CMSX-10 under Conditions of Creep and Fatigue Loading

Deformation and Fracture of Single Crystals of Nickel-Base Superalloys CMSX-4 and CMSX-10 under Conditions of Creep and Fatigue Loading

Thermally activated plastic deformation of Si single crystals at temperatures above 1173 K

The effect of high-temperature heat treatment during production on the mechanical property of Si wafer, namely yield stress, was studied through tensile tests of Si single crystals at 1123–1373 K, where stress–strain curves were obtained along the and directions. The critical resolved shear stress showed a remarkable temperature dependence, and it decreased with increasing test temperature. Below 1348 K, the activation enthalpy determined through strain rate jump tests showed no significant difference between crystals made by the Chokralski and the floating zone methods. This indicated that the solute oxygen does not influence the thermally activated dislocation glides. The activation enthalpy of 4.9 eV for a dislocation glide was much higher than that reported by previous studies (2.2 eV at temperatures below 1100 K), indicating that the thermal activation of dislocation glide is different from kink-pair nucleation. It was found that self-diffusion can assist the dislocation glide at temperatures above 1130 K.

Avalanches and rate effects in strain-controlled discrete dislocation plasticity of Al single crystals

Three-dimensional discrete dislocation dynamics simulations are used to study strain-controlled plastic deformation of face-centered cubic aluminium single crystals. After describing the rate and size dependence of the average stress-strain curves, we study the power-law distributed strain bursts and the average avalanche shapes, and find a universal power-law exponent $\tau \approx 1.0$ for all imposed strain rates and system sizes, characterizing both the event sizes and their durations. We discuss the dependence of our results on loading rate and compare these with previous studies of strain-controlled two-dimensional systems of discrete dislocations as well as of quasistatic stress-controlled loading of aluminium single crystals.

Witness to strain: Subdomain boundary length and the apparent subdomain boundary density in large strained olivine grains

Abstract Electron backscatter diffraction (EBSD) investigation of strain mainly uses polycrystalline samples to study fabric development. We extend the use of EBSD for the analysis of large single mineral grains by measuring the apparent surficial subdomain boundary density per unit area, reported here as unit segment length (USL). We apply this USL technique to examine and quantify the plastic deformation recorded by naturally shocked olivine in the low to moderately shocked ureilite meteorite Northwest Africa 2221 and the highly shocked martian dunitic cumulate meteorite Northwest Africa 2737, by assessing the types of subdomain boundaries and the increase of subdomain misorientation with increasing shock metamorphism. We further compare USL results for the shocked olivine in the meteorites with those for the terrestrial deformation of Hawaiian olivine. USL of olivine increases with shock level, and USL from shocked olivine is significantly greater than that of terrestrially deformed olivine. USL is a promising tool for the quantification of plastic deformation in large single crystals from shock as well as terrestrial deformation. The results derived from USL measurements along with local EBSD maps are complementary with quantitative 2D X-ray diffraction analysis of crystal deformation and disruption, leading to a more comprehensive understanding of characteristic shock deformation recorded by large single crystals.

Molecular dynamics study on defect evolution during the plastic deformation of nickel-based superalloy GH4169 single crystal under different rolling temperatures.

Nickel-based superalloy GH4169 is widely used as an important material in the aviation field. The rolling forming process can improve its surface quality and performance. Therefore, conducting an extensive investigation into the microscopic plastic deformation defect evolution process of nickel-based single crystal alloys during the rolling process is crucial. This study can offer valuable insights for optimizing rolling parameters. In this paper, a nickel-based superalloy GH4169 single crystal alloy was rolled at different temperatures from the atomic scale using the molecular dynamics (MD) method. The crystal plastic deformation law, dislocation evolution and defect atomic phase transition under different temperature rolling were studied. The results show that the dislocation density of nickel-based single crystal alloys increases as the temperature increases. When the temperature continues to increase, it is accompanied by an increase in vacancy clusters. When the rolling temperature is below 500 K, the atomic phase transition of the subsurface defects of the workpiece is mainly a Close-Packed Hexagonal (HCP) structure; when the temperature continues to increase, the amorphous structure begins to increase, and when the temperature reaches 900 K, the amorphous structure increases significantly. This calculation result is expected to provide a theoretical reference for the optimization of rolling parameters in actual production.

Complex severe plastic deformation of aluminum single crystal

A new route of severe plastic deformation – the complex shearing of extruded tube (CSET) technique – was proposed recently. In this route, a tube is produced from a rod via extrusion combined with two passes of an equal channel angular pressing like processing and with mandrel rotation. In the present paper, we describe and discuss the changes in the microstructure of an aluminum single crystal processed by CSET with respect to grain refinement, orientation changes and dislocation distribution.

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.

Molecular dynamics simulation of phase transition and crack propagation in metastable high entropy alloy

Crack propagation mechanisms and phase transformation play a crucial role in improving the formability of metastable high-entropy alloys (HEA). In this study, a multi-component single-crystal Ta 0.5 HfZrTi metastable high-entropy alloy with a single-sided corner crack is investigated during the stretching process by Molecular dynamics. Based on the stress state during stretching, crack propagation is divided into two groups, phase transition at the crack tip and crack growth. We are investigating the phase transformation behavior of metastable high-entropy alloys under different stress states by tensile and shear deformation of defect-free single crystals. This paper studies the crack propagation process by creating cracks of different angular sizes on the single side of a single crystal. The results explain the atomic motion pattern of the phase transformation in metastable high-entropy alloys from BCC to HCP structure and the reasons for creating FCC structures during the phase transformation. Tensile simulations of single crystals with single-sided cracks explain the relationship between crack propagation and phase transition.

Localized deformation at initial stages of plastic flow in high-manganese steel

The work is devoted to the study of macroscopic localization of plastic deformation during uniaxial tension of single crystals of the Hadfield steel (Fe – 13 % Mn – 1.03 % C). In the course of studies at the stage of easy sliding, significant differences were found in the nature of macrolocalization of plastic deformation in the single-crystal samples under study. All patterns of deformation localization observed in these cases can be divided into two types. The first type of strain localization corresponds to the initiation at the upper yield point and further propagation of the strain front, which gradually transfers the sample material from undeformed state to deformed one. This manifested itself most clearly in single crystals oriented along the tension axis [377] and [355], where the strain localization pattern appears as a single zone of localized deformation on the yield plateau. Such a deformation front passes through the sample volume only once as a Chernov-Luders band. In this case, the flow of the material is carried out without hardening until all its elements are transferred to the deformed state. Single zones of strain localization were also observed at the stages of easy sliding and yield plateau in the Hadfield steel single crystals oriented along the tension axis [123] and [012]. In the second type of localization, at the stage of easy sliding, synchronous movement along the pattern of several deformation centers occurs. Their movement can be unidirectional and counter, and the speeds are both the same and different from each other. Further deformation of the Hadfield steel single crystals oriented along the tension axis [355] or [012], led to the movement of two deformation localization centers at the stages of easy sliding. In single crystals oriented along [111], the strain localization pattern is respectively represented as four localized strain sites. Consequently, the synchronous movement of deformation fronts occurs along an already deformed, albeit to a small extent, material. As a reason for the difference between the two types of macrostrain localization at stage I (the easy sliding stage and the yield plateau), the number of active sliding systems or tensile twinning in the studied single crystals can be discussed based on crystallographic analysis and metallographic studies.