High Dislocation Density Research Articles

Effect of cryogenic rolling on the microstructure and properties of C70250 copper alloy

The application of cryogenic rolling technology serves to enhance the strength of a material by increasing the density of dislocations and refining the grain size. However, a high density of dislocations can lead to a reduction in its ductility. In this study, cryogenic rolling at low strain followed by subsequent aging treatment at temperatures between 450 and 550 ℃ was employed to introduce deformation twins into C70250 Cu alloys, aiming to balance both strength and electrical conductivity. The microstructural evolution and property changes of the alloy were examined throughout the cryogenic rolling and aging process using SEM, TEM, XRD, and various mechanical and electrical property tests. The results indicate that alloys subjected to cryogenic rolling and aging exhibit significantly improved strength compared to those treated at room temperature. The introduction of twinning through cryogenic rolling significantly enhances the efficiency of dislocation multiplication during rolling. This high dislocation density facilitates the nucleation of precipitated phases during the subsequent aging process, leading to superior mechanical properties. Within the integrated cryogenic rolling and aging treatment, the precipitated phases, dislocations, and twin boundaries collectively exert a synergistic reinforcing effect, resulting in exceptional yield and tensile strengths, reaching up to 685MPa and 744MPa, respectively. The findings in this study contribute to the development of novel methods for fabricating high-strength, high-conductivity copper alloys.

Microstructural evolution and high strain rate deformation response of SLM-printed CoCrFeMnNi after annealing and deep-cryogenic treatment

This study examines the microstructural evolution and high strain rate deformation response of Selective Laser Melted (SLM) CoCrFeMnNi high entropy alloys (HEAs) after annealing and deep cryogenic treatment. Annealing treatment has traditionally improved the ductility of selectively laser melted (SLM) materials. However, in this work, significant improvement in strength was observed in the annealed SLM CoCrFeMnNi after observing the high strain rate deformation response. TEM/HRTEM investigations revealed the formation of refined oxides, derived from the processing chamber and constituent powder feedstock. These oxides were homogenously distributed within microstructure reinforcing its structural integrity. Initial microstructural analysis of the as-printed samples showed the originally Mn2O3 oxides sparsely distributed within a cellular dislocation structure and significant Mn segregation. Unique grain growth with less prominent cellular dislocation structure were observed in the annealed specimen. Deep cryogenic treatment induced oriented cellular structures with higher dislocation density and round oxides 56 % smaller. High strain rate impact tests (up to 6500 s-1) demonstrated that the as-printed sample was sensitive to the strain rate and reached a yield strength of ~920 MPa at 6000 s−1 and strain deformation of ~55 % proving desirable for high strain rate applications. Remarkably, ~10 % higher ductility and strength, up to 22 % after annealing was achieved. The strengthening mechanisms in the samples and their contributions to the overall material strength were thoroughly analyzed. It was determined that a substantial portion of the strength in the annealed samples was due to the contributions of the precipitates within the alloy. The observed increase in strength was primarily attributed to the presence of two distinct nano-precipitates in the annealed specimens. However, there was no change in ductility after the deep cryogenic treatment but ~10 % higher yield strength values at equivalent strain rates also attributed to the increased dislocation density.

Severe plastic deformation of Mn-Al permanent magnets

Manganese-aluminum permanent magnets are promising candidates to fill the cost and performance gap between lower-performance bonded ferrites and high-performance magnets based on rare-earth elements. This is due to the favorable combination of saturation magnetization and magnetocrystalline anisotropy in the Mn-Al τ phase combined with low raw material cost. However, the τ phase is metastable and prone to decomposition at high temperatures, making processing by conventional milling and sintering difficult. Severe plastic deformation (SPD) is an alternative processing route to control the microstructure of a material by applying very high amounts of strain. In this study, equal-channel angular extrusion (ECAE) and high-speed high-pressure torsion (HS-HPT) were both tested as SPD processing routes. ECAE improved magnetic energy product, (BH)max, by 220% by refining the grain size and imparting a high density of dislocations. HS-HPT enabled a rapid phase transformation from the high-temperature ε phase to the τ phase but lowered Hci, making it better suited to soft magnet processing.

The effect of graphene nanoplatelets on the aging precipitation behavior and mechanical properties of magnesium matrix composite

Aging can effectively improve the mechanical properties of Mg alloys. The reinforcements can affect the aging kinetics of composites through interaction with the matrix. In this study, the effect of graphene nanoplatelets (GNPs) on the precipitation behavior of Mg-6Zn/GNPs composite was studied. The local region with high GNPs content exhibits a faster aging precipitation rate. Compared with Mg-6Zn alloy, the aging precipitation process of the composites has been accelerated as a whole. It is mainly attributed to the fact that the high density of dislocation near GNPs provides a high-speed channel between nucleation points and atoms for aging precipitation, which promotes aging precipitation. The strengthening effect of the composites mainly results from Orowan strengthening and fine grain strengthening generated by Mg4Zn7 and GNPs, respectively. The existence of GNPs enhances the aging hardening efficiency of the composites to a greater extent than that of the alloy matrix. This work provides a new approach for the design of aging behavior in magnesium matrix composites.

Improving interface joining strength of Ti6Al4V/AZ91D bimetal prepared by compound casting via Ni-coated Ti6Al4V lattice structure

The joining of titanium/magnesium (Ti/Mg) bimetals presents challenges due to the low mutual solubility and absence of metallurgical reactions between Ti and Mg. Herein we utilized the Ni-coated Ti6Al4V lattice structure to enhance the interfacial property of Ti6Al4V/AZ91D bimetal prepared by compound casting. The Box-Behnken design (BBD) was employed to optimize the lattice design. The resulting structure featured struts with a diameter (ds) of 2.4 mm, an aspect ratio (l/ds) ratio of 5.4, a tilt angle (ω) of 57°, and a node-to-strut diameter ratio (dn/ds) of 2.4. The optimized Ti6Al4V lattice structure manufactured by selective laser melting (SLM) exhibited α′ martensite with a high dislocation density, conferring exceptional tensile strength. The rough texture of the lattice surface enhanced adhesion with the Ni coating and improved wetting and reactivity between Ni and AZ91D alloy melt. This resulted in the formation of a serrated metallurgical interface with AZ91D alloy, which was primarily composed of α-Mg + Mg2Ni eutectic structure+τ-Ni2Mg3Al ternary phases. An impressive joining strength of 116.1 MPa was obtained under the optimized lattice structure, and the bimetal joint predominantly fails through the damage of AZ91D, aligning closely with simulated failure predictions.

Influence of different rolling passes and deformation amounts on the microstructure evolution and strengthening mechanism of Cu-Ni-Si alloy

Under the condition of controlling the total rolling deformation to 80.0%, the effects of multi-pass rolling, the ratio of deformation between the first and second stages in two-stage rolling, and aging parameters on the microstructural evolution and property enhancement of Cu-Ni-Si alloy were investigated. The results showed that the second-stage rolling promotes the formation of high-density dislocations, significantly enhancing dislocation strengthening. Simultaneously, the high-density dislocations facilitate the precipitation of the second phase during aging, and concurrently improving the strength and electrical conductivity of the alloy. In the two-stage rolling and aging process, a ratio of first-stage to second-stage rolling deformation less than 1 yields superior comprehensive properties. Specifically, when the first-stage rolling deformation is 35.0% and the second-stage deformation is 68.8%, the alloy achieves an optimal electrical conductivity of 49.53% IACS, hardness of 272.9 HV0.1, tensile strength of 773.0 MPa, and yield strength of 723.3 MPa. This is because a rolling ratio less than 1 results in higher dislocation density; the δ-Ni2Si precipitates have a coherent relationship with the Cu matrix, the interparticle spacing of precipitates is smaller. The average grain size is refined from 1.29 μm to 1.08 μm, significantly enhancing grain boundary strengthening. Dislocation strengthening and second-phase strengthening are the primary strengthening mechanisms of the alloy, and the calculated alloy strength agrees well with the experimental values, with errors less than 3.4%. Additionally, the Avrami equation in phase transformation kinetics was utilized to study the variation law of the volume fraction of the δ-Ni2Si phase with aging time.

Deformation mechanism of a metastable medium entropy alloy strengthened by the synergy of heterostructure design and cryo-pre-straining

Face-centered cubic (FCC) medium entropy alloys (MEAs) have received considerable attention due to their impressive mechanical properties and responses. However, their practical application is limited by their modest yield strengths. The potential enhancement of the mechanical properties of single-phase MEAs was explored in this study through a synergistic approach combining heterogeneous structure design with subsequent cryo-pre-straining. A heterogeneous lamella structure was produced in a single-phase Fe55Mn20Cr15Ni10 MEA via two-step rolling and annealing. Cryo-pre-straining at varying degrees (6, 12, 21, and 36%) introduced hexagonal close-packed (HCP) phase, high-density dislocations, twins, and stacking faults, leveraging the reduced stacking fault energy at cryogenic temperatures. This process enhanced the alloy's yield strength from 353 MPa to 1.2 GPa (compared to the baseline uniform coarse-grained structure), while maintaining an acceptable total elongation of 8.4%. The impact of cryo-pre-straining on the microstructure and mechanical properties of the MEA was assessed using in-situ synchrotron X-ray diffraction analysis. Cryo-pre-straining (36%) achieved a higher dislocation density (6.1 × 1015 m−2) compared to room-temperature straining (2.5 × 1015 m−2). The stress contribution from HCP-martensite and the evolution of dislocation density during loading were quantified, along with observations of negative stacking fault probability and strain-induced HCP→FCC reverse transformation in cryo-pre-strained samples under loading conditions. Furthermore, the contributions of regulated microstructures to the enhancement of yield strength were quantitatively assessed.

A novel cobweb-like sub-grain structured Al-Cu-Mg alloy with high strength-plasticity synergy

Al-Cu-Mg alloys, as the most widely used lightweight structural materials, have been recognized as promising candidates in the transportation field for a low-carbon economy. However, the tensile strength and plasticity of alloys cannot be simultaneously improved to satisfy the requirements of continuously upgraded transportation vehicles. In this work, inspired by high-tensile strength and high plasticity of cobweb structure, a novel cobweb-like sub-grain structure was developed in Al-Cu-Mg alloys by a successive solution, high-strain-rate rolling (4.4 s-1), cryogenic treatment (–196°C) and aging process (SRCA). Notably, the tensile strength and plasticity of this alloy were superior to those reported in the current study. An ultrahigh Vickers hardness and tensile strength value of 206.2 Hv and 619.6 MPa, which were 39.8% and 31.8% higher than those of traditional T6 heat-treated Al-Cu-Mg alloys, were obtained after SRCA. Meanwhile, an increase in the elongation of this alloy from 4.31% to 8.23% (increase of 90.9%) was also achieved. More importantly, the high strength-plasticity (“double high”) Al-Cu-Mg alloy was attributed to a cobweb-like sub-grain structure, which was proposed for the first time by utilizing reverse thinking to enhance plasticity through elevating dislocations, due to the formation of high-density dislocations from high-strain-rate rolling and rearrangement effect of dislocations from cryogenic treatment. Furthermore, the strength-plasticity mechanism was verified using in-situ tensile electron back scatter diffraction (EBSD), molecular dynamics (MD) simulations, and crystal plasticity (CP) models. The results indicated that the cobweb-like sub-grain structure, resembling countless walls, formed barriers that hindered dislocation migration towards high-angle grain boundaries (HAGBs) and absorbed them, thereby reducing the occurrence of stress concentration zones, i.e., the dislocation absorption and stress-strain sharing mechanisms. Additionally, the strengthening mechanism was associated with synergistic strengthening by multiscale microstructures, including micron-sized grains, micron-sized high-density dislocation lattices, and nanosized Al2CuMg phases, which were activated by successive deformation processes. Consequently, the concept of biomimetic structure design, which may serve as an effective method for achieving structural materials with high strength-plasticity synergy, can be extended to transportation fields, such as railway tracks and body structure design.

Effect of grain boundary engineering on corrosion behavior and mechanical properties of GH3535 alloy in LiCl-KCl molten salt

This study investigated the effect of grain boundary engineering (GBE) on the corrosion behavior and high-temperature mechanical properties of GH3535 alloy in 45LiCl-55KCl wt.% molten salt at 550°C. After corrosion for 300 h, a triple-layered product was formed on the solid solution specimen (Non-GBE), consisting of discontinuous NiCr2O4 outer-layer, Ni3Fe middle-layer, and NiCr2O4 inner-layer. For the GBE specimen, quite milder corrosion occurred on it that its surface still kept original polishing scratches. The real mass loss of the Non-GBE alloy (6.85 mg/cm2) is one order of magnitude higher than that of GBE (0.65 mg/cm2). The beneficial effect of GBE on improving alloy's corrosion resistance is owing to: surface carbide dissolution, discontinuous random high angle grain boundary and low dislocation density. High proportion of Σ3n grain boundaries and less carbide precipitation ensure stable high-temperature deformation performance of GBE sample in molten salt.

Enhanced strength-ductility synergy in a Ni–W–Co–Ta medium-heavy alloy via cryogenic supersonic fine particle bombardment

This study explores the influence of cryogenic supersonic fine particle bombardment (CSFPB) on a Ni–W–Co–Ta medium heavy alloy (MHA), and focus on the effect of gas pressure and impact time on the surface integrity, microstructural evolution, and mechanical properties of the MHA. CSFPB treatment creates a gradient structure, including surface layer with nanograins down to 9.0 nm due to severe plastic deformation, subsurface layer with high density dislocation structures and deformation twins due to weakened impact energy, and undeformed matrix. A key advantage of CSFPB is seen to be the cryogenic environment, which promotes superior surface integrity by reduced roughness. As the impact duration and gas pressure increase, the depth of deformation layer, surface hardness and strength of the MHA progressively rise. The optimal combination of strength and ductility is achieved at a gas pressure of 1.0 MPa for a duration of 90 s. This setting results in a maximum ultimate tensile strength of 1351 MPa and yield strength 796 MPa, with uncompromising elongation. However, excessively long treatment durations or high gas pressures can lead to the formation of surface microcracks, ultimately reducing the MHA's strength. Therefore, CSFPB offers the benefit of improved surface integrity through the cryogenic environment while maintaining a desirable balance between enhanced strength and ductility.

Research on the Strengthening Mechanism of MWCNTs-Cuf Composite Interlayer for Si3N4/TC4 Brazed Joints

With the rapid development of aerospace technology, the high-quality brazing connection between Si3N4 ceramic and TC4 titanium alloy has become a key factor in advancing the development of aircraft antenna covers. To improve the mechanical strength of the joints, this study used the electrophoretic deposition method to prepare a multi-walled carbon nanotubes-foam copper (MWCNTs-Cuf) composite interlayer and selected the optimal deposition parameters. The most suitable brazing parameters under this interlayer were also determined. The joints’ formation mechanism and fracture mode were revealed to elucidate the synergistic strengthening mechanism of the composite interlayer. The results showed that MWCNTs, based on their phase characteristics, produced high-density dislocations and fine crystal strengthening effects during the brazing cooling process. This effectively resisted the corrosion of the brazing material on the foam copper (Cuf), protected the integrity of the foam copper framework, and exerted the excellent plastic deformation ability of foam copper (Cuf). It reduced the residual stress in the joints, resulting in the highest shear strength of the MWCNTs- Cuf composite interlayer, reaching 96.23 MPa. Compared with only adding Ag-Cu-Ti active brazing filler metal and adding ordinary foam copper interlayer, the shear strength increased by 78.2% and 44.7%, respectively.

Evolution of Microstructures and Mechanical Properties with Tempering Temperature in a Novel Synergistic Precipitation Strengthening Ultra-High Strength Steel.

The evolution of microstructures and mechanical properties with tempering temperature of a novel 2.5 GPa grade ultra-high strength steel with synergistic precipitation strengthening was investigated. With increasing tempering temperature, the experimental steel initially progressed from ε-carbides to M3C and then to M2C, followed by further coarsening of the M2C carbides and β-NiAl. Concurrently, the martensite matrix gradually decomposed and austenitized. The ultimate tensile strength and yield strength initially increased and subsequently decreased with rising tempering temperature, reaching peak value at 460 and 470 °C, respectively. Conversely, the ductility and toughness initially decreased and then increased with rising tempering temperature, reaching a minimum at 440 °C. The increase in strength was attributed to the secondary hardening effects resulting from carbide evolution and the precipitation of β-NiAl. The subsequent decrease in strength was due to the recovery of martensite and coarsening of precipitates. The decrease in ductility and toughness was linked to the precipitation of M3C, while their subsequent increase was primarily attributed to the dissolution of M3C and an increase in the volume fraction of reverted austenite. The high dislocation density of martensite, the film of reverted austenite, nanoscale M2C carbides, and ultrafine β-NiAl obtained during tempering at 480 °C resulted in the optimal mechanical properties of the experimental steel. The strength contributions from M2C carbides and β-NiAl were 1081 and 597 MPa, respectively.

Dislocation‐induced local symmetry reduction in single‐crystal KNbO3 observed by Raman spectroscopy

AbstractIn recent years, dislocation‐tuned functionalized ceramics have become one of the focal points of modern materials research due to their outstanding properties. These range from improved electrical conductivity and ferroelectric properties to dislocation‐enhanced toughening and superconductivity, caused by local strain fields. The aim of this work is to investigate the dislocation‐induced structural changes in single‐crystal KNbO3 by micro‐Raman spectroscopy. Dislocation‐rich regions with tailored densities have been generated using the Brinell indenter scratching method. The influence of the dislocations on the single‐crystal structure can be observed in the Raman spectra. The activation of additional Raman modes is observed, which does not occur in regions of low dislocation density. This observation is confirmed by DFT calculations of vibrational modes and is attributed to a reduction in the crystal symmetry due to increased defect densities in plastically deformed KNbO3. In addition, an increase in compressive stress at higher dislocation densities can be demonstrated by a blueshift in Raman mode positions.

Effect of cryogenic and room-temperature rolling on the microstructural evolution and mechanical behavior of spray-formed 7055 Al-Zn-Mg-Cu alloy

This study investigates the effects of room-temperature rolling (RTR) and cryogenic rolling (CR) on the microstructure, mechanical properties, and fracture morphology of spray-formed (SF) 7055 Al-Zn-Mg-Cu alloy, with a focus on the deformation across reductions ranging from 20 % to 80 %. Utilizing SF as the base processing technique, the study aims to overcome challenges associated with the alloy's high content during conventional casting, such as segregation, grain coarsening, and the formation of internal defects. The findings indicate that CR significantly enhances the ductility and refines the microstructure of SF-7055 Al alloy compared to RTR, particularly at higher reductions. CR prevents the formation of severe cracks and maintains higher ductility and texture intensity, which are crucial for the demanding applications of this alloy in aerospace and transportation sectors. Microstructural analysis reveals that CR achieves a more uniform deformation, effectively reduces shear band formation, and facilitates the formation of finer and more evenly distributed precipitates due to suppressed solute atom mobility at cryogenic temperatures. Mechanical testing shows that CR enhances strength and hardness at lower reductions by maintaining high dislocation density, which does not annihilate as rapidly as in RTR. Tensile fracture analysis further demonstrates that CR leads to smoother fracture surfaces and fewer macroscopic cracks, indicating a more controlled failure mechanism. This study underscores the potential of cryogenic processing in improving the performance and applicability of high-strength Al alloys, offering significant insights for industrial applications where material reliability and enhanced mechanical properties are critical.

Stepwise warm rolling for synergistic strength and ductility enhancement in heterolamellar medium-Mn steel

Medium manganese steel represents a promising third-generation advanced high-strength steel. However, achieving excellent plasticity in high-yield-strength medium manganese steel remains challenging, particularly with lower alloying element contents. In this study, we employed an innovative stepwise warm rolling process on 5Mn medium manganese steel, developing a heterolamellar microstructure along the rolling direction. The resulting steel exhibited a yield strength exceeding 1.5 GPa while maintaining a uniform elongation of approximately 29%. The high yield strength is attributed to fine lamellar grains with high dislocation density, while the excellent uniform elongation is due to the synergistic effect of multiple plastic deformation mechanisms, which promoted prolonged strain hardening and delayed the onset of necking. These mechanisms include hetero-deformation induced (HDI) hardening generated during the early deformation of the heterolamellar structure, transformation induced plasticity (TRIP) effect-induced work hardening, and delamination cracking that alleviates interface strain concentration and delays material failure. Collectively, these mechanisms enabled the material to achieve an exceptionally high product of yield strength and uniform elongation of 45 GPa·%. This work provides new insights into the design of high-strength, ductile medium manganese steels, advancing the application of high-performance medium manganese steels.

Impact of boron and titanium on the mechanical properties and recrystallization behaviour of low carbon cold rolled and batch annealed HSLA steels

This study investigates the impact of boron (B) on the mechanical properties and recrystallization behaviour of cold rolled and batch-annealed titanium (Ti) microalloyed high-strength low-alloy (HSLA) steels. HSLA steels are essential in industries such as automotive and construction due to their superior mechanical properties and cost-effectiveness. The addition of microalloying elements, particularly Ti, has shown significant promise in enhancing these properties through mechanisms like precipitation strengthening and controlled recrystallization. However, the role of B in this context remains underexplored. Here, three alloy compositions were systematically examined: a reference low carbon steel base alloy with no Ti or B (Ref), the base alloy with added Ti (Ref + Ti), and the base alloy with both Ti and B additions (Ref + Ti + B). The findings showed that microalloying with Ti + B can provide excellent strength improvements in the hot rolled strip, mainly due to increased hardenability that promotes the formation of finer ferrite grains with a high dislocation density. However, the recovery and recrystallization behaviour is such that it is not possible to reproduce these benefits after cold rolling and batch annealing, highlighting the complexity of optimizing microalloying strategies for cold-rolled and batch annealed products. The insights gained from this study provide a deeper understanding of the mechanisms governing the recrystallization of Ti and B microalloyed HSLA steels, paving the way for the development of advanced materials with tailored properties for critical applications.

Exploring the mechanism of stress-induced passive layer degradation in additively manufactured Ni-Fe-Cr-based alloy 718

This study explores the formation and degradation mechanisms of the passive layer on laser powder bed fusion (L-PBF) processed Ni-Fe-Cr-based alloy 718 using high-resolution submicron analysis and microcapillary electrochemical techniques. The findings provide new insights into passive layer breakdown under tensile loading, revealing the influence of microstructural characteristics, dislocation distribution, and mechanical stresses. Tensile loading caused oxide layer cracking near cell boundaries with higher dislocation density. Detachment of the oxide layer from the matrix created voids, allowing aggressive ions to penetrate, promoting crevice corrosion. Cell boundaries remained mostly intact, as metallic particles within the surface oxide layer.

Influence of annealing on microstructures and mechanical properties of laser powder bed fusion and wire arc directed energy deposition additively manufactured 316L

The annealing response of 316L stainless steel manufactured with both laser powder bed fusion (PBF-LB) and wire-arc directed energy deposition (DED-Arc) was investigated in the context of microstructural evolution and mechanical properties. Because additive manufacturing (AM) comprises several technologies that differ in heat source, feedstock, and scan strategy, among other build variables, the final products can experience a range of thermal histories and defect (dislocation) populations. These unique thermal histories can subsequently influence as-built properties and annealing response of AM materials, most notably those manufactured with different AM deposition processes. The PBF-LB process (with higher cooling rates) yielded finer austenite microstructures having more lattice strain, higher dislocation densities, and higher yield strength values than the DED-Arc 316L process (with lower cooling rates). Electron backscattered diffraction (EBSD) data of the kernel average misorientation (KAM), boundary density, and geometrically necessary dislocation (GND) density support the differences in lattice strain. As a result, the PBF-LB 316L exhibited more recovery and recrystallization after annealing at elevated temperatures above 873 K based on changes to yield strength, work hardening behavior, and microstructure evolution. The DED-Arc 316L exhibited a δ-ferrite/austenite microstructure with microsegregation that influenced deformation mechanisms active after annealing. Tensile data, deformed microstructures and misorientation histograms from EBSD showed a decreasing amount of deformation twinning when comparing the as-built condition to annealed conditions (up to 1473 K/1h) of PBF-LB 316L. The opposite trend was noted in DED-Arc 316L. The behavior was interpreted to be due to the differences in chemical segregation during solidification and the effects of heat treatment on chemical homogenization and local stacking fault energy.

Effect of pre-aging on mechanical reinforcement of the Cu–Fe–Nb composites

Pre-aging treatment was demonstrated to significantly enhance the mechanical properties of Cu–10Fe–1Nb (wt.%) composites. Specifically, after rolling and aging at 400 °C for 8 h, the microhardness, tensile strength, and elongation of the pre-aged samples reached 163 HV, 559 MPa, and 11.2%, respectively. The refinement of Fe-rich phases in pre-aged samples was primarily attributed to the increased shear strain between the Fe-rich phases and the matrix, which was driven by the precipitation-strengthening effect induced by pre-aging. Additionally, the matrix of the pre-aged samples suffered significant refinement as dynamic recovery and recrystallization of the matrix were suppressed during the rolling process, forming a high-density dislocation structure that greatly enhances the work-hardening effect. The main contribution to strength improvement in the Cu–10Fe–1Nb composites was identified as precipitation strengthening, refinement strengthening, and work hardening. Moreover, compared with the sample without pre-aging treatment, the refinement strengthening and work hardening effects of pre-aged samples exhibited substantial improvements, with increment of 49 MPa and 21 MPa, respectively.

Dislocation Evolution in Cyclic-Loaded Cu Nanopillars with Different Configurations.

Small-sized metals generally exhibit unusual deformation responses subjected to cyclic loading, since their limited volume cannot effectively accommodate micro-sized dislocation patterns typically found in their bulk counterparts. Here, the cyclic behaviors in Cu nanopillars with different configurations are investigated using in situ transmission electron microscopy fatigue test. Dislocation tangles formed in single- and twinned-crystal nanopillars as a result of cycling-induced operations of multiple slip systems and further unpinning and absorption of pinned dislocations. While, nanopillars configured with low-angle grain boundary (LAGB) underwent the degradation and eventual decomposition of the LAGB due to the cycling-induced emission of grain boundarydislocations, which resulted in high-density mobile dislocations to withstand the cyclic loading. These findings contribute to a systematic and comprehensive understanding of the micro-mechanics of dislocation-related phenomena in the cyclic response of nanoscale metals.