Increase In Dislocation Density Research Articles

Step-edge-guided nucleation and growth mode transition of α-Ga2O3 heteroepitaxy on vicinal sapphire

Abstract Controlling the epitaxial growth mode of semiconductor layers is crucial for optimizing material properties and device performance. In this work, the growth mode of α-Ga2O3 heteroepitaxial layers was modulated by tuning miscut angles (θ) from 0° to 7° off the (10-10) direction of sapphire (0002) substrate. On flat sapphire surfaces, the growth undergoes a typical three-dimensional (3D) growth mode due to the random nucleation on wide substrate terraces, as evidenced by the hillock morphology and high dislocation densities. As the miscut angle increases to θ=5°, the terrace width of sapphire substrate is comparable to the distance between neighboring nuclei, and consequently, the nucleation is guided by terrace edges, which energetically facilitates the growth mode transition into the desirable two-dimensional coherent growth. Consequently, the mean surface roughness decreases to only 0.62 nm, accompanied by a significant reduction in screw and edge dislocations to 0.16×107 cm-2 and 3.58×109 cm-2, respectively. However, the further increment of miscut angles to θ=7° shrink the terrace width less than nucleation distance, and the step-bunching growth mode is dominant. In this circumstance, the misfit strain is released in the initial growth stage, resulting in surface morphology degradation and increased dislocation densities.

High-Entropy CeNbO4+δ-Based Ceramics with Ultrahigh Comprehensive Thermosensitive Performances.

Next-generation advanced high-temperature sensors rely heavily on negative temperature coefficient thermosensitive ceramics with low cost, small volume, high sensitivity, and fast response. However, thus far, the enormous challenge of achieving ultrahigh stability and accuracy has become a critical bottleneck restricting the development of thermosensitive ceramics in high-temperature sensor applications. Here, we propose a high-entropy strategy to design a "cation valence self-equilibrium" system in CeNbO4+δ-based ceramics introducing redox couple compensation and ultrahigh density dislocations to solve the problem of temperature-dependent oxygen nonstoichiometry that restricts the performances of high-temperature thermosensitive ceramics. Ferroelastic domains are generated by enhancing the configurational entropy at both A and B sites, resulting in a dramatic increase of dislocation density to >1010 mm-2, which ultimately optimizes the thermosensitive performances. Extreme temperature measurement accuracy with R2 as high as 999.98‰ and RSS as low as 0.011 and high-temperature stability with ΔR/R0 as low as 0.23% after aging at 873 K for 1000 h are realized in high-entropy CeNbO4+δ-based ceramics, indicating a breakthrough in the comprehensive performances of thermosensitive ceramics. This work opens up an effective way to design thermosensitive materials with ultrahigh comprehensive performance to meet the requirements of advanced high-temperature sensors.

The Effects of Edge Dislocations on The Corrosion Behavior of Pure Iron in Liquid Lead-Bismuth Eutectic: A Molecular Dynamics Study

The effect of liquid lead–bismuth eutectic (LBE) on the corrosion evolution of iron-based materials with varying densities of edge dislocation defects was studied. Molecular dynamics simulations were conducted at temperatures ranging from 823 K to 1173 K, and the process of penetration of Pb and Bi atoms at the dislocation core was analyzed. The results indicated that Fe atoms near the dislocation core have the lowest substitution energy (−4.79 eV/atom), making them more likely to be replaced by Pb and Bi atoms. Moreover, it was found that the increase in dislocation density did not result in a high penetration depth of LBE atoms, attributed to the interaction of dislocations. These findings provide crucial insights into the LBE corrosion mechanism in iron-based materials with dislocation defects.

Improvement in Grain Size Distribution Uniformity for Nuclear-Grade Austenitic Stainless Steel through Thermomechanical Treatment.

In this work, thermomechanical treatment (single-pass rolling at 800 °C and solution treatment) was applied to nuclear-grade hot-rolled austenitic stainless steel to eliminate the mixed grain induced by the uneven hot-rolled microstructure. By employing high-temperature laser scanning confocal microscopy, microstructure evolution during solution treatment was observed in situ, and the effect of single-pass rolling reduction on it was investigated. In uneven hot-rolled microstructure, the millimeter-grade elongated grains (MEGs) possessed an extremely large size and a high Schmid factor for slip compared to the fine grains, which led to greater plastic deformation and increased dislocation density and deformation energy storage during single-pass rolling. During subsequent solution treatment, there were fewer nucleation sites for the new grain, and the grain boundary (GB) was the main nucleation site in MEGs at a lower rolling reduction. In contrast, at a higher reduction, increased uniformly distributed rolling deformation and more nucleation sites were developed in MEGs. As the reduction increased, the number of in-grain nucleation sites gradually exceeded that of GB nucleation sites, and in-grain nucleation preferentially occurred. This was beneficial for promoting the refinement of new recrystallized grains and a reduction in the size difference of new grains during recrystallization. The single-pass rolling reduction of 15-20% can effectively increase the nucleation sites and improve the uniformity of rolling deformation distribution in the MEGs, promote in-grain nucleation, and finally refine the abnormally coarse elongated grain, and eliminate the mixed-grain structure after solution treatment.

EXPLORING STRENGTHENING MECHANISMS OF ULTRAFINE-GRAINED Fe35Mn27Ni28Co5Cr5 HIGH-ENTROPY ALLOY PROCESSED BY SEVERE COLD ROLLING PROCESS

This study describes the strengthening mechanisms of an ultrafine-grained (UFG) Fe35Mn27Ni28Co5Cr5 high-entropy alloy (HEA) processed by severe cold rolling (SCR) process at room temperature. Microstructural evaluations were performed by field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The findings demonstrated that the development of deformation microstructures consisted of a single face-centered cubic (FCC) phase with stretched grains along the rolling direction and lamellar deformation bands after a 90 % reduction in thickness. Using the Nix-Gao model, the dislocation density was determined by measuring the microhardness indentation size effect. The results indicated that an increase in rolling deformation leads to an increase in dislocation density. The dislocation density increased from 2.28 ×109 cm-2 for as-homogenized specimen to 8.65 ×109 cm-2 after 90 % reduction in thickness. The yield strength of the UFG Fe35Mn27Ni28Co5Cr5 HEA was 5.2 times (1155 MPa) higher than that of the as-homogenized state (225 MPa). Finally, an assessment was conducted on the relative contributions of individual mechanisms, such as dislocation and grain refinement, to the strengthening of the Fe35Mn27Ni28Co5Cr5 HEA.

Hydrogen-enhanced densified deformation twins in 304L austenitic stainless steel fabricated by selective laser melting

Twin boundaries are the preferred site for crack nucleation and propagation in a hydrogen-rich environment. The relationship among hydrogen, cellular structure, and deformation twins is significant in further enhancing the resistance to hydrogen embrittlement of austenitic stainless steels produced by SLM. It has been demonstrated that cellular structures with high dislocation densities play a positive role in increasing stress above a critical level for deformation twin formation. The cellular structure affects the distribution of hydrogen, with hydrogen presence at cellular boundaries reducing its accumulation at grain boundaries. Hydrogen increases the density of deformation twins and reduces the thickness of individual deformation twins. This phenomenon can be attributed to an increase in nucleation sites for the deformation twin, which is closely related to the decrease in stacking fault energy and the increase in dislocation density caused by hydrogen. Both cellular structure and deformation twins play a positive role in improving the hydrogen embrittlement resistance of austenitic stainless steels.

Investigation of ratcheting fatigue behavior and failure mechanism of 1Cr18Ni10Ti pressure pipe under different force amplitudes and internal fluid pressure

This work reports on the development of an improved testing system to examine the effects of force amplitude and internal fluid pressure on ratcheting behavior and failure mechanism of 1Cr18Ni10Ti aero-engine pipe. Experimental results indicate that the ratcheting displacement and its rate during steady stage increase with the increasing force amplitude or internal fluid pressure, exhibiting a reverse tendency to fatigue life. Continuous cyclic softening response until fatigue fracture was observed in all conditions. Furthermore, microstructural evolution was characterized by SEM, EDS, XRD, and EBSD. The critical force amplitude to trigger noticeable dislocation accumulation and transition from austenite to ferrite phase was evaluated to be around 1900 N. The results highlight the decreased high-angle grain boundary (HAGB) and increased dislocation density causing the sample with a higher force amplitude to be more inclined to fracture. The initiation of fatigue crack was accelerated by the accumulation of dislocation within ferrite phase grains. Similar fatigue fracture morphology with ovalization phenomenon was observed in all conditions. To predict the ratcheting fatigue life of aero-engine thin wall pipes, a validated fatigue life estimation model considering steady ratcheting displacement rate based on a finite element analysis (FEA) model was conducted, and all of the fatigue data are contained in a 1.1X scatter band.

Capture efficiencies of point defects by 1/2 〈111〉 edge dislocations in tungsten using atomistic simulations

We systematically study the interaction behaviors between a point defect (PD) and two types of 1/2 〈111〉 {110} and 1/2 〈111〉 {112} edge dislocations using molecular dynamics (MD), elastic dipole tensor, and kinetic Monte Carlo (KMC) methods in tungsten (W). We first determine the capture region of a vacancy and four types of self-interstitial atoms (SIAs) by calculating their binding energies to both edge dislocations using MD. We then find anisotropic distributions of the diffusion energy barriers of PDs in dislocation systems employing the MD and elastic dipole tensor methods. Subsequently, we utilize the KMC method to obtain the lifetime of PDs and calculate the capture efficiencies of both edge dislocations to PDs at various temperatures and dislocation densities. Results show the capture efficiency of a vacancy decreases with increasing temperature, while it first increases and then decreases with increasing temperature for SIAs. As dislocation density increases, the capture efficiency of PDs increases. Ultimately, the swelling rate is estimated based on the capture efficiency and falls within the range of experimental data. The swelling rate increases first and then decreases with increasing temperature, and the maximum swelling rate occurs around 1200 K, while it increases with increasing the dislocation density. The present results are critical for understanding the interaction behaviors between PDs and 1/2 〈111〉 edge dislocations in W, which provide an essential database for large-scale simulation methods such as rate theory and phase-field simulations.

Surface integrity and corrosion resistance of 18CrNiMo7-6 gear steel subjected to combined carburized treatment and wet shot peening

Typically, a cost-effective and versatile carburizing process is used to improve the surface integrity of high-value-added gear components. In this study, carburized treatment and wet shot peening (WSP) were applied to increase the corrosion resistance of 18CrNiMo7-6 gear steel. The surface integrity and corrosion resistance after carburizing and combined treatment (carburized treatment + WSP) were analyzed. The results indicated that the combined treatment converted the retained austenite surface layer within approximately 45 μm from the surface into the martensitic phase, with a 13.9 % reduction in equivalent grain size and a 23.6 % increase in dislocation density compared with carburizing. Furthermore, electrochemical experiments in a 3.5 wt% NaCl solution indicated that the combined treatment process increased the corrosion resistance compared with carburizing (55.4 % lower corrosion current density and a higher Fe2+/Fe3+ ratio). Despite the high surface roughness obtained with combined treatment, the improved corrosion resistance is primarily ascribed to the high compressive residual stress and dislocation density. This study provides insights into the surface strengthening design of 18CrNiMo7-6 gear steel for corrosive environments—particularly the synergistic strengthening effect of carburizing and WSP.

Strain rate-dependent tensile deformation and failure behavior in single-crystal β-Sn

Given that electronic components often undergo intricate thermal and mechanical loads during operation, comprehensively understanding lead-free solder, particularly solder based on [Formula: see text]-Sn, in various complex load conditions, plays a crucial role in ensuring the structural integrity and functional reliability of integrated circuits. Therefore, investigating the mechanical properties and fracture behavior of [Formula: see text]-Sn as a solder material holds paramount importance. In this study, we performed molecular dynamics simulations using the modified embedded atom method to investigate the mechanical properties and crack propagation of single-crystal [Formula: see text]-Sn under different strain rates. The research findings demonstrate that as the strain rate increases, the single-crystal [Formula: see text]-Sn exhibits elevated yield strength, fracture strength, and strain, while the elastic modulus decreases. Under higher strain rates, the relationship between dislocation density and strain rate in single-crystal [Formula: see text]-Sn is quantitatively elucidated. The substantial increase in internal dislocation density imparts conspicuous strain hardening to the material, rendering plastic deformation more challenging. This observation sheds light on the microscale mechanism of strain hardening at the atomic level. Our results shall facilitate a deeper investigation into the mechanical behavior of single-crystal [Formula: see text]-Sn while also paving the path for optimizing the design and application of lead-free solder materials in the electronics industry.

Microstructure and Physico-Mechanical Properties of Biocompatible Titanium Alloy Ti-39Nb-7Zr after Rotary Forging

The evolution of microstructure, phase composition and physico-mechanical properties of the biocompatible Ti-39Nb-7Zr alloy (wt.%) after severe plastic deformation by rotary forging (RF) was studied using various methods including light optical microscopy, scanning and transmission electron microscopies, X-ray diffraction, microindentation, tensile testing and investigation of thermophysical properties during continuous heating. The hot-rolled Ti-39Nb-7Zr with initial single β-phase structure is subjected to multi-pass RF at 450 °C with an accumulated degree of true deformation of 1.2, resulting in the formation of a fibrous β-grain structure with imperfect 500 nm subgrains characterized by an increased dislocation density. Additionally, nano-sized α-precipitates formed in the body and along the β-grain boundaries. These structural changes resulted in an increase in microhardness from 215 HV to 280 HV and contact modulus of elasticity from 70 GPa to 76 GPa. The combination of strength and ductility of Ti-39Nb-7Zr after RF approaches that of the widely used Ti-6Al-4V ELI alloy in medicine, however, Ti-39Nb-7Zr does not contain elements with limited biocompatibility and has a modulus of elasticity 1.5 times lower than Ti-6Al-4V ELI. The temperature dependences of physical properties (elastic modulus, heat capacity, thermal diffusivity) of the Ti-39Nb-7Zr alloy after RF are considered and sufficient thermal stability of the alloy up to 450 °C is demonstrated.

Improving strength-toughness of low carbon bainitic microalloyed steel via tailoring isothermal quenching process and niobium microalloying

This study focuses on improving the strength-toughness properties of low carbon bainitic steel through the optimization of the isothermal quenching process and the adoption of a microalloying strategy. The impact of Nb microalloying on the microstructure and mechanical properties was thoroughly investigated. The optimal isothermal quenching process for achieving a balance between strength and toughness is as follows: the steels were austenitized at 900 °C for 30 min and then subjected to an isothermal treatment at 450 °C for 10 min. The resulting microstructure consisted mainly of granular bainite (GB) and lath bainite (LB), with GB accounting for 60 % of the structure. After the optimized isothermal quenching process, the ultimate tensile strength and yield strength of the Nb microalloyed steel increased to 1210 MPa and 693 MPa, respectively. The impact energy, KU2, was measured at 41.8 J. The study revealed that Nb microalloying refines the bainite structure by reducing activation energy and increasing the nucleation rate. This refinement was observed in the reduced length and thickness of the bainitic laths, as well as the increased dislocation density. Additionally, fine composite precipitated particles (Nb, V)C with an average diameter of 8.2 nm were dispersed throughout the microstructure. The addition of Nb significantly enhanced the effects of fine grain strengthening, precipitation strengthening, and dislocation strengthening in low carbon bainitic microalloyed steel. As a result, the strength was greatly improved without sacrificing toughness, thanks to the combined actions of these three strengthening mechanisms.

Bromine-enhanced polarization for strengthening ultra-thin copper foil in lithium-ion battery

Reducing the weight of the negative current collector is an effective strategy for lightweighting vehicle batteries. Herein, thin copper foil with high tensile strength was prepared through electrodeposition in Br−-based aqueous solution. The synergistic effect of additive Br−, polyethylene glycol (PEG), Bis-(sodium sulfopropyl)-disulfide (SPS) on the microstructure and tensile strength of the copper foils have been systematically explored. It was found that the addition of Br− modifies the microstructure of copper via grain refinement, thereby enhancing the mechanical properties of copper foil. The obtained copper foil reaches an enhanced tensile strength of 469.8 N/mm2 and an elongation of 2.2%. The results of electrochemical measurements confirm that Br− enhances electrochemical polarization of PEG and attenuates the acceleration of SPS. The improved mechanical properties of copper foils are attributed to the closer proximity and stronger adsorption energy between Br− and Cu atoms, which results in a synergy of grain refinement and nanotwinned grains associated with increased dislocation density as well as dislocations entangled around nanotwin GBs.

Effect of equal-channel angular pressing on microstructure, aging kinetics and impact behavior in a 7075 aluminum alloy

Among the precipitation hardenable 7xxx series aluminum alloys, AA7075 alloys (one of the most important engineering alloys) due to their low density (lightweight), high toughness and strength, and enhanced fatigue behavior have been used over the years in aerospace, aircraft, automotive, construction and marine applications. In the present study, the influence of the artificial aging through conventional heat treatment (i.e., precipitation hardening) and the thermomechanical treatment (equal-channel angular pressing (ECAP) + post-ECAP aging) on the quasi-static tensile, impact toughness and precipitation behavior as well as on the microstructure of an AA7075 alloy is investigated systematically. The results indicate that the ECAP process as well as post-ECAP aging result in considerably increased strength and hardness of the AA7075 alloys because of the superimposed effects of grain boundary strengthening (Hall-Petch relation), strain hardening (by means of the increased dislocation density) and precipitation hardening (due to the fine precipitates formed in Al matrix). Multi-pass ECAP processing has been found to result in a considerable decrease of the impact toughness (from 15.3 J·cm−2 to 7.6 J·cm−2) associated with the failure mode (i.e., ductile-to-brittle transition) of the AA7075 alloys, whereas the artificial peak aging leads to a marked improvement (∼67 %) in the impact toughness in ECAPed conditions. Moreover, the ECAP process noticeably accelerates the precipitation kinetics of AA7075 alloys: The peak aging time in the ECAPed alloy is reduced significantly – from 30 h to 4 h. The results of the present study provide a deeper understanding of the combination of ECAP and heat treatment, and their effect on the fracture mode and toughness under impact loading, the aging kinetics and the microstructural evolution of an AA7075 alloy.

Correlation between pre-strain and hydrogen embrittlement behavior in medium-Mn steel

In this study, we investigated the correlation between the pre-strain and hydrogen embrittlement (HE) mechanisms in medium-Mn steel. Intercritically annealed Fe-7Mn-0.2C-3Al (wt.%) steel, which showed a two-phase microstructure comprising α ferrite and γR retained austenite, was used as a model alloy. As the pre-strain level increased from 0% to 45%, the volume fraction of γR gradually decreased owing to the strain-induced α′ martensite transformation accompanied by an increase in dislocation density. The HE resistance decreased with increasing the pre-strain level because the sample with a higher pre-strain level revealed a higher amount of dissolved hydrogen, combined with a more extensive brittle fracture region owing to the enhanced diffusion and permeation of hydrogen from the reduced γR fraction. Additionally, the H-assisted crack in the sample without pre-strain was initiated and propagated from the γR grains when the strain-induced α′ phase was formed, because most of the dissolved hydrogen was concentrated in the γR grains, and these grains were predominantly deformed compared to the other phases. However, the pre-strained sample showed more pronounced multiple H-assisted cracking at the constituent phases, such as α and α′, because it exhibited relatively well-dispersed hydrogen atoms and reduced microstrain localization at the γR grains, due to the reduced γR fraction.

Deformation behavior and magnetic properties of equiatomic FeNi single crystals

An equiatomic Fe–Ni alloy in its disordered A1 structure is a soft magnetic alloy. On ordering to the L10 ordered phase, it shows significant magneto-crystalline anisotropy and a strong permanent magnet behavior and is of interest as a rare earth-free permanent magnet. However, synthesis of an L10 phase in a bulk form remains a challenge due to its low critical ordering temperature Tc and consequent extremely slow ordering kinetics. This phase is present in asteroids, and how it was formed remains unclear. The likely mechanism is enhanced diffusion kinetics due to extreme dislocation densities and vacancy concentrations produced by deformation during asteroid collisions and the presence of S. Prior to examining extreme deformation in an FeNi alloy comparable to that in asteroid collisions, low strain rate deformation behavior, magnetic properties, and the structure of undoped and S-doped [100]-oriented FeNi single crystals were carried out. Controlled deformation at a strain rate of 1 × 10−5/s showed the yield point to be 89 MPa, and the critical resolved shear stress was 25.7 MPa. The dislocation densities obtained were ∼1017/m2. The saturation magnetization value was ∼147–151 emu/g both before and after deformation, comparable to NdFeB magnets. Coercivity increased slightly from ∼0.04–0.4 to ∼5 Oe after deformation due to an increase in dislocation density. The x-ray diffraction scan of S-doped and deformed single crystals after annealing at 300 °C, just below Tc, showed no evidence of L10 order. These data serve as a baseline for extreme strain rate deformation where much higher dislocation densities and vacancy concentrations can be obtained to facilitate L10 order.

Cryogenic rolling impacts on microstructures and properties of a novel Ni–W–Co–Ta medium-heavy alloy

A high-strength Ni–W–Co–Ta medium-heavy alloy (MHA) was prepared through the melting–casting–forging followed by cryogenic rolling process. Detailed microstructure and mechanical property characterizations were conducted to unveil the influence of cyrorolling on Ni–W–Co–Ta MHA. The results revealed that initial equiaxial grains were elongated along the rolling direction firstly and then transformed to fibrous texture with increase in accumulated deformation, in which a large number of slip bands were generated to coordinate the intensive plastic deformation. A sharp increase in dislocation density significantly promoted the dislocation interactions, which, in turn, refined the grains down to nanometer scale. The strength and hardness increased significantly with the increase of the deformation, whereas the elongation decreased sharply. The fracture morphology changed from a typical ductile mode for the undeformed sample gradually to quasi-cleavage and ductile mixed mode for 90% deformed material.

Decoupling the nonthermal effect of current by electrically assisted crystal plasticity modeling of Ni-based single crystal superalloys

The electrically assisted (EA) deformation process has received considerable attention in recent years, accompanied by research on current-induced deformation mechanisms. However, there are still challenges in eliminating thermal effects, which have prevented a comprehensive understanding of the underlying current-induced mechanisms. Opting for a single crystal (SC) in research provides advantages in decoupling the nonthermal effect of electric current at smaller scales and eliminating the complex interactions that exist in polycrystalline materials. Therefore, the innovation of this work lies in decoupling the nonthermal effect of electric current and conducting a comprehensive analysis of anisotropic deformation and mechanisms within a Ni-based SC with different crystallographic axes and various current directions during electrically assisted tensile simulation. A significant tension axis direction in the SC during EA tension was induced by the combination of a higher current direction factor (|cosθ|) and a dimensionless factor for the current density (|Jα/J0α|) along the [100] axis. The stress drop within the SC due to the nonthermal effect of electric current generally increased with increasing current direction. This was attributed to the increased dislocation density differences and decreased temperature. The increased stress anisotropy of the SC at a current direction of 45° was attributed to fewer activated (111) slip systems and the pinning effect of more dislocations within these systems. This study advances our understanding of the thermal and nonthermal effects of electric current and offers valuable insights for the informed application of EA deformations in industrial and aerospace settings with SC superalloys.

Oxidation Behavior of Pre-Strained Polycrystalline Ni3Al-Based Superalloy.

The harsh service environment of aeroengine hot-end components requires superalloys possessing excellent antioxidant properties. This study investigated the effect of pre-strain on the oxidation behavior of polycrystalline Ni3Al-based superalloys. The growth behaviors of oxidation products were analyzed by scanning electron microscope, transmission electron microscope, X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results indicated that the 5% pre-strained alloys exhibited lower mass gain, shallower oxidation depth and more compact oxide film structures compared to the original alloy. This is mainly attributed to the formation of rapid diffusion paths for Al atoms diffusing to the surface under 5% pre-strain, which promotes the faster formation of protective Al2O3 film while continuing to increase the pre-strain to 25% results in less protective transient oxidation behavior being aggravated due to the increase in dislocation density within the alloy, which prevents the timely formation of the protective Al2O3 film, resulting in uneven oxidation behavior on the alloy.

On the stable/metastable nature of the γ-hydride phase in Zircaloy-2: Microstructural characterization by electron diffraction, electron energy-loss spectroscopy, and diffraction line profile analysis

This work investigates the potential metastable versus stable nature of the γ-hydride in Zircaloy-2. Specimens were hydrided, and hydrides were precipitated through water-quenching. Synchrotron X-ray diffraction of the water-quenched sample revealed a diffraction peak with the d-spacing value of ∼2.70 Å. While this peak is conventionally attributed to {111}-γ planes, it could also stem from the (0004)-ζ plane. To clarify this ambiguity, the crystal structure of nano-hydrides was characterized by nano-beam electron diffraction (NBED) and electron energy-loss spectroscopy (EELS). While EELS detected nano-hydrides with plasmon energy (PE) values associated with the ζ-,γ-, and δ-phases, suggesting all three types of phases might be present, complementary NBED analysis revealed that regardless of the measured PE values, the examined nano-hydrides were of only γ- or δ-nature.Repeating the heating/quenching cycles reduced the γ-phase volume fraction until its (almost) complete disappearance after three cycles. δ-phase, however, was observed after each heating/quenching cycle. This observation, in accordance with previous reports, indicates that the γ-phase is metastable in Zircaloy-2, such that even during water-quenching (which is conventionally believed to facilitate the formation of γ-phase) only δ-hydrides form in cases where microstructural conditions are suitable.Diffraction line profile analysis and transmission electron microscopy revealed an increase in dislocation density during the first heating/quenching cycle, with no noticeable variations during subsequent cycles. A mechanism is proposed that links microstructure (i.e., dislocation structure) evolution during heating/quenching cycles to the suppression of the (metastable) γ-phase.