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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Linking microstructure to creep behavior in vertically and horizontally built LPBF Haynes 282 compared with wrought material via θ -projection

Laser Powder Bed Fusion (LPBF) has emerged as a promising route for fabricating intricate geometries in high-performance alloys. Haynes 282 (H282) is a strong candidate for applications such as heat exchangers or engines due to its excellent creep strength and thermal stability; however, the long-term creep behavior of LPBF-processed H282 remains poorly understood. In this study, the θ -projection method is used to analyze and extrapolate the creep behavior of vertically built LPBF, horizontally built LPBF, compared to wrought H282 tested at 816 °C. Vertically built LPBF H282 exhibits the lowest minimum creep rate (MCR), while the horizontally built condition shows a higher MCR comparable to that of wrought H282. Despite these differences, both LPBF conditions exhibit significantly shorter rupture life and reduced rupture strain than the wrought material, with the most severe degradation observed in the horizontal builds, consistent with an earlier onset of tertiary creep and accelerated strain-rate evolution. Microstructural characterization reveals that both LPBF and wrought H282 exhibit abundant twin-related boundary character; however, their grain boundary topologies differ markedly. The wrought alloy contains a higher fraction of low-angle grain boundaries and continuous twin lamellae, whereas the LPBF microstructure is characterized by a suppressed low-angle boundary population and fragmented twin-related boundaries embedded within irregular high-angle grain boundary networks. Fractographic analysis further reveals predominantly intergranular cracking in LPBF H282, accompanied by grain-boundary-decorated carbides, Al 2 O 3 inclusions, and high-aspect-ratio pores. These results demonstrate that grain boundary topology, rather than minimum creep rate alone, plays a critical role in governing creep damage accumulation and rupture behavior in LPBF and wrought H282.

Creep↗
DOE OSTI2026

Exploring the tempering behaviour of additively manufactured high-alloy tool steel using synchrotron X-ray and neutron techniques

Post-processing heat treatment provides a critical pathway toward the commercialisation of additively manufactured (AM) S390 high-speed steel, which is a representative high-alloy tool steel employed in precision manufacturing, offering up to 1.5 times longer tool life and over 20% higher cutting speeds compared to conventional grades. In this study, the phase evolution of AM S390 steel during heat treatment, with particular emphasis on carbide precipitation behaviour, was systematically investigated using a combination of synchrotron X-ray and neutron techniques. The metastable M2C carbides were found to dissolve during austenitisation, while the stable primary carbides MC and M6C experienced coarsening with an average size increase of about 60 nm after just 2 min of tempering. Moreover, the austenite lattice parameters reduced from 3.618 to 3.608 Å within the first 10 min of tempering, suggesting carbon depletion in the steel matrix was likely associated with the formation of secondary carbides. This interpretation was substantiated by small-angle scattering results, which revealed the presence of nanoscale precipitates with a volume fraction of 3.1% after 60 min of tempering. These microstructural evolutions collectively accounted for the observed peak hardness of 921 HV. Furthermore, a comparative analysis of synchrotron and neutron small-angle scattering data highlighted the complementary strengths of each technique, offering critical insight into their suitability for characterising nanoscale features in AM high-alloy steels.

Synchrotron X-ray diffraction↗
NASA NTRS2004

Effects of Initial Powder Size on the Mechanical Properties and Microstructure of As-Extruded GRCop-84

GRCop-84 was developed to meet the mechanical and thermal property requirements for advanced regeneratively cooled rocket engine main combustion chamber liners. It is a ternary Cu- Cr-Nb alloy having approximately 8 at% Cr and 4 at% Nb. The chromium and niobium constituents combine to form 14 vol% Cr2Nb, the strengthening phase. The alloy is made by producing GRCop-84 powder through gas atomization and consolidating the powder using extrusion, hot isostatic pressing (HIP) or vacuum plasma spraying (VPS). GRCop-84 has been selected by Rocketdyne, Ratt & Wlutney and Aerojet for use in their next generation of rocket engines. GRCop-84 demonstrates favorable mechanical and thermal properties at elevated temperatures. Compared to NARloy-Z, the currently used inaterial in the Space Shuttle, GRCop-84 has approximately twice the yield strength, 10-1000 times the creep life, and 1.5-2.5 times the low cycle fatigue life. The thermal expansion of GRCop-84 is 7515% less than NARloy-Z which minimizes thermally induced stresses. The thermal conductivity of the two alloys is comparable at low temperature but NARloy-Z has a 20-50 W/mK thermal conductivity advantage at typical rocket engine hot wall temperatures. GRCop-84 is also much more microstructurally stable than NARloy-Z which translates into better long term stability of mechanical properties. Previous research into metal alloys fabricated by means of powder metallurgy (PM), has demonstrated that initial powder size can affect the microstructural development and mechanical properties of such materials. Grain size, strength, ductility, size of second phases, etc., have all been shown to vary with starting powder size in PM-alloys. This work focuses on characterizing the effect of varying starting powder size on the microstructural evolution and mechanical properties of as- extruded GRCop-84. Tensile tests and constant load creep tests were performed on extrusions of four powder meshes: +140 mesh (great3er than l05 micron powder size), -140 mesh (less than or equal to 105 microns), -140 plus or minus 270 (53 - 105 microns), and - 270 mesh (less than or equal to 53 microns). Samples were tested in tension at room temperature and at 500 C (932 F). Creep tests were performed under vacuum at 500 C using a stress of 111 MPa (16.1 ksi). The fracture surfaces of selected samples from both tests were studied using a Scanning Electron Microscope (SEM). The as-extruded materials were also studied, using both optical microscopy and SEM analysis, to characterize changes within the microstructure.

Okoro, Chika L.↗
DOE OSTI2019

Nanocrystalline ZrN thin film development via atomic layer deposition for U-Mo powder

Zirconium nitride (ZrN) thin film deposited via thermal atomic layer deposition (ALD) has been recently chosen as a candidate technology for application of a diffusion barrier coating on the low enriched uranium alloy powder considered in the NNSA research reactor conversion program. Reported here is the first instance of using ALD for coating actinide materials. For this study, a modified ALD system was constructed to produce one micron thick zirconium nitride (ZrN) coating over spherical particulate of natural uranium-molybdenum (U-Mo) based fuel. The ALD system was designed to have a rotating drum system, with provisions for facilitating sequential exposures of chemicals such as tetrakis dimethyl amido zirconium (TDMAZr) and ammonia (NH 3 ) in order to deposit ZrN. The ALD system was successful in developing a highly conformal ZrN coating covering every individual U-7Mo particle. This article describes the ZrN film synthesis details and reports the produced microstructure and composition of the ALD ZrN as deposited on fuel particulates. The as-fabricated coating was determined to have a nanocrystalline structure in the cubic-ZrN (cF8) phase. It exhibited a dense microstructure with adequate interfacial bonding. TEM-EELS characterization demonstrated that the coating contains a very low amount of oxygen impurity. To understand the potential microstructural evolution for ALD ZrN during reactor operation, an in-situ heavy ion (Kr) irradiation experiment was performed at the IVEM-Tandem facility. A total fluence of 7.5 x 10 15 ions/cm 2 (similar to 10 dpa) was achieved, and apart from minor grain coarsening in the ALD ZrN coating, no significant radiation effects were observed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synergy between phase transformation and domain switching in two morphotropic phase boundary ferroelectrics

We present that many applications of ferroic materials take advantage of the microstructural redistribution under an external stimulus. Despite extensive studies on the microstructural evolution during both domain switching and phase transformations of high-performance ferroelectrics near morphotropic phase boundaries (MPBs), the synergetic interactions between both leading factors remain unclear. Herein, we have illustrated and discerned the correlative response of phase transformation and domain switching in an archetypical piezoceramic of PbTiO 3 -BiScO 3 using a combination of in situ high-energy synchrotron x-ray diffraction and phase-field simulations. The direct structural evidence and domain development from simulations reveal a significant reversible orientation-dependent emerging phase transformation and enhanced domain switching. Increasingly populated polarization variants aligned with the applied electric field owing to this strong synergistic interaction play an important role in enhancing the piezoelectric performances of MPB ferroelectrics. Lastly, in addition to providing further insight into the microstructures of ferroelectrics, the present results have the potential to guide the design of high-performance materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ex-situ Heat Treatment of TEM Foils in a Custom Titanium Fixture: A Case Study on Ni-based Superalloy

The advancement of microstructural characterization at the nanoscale is critical to understanding the microstructural evolution and performance of engineering materials. Transmission electron microscopy (TEM) plays a vital role in such investigations, particularly when coupled with controlled ex- and in-situ experiments. In this study, we introduce a novel method for ex-situ heat treatment (HT) of TEM foils using a custom-designed fixture, made from pure titanium, and vacuum furnace to inhibit oxidation. This approach ensures precise temperature control and minimal sample contamination during HT, critical for substructural characterization and analysis of metallic materials. The fixture consists of a titanium base with three slits, for three sample foils, and a titanium cap for closure. The entire assembly is placed in a vacuum heat treatment furnace with high vacuum capability to prevent oxidation. To validate the effectiveness of the setup, precipitation behavior and microstructural changes were studied in an IN725 variant heat-treated at 500°C for 1 hour and 282 variant heat-treated at 700°C for 1 hour, as case studies.

electron microscopy↗
DOE OSTI2025

Ab initio prediction of FeCr sigma (001)/FCC Fe(111) interfacial energy: Effect of interfacial doping of C, B, and N

Interfacial energy plays a crucial role for high-temperature material systems in determining their microstructure evolution and mechanical properties. Optimizing the interfacial energy through doping can improve the stability, performance, and overall functionality of these materials. Here, the present study delivers theoretical investigation on the sigma FeCr (001)//FCC Fe (111) interfacial energy using ab initio methods, focusing on the implications of interfacial doping with important interstitial elements carbon (C), boron (B), and nitrogen (N). The calculated interfacial energy without doping is 0.183J/m 2 . Upon doping, notable reductions in interfacial energy were observed. Doping with B decreased the interfacial energy to 0.046J/m 2 , with single C doping to 0.126J/m 2 , with two C doping to 0.098J/m 2 , and with a single N doping to 0.071J/m 2 . These findings not only shed light on the atomistic origin for the effect of stabilizing the microstructure of stainless steel at elevated temperatures by interstitial doping, but also present a systematic, thorough ab initio approach to predict interfacial doping properties and guide alloy design to enhance the performance and stability.

FeCr sigma phase↗
DOE OSTI2020

Anisotropic domains and antiferrodistortive-transition controlled magnetization in epitaxial manganite films on vicinal SrTiO 3 substrates

We studied the microstructural evolution and magnetism of ferroelastic La 0.9 Sr 0.1 MnO 3 (LSMO) epitaxial thin films grown on SrTiO 3 (001) substrates with different miscut angles. The substrate miscut angle plays a critical role in controlling the in-plane magnetic anisotropy. The microscopic origin of such magnetic anisotropy is attributed to the formation of anisotropic stripe domains along the surface step terraces. The magnetization in the LSMO films was found to be selectively modulated by the antiferrodistortive phase transition of the SrTiO 3 substrate. This phenomenon has been qualitatively explained by a strain modified Stoner–Wohlfarth model. We conclude that the magnetization modulation by the SrTiO 3 phase transition depends on h, the ratio of applied magnetic field to the saturation field. Such modulation is only visible with h < 1. The established domain microstructure–anisotropy–magnetism correlation in manganite films can be applied to a variety of complex oxide thin films on vicinal substrates.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Temperature-dependent stability of θ'-Al 2 Cu precipitates investigated with phase field simulations and experiments

The upper limit of service temperature for many Al-Cu alloys is determined by the thermal stability of strengthening θ' (Al 2 Cu) precipitates. Above a certain temperature, θ' precipitates will undergo morphological evolution and transform into the detrimental, equilibrium θ phase, leading to a rapid drop in strength. Certain alloying elements have recently been reported to increase the thermal stability of θ' precipitates, by mechanisms that are yet unclear. Herein, we investigate the effect of modified interfacial energy and solute chemical mobility on the thermal stability of θ' via high-throughput phase field study. We identify a critical θ' aspect ratio to predict the onset of θ formation. Using this criterion, we predict the time required for θ' to θ phase transformation as a function of temperature, Cu diffusivity, and the interfacial energy of θ' precipitates. The predicted times compare favorably with reported times for θ formation under similar experimental conditions. Furthermore, these phase field simulations predict that a moderate reduction in Cu mobilityis adequate to stabilize the as-aged microstructure up to 300 °C, while substantial reductions to both interfacial energy and Cu mobility are needed to achieve similar stability at 400 °C. Experimental microstructural evolution results in commercial (319) and thermally stabilized (RR350) cast aluminum alloys are presented to complement the simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Raman spectroscopy of neutron irradiated silicon carbide

The effects of neutron irradiation on microstructural evolution and the resultant changes in physical and mechanical properties are of critical importance for the development of silicon carbide (SiC) materials for nuclear applications. This study neutron-irradiated βSiC under a wide range of conditions at temperatures between 235 and 750°C and neutron doses of 0.01–11.8 displacements per atom, and then evaluated the effects on the SiC structure using Raman spectroscopy. The SiC optical phonon lines were shifted to lower wavenumbers by irradiation. Correlations were found among the wavenumber of the longitudinal optical phonon line, irradiation-induced swelling, and irradiation temperature. The peak shift also correlated indirectly with decreasing thermal conductivity of irradiated SiC. The irradiation-induced peak shift is explained by combinations of lattice strain, reduction of the elastic modulus, and other factors including decreasing coherent domain size. These findings bridge irradiation-induced microstructural changes and property changes and illustrate how Raman spectroscopy is a useful tool for nondestructively assessing irradiated SiC materials for nuclear applications.

Koyanagi, T.↗
DOE OSTI2022

Adversarial Ensemble Modeling of Multi-modal Mechanical Properties for Iron-Based Alloys

Mechanical properties of alloys are controlled by their microstructure; and microstructure evolution is controlled by internal and external stressors. Chemical complexity during the alloy processing may result in heterogeneity and observation of multimodal performance patterns. Thus, to ensure the desired performance of stressed components it is important to understand the origin and mechanisms of such behavior. Adversarial ensemble modeling was introduced here to explain multimodal mechanical properties of the iron-based alloys. The modeling results showed that the areas of a single mechanism predominance were contiguous across the alloy compositions clustered by similarity, with sharp and persistent boundaries separating the single-mechanism domains. The marginal compositions resulted in increased competition between the adversarial models but only led to the multimodal behavior when the competing models diverged. Transparency of the clustering method allowed explicit interpretation of the chemistries leading to such competition. The adversarial ensemble was interpreted through transition from ductile to brittle microstructure.

36 MATERIALS SCIENCE↗
NASA NTRS2014

Microstructure and Macrosegregation Study of Directionally Solidified Al-7Si Samples Processed Terrestrially and Aboard the International Space Station

This talk reports research that has been carried out under the aegis of NASA as part of a collaboration between ESA and NASA for solidification experiments on the International Space Station (ISS). The focus has been on the effect of convection on the microstructural evolution and macrosegregation in hypoeutectic Al‐Si alloys during directional solidification (DS). The DS‐experiments have been carried out under 1‐g at Cleveland State University (CSU) and under low‐g on the International Space Station (ISS). The thermal processing‐history of the experiments is well defined for both the terrestrially‐processed samples and the ISS‐processed samples. We have observed that the primary dendrite arm spacings of two samples grown in the low‐g environment of the ISS show good agreement with a dendrite‐growth model based on diffusion controlled growth. The gravity‐driven convection (i.e., thermosolutal convection) in terrestrially grown samples has the effect of decreasing the primary dendrite arm spacings and causes macrosgregation. In order to process DS‐samples aboard the ISS, dendritic‐seed crystals have to partially remelted in a stationary thermal gradient before the DS is carried out. Microstructural changes and macrosegregation effects during this period are described.

Angart, Samuel↗
DOE OSTI2025

Atomically Revealing Bulk Point Defect Dynamics in Hydrogen‐Driven γ‐Fe 2 O 3 → Fe 3 O 4 → FeO Transformation

Understanding how point defects in the bulk govern redox transformations is essential for advancing hydrogen-based metal production and designing high-performance oxide materials. This study reveals the atomic-scale mechanisms driving hydrogen-induced reduction of γ-Fe 2 O 3 to Fe 3 O 4 , focusing on how bulk vacancy dynamics dictate structural evolution and reaction kinetics. A key finding is the pronounced contrast in defect behavior between the two oxides: in γ-Fe 2 O 3 , intrinsic Fe vacancies promote oxygen vacancy clustering, destabilizing the local lattice and driving nanopore formation. In contrast, Fe 3 O 4 exhibits a higher oxygen vacancy formation energy and lacks intrinsic Fe vacancies, suppressing vacancy aggregation and maintaining a dense, pore-free structure. This divergence governs distinct reduction pathways—γ-Fe 2 O 3 undergoes an interface-reaction-limited transformation confined to the γ-Fe 2 O 3 /Fe 3 O 4 boundary, while Fe 3 O 4 supports a uniform increase in oxygen vacancy concentration, enabling bulk-phase reduction to lower-oxide FeO. Integrated in situ electron microscopy and density functional theory modeling uncover a vacancy-mediated mechanism, where synergistic cation-anion vacancy dynamics steer microstructure evolution and phase progression. These insights highlight the critical role of vacancy dynamics in controlling oxide reactivity and offer a pathway toward vacancy engineering to enhance reduction kinetics in hydrogen metallurgy and to tailor porosity, reactivity, and structural resilience in oxide-based catalysts and energy materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Dissimilar Joining of Pure Aluminum to SiC{sub p}/Al-MMCs Using an AlMgGaLi Active Interlayer Foil

To broaden the application of advanced metal matrix composites in the electronic packaging industry, a lead-free AlMgGaLi interlayer was developed for active soldering of aluminum to aluminum metal matrix composites. The effect of joining pressure on the microstructure evolution, interfacial wettability and mechanical properties of the dissimilar joints was investigated. The experimental results indicated that as the joining pressure increased, the mean thickness of the bond seam was 46.02 μm, and solidification of a solid solution occurred (detected by SEM/XRD analysis). The composition of the Al-based solid solution (in atom%) was 86.52% Al, 9.32% Mg, 2.56% O, 1.5% Ga and 0.1% Si. The pressure improved the interfacial wettability by enhancing the atom diffusion between the interlayer and parent materials. The joint shear strength initially increased and then decreased, and a sound joint with a maximum shear strength of ~ 45 MPa was produced at 450 °C and 0.75 MPa. The fracture crack initially occurred at the interfaces of the Al/filler metal and then propagated mainly along the Al{sub 2}O{sub 3} layer on the Al side. A novel model describing the pressure-induced microstructure changes within the joint and the formation of an Al{sub 2}O{sub 3} diffusion barrier layer at the Al/filler metal interface is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Joining AA7099 to Ni-Cr-Mo Steel Using Single Pass Friction Stir Dovetailing and AA6061 Butter Layer

A novel single pass friction stir dovetailing (FSD) was developed to join thick plate AA7099 to Ni-Cr-Mo steel in a lap configuration through the use of an AA6061 butter layer. The butter layer approach can be shown to significantly reduce interfacial failures by inhibiting the formation of brittle Fe–Al intermetallic compounds (IMCs) which are typically formed during conventional friction stir welding (FSW) of AA7099 directly to steel. This study evaluates the strength and microstructural evolution of the aluminum/steel joint interface between single pass FSD of AA7099/AA6061(butter)/steel fabricated using three different FSD tool configurations. The butter layer was achieved by placement of a free-floating strip of AA6061 within the dovetail groove that was pre-machined in the steel substrate. Friction stir welding was then used to simultaneously join the thick plate AA7099, the AA6061 strip and the AA7099 in a single weld pass. To optimize the joining process, three different pin geometries (full thread, half smooth/half thread, no thread) were evaluated; it was demonstrated that the half smooth/half thread tool produced the strongest weld joint due to the absence of a Zn rich layer at the Al/steel interface. The efficacy of this unique processing technique was tested using lap shear tensile testing as well as high resolution transmission electron microscopy (TEM). A discussion of the new FSD technique, joint configurations, and process parameters are provided along with joint microstructural analyses and mechanical performance.

Olszta, Matthew J.↗
DOE OSTI2025

An atomistic study connecting underlying dislocation behavior with superior mechanical properties of NiCoCr medium entropy alloy

NiCoCr-based medium-entropy alloy (MEA) with a simple face-centered cubic crystal phase exhibits excellent mechanical properties, often attributed to the synergy of multiple deformation mechanisms. However, the atomistic origin of their outstanding mechanical response, including microstructural evolution and dislocation behavior under varying strain-rates and orientation, remains unclear. In this work, we employ large-scale molecular dynamics (MD) simulations to investigate the changes in deformation mechanisms along three distinct orientations ([110], [111], [100]) under varying strain rates (1 ×10 8 /sec, 1 ×10 10 /sec, 1 ×10 12 /sec) in the NiCoCr MEA. The presence of the stair-rod and the Shockley partial dislocations under uniaxial tensile strain are found to play a key role in the formation of deformation twinning and ε-martensite, which positively correlates with strain-rate dependent dislocation analysis. These findings further establish the role of the dislocations in controlling the superior mechanical response and excellent fracture toughness of the NiCoCr MEA. Systematic transmission-electron microscopy tests performed on the [111]-oriented crystals, deformed at different strain levels, at room temperature provide clear evidence of both the extended stacking-fault and the stair rods, confirming the predicted microstructural features. Finally, this study offers key insights into the complex nucleation mechanisms of deformation twinning and ε-martensite, such as twinning – and transformation–induced plasticity (TWIP-TRIP), providing valuable guidelines for studying similar material classes.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Experimental investigation of the dependence of void nucleation and growth on initial microstructure in high-purity titanium under tension

An experimental investigation of failure mechanisms in relation to the initial microstructure in high-purity titanium samples is presented. The initial microstructure of the specimens was measured in 3D using diffraction-contrast tomography (DCT). Ex-situ X-ray computed tomography (XCT) was used to visualize voids in specimens at various levels of deformation attained by interrupted tensile testing. Electron backscatter diffraction (EBSD) mapping was used to characterize the deformed microstructures per specimen. The investigation showed that the location of failures was unrelated to the formation of the first voids, but rather the nucleation and growth of cracks were from heavily deformed surface regions. The areas surrounding the failure-causing cracks had the highest propensity for void development of any area in the specimen. This facilitated crack propagation through the specimen via “linking up”. The failure of the specimens by microvoid coalescence was bolstered by “dimpled” fracture surfaces. Paint composed of gallium embedded in rubber was used to track the displacement of points along the loading direction of the specimens, to relate the location of failure to the material's initial microstructure. However, the correlation proved difficult, due to complex microstructural evolution involving voids, grain fragmentations, and profuse twinning. Nevertheless, it was shown that necking occurred near the largest grain in the gauge section of the specimens. This is likely caused by the decrease in strength of larger grains, causing strain to concentrate in their vicinity. Here, a comprehensive picture of the failure processes in high-purity titanium under axial loading is presented and discussed in the paper.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructures and Impact Wear Behavior of Al-Alloyed High-Mn Austenitic Cast Steel After Aging Treatment

The microstructural evolution and impact wear behavior of Al-alloyed ultra-high-Mn austenitic cast steel were investigated after different heat treatments, including quenching (Q) and quenching + aging (Q + A). Another ultra-high-Mn austenitic cast steel without Al was compared under the same experimental condition. After Q + A, Al addition contributed to the precipitation of κ-carbides which improves the yield strength and wear resistance of the austenite matrix. However, the mechanical properties and wear resistance of the Al-free steel were strongly deteriorated due to the precipitation of plate-like M{sub 3}C-type carbides, as well as the worn surface of the Al-free steel had the feature of micro-scratches. After Q + A (2 h), the Al-alloyed steel obtained optimal wear resistance and the main wear feature was strain fatigue. But, excessive aging time (4 h) would lead to a large fragile peeling from the worn surface and the wear resistance was decreased. Also, the worn subsurface microstructures with different heat treatments were observed by transmission electron microscopy (TEM). These results show that the deformation microstructures of the Al-free steel contained stacking faults, dislocation tangle and deformation twins. The deformation character of Al-alloyed steel is dominated by planar glide, and with increase in the aging time, planar dislocation substructures gradually evolved, relating to dislocation pileups, Taylor lattices and micro-bands.

36 MATERIALS SCIENCE↗