Twin Chains Research Articles

Quantitative investigation on the {10–12} twinning-detwinning behavior and twinning transfer of an extruded Mg-2.8Y sheet during compression-tension loading via quasi-in-situ EBSD observation

Abundant {10–12} twins appeared in an extruded Mg-2.8Y (wt. %) sheet with rare-earth (RE) texture under compression along the transverse direction (TD). Twinning-detwinning behavior during compression-tension loading was quantitatively investigated via quasi-in-situ EBSD observation. The evolution of deformation mechanisms was quantitatively studied by calculation of the plastic strain fraction of twinning, detwinning, and dislocation slip. Twinning and detwinning were the dominant deformation modes in compression and reverse tension, respectively, owing to their relatively higher Schmid factors (SF) and lowest activation stresses (τ). Twin variants with SF ranking 1st and 2nd were activated preferentially while detwinning with low SF ranking showed high activation. The impact of texture and load path on variant selection was systematically discussed. Moreover, short twin chains only passing through two or three grains caused by twinning transfer were observed. Grain boundary misorientation angle (GBMA) and geometric compatibility factor (m’) were introduced to analyze the crystallographic characteristics of twinning transfer. GBMA ≤34.5° or m’ ≥ 0.80 is a necessary condition for most twinning transfer events. RE texture as well as the nearly uniform distribution of GBMA gave rise to short twin chains and restricted the formation of long twin bands. The relationship between GBMA and m’ was also discussed.

Cationic lipid-conjugated bis-arylidene oxindole derivatives as broad-spectrum breast cancer-selective therapeutics

Breast cancer is a heterogeneous malignancy with wide-ranging variations in therapeutic responses, overall survival etc. Major challenges for available chemotherapeutic agents in achieving clinical success are in maintaining systemic bio-distribution and avoiding non-specific adverse effects. Bis-arylidene oxindoles are estrogen receptor (ER)-selective bioactive molecules with moderate potency. In here, we have designed, synthesized and evaluated a series of twin aliphatic chain cationic lipid-conjugated bis-arylidene oxindole molecules with variations in nature of linker, lengths of carbon spacer and hydrophobic twin chains. We observed that among the various structural analogues, C8 twin-chain containing molecules, PGC8, S2C8 and S3C8 showed effective cancer cell-selective cytotoxicity in different cancer cell lines with an IC50 ranging from 4 to 7 µM. These molecules selectively induced apoptosis, ROS production and cell cycle inhibition at G1/S phase in ER + breast cancer cells but not in non-cancer cells. Additionally, these molecules formed homogenous self-assemblies exhibiting effective hydrodynamic diameter with positive surface charge. The self-assemblies also showed prominent cancer cell-selective uptake and DNA-binding abilities. Hence, we have shown successful incorporation of dexamethasone to the self-assemblies, and its enhanced cytotoxicity even in ER-negative breast cancer cells. All these results indicate that PGC8, S2C8 and S3C8 molecules, albeit their potent and selective ER-positive anti-breast cancer activity, can be repurposed as targeted delivery systems and hold promise as unique, broader spectrum breast cancer cell-selective therapeutic payloads.

Manufacturing of pure copper with extraordinary strength-ductility-conductivity balance by cryorolling and annealing

To obtain a pure copper with extraordinary strength-ductility-conductivity balance, asymmetric cryorolling followed by low-temperature (200 °C) annealing was employed. The microstructural-mechanical-electrical properties of the samples were investigated. The results showed that multiple twinning was formed after the partial annealing of deformed copper. The copper annealed for 60 min exhibited a hardness, yield strength, and tensile strength of 38.1 HB, 192 MPa, and 422 MPa, respectively, while a large total elongation of 37.2% was obtained. Also, the annealed copper had a larger strain hardening rate at ε higher than 0.023 owing to the creation of twin chains. The fracture surface of the 60-min annealed copper was dominated by only ductile dimple features. The post-annealed copper showed an extraordinary electrical conductivity of 99.58%IACS, which is much larger than that for all pure coppers with UTS higher than 400 MPa. It was found that using second phase particles with high electrical conductivity was a better strengthening mechanism than strain hardening and grain boundary strengthening. An extraordinary strength-ductility-conductivity balance was achieved in the current pure copper compared to other pure coppers. This was due to the existence of copper oxide, and the formation of twin chains in the present work.

Evolution of twinning during cyclic loading of magnesium alloy examined by quasi-in-situ EBSD

Most complex engineering components experience varied loading in use. We conducted successive experiments of cyclic tensile deformation followed by electron-backscattered diffraction imaging of the same area on each of several magnesium alloy (ZM) sample to investigate the microstructure and texture evolution during cyclic loading. In this way we correlated the evolving deformed microstructure of cyclically loaded magnesium to the initial grain orientations. To investigate the effects of the strain path, the behaviour of samples with and without pre-compression was compared. Twins can propagate from grain to grain and twin chains will form in the material without any pre-deformation. Twin chains are a result of twin transmission at grain boundaries and twin transmission frequency decreases with increasing grain boundary angles. In the absence of pre-compression, the extension twin fraction rises from 0.003 to 0.019 after two cycles of tensile loading to a strain of 0.03, after which it changes only slightly as strain is increased. Twin chains in the pre-compressed specimen are activated without any obvious dependence on the matrix orientation. The fraction of extension twinning is 0.2 for the pre-compressed specimen. After a cycle of tensile loading to a total plastic strain of 0.015, 90% of the extension twins undergo detwinning. The detwinning starts just after reverse loading. Secondary twins forming within primary twin interfaces start to nucleate in the microstructure of the pre-compressed material at an early stage (at plastic strain values of 0.056). This is different from the nucleation of secondary twins in the material without pre-compression that occurs at a strain of 0.104. The early formation of secondary twinning is due to the presence of residual primary twins in the microstructure of the pre-compressed material as a result of detwinning of the initial twins.

Effect of post-annealing on the microstructure and mechanical properties of nanostructured copper

Abstract In the current research, the effect of post-annealing treatment at 200 °C with four different holding times of 5, 10, 30, and 60 min on the asymmetrically cold-rolled pure copper was investigated. The microstructural evolution (via optical microscopy and scanning electron microscopy), mechanical properties (by tensile and hardness tests), and electrical conductivity of the post heat-treated copper sheets were evaluated. The static recrystallization (SRX) took place at a short annealing time due to the large strain stored energy caused by the asymmetric cold rolling as well as the presence of particles. The average grain size of the post-annealed sample for 5 min was about 96 nm. The copper after 60 min post-annealing consisted of many coarse polygonal grains, a few small grains, and multiple twinning (twin chains). The formation of multiple twinning and twin chains was due to the low-temperature annealing (200 °C) of rolled copper. The tensile properties indicated that the strength had a relatively low sensitivity to the increment of annealing time and the produced pure copper exhibited superior thermal stability. The formation of twin chains and the existence of copper oxide particles were responsible for this unusual behavior. The copper annealed for 60 min had a low YS-to-UTS ratio (0.378) and a high work hardening rate, which were equivalent to high formability. For the low annealing times of 5 and 10 min, there were both shear and equiaxed dimples on the fracture surface indicating a combination of ductile shear and ductile fractures. When the time of post-annealing was higher than 30 min, only the ductile dimples could be observed on the fracture surface. The post-annealing treatment for 60 min increased the electrical conductivity to from 84.10 to 87.52 %IACS due to the occurrence of recovery, recrystallization, and grain growth. Finally, it was found that adopting a high enough pre-deformation (96% strain) and a suitable annealing time (60 min) at a low annealing temperature (200 °C) in the pure copper could make a good balance between tensile and electrical properties.

Evolution of Twinning During Cyclic Loading of Magnesium Alloy ZM21 Examined by Quasi-in-Situ EBSD

Most complex engineering components experience varied loading in use. We conducted successive experiments of cyclic tensile deformation followed by electron-backscattered diffraction imaging of the same area on each of several ZM21 magnesium alloy sample to investigate the microstructure and texture evolution during cyclic loading. In this way we correlated the evolving deformed microstructure of cyclically loaded magnesium to the initial grain orientations. To investigate the effects of the strain path, the behaviour of samples with and without pre-compression was compared. Twins can propagate from grain to grain and twin chains will form in the material without any pre-deformation. Twin chains are a result of twin transmission at grain boundaries and twin transmission frequency decreases with increasing grain boundary angles. In the absence of pre-compression, the fraction of extension twins increases from 0.003 to 0.019 after two cycles of tensile loading to a strain of 0.03, after which it changes only slightly as strain is increased. Twin chains in the pre-compressed specimen are activated without any obvious dependence on the matrix orientation. The fraction of extension twinning is 0.2 for the pre-compressed specimen. After a cycle of tensile loading to a total plastic strain of 0.015, 90% of the extension twins undergo detwinning. The detwinning starts just after reverse loading. Secondary twins forming within primary twin interfaces start to nucleate in the microstructure of the pre-compressed material at an early stage (at plastic strain values of 0.056). This is different from the nucleation of secondary twins in the material without pre-compression that occurs at a strain of 0.104. The early formation of secondary twinning is due to the presence of residual primary twins in the microstructure of the pre-compressed material as a result of detwinning of the initial twins.

Analysis of {10–12} twinning variants’ selection behavior during multi-directional compression in Mg–3Al–1Zn magnesium alloy

The {10–12} twinning activities of Mg–3Al–1Zn magnesium alloy during multi-directional compression were investigated by in situ EBSD technology. The specimen was pre-compressed to a strain of 3.2% along TD, followed by a compression with a strain of 2.6% along RD, and finally a compression with a strain of 2.5% along TD. The Schmid factor, strain compatibility factor (m′) and twinning strain tensor (e) were calculated to analyze the twinning variant selection. The results show that four types of twinning behaviors can be observed during multi-directional compression: (1) the growth of twin lamellas generated from previous compression; (2) the nucleation of new {10–12} twins in existing twins; (3) the nucleation of new {10–12} twins in initial grains; and (4) detwinning. Some grains show only one twinning behavior within a grain, while some grains exhibit two or more twinning behaviors within a single grain. The variant selection of {10–12} twins for twin pairs and twin chains in neighboring grains is dominated by high Schmid factor and high strain compatibility factor. Because of good accommodation between neighboring grains, the simultaneous detwinning and retwinning behaviors developed in twin pairs or twin chains during multi-directional compression.

Observation of Twin Transmission Process in Mg Alloys by In Situ EBSD

Twin pairs are frequently observed at the common grain boundaries of Mg alloys. The formation of twin pairs is associated with a twin transmission (TT) process. Investigating the TT process is important for understanding the deformation mechanism of Mg alloys. Here, the authors report an in situ electron backscatter diffraction (EBSD) examination on the TT process in AZ31 Mg alloys subjected to tensile deformation. TT process is clearly observed by band contrast images resulting in the formation of twin chains as strain increases. Interestingly, transmitted twins are developed in advance in form of non‐indexing dislocations or twins in neighboring grain. The TT direction is roughly along the shear plane normal or shear direction of the paired twins. In addition, multiple twin variants are activated by TT mechanism and nucleation of new twins at pre‐existing twin boundaries.

Dual Emissions and Thermochromic Luminescence Behavior of Chloroplumbate Organic–Inorganic Hybrid Crystals

Two hybrids, [BMIP][Pb2Cl6] (1) and [BMIP][Pb1.5Cl5]·H2O (2) {BMIP2+ = 1,3‐bis(1‐methylimidazolium)propane}, are achieved by mutual diffusion of inorganic and organic components in anhydrous DMF and DMF with a trace amount of water (the trace amount of water originates from MnCl2·4H2O), respectively. Single‐crystal X‐ray diffraction data are collected for 1 in 300–100 K and 2 in 370–100 K, revealing that 1 and 2 crystallize in monoclinic space group P21/c and triclinic space group P1, respectively. Crystal 1 contains [Pb4Cl12]∞ twin chains, rarely reported, constructed from edge‐sharing PbCl6 octahedra, and dications surround the [Pb4Cl12]∞ twin chains. Crystal 2 includes [Pb3Cl10]∞ single chains, comprised of distorted PbCl6 octahedra linked together in face‐ and edge‐sharing manners, with dications occupying the space among the [Pb3Cl10]∞ chains. The solid‐state UV/Visible absorption spectra at ambient temperature, and the excitation and emission spectra in 10–300 K for 1 and 2 are investigated, showing dual emissions and thermochromism, originating from the distinct response of the two emission bands to temperature. In particular, the plots of the intensity ratio between the two emission bands versus the temperature display a linear relationship in 10–85 K and 150–300 K for 2, respectively, indicating its potential application in luminescent thermometers, a phenomenon which has scarcely been reported in lead–halide‐based hybrids.

Syntheses, crystal structures and photoluminescence properties of five Cd/Zn–organic frameworks

Luminescent metal–organic frameworks (MOFs) have displayed extensively potential applications for photocatalysis, photoluminescence, electroluminescence, chemical sensors et al. Herein, five new Cd/Zn−organic frameworks of [Cd(HL)C2H5OH] (1), [Cd(HL)(2,2′-Bpy)H2O] (2), [Cd2(HL)2(Phen)2] (3), [Zn(HL)BIMB] (4), [Cd3(HL)3(4,4′-Bpy)DMF]·(H2O) (5) have been deliberately constructed via solvothermal reactions of d10 transition metal salts, i.e. Cd(NO3)2∙4H2O or Zn(NO3)2·6H2O, and a V-shaped semi-rigid organic linker of 4,4'-(hydroxymethanediyl) dibenzoic acid (H3L) along with the auxiliary poly-nitrogen ligands of 2,2′-Bpy(2,2′-bipyridine), Phen(phenanthroline), BIMB(1,1′-benzene-1,4-diyldimethanediyl-bis-1H-imidazole) and 4,4′-Bpy(4,4′-bipyridine). The crystal structures of compounds 1–5 were precisely determined by single-crystal X-ray diffraction (SC-XRD), Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR) and Thermogravimetic analysis (TGA). As revealed by SC-XRD, the isolated 1 presents a 2-periodic framework encompassing side-by-side channel-typed helical tubes. Compounds 2–4 display Z-shaped 1-periodic single chains, concomitant with twin chains and tubular structure, respectively. Interestingly, compound 5 demonstrates a two-fold interpenetrated 3-periodic skeleton in the presence of a rigid pillar of 4,4′-Bpy. Additionally, photoluminescence properties of 1–5 were lastly investigated.

Initiation and strain compatibility of connected extension twins in AZ31 magnesium alloy at high temperature

Uniaxial compression tests were carried out at 350°C and a strain rate of 0.3s−1 on as-extruded AZ31 magnesium alloy samples. At a true strain of −0.1, extension twin pairs in a grain and twin chains across adjacent grains were detected. The orientation of selected twins and their host grains were determined by electron backscattered diffraction (EBSD) techniques. The Schmid factors (SFs), accommodation strains and geometric compatibility factors (m′) were calculated. Analysis of the data indicated that the formation of twin pair and twin chain was related to the SF and m′. Regarding to twin chain across adjacent grains, accommodation strain was also involved. The selection of twin variants in twin chain was generally determined by m′. When the twins required the operation of pyramidal slip or twinning in adjacent grain, the corresponding connected twins with a relative high m′ were selected in this adjacent grain.

Twin pattern evolution in a fine-grained Mg alloy subjected to indentation

A Vickers diamond pyramid indenter was impressed on a fine-grained polycrystalline Mg–3Al–1Zn alloy. Serial polishing in combination with quasi-in-situ electron backscatter diffraction (EBSD) examinations revealed the presence and the 3D spatial distributions of {10–12} extension twins around the indent. Twin chains and completely twinned areas were found in some regions close to the indent. A model of twin pattern evolution around the indent was proposed based on the experimental observations and local strain accommodation analysis.

Twinning characteristic in tension of magnesium alloys and its effect on mechanical properties

Twinning is an important deformation mechanism for Mg alloys and it generally nucleates from grain boundaries (GBs). When grains are refined, the fraction of GBs will largely increase, which may affect the activation mode of twinning. The present study aims to understand the characteristic of twinning in tension of fine and coarse grained Mg alloys and its effect on mechanical behavior. The experimental results showed that crossed twin lamellae were present within grains in coarse-grained (CG) sample, whereas long twin chains or twin bands crossing many grains were dominant in fine-grained (FG) sample. Because of the different activation mode of twinning, FG sample did not exhibit obviously higher yield strength compared to CG sample. Statistical analyses indicated that the high geometric compatibility factor, low angle boundary misorientation and fine grain size are favorable factors for the formation of twin chains or twin bands in FG sample.

A study of deformation twinning in a titanium alloy by X-ray diffraction contrast tomography

A specimen of Ti–4Al deformed in-situ to about 0.7% compressive strain using neutron diffraction, and showing early stages of twinning, has been investigated in 3D using synchrotron X-ray diffraction contrast tomography (DCT). A cylindrical volume of 900 μm × 400 μm diameter was observed using DCT, containing about 400 grains of which almost 60 grains were identified to have twinned predominantly by {101¯2} 〈1¯011〉 011 tensile twinning. To consider possible twin nucleation criteria, non-twinned grains of similar orientation to the twinned grains were compared against the family of twinned grains. Such comparison highlights that the twinned grain family has a grain size distribution shifted to a higher mean value than the corresponding family of grains that has not twinned. An initial neighbourhood analysis did not reveal any significant differences of the two grain families. However, complex twin chains and clusters were identified forming a slightly imperfect network demonstrating the importance of the 3D analysis. Analysis of the parent grain orientations within those chains/clusters using the Luster-Morris parameter revealed a significantly higher propensity of prismatic 〈a〉 slip transfer compared to the neighbourhood of the non-twinned grain family while no difference was observed for the likelihood of twin shear transfer. The findings suggest that grain chains/clusters with high ability of prismatic 〈a〉 slip activity and slip transfer does promote formation and clustering of twins, which is likely associated with the build up of tensile intergranular strain along the 〈c〉 axis perpendicular to the loading direction recently suggested by crystal plasticity modelling.

Two in one: switchable ion conductivity and white light emission integrated in an iodoplumbate-based twin chain hybrid crystal.

An iodoplumbate-based hybrid, [C7-Apy][PbI3] (1), where C7-Apy(+) = 1-heptyl-4-aminopyridinium, was prepared using a simple solution process. Three sequential phase transitions occur in the range of 402-443 K. In both the lowest and highest temperature phases, hybrid crystal 1 is composed of discrete [Pb2I6]∞ twin chains surrounded by C7-Apy(+) cations. The connectivity between PbI6 octahedra within a [Pb2I6]∞ twin chain and the arrangement of cations are quite difference between the lowest and highest temperature phases. Hybrid crystal 1 shows switchable ion conductivity due to the structural phase transition and white light emission attributed to the broad band semiconductor emission of the twin chain. The former functionality has potential application in ion conductor devices; the single-phase white light emitter is a useful material in low-cost, easily-made, high-efficiency white light-emitting diodes.

Exploring architectures at the nanoscale: the interplay between hydrophobic twin lipid chains and head groups of designer peptide amphiphiles in the self-assembly process and application.

The self-assembly of peptide amphiphiles (PAs) is found to be governed by the hydrophobic interactions induced by the hydrophobic groups/number of alkyl chains and the hydrophilic head groups. In this study, an assessment of the nanostructures formed by the self-assembly of simple twin chained PAs was carried out and compared to their single chain/short analogues. The spectroscopic and microscopic analysis revealed the fact that the twin chained amphiphiles had a high inclination to form β-sheet nanofibers and further towards hydrogelation. The mixture of twin chained PAs also exhibited cooperative self-assembly with improved aggregation behavior, although not much augmentation in β-type structuring was found. In contrast, the single chain/short analogue containing PAs showed very less of β-sheet type structures to a lesser extent and no hydrogelating behavior but resulted in mostly random conformations. The increase in the number or alteration of polar head groups in double chained PAs induced higher extent of β-type conformation and better gelling capability due to the combined hydrophobic effect of the twin chains. The overall results delineated the dominance of hydrophobic interactions. Finally, calcium phosphate bio-mineralization was done in the hydrogels of twin chained PAs with the aim of developing future biomaterials.

Strain compatibility effect on the variant selection of connected twins in magnesium

Abstract Profuse extension twinning was activated in compression of a rolled Mg alloy along the transverse direction. The variant selection in twin pairs, twin chains and multiple twins inside one grain was studied by geometric compatibility factor ( m ′) and Schmid factor (SF). The results show that most connected twins have both high SF and high m ′. In some cases (∼23%), m ′ rank is more important than SF rank for variant selection in the connected twins. Due to the importance of local strain compatibility, synergetic nucleation of twins, twin transfer across neighboring grains and coexistence of ortho-position variants inside one grain are prevalent in the compressed sample. Such characteristics of variant selection affect microstructural evolution and plasticity of materials and should be considered into the development of physics-based simulation models for Mg alloys.

Understanding of variant selection and twin patterns in compressed Mg alloy sheets via combined analysis of Schmid factor and strain compatibility factor

Twinning is an important deformation mechanism for Mg alloys, which is intimately related to their mechanical behaviors, such as yield strength, strain hardening, ductility and so on. Therefore, a fundamental understanding of twinning behavior and mechanism under various conditions is essential for improving the mechanical properties of Mg alloys. This study aims to extend understanding the mechanism of {10–12} twin variant selection and twin patterns in compression of basal textured AZ31 Mg alloy sheet along transverse direction. Various twin patterns such as independent or intersecting multi-twins in a grain, paired twins in two neighboring grains, and twin chains across many grains were observed in the 3% compressed AZ31 sample. The variant selection of {10–12} twins in the various twin patterns were studied by a combined analysis of Schmid factor and strain compatibility factor, m′. Multiple twin variants can be formed in a grain and the non-Schmid twin variant could be induced by the impingement of a neighboring twin at grain boundary. Paired {10–12} twins are likely formed when the Schmid factors of both twins and their strain compatibility factor are very high. The paired twins can propagate throughout the grains and transfer to more neighboring grains (termed as twin–twin transfer behavior). Such continuous twin–twin transfer behavior across more than three neighboring grains results in the formation of twin chains. In addition, strain accommodation among the different twin variants in the same grain, and the orientation relationship between the paired twins and their common grain boundary direction are discussed. A comprehensive understanding of the twin patterns and variant selection was achieved by such a combined analysis of Schmid factor and strain accommodation factor.

Redefining the Waitemata Basin, New Zealand: A new tectonic, magmatic, and basin evolution model at a subduction terminus in the SW Pacific

The early Miocene Waitemata Basin has long been described as an interarc/intra‐arc basin, formed between twin chains of arc volcanoes in Northland, New Zealand. However, deep marine, polymict, volcaniclastic conglomerates within the basin reveal tectonic and magmatic signals that are not evident from neighboring volcanic edifices. The conglomerates were deposited by high‐density turbidity currents and debris flows and include single sediment cycle megaclasts of lava. These basaltic lavas have ocean island basalt (OIB)‐like geochemical affinities and are precisely dated at 20 Ma by 40Ar‐39Ar methods. Their age and the occurrence of subordinate clasts derived from an ophiolitic nappe to the north indicate the basin postdates the initiation of collision in the wider region. Contemporaneous calc‐alkaline volcanism did occur some 250 km NW of the basin. However, the conglomerates lack clasts of calc‐alkaline/arc affinities indicating an absence of arc‐like volcanism in the vicinity of the basin. Recent tectonic models for the SW Pacific region and mantle tomography highlight the importance of wholesale slab detachment in driving early Miocene calc‐alkaline volcanism and basin development. Although such models provide a slab window for the eruption of nonarc OIB‐like magmas, they would not explain their localized occurrence at the proposed leading edge of the tear (Waitemata Basin), rather than progressively along the entire length of the detachment (Northland), as seen in other detachment settings. In addition, OIB‐like volcanism predates the adjacent calc‐alkaline volcanism on the margin of the basin, a transition that is the opposite of that found at other slab detachment settings. The occurrence of OIB‐like volcanism is better explained by a lateral slab termination in the vicinity of the Waitemata Basin that allowed asthenospheric‐derived magmas to erupt. The basin is inferred to have developed in response to asthenospheric upwelling and associated lithospheric extension or deformation associated with a slab termination zone. This study highlights the importance and potential of combined geochemical, geochronological, and sedimentological studies of conglomerates in reconstructing the geodynamic setting of a basin.

Quantitative microstructure characterization of self‐annealed copper films with electron backscatter diffraction

AbstractElectron backscatter diffraction (EBSD) was applied to analyze cross sections of self‐annealed copper electrodeposits, for which earlier the kinetics of self‐annealing had been investigated by in‐situ X‐ray diffraction (XRD). The EBSD investigations on the grain size, grain boundary character and crystallographic texture of copper films with different thicknesses essentially supplement results from in‐situ XRD. Twin relations between neighboring grains were identified from the orientation maps and the observed twin chains confirm multiple twinning in copper electrodeposits as the mechanism of microstructure evolution at room temperature (self‐annealing). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)