Fine Lamellae Research Articles

Heterogeneous lamella mixed grain structures of strength-ductility synergy in medium strain rate rolled AZ31 magnesium sheets

The increase in strength of Mg and its alloys, like other metals, usually couples with a large reduction in ductility, which limits its widely application. A novelty heterogeneous lamella mixed grain structures could effectively achieve high strength-ductility synergy and are obtained by medium-strain rate rolling with high reduction in single-pass which is an industrial process that can be easily scaled up for large-scale production at low cost, i.e. tensile strength of ∼279 MPa and elongation of ∼21.2 % in low alloying magnesium alloy (AZ31). This novelty heterogeneous lamella mixed grain structure displays fine grain lamella and mixed grain lamella alternative distribution, and twins exist inside mixed grain lamella. During deformation, the twinning occurs in the mixed grain lamella and the heterogeneous lamella mixed grain structures have high Schmid factor (SF) for non-basal slip, resulting in the excellent plasticity. The strength is mainly provided by the fine grain lamella and the twins inside mixed grain lamella. The back stress induced by the heterogeneous structure could dynamically achieve strength and ductility. This work provides a new sight to design the heterogeneous lamella mixed grain structure to obtain different combination of strength and plasticity by adjusting grain size distribution, twin density in mixed grain lamella, aspect ratio of coarse grain and misorientation among coarse grain, fine grain and twin.

Investigation of machining performance in SS904L alloy under hybrid cooling conditions

ABSTRACT Hard turns in machining present substantial obstacles to chip removal. An effective heat management system is needed to avoid tool overheating and reduce cutting capacity. Therefore, the present investigates the effectiveness of a comparative study of four cooling methods, such as dry turning, minimum quantity lubrication (MQL), cryogenic (LN2), and the hybrid Cryo-nMQL approach, on machining performance during the machining of SS904L alloy. Machining conditions included 75 and 150 m/min cutting velocities and feed rates of 0.1 and 0.2 mm/rev, respectively. Results indicate that cryo-nMQL exhibited superior performance matched to the other cooling methods, with a maximum improvement of surface roughness by 57.73% and nose wear by 13.87%, flank wear by 67.48%, crater wear by 8.42%. In addition, chip production indicates a fine lamella structure with less serration under cryo-nMQL. In addition, the combination of cryo-nMQL resulted in enhanced tool life and a notable decrease in tool wear with a research gap, indicating future work to assess the benefits of hybrid cooling methods in SS904L machining, thereby showcasing the potential of these innovative technologies in mechanical engineering applications.

Novel Fe-rich hypo-eutectic high entropy alloy developed for laser powder bed fusion in the Al-Co-Cr-Fe-Ni-Zr system

A novel heat resistant Fe-rich hypo-eutectic high entropy alloy (HEA) was manufactured using laser powder bed fusion (LPBF). The prealloyed Al1/4Co2Cr2Fe6Ni3/2Zr powder was characterized and processed using different preheating temperatures (650°C, 700°C and 800°C). The as-built microstructure showed dissimilar morphologies throughout the melt pool, with eutectic grains of ultra fine lamella spacing (λ≈25 nm) inside the core regions, and coarser dendritic and globulitic growth patterns at the interlayer boundaries (ILBs). An annealing treatment at 1000°C for 6 h yielded a homogenous composite microstructure of a Fe-rich matrix with ∼40 % of fine dispersed Zr-rich intermetallic (IM) phases of submicron size. Synchrotron high energy x-ray diffraction (HEXRD) revealed M2Zr Laves (M = Co, Fe, Ni) as the main IM for the as-built condition and the additional growth of M23Zr6 upon annealing. Further HEXRD in-situ high temperature tests examined the lattice parameter evolution and coefficient of thermal expansion (CTE) up to 1100°C. The mechanical performance of the as-built and annealed condition was evaluated through hardness and compression testing at room temperature (RT). Additional compression testing from RT to 1000°C were conducted on the annealed condition to assess the high temperature strength and give comparison to other high temperature materials like Ni-based superalloys.

Significantly Promoting the Thermal Conductivity and Machinability of Negative Thermal Expansion Alloy via In Situ Precipitation of Copper Networks.

Rapid advancements in electronic devices yield an urgent demand for high-performance electronic packaging materials with high thermal conductivity, low thermal expansion, and great mechanical properties. However, it is a great challenge for current design philosophies to fulfill all the requirements simultaneously. Here, an effective strategy is proposed for significantly promoting the thermal conductivity and machinability of negative thermal expansion alloy (Zr,Nb)Fe2 through eutectic precipitation of copper networks. The eutectic dual-phase alloy exhibits an isotropic chips-matched thermal expansion coefficient and a thermal conductivity enhancement exceeding 200% compared with (Zr,Nb)Fe2, along with an ultimate compressive strength of 550MPa. The addition of copper reorganizes the composition of (Zr,Nb)Fe2, which smooths the magnetic transition and shifts it toward higher temperature, resulting in linear low thermal expansion in a wide temperature range. The highly fine eutectic copper lamellae construct high thermal conductivity networks within (Zr,Nb)Fe2, serving as highways for heat transfer electrons and phonons. The in situ forming of eutectic copper lamellae also facilitates the mechanical properties by enhancing interfacial bonding and bearing additional stress after yielding of (Zr,Nb)Fe2. This work provides a novel strategy for promoting thermal conductivity and mechanical properties of negative thermal expansion alloys via eutectic precipitation of copper networks.

Hierarchically heterogeneous microstructure and mechanical properties in laser-directed energy deposition of γ-TiAl alloy through intrinsic cyclic heat treatment

The complex thermal effects of laser direct energy deposition (L-DED) provide significant advantages for production of high-performance γ-TiAl alloy, whereas challenges still exist in microstructure tailoring and mechanical properties. This work focuses on the influence of intrinsic cyclic heat treatment (ICHT) on the evolution of microstructures and mechanical properties in different building height regions of an L-DED TiAl alloy thin-wall sample. The results indicate that ICHT induces discontinuous coarsening (DC) effects by consuming the lamellar interface energy of the initial lamellae, resulting in grain refinement. With the increase in building height, the thermal accumulation leads to an increase in the initial lamellar spacing, which weakens the DC effect. At the top, insufficient thermal cycles prevent fine grain growth and erode coarse grains, hindering overall grain refinement. Ultimately, the hierarchically heterogeneous microstructure forms in the L-DED TiAl alloy, including refinement of hierarchical lamellar colony structure decorated with fine (α2+γ) lamellar structure and (α2+6H-LPS) lamellar structure (6H-LPS refers to 6H long-period structure phase). Specifically, the bottom region exhibits the best combination of ultimate tensile strength (706 ± 33 MPa) and strain (0.68 ± 0.05 %). The high tensile strength can be attributed to the hindrance of dislocation movement by the fine lamellae and the 6H-LPS phase ,caused by the high cooling rate of L-DED, while the elongation is attributed to the reduction in crack propagation energy due to the presence of fine grains.

Mechanical properties and microstructure evolutions of deposited Ti–6Al–4V titanium alloy under short-term stress relaxation at elevated temperatures

This study investigates the stress relaxation behavior and associated microstructure evolution in laser melted deposited Ti–6Al–4V alloy under various temperature and pre-strain conditions for the first time. A set of stress relaxation and tensile tests has been performed to characterize the stress and strength evolution properties of the as-deposited alloy, and microstructural analysis has also carried out for mechanisms identification. It is found that the as-deposited alloy exhibits a lower threshold stress (less than 10 MPa), faster relaxation rate, and a more significant decrease in strength (9.9%∼15.8%) when compared with the same testing conditions of conventionally extruded alloy. Based on the microstructural evolutions, as well as the stress exponent analysis, the stress relaxation mechanisms have been identified: at low pre-strain and temperature (700 °C and 0.5%), diffusion creep plays the dominant role, while with the increasing pre-strains and temperatures, the mechanism transits to dislocation climb, and eventually to grain boundary sliding, at 750 °C and 10%. It is observed that the fine lamellae in the as-deposited alloy are susceptible to morphological changes during relaxation, including dislocation rearrangement, lamellae spheroidization and coarsening. These microstructural evolutions lead to the creep mechanism transitions, as well as the noticeable reduction in yield strength after relaxation. The results could provide insights into designing appropriate stress relaxation parameters for deposited alloys in hybrid additive manufacturing processes.

Growth mechanisms of eta phase in 718Plus alloy

Growth mechanisms of eta phase in 718Plus alloy were investigated by high-resolution scanning transmission electron microscopy. The results demonstrated the nucleation and growth of the η platelets were arranged along the {111}γ habit planes. The fine lamellae γ phase, enveloped in the η platelets blocks, was determined. The possible occurrence of interfacial misfit dislocations could effectively release the mismatch strain, and enhance the ledges nucleation on the {0001}η plane. Analysis of the experimental observations, and possible mechanisms of growth were also addressed.

Plastically deformable polyethylene with excellent transparency and stress whitening resistance properties fabricated by constructing massive chain entanglement

AbstractStress whitening is one of the most prominent macroscopic defects for polyethylene (PE), which greatly affects the appearance and quality of its commodity. In order to eliminate the stress whitening defects of PE, ultrahigh molecular weight polyethylene (UHMWPE) was blended with PE to fabricated PE/UHMWPE, and the enhanced intermolecular entanglement and stretchability was achieved, which greatly suppressed and impeded the occurrence of heterogeneous plastic deformation and fibrillar bundle structure during applying tensile stress, resulting in the sharply deceased of the nanoscale cavities defects for the sample. And thus, the elimination of stress whitening defects and high‐light transmittance in the visible region with excellent optical transparency performance were successfully achieved for PE/UHMWPE. Moreover, introduction of UHMWPE chains significantly improved the orientation degree and formed a dense oriented crystalline network with fine lamellae for the sample, which highly enhanced the mechanical strength of PE/UHMWPE after applying stress. This work provided a new strategy for developing stress whitening eliminating polyolefin materials with high performance, which was of great significance for sustainable development and environmental friendliness.

Synthesis and application of Setaria viridis‐like heterostructures using nickel phyllosilicate decorating polyaniline nanorods: Toward the robust and wear‐resisting epoxy‐based composites

AbstractPerformance improvement to epoxy (EP)‐based composites is imperative yet a challenge for the application of high‐quality tribo‐materials. In this study, we reported the successful construction of a Setaria viridis‐like heterostructure using the fine nickel phyllosilicate lamellae to decorate the rod‐shaped polyaniline, and the corresponding polymer composites involving diverse mass ratios of EP resin and the heterostructures were prepared successively. The dry‐sliding tests confirmed the created composites had a significantly enhanced resistance to wear, and a concentration of 5% heterostructures dropped the wear rate to the lowest value of 1.5 × 10−5 mm3/Nm, which was ca. 78.6% lower than pure resin. The augmented wear resistance should be closely related to the enhanced strength, stiffness, and hardness. Moreover, the introduced heterostructures also improved the thermal stabilities of EP‐based composites, shifting the thermal decomposition to higher temperatures and restraining the mass loss rate to some extent. This study offered a promising pathway to develop high‐quality polymeric tribo‐materials.Highlights A Setaria viridis‐like heterostructures of PANI@NiPS were facilely synthesized. Adequate PANI@NiPS enhanced the tensile properties and hardness moderately. PANI@NiPS showed a considerable positive influence on wear resistance. PANI@NiPS improved the thermal stabilities of EP composites.

Deformation behavior of LPSO phases with regulated morphology and distribution and their role on dynamic recrystallization in hot-rolled Mg–Gd–Y–Zn–Zr alloy

Three relatively novel initial microstructures of Mg–Gd–Y–Zn–Zr alloy were regulated by heat treatment, the deformation behavior of long period stacking ordered (LPSO) phases with different morphology and distribution and their role on recrystallization during thermal deformation were systematically investigated. The interdendritic block-shaped LPSO phases exhibit higher deformation resistance, and shearing, bending, kinking, tearing, dissolution, together with the breaking of plate-shaped lamellae produced by dissolution, are the main deformation mechanisms for them to coordinate deformation. As for the lamellar LPSO phases, deformation behaviors such as shearing, bending, kinking and breaking mainly occur. The interdendritic block-shaped LPSO promote recrystallization through the particle-stimulated nucleation (PSN) mechanism, and the PSN effect is enhanced with the increasing phase fraction, also, the broken block-shaped LPSO have better PSN effect. Recrystallized grains tend to nucleate at the kink of lamellar LPSO and form recrystallized grains bands along the kink bands; the fragmented fine lamellae have better PSN effect, promoting numerous recrystallization nucleation in the severely deformation zone, meanwhile, the joint pinning effect of the fragmented lamellae and precipitates β-phase results in the smaller recrystallized grains size. However, the intragranular continuous large-sized lamellar LPSO strongly pin the dislocation movement and hinder migration of recrystallized grain boundaries along the basal plane and c-axis of lamellar LPSO, making it difficult to achieve extensive lattice rotation, which is not conducive to the recrystallization nucleation. The most remarkable work in this paper is that we clarified the mechanism of different LPSO phases, especially lamellar LPSO phase, on recrystallization behavior, and these findings will provide microstructure regulation guidance for thermal-deformed Mg–Gd–Y–Zn–Zr alloys containing LPSO.

Designing hierarchical eutectic high-entropy alloys via partial similar substitution in the Ni-Fe-Ti-Hf-Nb alloys

Hierarchical eutectic high entropy alloys show distinguished mobility and castability, the fine lamella structure, and the excellent compression property, but their development still faces challenges. Here, the partial similar substitution method is to design hierarchical eutectic high-entropy alloys. This concept successfully developed a hierarchical eutectic Ni3FeTi3HfNb2 high-entropy alloy composed of B2 intermetallic compounds and disordered body-centered cubic (BCC) phases. It displays an outstanding compression property, with the yield strength (σs) as high as 1407 MPa, the large fracture strain of 22.1% and the large elastic strain of 3.0%. The combination of high strength and good ductility exhibits a promising application in industry. Moreover, the anisotropy and the relationships among microstructure evolution, mechanical property and Nb concentration are systematically discussed.

Mechanism of Low‐Temperature Brittle–Ductile Transition of Polypropylene/Low‐Density Polyethylene Blend Foam under Compressive Stress Caused by Cell Stretching

To enhance the low‐temperature toughness of polypropylene/low density polyethylene (PP/LDPE) blend, which is a crucial blend for polyolefin material with wide applications in frigid regions, the PP/LDPE blend foam with stretched cells is fabricated via a facile injection foaming together with open‐mold stretching process. During the open‐mold stretching, the relatively miscible PP and LDPE chains are debonded, and then the stretched and oriented cells structure with lots of tiny interphase cavities between the PP and LDPE phases and the fine lamellae are formed in the foam system. Such interphase cavities provide an adequate movement space for the frozen PP and LDPE chains and lamellae, and effectively relaxed and transferred stress, which greatly promote the uniform compressive behavior accompanied by the completely compacted cells at −25 °C. Moreover, the compressive fracture surface changes from relatively flat and smooth for the stretched PP foam to obvious yield folds and deformation for the stretched blend foam, and the compressive strain of stretched PP/LDPE blend foam is highly enhanced by a roughly 31%, 53%, and 44% increase than that of PP, PP/LDPE, and stretched PP foam samples, respectively, achieving the low‐temperature brittle–ductile transition for PP.

Effect of solution annealing temperature on microstructural evolution and mechanical properties of NbC-reinforced CoCrFeNi based high entropy alloys

Recent studies have shown that NbC precipitates in high-entropy alloys (HEAs) are strong obstacles for dislocation motion, which can substantially contribute to the mechanical performance over a wide temperature range. However, there are limited reports discussing the exceptional adjustability of microstructures and mechanical properties using thermomechanical processing (TMP). Therefore, the microstructures and mechanical properties of NbC-reinforced CoCrFeNi based high entropy alloys (HEAs) tuned via TMP were systematically investigated. Homogenized HEAs with ∼0.3 at% C and Nb were solution annealed at 1100, 1200 and 1300 °C, followed by cold-rolling plus annealing. The microstructures and mechanical properties of the HEAs were systematically characterized using scanning electron microscopy, transmission electron microscopy and uniaxial tensile tests. The results indicated that NbC distribution evolved from eutectic-like primary NbC clusters surrounded by disorderly distributed secondary NbC to dispersive nano-sized secondary NbC as the solution annealing temperature increased above the NbC solvus temperature. Two kinds of microstructures were correspondingly produced: 1) samples solution annealed at 1100 and 1200 °C consisted of fine grain lamellae embedded with NbC precipitates and coarse grain lamellae without precipitates, which exhibited a combination of high strength (UTS ∼740 MPa) and good ductility (elongation ∼60%); and 2) samples solution annealed at 1300 °C obtained a homogeneous fine grain microstructure, which demonstrated excellent synergy of high strength (UTS ∼760 MPa) and exceptional ductility (elongation ∼63%). The enhanced strength of samples solution annealed at 1100 and 1200 °C originated primarily from the high back stress strengthening of lamellar microstructure, while precipitation strengthening caused by dispersed nanosized NbC precipitates and grain boundary strengthening provided extra strengthening for the sample annealed at 1300 °C. This work provides a new strategy for tailoring the microstructure and mechanical properties of NbC-reinforced HEAs via adjusting the solution annealing temperature of TMP.

Dynamic recrystallization and twinning behavior of magnesium alloy during hot tension

In this study, {10–12} tensile twins (TTs) were induced in hot-rolled AZ31 Mg sheets via hot tension along the normal direction. The results demonstrate that the volume fraction of TTs at 2 mm/min is greatly lower than their counterparts at 0.5 mm/min at 100 °C and 200 °C. Dynamic recrystallization (DRX) can decrease twin nucleation rate during hot tensile when the strain rate reaches 2 mm/min. Decrease in critical resolved shear stress of non-basal slips at 200 °C enhances the deformation capability among grains, which dramatically reduces the volume fraction of TTs. Hence, TTs are hardly observed in 200°C-2mm/min sample. Tensile temperature significantly affects the morphology of TT lamellae. Grain boundaries prevents the longitudinal growth of the TTs, and then the thickness of TTs begins to grow to coordinate the deformation, resulting in fine TT lamellae in 100°C-0.5 mm/min. Compared with AR, the basal texture intensity of 100°C-2mm/min and 200°C-2mm/min increases and the occurrence of DRX is the main reason, while basal texture weakening of 100°C-0.5 mm/min and 200°C-0.5 mm/min depends on the formation of TTs. Compared with samples at 200 °C, the samples at 100 °C have higher tensile stresses. The maximum stress of 100°C-0.5 mm/min is 64.97 MPa when tensile strain reaches 0.15 owing to its highest dislocation density. 200°C-2mm/min possesses the highest hardness among the four tension samples, which is associated with the largest fraction of DRXed grains (68.8%) and its refinement strengthening effect. Dislocation strengthening exerts more influence on the hardness of 100°C-0.5 mm/min.

Gills of Molly Fish: A Potential Role in Neuro-Immune Interaction

This study identified the cellular compositions of the gills in molly fish and their role in immunity using light-, electron- microscopy, and immunohistochemistry. The molly fish gills consisted of four holobranchs spaced between five branchial slits. Each hemibranch carried many fine primary and secondary gill lamellae. The gill arch was a curved cartilaginous structure, from which radiated the bony supports of the primary lamellae. The gill arch contained the afferent and efferent brachial arteries. The gill arch was covered by epidermal tissue rich with mucous cells. The primary lamella had a central cartilaginous support and efferent and afferent arterioles and was covered with pavement cells (PVC), salt-secreting chloride cells, and pale-staining mucous cells. These chloride cells contained abundant mitochondria and tubulovesicular system and are involved in ionic transport with a potential role in detoxification. The surface of the secondary lamellae (site of gaseous exchange) consisted of overlapping or interdigitating PVC supported and separated by pillar cells. Other cells were found within the gill epithelium and interstitial connective tissues, including lymphocytes, macrophages, monocytes, telocytes, stem cells, astrocytes, and neuroepithelial cells. The immunohistochemical analysis revealed that APG-5, iNOS-2, IL-1β, NF-κB, and TGF-B showed positive immunoreactivity in macrophages. The epithelium of the primary gill lamellae contained positive-GFAP astrocytes and S100 protein—chloride cells. The stem cells expressed SOX9, myostatin, and Nrf2. Neuroendocrine cells expressed S100 protein. In conclusion, the current work suggests that the gills of molly fish are multifunctional organs and are involved in immune reactions.

Analysing strength, hardness and grain-structure of 0.2%-C steel specimens processed through an identical heating period with different continuous transformation rates

The present work deals with improvement of mechanical properties and refining the microstructure of low carbon steel (0.2%-C) after applying heat treatment techniques. For the purpose, five different samples were taken under study. First sample was kept in ‘as received’ condition and other four samples were undergone into heating process in an Induction furnace. The holding temperature of all the four samples were kept common i.e., 850 °C for a fixed period of 2.5 h. Then, these four samples were cooled into four different cooling media i.e., Air, Water, Oil, and Furnace. All the samples were in the form of rods with 195 mm length and 32 mm diameter. The universal testing machine was used to determine the tensile strength of all the samples. Rockwell hardness tester was used to find the hardness of samples. The microstructural variation was analysed through an optical microscope. All the results were analysed and compared with ‘as received’ sample. The Oil cooled sample showed the highest tensile strength of 585 MPa. The microstructural orientation of oil cooled sample i.e., bainite + fine lamella of ferrite and cementite, provides a good hardness, strength, and toughness to the steel. In addition, XRD and fractography analysis of the samples were also carried out.

Creep properties of Ti–48Al–2Cr–2Nb alloy having similarly oriented lamellae with fine lamellar spacing

The tensile creep behavior of suction-cast and heat-treated Ti–48Al–2Cr–2Nb (at. pct., SC4822) alloy featuring aligned lamellar microstructure with fine lamellae was investigated. The alloy showed excellent creep performance in the temperature range of 775–825 °C under applied stresses varying from 200 to 350 MPa. The creep properties of SC4822 alloy greatly outperformed that of several other typical TiAl alloys with randomly oriented lamellae. The stress exponent (n) for SC4822 alloy was calculated to be 5.1 at 800 °C under different stresses, whereas the apparent activation energy (QC) was found to be 397.18 kJ/mol under 300 MPa at different temperatures. This suggested that creep deformation was dominantly controlled by dislocation climb, as confirmed by subsequent microstructure observation. Besides, dynamic recrystallization, twinning and slipping were also found to contribute to the deformation of creep.

Ductile and ultrahigh-strength eutectic high-entropy alloys by large-volume 3D printing

3D printing of high-strength alloys enables efficient manufacturing of complex metallic components. Yet, the as-built parts are often characterized by unsatisfied ductility due to micro-defects, requiring additional heat treatment to optimize the structure before in-site applications. The post heat-processing, however, often changes the shape of the printed parts, deteriorating the quality of the printed components. In addition, many printed large-scale alloy parts with complex shapes are difficult to be processed by hot isostatic pressing. This requires that the alloys can be printed with good strength and ductility without the necessity of additional thermal processing. Here, we show that excellent ductility and ultrahigh strength can be achieved in a eutectic high-entropy alloy (EHEA) by large-volume 3D printing. The as-printed EHEA has a tensile yield strength of 1040 MPa, and a total elongation of 24%, as well as superior corrosion resistance in seawater environment. The excellent combination of properties outperforms that of all other existing metallic materials. Note that these astonishing properties are from specimens directly after 3D printing without any subsequent heat treatment and hot isostatic pressing. The exceptional mechanical properties are mainly ascribed to the fine lamella spacing in the composite structure consisting of face-centered cubic matrix and B2 precipitates, which renders high resistance for dislocation movement and extends work hardening capability. The EHEA printed in large volume without post processing thus shows high applicability for mass-production at an industrial scale.

Twinning and antitwinning in body-centered cubic metals

Deformation twinning in body-centered cubic (BCC) metals occurs by shearing the crystal along {112} planes parallel to 〈111〉 directions. One of these directions (twinning shear) produces a twin, but it is often argued that the opposite sense of shearing (antitwinning shear) does not lead to twin formation. However, recent slip trace and orientational mapping analyses made on many BCC metals after low-temperature plastic deformation show clear evidence of fine misoriented lamellae along the traces of {112} planes sheared in the antitwinning sense. To resolve this controversy, we have utilized molecular statics simulations to determine the energy barriers for uniformly shearing all transition and alkali BCC metals in the twinning and antitwinning sense. The results of these simulations show that twins in transition BCC metals of the 5th and 6th groups can be produced on both types of {112} planes, irrespective of whether the shear is applied in the twinning or the antitwinning sense. However, this is not the case for α-Fe and the BCC structures of the alkali metals Li, Na, and K, where twins are likely to occur only on {112} planes sheared in the twinning sense. Furthermore, we have used TEM diffraction pattern analyses to investigate the characters of misoriented deformation lamellae in Nb and Cr compressed at 77 K, which were found along {112} planes sheared in the antitwinning sense. We demonstrate that these regions constitute regular twins. Similar studies on α-Fe compressed at 77 K prove that twinning in this material takes place exclusively on {112} planes sheared in the twinning sense.

Microstructure and Mechanical Behavior of Cu–Al–Ag Shape Memory Alloys Processed by Accumulative Roll Bonding and Subsequent Annealing

Ultrafine-grained Cu/Al/Ag composites were processed by an accumulative roll bonding (ARB) technique from pure copper and aluminum sheets and a silver powder. The Al content was fixed to 11 wt.% while the silver concentration was 1, 2, or 3 in wt.%. The ARB-processed samples were heat treated at different temperatures between 750 and 1050 °C for 60 min and then quenched to room temperature (RT) for producing Cu–Al–Ag alloys. The effect of the addition of different Ag contents and various heat treatment temperatures on the structural evolution was investigated. The ARB-processed samples were composed of Cu and Al layers with high dislocation density and fine grain size (a few microns). During heat treatment of the ARB-processed samples, new intermetallic phases formed. For the lowest Ag content (1 wt.%), the main phase was a brittle simple cubic Al4Cu9, while for higher Ag concentrations (2 and 3 wt.%), the quenched samples contain mainly an orthorhombic β1-AlCu3 martensite phase. The martensite phase consisted of very fine lamellas with a thickness of one micron or less. The heat treatment increased the microhardness and the strength of the samples at RT due to the formation of a fine-grained hard martensite phase. For 2 and 3% Ag, the highest martensite phase content was achieved at 850 and 950 °C, respectively. The annealed and quenched samples exhibited good shape memory behavior at RT.