Lamellar Spacing Research Articles

Sintered Nd-Fe-B magnets from gas-atomized powders and the effect of lubricants

The production of sintered Nd-Fe-B magnets currently relies on alloys solidified via strip casting. However, the spacing of Nd2Fe14B lamellae in the strip-cast alloys is not optimal for obtaining monocrystalline powders with a mean particle size significantly smaller than 3 μm. Magnets made of finer monocrystalline powder are expected to have smaller grains and a higher coercivity, which would reduce current reliance on scarce and expensive heavy-rare-earth elements. Because of finer Nd2Fe14B grains, gas atomized Nd-Fe-B alloys generally yield more homogeneous fine powders than the strip-cast alloys. In this study, sintered Nd-Fe-B magnets were prepared from gas-atomized alloy and their properties were compared with those of magnets made from the strip-cast alloy of the same chemical composition. The gas-atomized alloy was found to contain an additional metastable phase of the TbCu7-type structure. As compared to the strip-cast alloy, the gas-atomized alloy yielded a jet-milled powder with smaller mean particle diameter and sintered magnets with finer grains and a higher coercivity. The metastable phase specific to the gas-atomized alloys was eventually eliminated during the sintering process without damaging the magnetic properties. Treatment of the new ultrafine powders prior to their compaction in a magnetic field with lubricants ensured a higher degree of the crystallographic alignment and lead to a higher coercivity while still maintaining high remanence. In particular, a magnet prepared from the gas-atomized alloy treated with methyl octanoate exhibited a remanence of 1.38 T, a coercivity of 1278 kA/m, and a maximum energy product of 359 kJ/m3. The results indicate that a simultaneous utilization of the gas-atomized alloys and appropriate lubricants may reduce the need for the heavy rare earths, making the magnets more sustainable.

Unveiling microstructural evolution and its effect on mechanical performance in a Cu-9Ni-6Sn alloy

Cu-9Ni-6Sn alloy exhibits profoundly potential as a new environmental-friendly conductive elastic material. In this work, the formation and growth mechanism of discontinuous precipitation, as well as its effect on mechanical properties of Cu-9Ni-6Sn alloy are systematically studied. The investigation indicated that the discontinuous precipitation does easily initiate from random grain boundaries but showing opposite result for Σ3 boundaries. The lower frequency Σ3 boundaries relatively, the more intense the solute diffusion, resulting in a higher volume fraction of discontinuous precipitation. The increasing aging temperature and time will accelerate the grain boundary discontinuous reaction, and the fine-grained samples exhibit a higher volume fraction of discontinuous precipitates and smaller lamellar spacing due to the more nucleation sites and increased interfacial energy. The strengthening mechanism of Cu-9Ni-6Sn alloy mainly focus on dislocation strengthening and precipitation strengthening, in which the D022 or L12-γ′ phases exhibit more significantly precipitation strengthening effect but is difficult to guarantee ductility. The localized grain boundary discontinuous precipitation detrimentally affect both the tensile strength and ductility.But the nano-lamellar discontinuous precipitation is beneficial to the strength-ductility trade off when it occupies the entirely Cu matrix. This work establishes a robust foundation for the microstructural optimization and multi-component design of Cu-9Ni-6Sn alloy.

Grain refiner fabricated by spark plasma sintering for hypoeutectic Al–Si alloy cast and its refining ability

Grain refiner fabricated by spark plasma sintering (SPS) for an as-cast hypoeutectic Al–Si alloy were proposed. The proposed grain refiner contains Al3Ti and Na flux particles in an Al-11 mass%Si alloy matrix. Through SPS, the grain refiner were obtained without any reaction between the Al3Ti particles, Na flux particles, and Al-11 mass%Si alloy matrix. Casting tests were conducted using the proposed grain refiners, and the refiners reduced the dendrite cell size and the dendrite arm spacing of the primary α-Al phase, as well as the lamellar spacing of the eutectic structure. The eutectic Si phase changed to a granular shape upon the refinement of the eutectic structure. Furthermore, the tensile strength and ductility of the as-cast Al-11 mass%Si alloy were drastically improved by adding the proposed grain refiner. This improvement was attributed to the refinement and granulation of the eutectic Si phase.

Statistical analysis of lamellar and Widmannstätten structures obtained in Nb-rich γ-TiAl alloy with varied cooling rate and annealing duration

Nb-rich γ-TiAl alloys are of interest for enhanced mechanical properties and oxidation resistance. The influence of cooling rate and annealing duration on microstructural evolution of Nb-rich γ-TiAl alloy (Ti-45Al-8Nb-0.2B) has been meticulously investigated, with emphasis on phase volume fraction, grain size, and lamellar spacing. The alloy was annealed at 1320 °C for 15 min, and then furnace-cooled, oil-quenched or cryogenic quenched, whereas annealing for 2 h and 26 h was followed by water quenching. The post-anneal microstructures were characterized using X-ray diffraction, optical and scanning electron microscopy, along with energy dispersive spectroscopy and electron backscattered diffraction. Across all samples, a fully lamellar microstructure comprising α2 and γ phases has been consistently achieved, along with sporadically observed small β precipitates, and elongated ribbon-like TiB2. Widmannstätten colonies (WC) have been observed with diverse morphologies, most of which exhibited an angle of around 64° to regular lamellae, supporting the theory of {1‾1‾22} twinning in the α-phase for WC formation. The γ phase fraction has decreased with increasing cooling rate and annealing time. Grain size and lamellar spacing have also declined with cooling rate but increased with annealing time. Additionally, the mean size of equiaxed γ grains has enlarged with annealing duration.

Effect of Rare Earth Ce on Structure and Properties in 7CrSiMnMoV Die Steel Castings

In this study, rare earth (RE) Ce is used to modify the interaction between atoms in 7CrSiMnMoV die steel castings. The tensile properties are performed, and strengthening mechanism are analyzed by investigated fracture surface, and microstructure by optical microscopy (OM) and scanning electron microscope‐energy dispersive spectrometer (SEM‐EDS). And ab initio molecular dynamics (AIMD) is used to simulate the effect of the Ce element on the local atomic structure of the FeCeC system alloy steel. The results indicate the strength can increase from 722.55 to 1074.27 MPa, and the elongation can increase from 24.86% to 44.22% with a RE Ce concentration of 0.009%. It is attributed to that doping of Ce can inhibit the formation of network eutectic cementite, refine the lamellar spacing of pearlite, and even form granular cementite and martensite structures. AIMD simulation results show that C atoms tend to be surrounded by Fe, and the strong chemical bonds of FeC make the Fe‐centered C more stable with an increase in RE Ce concentration. And doping Ce can introduce new local topological and chemical orderings such that the FeCFe triplets predominantly form small and big angles shifting from near 75° and 136° to 47° and 81°, respectively.

Spin-coating ANF based multilayer symmetric composite films for enhanced electromagnetic interference shielding and thermal management

The demand for flexible composite films with electromagnetic interference (EMI) shielding capabilities is rapidly increasing. Balancing high EMI performance with flexibility and portability has become a critical research focus in practical applications. In this study, an optimized strategy for aramid nanofibers (ANF) films was developed using spin-coating and sol–gel techniques. The resulting film features a smooth surface and excellent mechanical properties. ANF, initially an insulator, was transformed into a conductor through the in-situ polymerization of ion-doped polypyrrole (PPy). Leveraging a multilayer structural strategy, we prepared a symmetric composite film, ANF@PPy-(TA-MXene)-AgNWs-(TA-MXene)-ANF@PPy (PMA), using vacuum-assisted filtration and lamination hot pressing. This film, composed of ANF@PPy (PA) as the matrix, tannic acid (TA) modified MXene, and silver nanowires (AgNWs) as fillers, exhibited multiple shielding mechanisms as electromagnetic wave (EMW) passed through its various layers. This multilayer configuration provides significant flexibility in EMW shielding. Moreover, TA-modified MXene expands the lamellar spacing, enhancing the scattering efficiency of EMWs within the film, and serves as a medium connecting the upper and lower layers. This results in the efficient integration of the multilayer structure, synergistically improving both EMI shielding performance and mechanical properties. When the ratio of PA/MXene/AgNWs was 1:3:1, the film demonstrated optimal properties, including an EMI shielding effectiveness of 70.2 dB, thermal conductivity of 4.62 W/(m•K), and tensile strength of 50.2 MPa. Due to the exceptional EMI shielding and thermal properties of the PMA composite film, it holds great potential for applications in artificial intelligence, wearable heaters, and military equipment.

Investigation of the Microstructure, Mechanical Properties, in Vitro Degradation Behavior, and Biocompatibility of Newly Developed Zn‐0.6%Li Alloy

Zn–Li alloys are considered as one of the promising materials in biodegradable bone implants because they have excellent biocompatibility and high strength. This study examines the extrusion deformation effects on the microstructure, mechanical characteristics, in vitro degradation behavior, and biocompatibility of Zn‐0.6Li alloy. It is shown that primary α‐Zn and LiZn4 precipitates of as‐extruded Zn‐0.6Li alloy are significantly refined. The dendritic primary α‐Zn is refined into fine equiaxed grains. The eutectic (α‐Zn + LiZn4) lamellar spacing distributed in dendrites are refined from 0.86 ± 0.5 to 0.57 ± 0.4 μm. The extruded Zn‐0.6Li alloy of the yield strength, ultimate tensile strength, and elongation are significantly enhanced, reaching 365, 498 MPa, and 13.55%, respectively. In Hanks’ solution, the electrochemical corrosion rate and immersion corrosion rate of extruded Zn‐0.6Li alloy are 1.479 ± 0.061 and 0.878 ± 0.006 mm year−1. In addition, the cytotoxicity test and CCK‐8 evaluation demonstrate that the extruded Zn‐0.6Li alloy displays a good biocompatibility.

Effect of cooling temperature on microstructure and mechanical properties of Nb microalloyed hot-rolled rebar

In this study, the Gleeble-3800 thermal simulation tester was used to simulate various cooling temperature processes for two groups of rebar. Then, the microstructure, precipitation, and mechanical properties of the rebars were characterized using SEM (scanning electron microscopy), EBSD (electron backscatter diffraction), HRTEM (high resolution transmission electron microscopy), and MST810 (universal tensile testing machine). The effect of cooling temperature on the microstructure and mechanical properties was systematically investigated. The results showed that reducing the cooling temperature from 750 °C to 600 °C decreased the ferrite grain size in 0.032 wt % Nb rebar to 7.03 ± 1.5 μm, compared to the 0 wt% Nb rebar. In addition, the pearlite lamellar spacing was refined to 0.103 ± 0.5 μm, and the average particle size of elliptical Nb-rich composite carbides was 9 nm. The tensile strength and yield strength reached 795 ± 9 MPa and 638 ± 8 MPa, respectively, with an elongation after fracture of 17.78 ± 1.0 %. The fracture surface exhibited a dimple morphology.

Effect of trace niobium on the microstructure and properties of full-pearlite steel used in the high-strength hypereutectoid wire rods

The present study investigated the impact of 20–80 ppm Nb on the microstructure and properties of hypereutectoid pearlite steel. Remarkably, even trace amounts of Nb exhibited a favorable effect on the refinement of austenite grain. The addition of the Nb element resulted in a reduction of pearlite transition temperature, leading to a decrease of approximately 13% in lamellar spacing and 11% in the size of pearlite colonies. Furthermore, the dragging effect of the Nb element on the carbon atoms in hypereutectoid steel facilitated the control and refinement of network carbides. These findings offer valuable theoretical guidance for the production of ultra-high-strength wire rods. When the Nb content reached 80 ppm, it promoted the precipitation of (Ti, V)C, while simultaneously improving the morphology of square carbides. The grain refining strengthening mechanism accounted for about 70% of the overall strengthening effect observed in high carbon wire rods, with the influence of the Nb element primarily targeting grain refinement. Consequently, the incorporation of minute quantities of Nb presents a promising avenue for the development of ultra-high-strength hypereutectoid wire rods, offering significant potential for enhancing their strength properties.

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.

Controllable synthesis of NiCoMo-LDH with nanofloral structure assisted by monodisperse spherical silica for asymmetric supercapacitor

Traditional layered double hydroxides (LDH) have disadvantages such as small layer spacing, insufficient active sites and poor electrical conductivity, which seriously restricts their future utilization in the realm of energy storage. In this paper, a controlled synthesis strategy of tercomponent metal NiCoMo-LDH is proposed by using the structural advantages of metal-organic skeleton (MOF) templates, combining structural regulation and atom doping. On the basis of the synthesis of Ni-MOF 74, Co and Mo atoms are introduced for a small amount of doping, and the monodisperse spherical SiO2 is inserted to adjust the pore structure of NiCoMo-MOF, expand the lamellar spacing, and effectively avoid the accumulation and agglomeration of lamella. Finally, NiCoMo-LDH cathode material with loose porous and coarsely curled nanosphere structure was synthesized through the chemical reaction of OH− with SiO2 and the destruction of the skeleton structure of MOF. The specific capacitance of the material is 1423.3 F·g−1 at 0.5 A·g−1, and after 5000 cycles of charging and discharging, 80.0% of the original specific capacitance is sustained. Moreover, NiCoMo-LDH//AC ASC possesses a high energy density of 39.1 Wh·kg−1 at the power density 400 W·kg−1. Combined with density functional theory (DFT) calculation, the fact that metal doping can not only effectively improve the conductivity of electrode materials has been further proved, but also accelerate the electron/ion migration rate, which successfully reveal the synergistic enhancement mechanism of electrochemical properties of materials.

An integrated exploration from microstructure to mechanics in austenite to pearlite transformation of high carbon steel under high magnetic fields

The effects of a high magnetic field (12 T) on the microstructural evolution and mechanical properties of high carbon steel during isothermal pearlitic transformation at 720 °C were investigated. The application of a high magnetic field effectively promotes pearlitic transformation and leads to a reduction in the lamellar spacing and the geometrically necessary dislocation density (GND) as well as to a slight increase in the grain size of the pearlite, which leads to a decrease in hardness. This is because the magnetic field reduces the magnetic Gibbs energy of ferrite and cementite, resulting in an increase in the driving force of phase transformation, which shortens the pearlite maturation time and reduces the nucleation barriers of pearlite, thereby accelerating the growth rate of pearlite. In addition, the interfacial energy of ferrite/cementite was found to be increased by the magnetic field from the thermodynamic point of view, and the mechanism of action of the magnetic field -induced precipitation of cementite in the form of particles and short rods was elucidated. The present work will enhance the understanding of the mechanism of magnetic field-induced phase transformation in iron-based materials.

Protein Charge Neutralization Is the Proximate Driver Dynamically Tuning Reflectin Assembly.

Reflectin is a cationic, block copolymeric protein that mediates the dynamic fine-tuning of color and brightness of light reflected from nanostructured Bragg reflectors in iridocyte skin cells of squids. In vivo, the neuronally activated phosphorylation of reflectin triggers its assembly, driving osmotic dehydration of the membrane-bounded Bragg lamellae containing the protein to simultaneously shrink the lamellar thickness and spacing while increasing their refractive index contrast, thus tuning the wavelength and increasing the brightness of reflectance. In vitro, we show that the reduction in repulsive net charge of the purified, recombinant reflectin-either (for the first time) by generalized anionic screening with salt or by pH titration-drives a finely tuned, precisely calibrated increase in the size of the resulting multimeric assemblies. The calculated effects of phosphorylation in vivo are consistent with these effects observed in vitro. The precise proportionality between the assembly size and charge neutralization is enabled by the demonstrated rapid dynamic arrest of multimer growth by a continual, equilibrium tuning of the balance between the protein's Coulombic repulsion and short-range interactive forces. The resulting stability of reflectin assemblies with time ensures a reciprocally precise control of the particle number concentration, encoding a precise calibration between the extent of neuronal signaling, osmotic pressure, and the resulting optical changes. The charge regulation of reflectin assembly precisely fine-tunes a colligative property-based nanostructured biological machine. A physical mechanism is proposed.

Formation Mechanism of Eutectic Microstructure for Ca(Zr,Hf)O3/(Zr,Hf)O2 by Rapid Solidification Process at High Temperature

Abstract: Ca(Zr1-x,Hfx)O3/(Zr1-xHfx)O2 (x=0, 1/3, 0.5) eutectic film was prepared by rapid solidification process using high power laser irradiation method. The coating process was performed in an electric furnace at 1300°C. Solidified film with fine lamellar structure were obtained. When the Zr site was substituted with Hf, the lamellar spacing increased with the amount of the substitution. Separate from the solidification film prepared by laser irradiation, rapidly solidifying sample with x=0.1 composition was prepared using optical floating zone apparatus. The melt of the sample was free-fallen onto a copper dish. No film-like rapidly solidified sample was obtained. Hf ion was homogeneously solid-soluble in both phases of CaZrO3 and phase ZrO2.

Pearlite Growth Kinetics in Fe-C-Mn Eutectoid Steels: Quantitative Evaluation of Energy Dissipation at Pearlite Growth Front Via Experimental Approaches

Essential understanding of the pearlite growth kinetics is of great significance to predict the lamellar spacing and the resultant mechanical properties of pearlitic steels. In this study, a series of eutectoid steels with Mn addition up to 2 mass pct were isothermally transformed at various temperatures from 873 K to 973 K to clarify the pearlite growth kinetics and the underlying thermodynamics at its growth front. The microscopic observation indicates the acceleration in pearlite growth rate and refinement in lamellar spacing by decreasing the transformation temperature or the amount of Mn addition. After analyzing the solute distribution at pearlite growth front via three-dimensional atom probe, no macroscopic Mn partitioning across pearlite/austenite interface is detected, whereas Mn segregation is only observed at ferrite/austenite interface. Furthermore, in-situ neutron diffraction measurements performed at elevated temperatures reveal that the magnitude of elastic strain generated during pearlite transformation is very small. Based on the thermodynamic model, these experimental results are used to estimate the contribution of various factors to the total energy dissipation. Compared with the Mn-free alloy, the retardation effect of Mn addition on pearlite growth kinetics, which is partly due to the reduced driving force for pearlite growth, can be well explained by further considering the solute drag effect of Mn.

Inhomogeneous deformation behavior and recrystallization mechanism of Mg-Gd-Y-Zn-Zr alloy containing only intragranular lamellar LPSO phase

Inhomogeneous plastic deformation and recrystallization behavior of Mg-Gd-Y-Zn-Zr alloy containing only intragranular lamellar long-period stacking ordered (LPSO) phase were investigated by isothermal compression experiments at the temperatures of 350–450 °C, and the strain rates of 0.001 ∼ 10 s−1. Results showed that Mg-Gd-Y-Zn-Zr alloys with varying degrees of bimodal structures were obtained after compression. The lamellar LPSO phase directions in residual coarse grains were aligned in the radial direction (RD). Dynamic recrystallization (DRX) grains induced at grain boundaries, kinked bands, and lamellar shearing regions during compression synergistically promoted coarse grain refinement. Moreover, the condition of high temperature and medium strain rate (450 °C-0.1 s−1) contributed to the uniform extension of "mantle layers" of fine DRX grains. In contrast, the condition of medium temperature and high strain rate (400 °C-10 s−1) could accelerate the deflection of CD-directed (compression direction) LPSO lamellae and the formation of local high-energy regions, facilitating the generation of recrystallization band. In addition, a high strain rate (400 °C-10 s−1) is more conducive to the formation of a heavily bimodal structure than a high temperature (450 °C-0.1 s−1). Only a larger spacing of LPSO lamellae (∼1.4 μm) could meet the spatial requirements of recrystallization. Further analysis revealed that the continuous dynamic recrystallization (CDRX) mechanism characterized by the expansion of "mantle layers" and nucleation along kinked boundaries and lamellar shearing regions was the primary grain refinement mechanism. The discontinuous dynamic recrystallization (DDRX) mechanism only exhibited a limited role due to the inhibition of the highly dense lamellar LPSO phase on grain boundaries bulging. After compression, the orientation of residual coarse grains gradually deviated toward the CD. While the recrystallization with limited proportion and random orientation cannot significantly weaken the basal texture.

Formation of lamellar eutectic structure and improved mechanical properties of directional solidified Al0.9CoCrNi2.1 high-entropy alloy

In this study, Al0.9CoCrNi2.1 EHEA was prepared by directional solidification at various withdrawal rates from 6 to 120 μm/s. The lamellar eutectic structure is formed containing FCC (L12) and BCC (B2) at different withdrawal rates during directional solidification. The solid-liquid interface of the alloy transfers from nearly-planer to cellular eutectic interface and the lamellar spacing decreases from 7.17 μm to 1.65 μm as the withdrawal rate increases. The lamellar spacing is negatively correlated with withdrawal rates which was identified by the Jackson-Hunt model and its growth rate index (0.484) is closely related to the theoretical value (0.5). The tensile experiment demonstrates that the structure of Al0.9CoCrNi2.1 EHEA is finer and the ultimate tensile strength and elongation increase as the withdrawal rate increases. The elongation of Al0.9CoCrNi2.1 EHEA is two times higher than that of the as-cast alloy at the withdrawal rate of 120 μm/s. It is concluded that the formation of the L12 phase and Cr-rich precipitated phases in the directional solidified eutectic structure are associated with the enhancement of mechanical properties due to grain refinement at high withdrawal rates.

Analyzing the Effects of Cr and Mo on the Pearlite Formation in Hypereutectoid Steel Using Experiments and Phase Field Numerical Simulations.

In this study, we quantitatively investigate the impact of 1.4 wt.% chromium and 1.4 wt.% molybdenum additions on pearlitic microstructure characteristics in 1 wt.% carbon steels. The study was carried out using a combination of experimental methods and phase field simulations. We utilized MatCalc v5.51 and JMatPro v12 to predict transformation behaviors, and electron microscopy for microstructural examination, focusing on pearlite morphology under varying thermal conditions. Phase field simulations were carried out using MICRESS v7.2 software and, informed by thermodynamic data from MatCalc v5.51 and the literature, were conducted to replicate pearlite formation, demonstrating a good agreement with the experimental observations. In this work, we introduced a semi-automatic reliable microstructural analysis method, quantifying features like lamella dimensions and spacing through image processing by Fiji ImageJ v1.54f. The introduction of Cr resulted in longer, thinner, and more homogeneously distributed cementite lamellae, while Mo led to shorter, thicker lamellae. Phase field simulations accurately predicted these trends and showed that alloying with Cr or Mo increases the density and circularity of the lamellae. Our results demonstrate that Cr stabilizes pearlite formation, promoting a uniform microstructure, whereas Mo affects the morphology without enhancing homogeneity. The phase field model, validated by experimental data, provides insights into the morphological changes induced by these alloying elements, supporting the optimization of steel processing conditions.

Evolution of elliptical SAXS patterns in aligned systems.

Small-angle X-ray and neutron scattering (SAXS and SANS) patterns from certain semicrystalline polymers and liquid crystals contain discrete reflections from ordered assemblies and central diffuse scattering (CDS) from uncorrelated structures. Systems with imperfectly ordered lamellar structures aligned by stretching or by a magnetic field produce four distinct SAXS patterns: two-point 'banana', four-point pattern, four-point 'eyebrow' and four-point 'butterfly'. The peak intensities of the reflections lie not on a layer line, or the arc of a circle, but on an elliptical trajectory. Modeling shows that randomly placed lamellar stacks modified by chain slip and stack rotation or interlamellar shear can create these forms. On deformation, the isotropic CDS becomes an equatorial streak with an oval, diamond or two-bladed propeller shape, which can be analyzed by separation into isotropic and oriented components. The streak has elliptical intensity contours, a natural consequence of the imperfect alignment of the elongated scattering objects. Both equatorial streaks and two- and four-point reflections can be fitted in elliptical coordinates with relatively few parameters. Equatorial streaks can be analyzed to obtain the size and orientation of voids, fibrils or surfaces. Analyses of the lamellar reflection yield lamellar spacing, stack orientation (interlamellar shear) angle α and chain slip angle ϕ, as well as the size distribution of the lamellar stacks. Currently available computational tools allow these microstructural parameters to be rapidly refined.

Revealing the high strength and high thermal stability of a nano-lamellar Cu-0.1 at.% Zr alloy

Nano-lamellar structured Cu-0.1 at.% Zr alloys are prepared by the combination of equal channel angular pressing and subsequent cryogenic rolling. The advanced processing route enables a systematic reduction of the lamellae boundary spacing down to 45 nm and a concurrent increase of yield strength up to 626 MPa. Subsequent annealing at temperatures up to 673 K induced recovery processes and uniform coarsening through triple junction motion, avoiding a catastrophic degradation of the microstructure and performance and preserving the yield strength at a level comparable to ultrafine-grained copper. Simultaneously, the tensile uniform elongation experienced a substantial recovery up to 11.9 %. The high thermal stability is mainly attributed to the low mobility of grain boundary and the relaxation of non-equilibrium grain boundaries, both of which are facilitated by the microalloying of Cu with Zr. Based on the theory of dislocation pile-up at boundaries, the Hall-Petch equation is adopted and extended to the lamellar structured Cu-0.1 at.% Zr alloy, revealing a lower-critical bound of 90 nm for lamellae boundary spacing, corresponding to an effective boundary spacing of about 150 nm.