Crystallographic Evolution Research Articles

Temperature and Pressure Effects on Phase Transitions and Structural Stability in CsPb2Br5 and CsPb2Br4I Perovskite-Derived Halides.

All-inorganic perovskites exhibit outstanding light absorption properties in the visible range suitable for solar energy applications. We focus on the synthesis of CsPb2(Br,I)5 using mechanochemical procedures. Synchrotron X-ray diffraction (SXRD) data are essential for determining the crystallographic evolution in the 295-753 K temperature range. From room temperature to 573 K, the crystal structure is refined in a two-dimensional (2D) tetragonal framework (space group: I4/mcm) consisting of layers of face sharing [Pb(Br,I)8] polyhedra. Above a transition temperature of Tt = 630 and 621 K, identified from differential scanning calorimetry (DSC) curves for CsPb2Br5 and CsPb2Br4I, respectively, a cubic three-dimensional (3D) corner-sharing perovskite structure is identified, showing substantial Cs and (Br,I) deficiency. A more ionic character for Cs-halide versus Pb-halide is derived from the evolution of the anisotropic atomic displacements. An ultralow thermal conductivity of 0.35-0.18 W m-1 K-1 is related to the low Debye temperatures. From high-pressure SXRD studies, the change in B0 can be attributed to a basic expansion of the unit-cell volume caused by the chemical pressure from iodine within the CsPb2Br5 framework. UV-vis-NIR spectroscopy revealed optical gaps of approximately 2.93 and 2.50 eV, respectively, which agrees with ab initio calculations.

Directed energy deposition combined with interlayer remelting for improving NiTi wear resistance by grain refinement

Directed energy deposition of NiTi coatings has received much attention, however, its performance is difficult to meet the increasing requirements in the engineering field. In order to refine the grains to improve wear resistance, a novel interlayer remelting method for fabricating NiTi alloys by directed energy deposition is proposed in this study. The influence of laser interlayer remelting parameters on lattice structure, phase transformation behavior, microstructure, crystallographic evolution, and microhardness was thoroughly analysed in comparison. Good formability is demonstrated after interlayer remelting, while the high energy density leads to microstructure refinement and eutectic regions are observed between dendrites. The grain size decreases with increasing remelting speed, which is due to the faster cooling rate having a greater degree of subcooling with more nucleation points. The faster interlayer remelting speed shows a higher microhardness (586 HV0.2) with higher wear resistance, which is attributed to its finer grain size and significant grain boundary strengthening. Reciprocating sliding wear experiments show that the wear resistance is improved after interlayer remelting, especially at a load of 30 N, the specific wear rate is 1.35 * 10−4mm3/Nm, which is only 47 % of that of the untreated sample. This study proposes a technique to achieve synergistic enhancement of microhardness and sliding wear properties of reinforced coatings, which provides a theoretical basis for the application of NiTi coatings in engineering and extends the field of additive manufacturing.

High temperature evolution of a confined silicon layer

The temperature-induced phase and morphology changes of a thin layer sandwiched between two substrates which it partially wets are investigated using transmission electron microscopy, scanning electron microscopy, and x-ray scattering techniques. For this, SiC wafers were bonded with Si layers of various thicknesses and annealed at temperatures below and above the Si melting point. Below the melting point of Si, solid-state dewetting occurs. It starts with the heterogeneous nucleation of pits at the Si/SiC interfaces and progresses to their partial transformation into voids crossing the whole film. The further growth of voids is accompanied with an increase in the Si film thickness. Final equilibrium is shown to be impacted by Si crystallographic state evolution. Above the Si melting temperature, liquid Si drives SiC interfaces step bunching. When high steps and large terraces are formed over the two SiC surfaces, Si is shown to be trapped within quasi-closed pockets. Eventually, the interface locally closes around these Si inclusions with the creation of SiC/SiC direct contacts. The influence of both annealing temperatures and Si film thickness on all these processes is discussed.

Challenges in Chemical Vapour Deposition of Graphene on Metallurgical Alloys Exemplified for NiTi Shape Memory Alloys

Atomically-thin two-dimensional (2D) materials like graphene have been suggested as ultimately thin corrosion barriers and functional coatings for modern metallurgical alloys. The challenges of chemical vapour deposition (CVD) of such 2D materials, particularly graphene, on modern metallurgical alloys are discussed and reviewed here, focusing on the key problems with the metallurgical alloys’ often limited catalytic activity towards 2D materials growth and the key need to preserve the metallurgical alloys’ bulk properties during the high temperature 2D materials CVD processes. Using graphene CVD on NiTi (Nitinol) shape memory alloys as a case study, we illustrate the constraints arising from low catalytic activity and tendency to form oxides due the Ti in the NiTi alloy in terms of graphene growth results. We show that, by using a scalable low-temperature CVD process at 650 to 750 °C, we can deposit fully covering carbon films on the NiTi, albeit at limited structural quality. Notably, we also demonstrate that our CVD process does not degrade the bulk microstructure of the NiTi during carbon deposition and, importantly, leaves the crystallographic shape memory effect evolution intact. This underscores the potential of CVD for depositing graphene films on NiTi alloys while emphasizing the necessity for further exploration of CVD conditions to achieve high-quality graphene deposits akin to those on prior widely investigated dedicated (often sacrificial) high-purity metal substrates such as Ni.

Comprehensive study of high-temperature calendar aging on cylinder Li-ion battery

Calendar aging at high temperature is tightly correlated to the performance and safety behavior of lithium-ion batteries. However, the mechanism study in this area rarely focuses on multi-level analysis from cell to electrode. Here, a comprehensive study from centimeter-scale to nanometer-scale on high-temperature aged battery is carried out. After short-time high-temperature aging, measurements of electrochemical performance show notable decay of capacity and increase of internal resistance. The thermal safety behavior is studied through accelerating rate calorimeter (ARC), which indicates that the heat output of the aged battery during thermal runaway is largely increased. The aging mechanism of high temperature is investigated under various scales. Incremental capacity (IC) curves depict the deterioration of electrodes and increase of ohmic resistance. Computational Tomography (CT) reveals structure evolution of aged battery at millimeter scale, indicating gas generation after high-temperature aging. Scanning electron microscope (SEM) shows thickened solid-state-electrolyte (SEI) on anode and cracks on cathode at sub-micrometer scale. X-ray diffraction (XRD) patterns present crystallographic evolution of both anode and cathode. Thus, the cell degradation-mechanism after high-temperature aging is interpreted at multi-level, that high temperature induces deterioration of electrodes, formation of SEI and evolution of gas.

Aging Treatment Induces the Preferential Crystallographic Orientation of αs in the Near-α Titanium Alloy Ti60

In this article, we subjected the Ti60 alloy to solid-solution treatment at 1020 °C and aging treatment at 600 °C, respectively, achieving a bimodal microstructure. The microstructures obtained after aging treatment showed no significant difference in the primary α-phase content, size, and width of the lamellar α phase. This suggests that the final microstructure morphology is primarily determined by the solid-solution temperature, with the aging process exerting less pronounced effects on microstructural alterations. Furthermore, we investigated the effect of solid-solution and aging treatment on the crystallographic orientation evolution of the secondary α phase (αs) in the near-α titanium alloy Ti60. The αs phase displays a random orientation in solid-solution treatment sample, while it demonstrated a preferential {0 1 −1 0} orientation after aging treatment. This interesting phenomenon is attributed to the enhanced variant selection resulting from the dissolution of variant near 60° and 90° during aging. Furthermore, the αs with {0 1 −1 0} orientation nucleated at the grain boundary and coalesced into larger αs lath with increasing aging time, further contributing to the αs {0 1 −1 0} texture.

Microstructural studies of CuCrFeNi2Mn0.5 high entropy alloy during cold rolling

A study was conducted to determine the impact of cold rolling on the evolution of the microstructure of the CuCrFeNi2Mn0.5 high entropy alloy. Cold rolling resulted in the development of crystallographic textures and microstructure evolution. It was observed that the main deformation mechanism during cold rolling of the mentioned alloy is the movement of dislocations and the formation of mechanical twins, which lead to the formation of shear bands by increasing the amount of deformation. Microstructural studies suggest that the decrease in the microhardness of cold-rolled samples is caused by the formation of strain-free grains on the shear bands. The development of strain-free grains is aided by the rotation of subgrains on the shear bands.

Combining crystal plasticity and phase field model for predicting texture evolution and the influence of nuclei clustering on recrystallization path kinetics in Ti-alloys

A three-dimensional computational framework has been developed combining a crystal plasticity (CP) and a phase-field (PF) approach that can efficiently simulate static recrystallization (SRX) and grain growth during the hot-forming in Ti-alloys. In the framework, the CP slip system parameters have been accurately calibrated by solving an inverse optimization problem from available experimental tension and compression stress–strain data through CP simulations performed via an orientation distribution function (ODF)-based computational model. Using the CP model, the evolution of inhomogeneous local deformation, deformed texture, and grain dislocation density have been simulated in the plastically deformed polycrystalline Ti-alloys. The PF model then predicts microstructure evolution and kinetics of SRX from CP-informed dislocation density during the annealing phase. Experimental information on microstructural heterogeneity in terms of the initial arrangement of nuclei distribution has been used to guide the development of the framework that can provide deeper insights into unique morphological evolution for various types of grain impingement as well as experimental validation of SRX kinetics. Finally, when the proposed model has been quantitatively validated through experimentally measured texture evolution and SRX path kinetics, excellent agreement is achieved. The current study highlights a systematic modeling framework that is capable of predicting crystallographic texture, microstructural evolution, and kinetics in the course of SRX for a clear understanding of the relationship between the mechanical properties, various microstructural descriptors, and thermo-mechanical process in the regime of material design.

Insights into the kinetics–morphology relationship of 1-, 2-, and 3D TiNb2O7 anodes for Li-ion storage

Understanding the influence of electrode material’s morphology on electrochemical behavior is of great significance for the development of rechargeable batteries, however, such studies are often limited by the inability to precisely control the morphology of electrode materials. Herein, nanostructured titanium niobium oxides (TiNb2O7) with three different morphologies (one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D)) were synthesized via a facile microwave-assisted solvothermal method. The influence of the morphological dimension of TiNb2O7 as electrode material on the electrochemical performance in Li-ion batteries (LIBs) and the underlying correlation with the electrochemical kinetics were studied in detail. 2D TiNb2O7 (TNO-2D) shows a superior rate capability and cycling stability, associated with improved kinetics for charge transfer and Li-ion diffusion, compared to the 1D and 3D materials. Operando X-ray diffraction measurements reveal the structural stability and crystallographic evolution of TNO-2D upon lithiation and delithiation and correlate the Li-ion diffusion kinetics with the lattice evolution during battery charge and discharge. Moreover, carbon-coated TNO-2D achieves enhanced rate capability (205 mAh·g−1 at 50 C) and long-term cycling stability (87% after 1000 cycles at 5 C). This work provides insights into the rational morphology design of electrode materials for accelerated charge transfer and enhanced fast-charging capability, pushing forward the development of electrode materials for high-power rechargeable batteries in future energy storage.

Microstructural mechanisms imparting high strength-ductility synergy in heterogeneous structured as-cast AlCoCrFeNi2.1 eutectic high-entropy alloy

The dual-phase AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) presents a promising solution to the strength-ductility trade-off dilemma, making it a highly desirable option for structural materials with vast potential applications. However, the relationship between the mechanical properties and the unique as-cast heterostructures needs to be further revealed. Here, we conducted in-situ tensile experiments of the as-cast EHEA to unveil the mesoscopic/microscopic microstructural mechanisms of strength-ductility synergy via investigating the dynamic real-time plastic deformation behaviors and crystallographic information evolution, as well as characterizing the deformed microstructures via transmission electron microscopy. The results indicate that the sequential dominant heterogeneous deformation induced hardening resulting from the incompatible plastic deformation between different types of heterogeneous microstructures is the primary source of its remarkable strength-ductility synergy. Moreover, the unique elongated lamellar microstructures of the as-cast EHEA offer numerous phase boundaries, and the growth twins in the face-centered cubic (FCC) phase generate abundant twin boundaries, all of which contribute to boundary strengthening and further enhance the strength and ductility of the as-cast EHEA. Furthermore, abundant cross-slip and dislocation substructures in the FCC phase provide strain hardening for as-cast EHEA, while body-centered cubic phase contributes to the high strength through precipitation hardening. Consequently, the heterostructure induced multiple strengthening mechanisms are responsible for the high strength-ductility synergy in the as-cast EHEA. The present work provides a new perspective to explain the strength-ductility synergy of similar heterogeneous structured alloys.

Simultaneous remediation of Cr and Ni from waste water using efficient Schiff-base resin bis(2-methoxy-1-napthaldehy)-O-phenylene diimine as an adsorbent

In this study, we report the synthesis of a Schiff base, bis(2-methoxy-1-napthaldehy)-o-phenylene diimine (BMNOPhen), and a Schiff-base resin, bis-2-methoxy-1-napthaldehy-o-phenylenediimine (PMBMNOPhen). The materials were characterized via different spectroscopic techniques; CHN analysis, FT-IR, TGA, EDS, SEM, and XRD to analyze the structure and surface morphology and crystallographic evolution of the polymeric resin. The synthesized resin was used for uptake studies with Ni(II) and Cr(VI) ions. The optimum conditions were determined by different parameters used to describe the effects of uptake including initial concentration, temperature, time, and pH through batch adsorption methods. Different functional groups like azomethine, OH, and amine present in the Schiff-based resin structure contain donor N and O atoms which can coordinate cationic metal ions, supported by the active adsorption of chromium(VI) and nickel(II). The isotherm data are informative and useful for calculating and modeling adsorption capacity and exploring the mechanism of removal by the adsorbent Different types of adsorption isotherms like Langmuir, Freundlich, and kinetic studies were used on environmental water samples. The polymeric resin PMBMNOPhen was used for elimination of Cr(VI) and Ni(II) ions in real water samples from different agricultural cities of Sindh (Province of Pakistan) such as Sanghar, Tando-Adam, Kotri, and Jamshoro.

The response of silicon carbide composites to He ion implantation and ramifications for use as a fusion reactor structural material

Silicon carbide fibre–reinforced silicon carbide matrix (SiCf/SiC) composites are desirable in structural nuclear applications due to their low density, high temperature strength and tolerance to energetic radiation. We have subjected two industrial grades of SiCf/SiC to high energy He²⁺ ion irradiation, up to 10,000 appm implanted He at 700 °C, to determine their suitability for blanket structural applications in nuclear fusion. Minor crystallographic evolution is observed following irradiation, with evidence of phase localised stress, intragranular strain, and lattice swelling. This is attributed to vacancy production and subsequent He bubble formation, both intragranular and at grain boundaries.During post-irradiation annealing up to 1300 °C, varying degrees of He bubble evolution are observed, with the Si phase showing the highest level of instability. The fibres appear stable, with no detectable radiation-induced defects. Meanwhile, bubbles in the fibre coating and matrix grains grow and agglomerate. Despite this, no delamination or microcracking is observed.

Ion- and temperature-induced 3-dimensional nanoscale patterning in Ti1-xAlxN deposited by High Power Impulse Magnetron Sputtering

We report on surface-driven self-organization in the TiN-AlN binary system during ion-assisted deposition at elevated temperatures. With an Al:Ti ratio slightly above the boundary of stable cubic growth, various morphologies from single-phase films to highly ordered two-phase films with v-shaped and oblique, striped structures were obtained. The high metal ion fractions and high ion energies obtained by High Power Impulse Magnetron Sputtering result in unique morphologies that are not accessible by conventional magnetron sputtering. A comprehensive structural and chemical analysis of the two-phase films is presented to enlighten the mechanism of phase separation and crystallographic orientation evolution.

The effect of deformation temperature on the microstructure and crystallographic orientation evolution of Ti60 alloy after annealing

The effect of deformation temperatures, 900 °C and 980 °C, on the microstructure and crystallographic orientation evolution of Ti60 alloy with lamellar microstructure had been studied in our previous work. In this paper the characterizations of the microstructure and texture as well as the macrozone evolution after annealing at 1020 °C were studied for samples deformed at the both temperatures with 70% height reduction by optical microscope (OM), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). A fine homogenous bimodal microstructure in terms of morphology and orientation distribution was found in the sample deformed at 900 °C after annealing. In contrast, a sharp textured microstructure with macrozones was also produced after annealing in the sample that had deformation at 980 °C. Moreover, the prior β texture and the primary α texture were analyzed. The formation of the main transformed α texture, <11–20> parallel to compression direction (CD) fiber texture, which was reinforced with an increase in deformation temperature, was found to be related to the <100>//CD β fiber texture and variant selection effected by primary α grains. Finally, the mechanisms by which the macrozones formed for bimodal microstructure are discussed. In this study, a relationship between the microstructure and texture evolution is established to reveal the influence of deformation temperature on the microstructue and crystallographic orientation of Ti60 alloy after annealing.

Tension induced detwinning of hierarchically twinned non-modulated martensite in Ni-Mn-Ga alloys

Detwinning of martensite accounts for the macroscopic deformation in shape memory alloys, yet the corresponding microstructural and crystallographic evolution remains less understood. Here, the detwinning behaviors of hierarchically twinned non-modulated (NM) martensite in a directionally solidified Ni54Mn24Ga22 alloy under uniaxial tension along the <001>A direction of austenite are systematically investigated. Based on the interrupted in-situ EBSD measurements, it is demonstrated that tensile loading leads to the thickening of favorable variants with the <001>NM parallel to the loading direction through intensive detwinning, which follows the route of detwinning of internal nanotwins as well as collective detwinning of internal nanotwins and inter-plate major-major variant pairs. Besides, the internal detwinning is also coupled with the rigid body rotation owing to the constraints of inter-plate boundaries, resulting in the refinements in the inter-plate correlation as the variation of thickness ratio of nanotwins. Consequently, the hierarchically twinned microstructure finally evolves into a single-variant state with the <001>NM along the loading direction. This work provides clear demonstrations on the detwinning behaviors of hierarchically twinned NM martensite induced by tensile loading, which allows us to gain deep crystallographic insights into the stress-induced rearrangement of martensite variants in association with the macroscopic deformation.

Effect of torsional deformation on crystallographic evolution of carbide-free nano-bainitic steels prepared at two different austempering temperatures

The current study investigates the nature and extent of crystallographic change after torsional deformation in nano-structured bainite. This is extremely useful as nano-structured bainite is not stable under mechanical deformation and the evolved structure under torsion is finally going to determine other mechanical responses like fracture and fatigue. Two blocks of nano-bainitic steels were prepared after austenitization at 950°C and austempering at 250°C (NB250) and 350°C (NB350) respectively. It was found that there was a decrease in the bainitic ferrite (BF) and retained austenite (RA) length scale with a reduction in austempering temperature along with reduction in the RA content. Specimens from the undeformed two blocks (NB250-UD and NB350-UD) were subjected to torsional deformation till failure (NB250-T and NB350-T) and the crystallographic characteristics of the torsion-tested and undeformed specimens were obtained using electron back-scattered diffraction (EBSD). The orientation relationship (OR) between BF and RA for NB250-UD and NB350-UD was close to Kurdjumov-Sachs (K-S) which changed to predominantly Nishiyama Wassermann (NW) after torsion deformation (NB250-T and NB350-T). Significant refinement in packet and block was observed as a result of torsional deformation. Variant selection was stricter for NB350-UD than NB250-UD but torsional deformation led to weakening of variant selection. The extent of lowest misorientation V1-V4 variant pairing was higher for NB350-UD but it did not change much with torsion in case of NB250-T whereas NB350-T displayed a reduction. Fractography revealed that the dimple size corresponded to block size range between the undeformed and torsion-tested sample for the respective austempering condition.

Hardness enhancement mechanism of AlxCoCrFeNiSi high-entropy alloy coatings prepared by laser cladding

In the present work, AlxCoCrFeNiSi high-entropy alloy coatings with Al content of 0.3 and 1.0 were prepared by laser cladding technology. The microstructure and crystallographic structure evolution, hardness, and strengthening mechanisms were systematically investigated. The coherent interface between the BCC phase and Al–Ni nano-precipitate was confirmed by TEM analysis. Al0.3 coating exhibited a greater dislocation density and lots of sub-grain structures with grain boundary misorientation of less than 2.5°. The average grain size decreased from 29.94 μm to 20.05 μm with the increase of Al from 0.3 to 1.0. Dislocation strengthening and solid solution strengthening were the major strengthening mechanisms for Al0.3 coating resulting in a hardness of 692 HV0.2, while solid solution strengthening and fine-grain strengthening were the strengthening mechanisms for Al1.0 coating with a hardness up to 711 HV0.2.

Microstructural, crystallographic, and mechanical characteristics in Ni-Mn-Ga alloys directionally solidified under a transverse magnetic field

• Magnetic field-assisted directional solidification (MFADS) can control structure. • Macro-/micro-segregation and orientation can be adjusted by MFADS. • Microsegregation-induced microstructure influences mechanical properties. • Stress-induced crystallographic evolution is traced by in-situ EBSD. Abstract In this study, the effect of transverse magnetic field-assisted directional solidification (MFADS) on the microstructures in Ni-Mn-Ga alloys has been investigated. The results show that the magnetic field is capable of inducing transversal macrosegregation perpendicular to the magnetic field, causing the emergence of martensite clusters in the austenite matrix. Moreover, the magnetic field alleviates the microsegregation on a dendritic scale and promotes the preferred growth of austenite dendrites. On the basis of the above investigation, several special samples are designed using the MFADS to study the crystallographic evolution and mechanical behavior during thermal/stress-induced martensite transformation. The martensite cluster in the austenite matrix is used to investigate the martensite transformation and growth under cooling-heating cycles. The crystallographic relationship and phase boundary microstructure between martensite and austenite have been characterized. In addition, the microsegregation on a dendritic scale can significantly influence the martensite variant distribution, corresponding to the performance during compressive circles based on the analysis of the deformation gradient tensor. The stress-induced superelasticity is closely dependent on orientation, well explained from the perspective of different resolved shear stress factors and correspondence variant pair formation transformation strain. The crystallographic evolution has been characterized during in-situ stress-induced transformation. The findings not only deepen the understanding of martensite transformation and mechanical behavior under a thermal/stress field in Ni-Mn-Ga alloys but also propose a promising strategy to obtain microstructure-controllable functional alloys by MFADS.

Twinned dendrites growth in wire arc directed energy deposition of Al-Zn-Mg-Cu alloy

Twinned dendrites have attracted worldwide attention in the past half century due to their unusual orientation and crystallographic symmetry. Successive research has established a basic understanding of them in relatively steady processes like direct chill casting and directional solidification. This work, for the first time, investigated the growth behaviors of twinned dendrites in the wire arc directed energy deposition. The crystallographic characteristics, formation, and evolution laws of the twinned dendrites in the unsteady localized solidification condition are explored via experiments and numerical simulations. Results show that stacking faults are vital in the longitudinal growth of twinned dendrites by adjusting intermittent twin boundaries. During deposition, Mg, Zn, and Cu, which have low stacking fault energy, can promote the growth of twinned dendrites. The molten pool tail has large temperature gradients, crystallization velocities, and sufficient convection, providing advantageous growth conditions for twinned dendrites. Competitive relationships form between twinned and regular dendrites at the molten pool center. However, the twinned dendrites also cooperate with regular dendrites in epitaxial growth via their 〈100〉 lateral branch. With the remelting depth increasing, the twinned dendrite morphology changes from lamellar to isolated unilateral feather shape, then to unchained islands, and finally disappear.

Phase transformations and thermal expansion coefficients of unirradiated U-X wt.% Zr (X = 6, 10, 20, 30) measured via neutron diffraction

This work characterizes the crystallographic evolution of unirradiated U-X wt.% Zr (X = 6, 10, 20, 30) while cooling from equilibration, single phase γ-U-Zr, at 900 °C to ambient temperature using time-of-flight neutron diffraction. The β-U phase was unobserved during cooling at 1 °C/min in all alloys. All alloys followed the phase transformation pathway of γ-U-Zr→γ-U-Zr+α-U→α-U +δ-UZr2 with an observed miscibility gap in γ-U-Zr. The α-U and δ-UZr2 transformation took place simultaneously in the U-30 wt.% Zr sample. These findings strengthen the need to re-approach the U-Zr phase diagram in entirety. Bulk volumetric CTEs agree well with published data, strengthening the quantification of lattice-specific CTEs reported in this study. A compositionally dependent discontinuity in thermal expansion, increasing in magnitude with decreasing U content, occurs during the γ-U-Zr→α-U+δ-UZr2 transformation. The γ-U-Zr lattice parameter was measured to have a compositional dependency.