Boundary Composition Research Articles

Influence of grain boundary segregation on the deformation behavior of nanocrystalline Ni50Co50 solid solution alloys investigated by molecular dynamics simulations

Molecular dynamics simulations were carried out to investigate the tensile deformation behavior of Ni50Co50 solid solution nanocrystalline alloys with varying degrees of grain boundary segregation. A comprehensive analysis disclosed that the observed strengthening in the Ni-rich grain boundary model is primarily due to the formation of Lomer-Cottrell locks and dislocation networks which impede dislocation motion. Plastic deformation, on the other hand, is predominantly governed by enhanced grain boundary migration, grain rotation, and deformation twinning. In the Co-rich grain boundary model, the interactions among twins, dislocations, and grain boundaries, stemming from the formation of extensive stacking faults and twinning, dictate the plastic deformation and strengthening. Fluctuations in grain boundary composition promote stress concentration, thereby facilitating plastic deformation and dislocation accumulation within the grain, which in turn enhances strain hardening. The study reveals that the Ni50Co50 solid solution nanocrystalline alloys exhibit both high tensile strength and favorable plasticity for models with grain boundary segregation around ±10%. These insights provide valuable guidance for the development of Ni50Co50 nanocrystalline alloys with optimized strength and toughness.

Synergistic contributions of the poling field-induced changes in local structure on the piezoelectric properties of modified BaTiO3 system

Abstract Local structural heterogeneity is a key factor in improving the piezoelectric properties of non-centrosymmetric piezoelectric systems. This work investigates electric field-induced structural and microstructural changes at localized and average scales to elucidate the structure-property correlations that enhance piezoelectric performance in Sn-doped BaTiO3 systems exhibiting coexisting phase boundaries. Despite showing field-induced structural phase transformation, the sample displays variations in piezocoefficient values with the nature of phase boundary compositions. Raman spectroscopy measurements reveal that the TiO6/SnO6 octahedra near the tetragonal-orthorhombic phase boundary exhibit significantly greater poling field-induced structural heterogeneities in local structure compared to those near the orthorhombic-cubic phase boundary. X-ray absorption spectroscopic results on Ti and Sn K-edge in unpoled and poled samples reveal that the dipolar contribution responsible for the piezoelectricity originates from field-induced distortion associated with both TiO6 and SnO6 octahedra. Near the vicinity of the tetragonal-orthorhombic phase boundary, both the TiO6 and SnO6 contributions are cumulative and exhibit better piezoelectricity. On the other hand, at the orthorhombic-cubic phase boundary, the dipolar contributions from these octahedra are counterintuitive, resulting in a reduction of piezoelectricity. These results could provide a pathway to design materials with an enhanced piezoelectric response by considering various phase boundary aspects before applying a poling field prior to making them piezoactive.

Optimization of Parameters for Atom Probe Tomography Analysis of β-Tricalcium Phosphates.

The biocompatibility and resorption characteristics of β-tricalcium phosphate (β-TCP, Ca3(PO4)2) have made it a coveted alternative for bone grafts. However, the underlying mechanisms governing the biological interactions between β-tricalcium phosphate and osteoclasts remain elusive. It has been speculated that the composition at grain boundaries might vary and affect β-TCP resorption properties. Atom probe tomography (APT) offers a quantitative approach to assess the composition of the grain boundaries, and thus advance our comprehension of the biological responses within the microstructure and chemical composition at the nanoscale. The precise quantitative analysis of chemical composition remains a notable challenge in APT, primarily due to the influence of measurement conditions on compositional accuracy. In this study, we investigated the impact of laser pulse energy on the composition of β-TCP using APT, aiming for the most precise Ca:P ratio and consistent results across multiple analyses performed with different sets of analysis conditions and on two different instruments.

Influence of Grain Size on the Electrochemical Performance of Li7‐3xLa3Zr2AlxO12 Solid Electrolyte

AbstractContemporary Li‐ion batteries are facing substantial challenges like safety and limited energy density. The development of all‐solid‐state battery cells mitigates safety hazards and allows the use of Li‐metal anodes increasing energy density. Garnet‐type solid electrolytes can be vital to achieving an all‐solid‐state cell and an understanding of the influence of its microstructure on the electrochemical performance is crucial for material and cell design. In this work the influence of grain size on the Li‐ion conductivity of Li7‐3xLa3Zr2AlxO12 (x=0.22) is presented. The synthesis and processing procedure allows changing the ceramic grain size, while maintaining the same synthesis parameters, eliminating influences of the synthesis on grain boundary composition. Field assisted sintering technology is a powerful method to obtain dense, fine‐grained ceramics with an optimal grain size of 2–3 μm, where the conductivity is double that of the counterpart (0.7 μm). A total Li‐ion conductivity of 0.43 mS cm−1 and an activation energy of 0.36 eV were achieved. The oxide‐based all‐solid‐state battery cell combining the garnet‐type electrolyte, a Li‐metal anode and a thin‐film LiCoO2 cathode was assembled and cycled at room temperature for 90 hours. This represents a proof of concept, for the application of oxide‐based electrolytes at ambient temperatures.

Morphotropic phase boundary composition PNN-PZT ceramics and their outstanding electromechanical properties

xPb(Ni1/3Nb2/3)O3-(1-x)Pb(Zr,Ti)O3 (x = 0.12, 0.24, 0.36, 0.42, 0.55 and 0.64) ceramics were prepared using conventional solid-state reaction. The morphotropic phase boundary (MPB) composition region, sintering characteristics and performance parameters of ceramic samples with different PNN compositions were studied. The phase structure, microstructure and electrical properties were characterized in detail. The results show that the Curie temperature (TC) of PNN-PZT ceramics decreases from 324 °C to 44 °C while the piezoelectric coefficient (d33) changes from 43 pC/N to 1170 pC/N with PNN content from 0.12 to 0.64. Interesting phenomena were observed, which can provide useful information for practical applications of PNN-PZT ceramics.

Theoretical Prediction of Strengthening in Nanocrystalline Cu with Multi-Element Grain Boundary Segregation Decoration.

The composition of grain boundaries (GBs) determines their mechanical behavior, which in turn affects the mechanical properties of nanocrystalline materials. Inspired by GB segregation and the concept of high-entropy alloys (HEAs), we investigated, respectively, the mechanical responses of nanocrystalline Cu samples with and without multi-element GBs, as well as the grain size effects, aiming to explore the effects of GB composition decoration on mechanical properties. Our results show that introducing multi-element segregation GBs can significantly improve the mechanical properties of nanocrystalline Cu by effectively inhibiting GB migration and sliding. Additionally, we proposed an improved a theoretical model that can reasonably describe the strengths of the materials with multi-element or single-element segregation GBs. Notably, the introduction of multi-element segregation GBs inhibits both migration and sliding behavior, with migration being more effectively suppressed than sliding. These results present a novel approach for designing high-performance nanometallic materials and offer valuable insights into the role of GB composition decoration in enhancing mechanical properties.

LiNbO3-induced phase structure evolution and improved piezoelectric properties in BiFeO3–BaTiO3 ceramics

Eco-friendly (0.73-x)Bi1.05FeO3-xLiNbO3-0.27BaTiO3 ternary ceramics were designed and prepared via a solid-state sintering route. Based on the X-ray diffraction results and Rietveld refinement, it was found that the structure of the ceramics transformed from rhombohedral to tetragonal symmetry with the addition of LiNbO3, and at x = 0.003, there existed a morphotropic phase boundary separating the two phases. Near the phase boundary, the largest values were achieved for the piezoelectric constant d33 and planar electromechanical coupling coefficient kp, being 180 pC/N and 0.27, respectively. Due to the addition of LiNbO3, the grain size tended to become smaller. Additionally, the ceramics were transitioned from normal to relaxor ferroelectrics with increasing x. Despite the fact that the LiNbO3 addition would result in a gradual decrease of Curie temperature, a relatively high Curie temperature (535 °C) was still maintained at x = 0.003, the phase boundary composition, which also showed good temperature stability of piezoelectric properties. These experimental results can provide a reference for the practical applications of high-temperature lead-free ceramics.

Investigation of Dielectric Properties of Quaternary Ceramic 0.47BNT-0.04BT-0.37PMN-0.18PT

Dielectric dispersion analysis has been carried out for the first time on a new quaternary ceramic [0.47(Bi0.5Na0.5)TiO3-0.04BaTiO3-0.31Pb(Mg1/3Nb2/3)O3-0.18PbTiO3] having a morphotropic phase boundary composition. The measurement of the dielectric parameters has been carried out in the frequency range of 200 Hz to 2 MHz and temperature range from 30 oC to 300 oC. The material showed high dielectric constant, low dielectric loss, negligible DC conductivity and high ferroelectric to paraelectric transition temperature. A clear Debye type relaxation was observed in the dielectric constant and dielectric loss data. An interesting feature of two Debye peaks has been noticed in dielectric loss versus frequency curves in the temperature range 125 oC to 175 oC. These peaks shift towards higher frequencies when temperature is increased. The extracted relaxation times of the two peaks are three orders of magnitude different and have been found to follow the Arrhenius law with significantly different activation energies.

Effects of Co on the microstructure evolution and mechanical properties of Ti-4Al-6Cr-5Mo-8 Nb alloy by ultrasonic vacuum melting

An investigation was conducted into the impact of low cobalt content on the microstructure and mechanical properties of titanium alloys. Ti-4Al-6Cr-5Mo-8 Nb-xCo (x = 0, 2, 3, 4, and 5) alloys were prepared by ultrasonic-assisted melting and casting. The changes in microstructure, mechanical properties, and the strengthening and toughening mechanisms were researched. Results show that, when the cobalt content increases from 0 to 5 wt%, the as-cast structure is all β phase. The lattice parameter of the β phase decreases from 0.3663 to 0.3114 nm, a 15% decrease. The size of primary β grains decreases from 676.8 to 310.7 μm, a 54% decrease. When the cobalt content exceeds 3 wt%, the segregation energy of cobalt increases and grain boundary segregation occurs. Grain refinement is due to constitutional supercooling caused by the β-stable element cobalt, as well as the solute drag caused by the differences in intragranular and grain boundary compositions. In addition, the size mismatch between cobalt and titanium atoms leads to lattice distortion. As the cobalt content increases from 0 to 3 wt%, the tensile strength increases from 918.1 to 1147.8 MPa, a 25% increase, while the fracture toughness increases from 51.7 to 59.7 MPa·m1/2, a 15% increase. At 5 wt% cobalt, the tensile strength and fracture toughness diminished to 247.5 MPa and 14.8 MPa·m1/2, respectively. The decrease in lattice parameters mainly lead to an increase in strength. The secondary crack leads to an increase in toughness. The decline in strength and toughness results from cobalt segregating at grain boundaries, leading to embrittlement.

Tuning the electrical conductivity and Maxwell-Wagner relaxation in BiFeO3–BaTiO3 piezoceramics

Recent research has emphasized the investigation of BiFeO3–BaTiO3 (BFO–BT) piezoelectric ceramics due to their elevated Curie temperature. Nevertheless, the substantial electrical conductivity of these ceramics poses practical challenges. This study evaluates the influence of post-annealing and manganese (Mn) doping on the conductivity, dielectric behavior, and ferroelectric properties of (1-x)BFO–xBT ceramics with a morphotropic phase boundary composition (x = 0.33). The results demonstrate that the conductivity of the ceramics in the as-sintered state is affected by Maxwell-Wagner effects arising from variations in conductivity at grain boundaries. Annealing under specific atmospheres indicates that the electrical conductivity is of the p-type, potentially associated with Fe4+ defects. Furthermore, annealing in a carefully controlled atmosphere or the introduction of Mn doping significantly alleviate these effects, leading to an enhancement in domain switching characteristics. The insights garnered from this investigation regarding annealing and doping have the potential to advance lead-free BFO–BT piezoelectric ceramics.

In-situ Li2O-atmosphere assisted solvent-free route to produce highly conductive Li7La3Zr2O12 solid electrolyte

Solid-state batteries have garnered attention due to their potentiality for increasing energy density and enhanced safety. One of the most promising solid electrolytes is garnet-type Li7La3Zr2O12 (LLZO) ceramic electrolyte because of its high conductivity and ease of manufacture in ambient air. The complex gas-liquid-solid sintering mechanism makes it difficult to prepare LLZO with excellent performance and high consistency. In this study, an in-situ Li2O-atmosphere assisted solvent-free route is developed for producing the LLZO ceramics. First, the lithium-rich additive Li6Zr2O7 (LiZO) is applied to in-situ supply Li2O atmosphere at grain boundaries, where its decomposition products (Li2ZrO3) build the bridge between the grain boundaries. Second, comparisons were studied between the effects of dry and wet routes on the crystallinity, surface contamination, and particle size of calcined powders and sintered ceramics. Third, by analyzing the grain boundary composition and the evolution of ceramic microstructure, the impacts of dry and wet routes and lithium-rich additive LiZO on the ceramic sintering process were studied in detail to elucidate the sintering behavior and mechanism. Lastly, exemplary Nb-doped LLZO pellets with 2 wt% LiZO additives sintered at 1,300 °C × 1 min deliver Li+ conductivities of 8.39 × 10-4 S cm-1 at 25 °C, relative densities of 96.8%, and ultra-high consistency. It is believed that our route sheds light on preparing high-performance LLZO ceramics for solid-state batteries.

A grain boundary model of metamorphic reaction

A model is presented whereby metamorphic parageneses are governed by local, nano-scale reactions among adjacent phases along grain boundaries that are driven by local disequilibrium between the solid phases and the grain boundary composition. These reactions modify the grain boundary composition setting up compositional gradients that drive diffusion and change the grain boundary composition elsewhere in the rock, which drive local reactions in these locations. The process may be triggered by the nucleation of a new phase that is out of equilibrium with the existing assemblage and an example is presented based on the transformation of kyanite (Ky) to sillimanite (Sil). Model results reveal that a simple polymorphic transformation (Ky→Sil) can result in local reactions among all phases in the rock and some phases may grow in one locale and be consumed in another. An implication of these results is that interpretation of metamorphic parageneses based on growth or resorption and compositional changes of phases requires careful evaluation of nano-scale processes.

Optical properties of crystalline materials based on AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems

For the development of optical technologies aimed at research, diagnostics and operation in a wide spectral range, the creation of new materials capable of being highly transparent and effective for transmitting electromagnetic waves in the visible, IR and THz regions is required. This article studies the properties of single crystals and two-phase ceramics based on solid solutions of the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems. The materials showed transparency in the range of 0.4–60.0 and 350–1500 μm (0.20–0.86 THz). With an increase in the proportion of thallium halides in the AgCl0.25Br0.75 solid solutions, a shift and the transmission spectrum broadening to longer wavelengths was observed. These effects are typical for compounds with both Fm3m and Pm3 m type cubic crystal lattice. The refractive indices of the developed materials have normal wavelength dispersion and vary from 2.107 to 2.539 depending on the system and composition. The indicators for solid solutions with an intermediate composition of homogeneity regions lie within the values characteristic of boundary compositions. Based on this data a description of the index dependence by the Sellmeier equation, adapted by Fleming, was obtained. The refractive indices imaginary parts of all developed materials were 0.11*10−4–3.55*10−4, which was 2–4 times lower in comparison with other substances based on silver and thallium halides. The materials were characterized by a photostability improvement with an increase in the part of thallium halides in the solid solution, as well as with a growth in the amount of the orthorhombic phase in the case of two-phase ceramics. The materials showed low values of optical losses, as well as high functional properties. This makes single crystals and ceramics promising for transmission and fiber optics designed to operate in a wide spectral range.

A new approach to design advanced superalloys for additive manufacturing

A novel approach centered on a high Ta/Al ratio and a significant dependence on the boundary composition addressed the challenges in the manufacturability and material performance of additive-manufactured nickel (Ni)-based superalloys. This approach integrated alloy composition, defect management, and mechanical behavior considerations. This study investigated the impact of this approach on microstructural characterization, solidification behavior, elemental microsegregation, and precipitation, demonstrating its efficacy in crack resistance and performance enhancement. Ultimately, this approach facilitated the successful design of a crack-free Ni-based superalloy, ZGH451–1, featuring a high γ′-phase content. Extensive comparisons of mechanical properties, including tensile and creep tests, against reported AM-ed superalloys and partially heat-treated first-generation Ni-based single-crystal superalloys validated the superior mechanical properties and processability of the newly designed alloy. The rationality and feasibility of this approach for achieving collaborative optimization of properties and formability were demonstrated, paving the way for the design of new high-performance superalloys suitable for additive manufacturing.

Thermal transformation arrest austenite in Ni-Co-Mn-In alloys within the martensite/strain-glass phase boundary

Thermal transformation arrest austenite is a remarkable phenomenon observed in alloys in which the martensitic transition is suppressed during the field cooling process, and austenite is reserved at low temperatures upon subsequent withdrawing magnetic field. Recent studies showed that thermal transformation arrest austenite is a special frozen state of strain glass, which only occurs in the martensitic/strain-glass phase boundary composition with a two-step transition. However, this phenomenon has just been verified in the Ni-Co-Mn-Sn system, and whether it is equally effective for other systems needs to be detected. To verify this viewpoint, the phase transforming properties of Ni45Co5Mn50-xInx (x = 13.3∼13.75) alloys are explored. We found that Ni45Co5Mn36.5In13.5 undergoes a two-step transition and exhibits thermal transformation arrest austenite behavior. Our experimental results show that thermal transformation arrest austenite is exclusively observed within the phase boundary in Ni45Co5Mn50-xInx system and provide valuable insights into the peculiar transformation behaviors in this system.

Comprehensive Study on the Age-Strengthened Mg-Zn-Mn-Ca/ZnO Composites for Fracture Fixation: Microstructure, Mechanical, and In Vitro Biocompatibility Evaluation.

The present work investigates the use of age-strengthened Mg-Zn-Mn-Ca/xZnO as resorbable materials in temporary orthopedic implants. Quaternary Mg-Zn-Mn-Ca alloy, reinforced with zinc oxide particles, was stir-cast, followed by solution treatment and a range of aging treatments. Optical and electron microscopy, mechanical, electrochemical, immersion, and dynamic mechanical testing, with biocompatibility assessment were carried out. The observed 2θ shift in the (101) peaks of ZMX611/ZnO-ST and ZMX611/ZnO-H indicated lattice shrinkage. The formation of Mg7Zn3 and Ca2Mg6Zn3 in the grain boundary compositions was observed. ZMX611/ZnO-ST had a smaller β-phase fraction, indicating a finer microstructure. ZMX611/ZnO-H had the highest tensile yield strength (102.97 ± 3.92 MPa), and ZMX611/ZnO-ST showed the highest ultimate tensile strength (127.21 ± 7.48 MPa), indicating precipitation hardening of Zn enrichment. The uniformly dispersed secondary phases played a dual role in corrosion behavior. ZMX611/ZnO-ST showed a better cytocompatibility response among all samples. Composite materials exhibited satisfactory biocompatibility and mechanical compatibility as indicated by in silico results of deviatoric strain-based mechanical stimuli at the fracture interface.

Revealing the characteristic aroma and boundary compositions of five pig breeds based on HS-SPME/GC-O-MS, aroma recombination and omission experiments

To clarify the characteristic aroma compounds and flavor discrepancies of five Chinese typical pig species, headspace-solid phase microextraction gas chromatography–olfactometry-mass spectrometry (HS-SPME/GC-O-MS), electronic nose (E-nose), aroma recombination and omission experiments were used to analyze the characteristic aroma and boundary of five boiled pork. A total of 38 volatile compounds were identified, of which 14 were identified as important odorants with odor-activity values (OAVs) greater than 1. Aroma recombination and omission experiments revealed 8 key characteristic aroma compounds, which significantly contributed to the overall aroma. Sensory evaluation of the recombination model with the 8 aroma compounds scored 3.0 to 4.0 out of 5 points. 12 potential markers were identified to distinguish by principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA), including (E)-2-octenal, 3-ethyl-2-methyl-1,3-hexadiene, (E)-2-heptenal, 2-pentylfuran, cyclooctanol, 1-heptanol, sec-butylamine, D-limonene, N-vinylformamide, 2,3-octanedione, 2-ethylfuran and 3-pentanamine. Alongside benzaldehyde and pentanal, the combinations and fluctuations of these 14 aroma markers were proposed to constitute the aroma boundaries of different pork breeds. The aroma-active substances were able to effectively differentiate different breeds.

Ordering by cation replacement in the system Na2-xLixGa7.

Samples of the pseudo-binary system Na2-xLixGa7 (x ≤ 1) were synthesized from the elements at 300 °C in sealed Ta ampoules or by the reaction of Na2Ga7 with LiCl. The peritectic formation temperature decreases with increasing Li content from 501(2) °C (x = 0) to 489(2) °C (x = 1). The boundary compositions Na2Ga7 and Na1Li1Ga7 crystallize with different structure types related by a group-subgroup relation. While the Na-rich compositions (x ≤ 0.5) represent a substitutional solid solution (space group Pnma), the Li-rich compositions feature an unconventional replacement mechanism in which Li atoms occupying interstitial positions induce vancancies at the Na positions (space group Cmce). The crystal structure of Na1Li1Ga7 (a = 8.562(1) Å, b = 14.822(2) Å, c = 11.454(2) Å; Z = 8) was determined from X-ray single-crystal diffraction data, and reveals an anionic framework comprising 12-bonded Ga12 icosahedra and 4-bonded Ga atoms, with alkali-metal atoms occupying channels and cavities. The arrangement of cations makes NaLiGa7 a new structure type within the MgB12Si2 structure family. Band structure calculations for the composition NaLiGa7 predict semiconducting behavior consistent with the balance [Na+]2[Li+]2[(Ga12)2-][Ga-]2, considering closo Wade clusters [(12b)Ga12]2- and Zintl anions [(4b)Ga]-. Susceptibility measurements indicate temperature-independent diamagnetic behavior.

Effects of Matrix and Dendrite Boundary Composition on Stress Corrosion Cracking Performance of Alloy 52M Buttering Layer in Simulated Pressurized Water Reactor Primary Water

The oxidation and stress corrosion cracking (SCC) behaviors of Alloy 52M buttering (52Mb) layer were studied in simulated pressurized water reactor (PWR) primary water after microstructure characterization. The 52Mb layer was first postweld heat treatment (1st-PWHT) and follow-up PWHT (FU-PWHT). Two dilution zones (DZs) were found in both the 1st-PWHT and FU-PWHT 52Mb samples. FU-PWHT decreased the Cr content in the first DZ, enhancing the oxidation rate and accelerating the formation of the local oxidation penetration zone at the oxide/substrate interface. Lower Cr content and high Fe content in the DZ were detrimental to the SCC resistance of the 52Mb in PWR primary water.

Piezoelectric, ferroelectric and dielectric characterizations of a new ceramic solid solution (1-x)Ba(Cu1/3Nb2/3)O3-xPbTiO3 with morphotropic phase boundary

The understanding of structure-property co-relations is a key to utilising the materials for their best performances. This paper focuses on the physical property characterization of a new binary solid solution series with formula (1-x)Ba(Cu1/3Nb2/3)O3-xPbTiO3. A unique type of crystal structure evolution as a function of composition has been observed for this solid solution series, where a two-phase coexistence is observed in a very large span of compositions at room temperatures. The microstructure, piezoelectric, ferroelectric and dielectric properties along with their entanglement with crystal structure, have been investigated in detail. The compositional homogeneity of selected compositions has been verified with EDS and XPS. The higher responses in the physical properties have been observed near morphotropic phase boundary compositions. On heating above room temperature, peaks in dielectric permittivity responses have been observed that correspond to the phase transitions of non-centrosymmetric phases. The solid solution's best piezoelectric and ferroelectric responses are observed for the x = 0.70 composition showing higher densification, larger grain size and low dielectric losses, and lies near the morphotropic phase boundary region. The solid solution has enormous potential in piezoelectric industries as it possesses morphotropic phase boundary and high-temperature piezoelectricity.