High Interfacial Energy Research Articles

Creep lifetime and microstructure evolution in boron-added 9Cr–1Mo heat-resistant steel

The relationship between creep lifetime and microstructure, especially precipitate morphology, of a new 9Cr heat-resistant steel containing 0.011 wt% boron was examined. The B-added steel showed superior creep lifetime compared to conventional Gr. 91 steel due to the microstructural stability of the new steel at 873 K. The new steel also exhibited prior-austenite grain boundaries with a high coverage of precipitates, which increased from ~30% to ~40% during creep tests, whereas that of the conventional Gr. 91 steel was nearly stable, at ~25%. In addition, the B-containing M23C6 in the B-added steel had a lower coherency, i.e., a higher interface energy, between the precipitate and the matrix when compared to conventional Gr, 91 steel. These factors led to a higher pinning pressure to resist interface migration in the B-added steel. Microscopy revealed that chemical stabilization had a significant effect on the coarsening behavior of M23C6. Chemical analyses revealed that M23C6 became Cr-rich during the early stages of creep, in which rapid coarsening was observed at a rate contrast of >1.0 × 10−28 m3/s; in this state, M23C6 was approaching equilibrium Cr concentration. In later stages of creep, moderate coarsening occurred with a rate constant of ~8.1 × 10−30 m3/s; in this state, chemical stability was achieved but diffusion and dissolution of small precipitates were dominant.

Heat input, intermetallic compounds and mechanical properties of Al/steel cold metal transfer joints

Cold metal transfer welding/brazing of AA5754 aluminum alloy and Q235 low carbon steel was performed in a lap joint configuration using an AlSi12 filler wire. The effect of heat input on intermetallic compounds (IMC) formations and mechanical properties has been investigated. At a low heat input of 157 J/mm, a layer of IMC, with a composition of Al7.2Fe1.8Si was generated at the fusion zone/steel interface. Low interfacial energy and good interfacial bonding between fusion zone and Al7.2Fe1.8Si led increased joint strength. An additional Fe(Al,Si)3 IMC formed at the interface in conjunction to Al7.2Fe1.8Si at a high heat input of 201 J/mm. The joint strength was significantly decreased and attributed to a high interfacial energy and poor interfacial bonding between Al7.2Fe1.8Si and Fe(Al,Si)3. The results showed that the interfacial energy at interphase boundaries had remarkable effect on the joint strength.

Laser nanocomposites-reinforcing/manufacturing of SLM 18Ni300 alloy under aging treatment

Selective laser melting (SLM) is an additive manufacturing technology which can be used to explore the near-net shaping of large components and net shaping of small complex structures. In this study, the microstructures and mechanical properties of SLM 18Ni300 alloy with variations of the aging time/temperature were investigated in details. Experimental results indicated that the tensile strength and micro-hardness of the SLM 18Ni300 alloy were increased due to the precipitations of the intermetallics during an aging treatment. When the aging temperature was 490 °C, the tensile strength of SLM 18Ni300 alloy increased significantly with the aging time prolong free of the softening, but the elongation decreased continuously. In order to improve the surface performance of SLM 18Ni300 alloy substrate, the mixed powders of NiCoCrAlY-SiC-Mo-Cu were deposited on the substrate (1 h, 520 °C aging treatment) by mean of a laser cladding (LC) technique. The production of the nanostuctured composites led its melting point to decrease, so the high interface energy of NPs became the driving force of the atomic motions, favoring a compact structure to be formed. Identification of the synthetic nanoscale particles (NPs) in such LC composites contributes theoretical and experimental basis to improve the quality of the laser 3D print materials.

Laser deposition-additive manufacturing of ceramics/nanocrystalline intermetallics reinforced microlaminates

Laser rapid prototyping (LRP) of the Stellite12-B4C-Y2O3 mixed powders produced a bottom layer; then the Stellite12-B4C-Cu-Y2O3 mixed powders were deposited on this bottom-layer to form the microlaminates. This upper-layer showed higher wear resistance and micro-hardness than those of the bottom layer due to an action of Cu; Cu-added led lots of the AlCu2Ti intermetallics ultrafine nanocrystals (UNs) to be produced, which distributed uniformly in some location of the upper-layer matrix. UNs may destroy the atomic equilibrium state, increasing the potential/free energy and the strength/hardness of such microlaminates. The temperature of the laser induced molten pool (laser-pool) was very high, favoring the defects to be formed; UNs did not need the long waiting time to change from the normal lattice point to the interstitial particles; also the AlCu2Ti UNs had a high interface energy, which became the driving force of the atomic motions, favoring a compact fine microstructure to be formed. The AlCu2Ti UNs in laser-treated composites provides essential theoretical and experimental basis to promote the development of the laser 3D printing nano technologies.

Co-growing mechanism of γ/γ′ eutectic on MC-type carbide in Ni-based single crystal superalloys

To clarify and comprehend the co-growing mechanism of γ/γ′ eutectic on MC-type carbide in a single crystal CM247LC superalloy, the interface and the elements' segregation between MC-type carbide and γ/γ′ eutectic was investigated in this paper. The results show that a semi-coherent boundary was observed having an orientation relationship of {1¯1¯1}MC‖{1¯1¯1}γ/γ′ with <011>MC || <011>γ/γ′. This interface structure resulted in a high interface energy, and a reduced preference of γ/γ′ eutectic's nucleation on MC-type carbide. However, this unfavorable interfacial feature was offset by the elements' segregation profile during the MC-type carbide's solidification, which is characterized by Al, Ni, Co and Cr enrichment and a co-growing mode.

Toward Phase and Catalysis Control: Tracking the Formation of Intermetallic Nanoparticles at Atomic Scale

Summary Intermetallic nanoparticles (iNPs) have yielded enormous successes in catalytic applications by the formation of ordered phases. However, atomic-level understanding of the alloying mechanism, which plays a pivotal role in controlling intermetallic phases and tailoring their catalytic properties, is still elusive. In this study, we discovered a consecutive formation of ordered Pt3Sn and PtSn phases during the growth of Pt-Sn iNP inside a well-defined nano-reactor at elevated temperature by using in situ scanning transmission electron microscopy. We found that the surface-mediated diffusion of Sn controls overall dynamics of the reaction, while the unique coherent interfacial structure is determinative for the PtSn transformation. We then further controlled the phase selection of Pt-Sn iNPs and demonstrated their distinguishable catalytic behaviors. Our findings not only provide detailed experimental evidence on the alloying mechanism in intermetallic nanoscale systems but also pave the way for mechanistic control of synthesis and catalytic properties of iNPs.

Local topology and its effects on grain boundary and solute segregation in HCP magnesium

First principles simulations were carried out to study the energetics of ten special grain boundaries in pure magnesium. The relaxed systems were subjected to topological analysis which revealed correlation between grain boundary energy and local structures conforming to the Mg bulk symmetry. In addition, three different elements with various observed effects were selected from groups 4, 12 and lanthanides of the periodic table and energetic changes imparted by them were calculated for two boundaries with the lowest and higher interfacial energy, respectively. Local topological analysis based on Voronoi polyhedra was utilized to estimate the atomic volume of each segregant and the strain energy associated with it. The contributions of strain and chemical bonding to the grain boundary energetics were then assessed. It was found that while the variation of computed energetics can be justified by the cooperative and competitive role of the strain and chemical bonding respectively, topological analysis applied to the boundary served as an effective complementary method to explain segregation-induced energetic variations.

Interface-Driven Phase Transition of Phase-Change Material

In order to be able to control the phase transition of engineered phase-change materials, the specific understanding of phase transition processes is essential. To understand the effect of dopant on phase transition, the phase transition processes of Bi5.5(In3SbTe2)94.5 (Bi-IST) are quantitatively investigated with regard to the interfacial, bulk, entropy, and Gibbs free energies involved in the intermediate InSb and InTe phases and the crystallized Bi-IST. In the first step, InSb is crystallized; InTe and Bi are present in the amorphous phase. In the second step, heterogeneous nucleation of crystalline InTe occurs on the InSb. The energy barrier calculated for this nucleation of crystalline InTe is reduced by 1.5 times owing to the interfacial reaction of 5.5 atom % of Bi atoms compared to the case without Bi. In the third step, crystalline InSb and InTe are crystallized to Bi-IST since Bi atoms substitute Sb sites with a higher interfacial energy. The difference in the Gibbs free energy of the Bi-IST is −1.4 × 105 eV, which is lower than the −1.1 × 105 eV of the IST; this is because the differences in entropy with an increase in temperature and the interfacial energy are increased owing to the added Bi atoms. This lower Gibbs free energy becomes a driving force for the stable phase transition of Bi-IST at a lower transition temperature compared with that of the IST. With these phase transition processes, the contribution shares of enthalpy, entropy with temperature change, and interfacial energy are quantitatively analyzed; moreover, we recommend one of the various methods to design a novel phase-change material.

TiO2 Surface Engineering to Improve Nanostability: The Role of Interface Segregation

Nanoparticle stability against coarsening is one of the keys to allow better exploitation of the properties of nanoscale materials. The intrinsically high interfacial energies of nanoparticles constitute the driving force for coarsening, and therefore can serve as targets to design materials with improved thermal stability. In this study, we discuss the surface engineering of TiO2 nanocatalysts for artificial photosynthesis by exploiting the spontaneous segregation of Ba2+ ions to the interfaces of TiO2 nanocrystals. Ba2+ is a strong candidate for photoelectrocatalytic reduction of CO2 and its effects on interfacial energies lead to a remarkable increase in thermal stability. By using a systematic lixiviation method, we quantified the Ba2+ content located at both the surface and at grain boundary interfaces and combined with direct calorimetric measurements of surface energies and microstructural studies to demonstrate that Ba2+ excess quantities directly impact coarsening of TiO2 nanocatalysts by creatin...

Graphene and graphene oxide in calcium silicate hydrates: Chemical reactions, mechanical behavior and interfacial sliding

We investigate chemical reactions, mechanical behaviors and interfacial sliding of calcium silicate hydrates (CSH) incorporating graphene nanosheet (GNS) and graphene oxide (GO) containing epoxides (GO-Oo) and hydroxyls (GO-OH) through molecular dynamics simulation. Structural analysis reveals that chemical reactions occur at the interface between GO and CSH matrices because the alkaline environment in CSH provides Ca2+ coordination and hydrogen bonds with GO. The Young's modulus and strength of CSH are enhanced by 52.6% and 23.3% with the incorporation of GO-OH while an increase of 31.6% and 17.5% in Young's modulus and strength is achieved by incorporating GO-Oo, attributed to high interfacial interaction energy and mechanical interlocking. However, GNS can hardly enhance the mechanical properties of CSH because its 2D surface has no interlocking with the matrix. The pull-out test reveals that mechanical interlocking plays a decisive role in the enhancement of the interfacial shear strength. During the pull-out process, functional groups are exfoliated from GO, which is harmful to its reinforcing ability. This study provides, for the first time, valuable insight into interfacial reaction mechanisms and working mechanisms of GNS/GO in realistic CSH structure.

Ultrathin ceramic nanowires for high interface interaction and energy density in PVDF nanocomposites

AbstractDielectric nanocomposites with ceramic fillers have a crucial role in energy storage applications. Therefore, poly(vinylidene fluoride) (PVDF) based nanocomposites filled with 20 nm diameter, surface hydroxylated BaTiO3 nanowires (BTnws) were produced by solution‐casting method in this work, in which BTnws were synthesized via solvothermal method. The dielectric constant of BTnws/PVDF nanocomposites was 24 when the content of fillers was 10vol% at 100 Hz and the breakdown strength could increase up to 417 kV/mm before decreasing. The nanocomposites showed enhanced energy density performance and the maximum energy density could reach to 8.1J/cm3 at 320 kV/mm with 10vol% BTnws, nearly tripled that of pure PVDF at 300 kV/mm. Finite element and molecular dynamic simulation results revealed that thin BTnws could create dielectric homogeneity in the nanocomposites and have strong interface interaction with PVDF molecular. The ultrathin BTnws provided the possibility that single PVDF molecular could wrap on its surface, but this molecular wrapping pattern would not occur when the diameter of BTnws was large. Besides, the wrapping pattern could be reinforced by interactions between surface hydroxyl groups of BTnws and F atoms of PVDF molecular. Such contributions could induce good interface compatibility and lead to the improvement of energy density.

Relating Organic Fouling in Membrane Distillation to Intermolecular Adhesion Forces and Interfacial Surface Energies

This study investigates the fouling mechanisms in membrane distillation, focusing on the impact of foulant type and membrane surface chemistry. Interaction forces between a surface-functionalized particle probe simulating a range of organic foulants and model surfaces, modified with different surface energy materials, were measured by atomic force microscopy. The measured interaction forces were compared to those calculated based on the experimentally determined surface energy components of the particle probe, model surface, and medium (i.e., water). Surfaces with low interfacial energy exhibited high attractive interaction forces with organic foulants, implying a higher fouling potential. In contrast, hydrophilic surfaces (i.e., surfaces with high interfacial energy) showed the lowest attractive forces with all types of foulants. We further performed fouling experiments with alginate, humic acid, and mineral oil in direct contact membrane distillation using polyvinylidene fluoride membranes modified with various materials to control membrane surface energy. The observed fouling behavior was compared to the interaction force data to better understand the underlying fouling mechanisms. A remarkable correlation was obtained between the evaluated interaction force data and the fouling behavior of the membranes with different surface energy. Membranes with low surface energy were fouled by hydrophobic, low surface tension foulants via "attractive" and subsequent "adsorptive" interaction mechanisms. Furthermore, such membranes have a higher fouling potential than membranes with high or ultralow surface energy.

A comparative study of a NiTi alloy subjected to uniaxial monotonic and cyclic loading-unloading in tension using digital image correlation: The grain size effect

The present digital image correlation study characterised the local axial and shear strain fields of a 56Ni44Ti wt.% shape memory alloy with an average grain size of 100 μm, under uniaxial monotonic and cyclic loading-unloading in tension. To elucidate the grain size effect, the results were compared with a previous investigation of the same alloy with an average grain size of 10 μm. The maximum local axial strain rate signified the direction and extent of the localised transformation. The widened single inclined transformation band and multiple criss-crossing patterns assist in straightening the sample edge by releasing an in-plane moment instigated by local shear strains. Electron back-scattering diffraction analyses showed that the plastic strain within the B2 grains and the remnant B19′ variants account for the residual strains after unloading. Smaller grain sizes correspond to greater constraint from grain boundaries, higher interfacial energy and higher elastic strain energy barrier for transformation, and smaller intragranular heterogeneity of plastic deformation. This is reflected in the increases to the transformation start stress, stress level and stress-strain slope within the macroscopic stress plateau region and smaller complete transformation strain, super-elastic and residual strains upon unloading.

Interface engineering of sulfide electrolytes for all-solid-state lithium batteries

All-solid-state lithium batteries (ASSLIBs) employing sulfide solid electrolyte hold high promise to replace traditional liquid-electrolyte LIBs due to their high safety and energy density. However, Li dendritic growth in sulfide electrolyte limits the realization of the high energy of ASSLIBs. In this work, we use LiF (or LiI) layer at the interface between Li and sulfide electrolyte and penetrated HFE (or I solution) inside of sulfide electrolyte to suppress the Li dendrite growth. Due to the higher interface energy of LiF/Li than that of LiI/Li, LiF interlayer show much higher capability than LiI in suppressing the Li dendrite. Even if the Li dendrite breaks through LiF (or LiI) interlayer, the Li dendrites will be consumed by coated/penetrated HEF (or I) forming LiF (or LiI) thus preventing Li dendrite growth. A LiNbO3 @LiCoO2/Li7P3S11/Li ASSLIB employing HFE coated/infiltrated Li7P3S11 glass-ceramic as electrolyte, and LiF coated Li metal as anode shows a high reversible discharge capacity of 118.9 mAh g−1 at 0.1 mA cm−2 and retains 96.8 mAh g−1 after 100 cycles. The designed solid electrolyte interphase between Li and solid electrolyte that has a high interface energy to Li provides new opportunity to commercialize the Li metal batteries.

Investigation of the effect of titanium dioxide and clay grafted with glycidyl methacrylate by gamma radiation on the properties of EVA flexible films

Many studies report that nanocomposites obtained by dispersion of a small amount nanofiller into the polymer have remarkable improvements achieved in the mechanical and physical properties. However, in order to achieve this great improvement in properties, it is necessary that the nanofillers be dispersed homogeneously into the polymeric matrix. Often this dispersion is difficult to achieve due to the high interfacial energy of the nanoparticles present. This study reports the effect of gamma irradiation induced graft of glycidyl methacrylate (GMA) onto the surface of TiO2 and Clay nanofillers to improve their dispersion into the EVA matrix. The physical and mechanical properties of Ethylene-vinyl acetate copolymer (EVA) flexible films with these nanoparticles were studied. EVA nanocomposite with adding of the different amount of TiO2 and modified montmorillonite clay grafted and un-grafted with glycidyl methacrylate (GMA) using gamma irradiation have been prepared by melt extrusion. The nanocomposite flexible films were produced using a flat die extrusion process. The PGMA-grafted nanofillers were characterized by XRD and TEM analysis. The flexible films were characterized by Tensile tests, ATR–FTIR, UV–VIS, XRD, TG, and FE-SEM analysis to understand the nature of the interaction between the nanofillers and EVA matrix. The results showed that the addition of PGMA-grafted TiO2 and Clay nanofillers into EVA matrix improved the bonding between the nanofillers and matrix. It was also found that the PGMA-grafted nanofillers could be well dispersed into an EVA matrix in contrast to that of un-grafted. The tensile strength and modulus of the resulting EVA/TiO2-PGMA enhanced in comparison to that of un-grafted TiO2. The EVA/Clay-PGMA had slightly decreased tensile strength comparable to that of EVA/Clay but had considerably improved elastic modulus. In addition, the flexible films based on TiO2 exhibited high UV–Vis light absorption with energy gap shifted to the visible region. The results demonstrated that TiO2 and Clay nanofillers grafted with GMA by gamma radiation can be used to prepare EVA flexible films with improved bonding between the nanofillers and matrix and, consequently, enhanced properties for food and cosmetic packaging application.

A power model to predict the electrical conductivity of CNT reinforced nanocomposites by considering interphase, networks and tunneling condition

This study develops a power-law model for characterizing the conductivity of polymer carbon nanotube (CNT) nanocomposite by defining the “b” exponent as a function of main parameters such as filler dimensions, filler waviness, interphase thickness, network fraction, tunneling distance, and polymer-filler interfacial energy. Both “b” and conductivity are calculated, and the effects of these parameters on the conductivity are determined. The model accurately predicts the experimentally measured conductivity of the samples. The highest filler conductivity and the lowest “b” exponent cause the maximum conductivity. Some parameters, such as tunneling distance, filler concentration, filler radius, interphase thickness, and waviness, directly affects the “b” exponent, while other parameters, such as the fraction of percolated CNT, interfacial energy, and filler length, demonstrate an inverse relationship with “b.” In addition, short tunneling distance, high filler fraction, thin and large nanotubes, thick interphase, poor waviness, high network fraction, and high interfacial energy produce a high conductivity.

Sequential precipitation behavior of Mg17Al12 and Mg2Sn in Mg-8Al-2Sn-1Zn alloys

The precipitation behavior of Mg-8Al-2Sn-1Zn (ATZ821) alloy was investigated. Sn addition to the AZ81 alloy greatly influenced the initial precipitation behavior in the following two aspects: (i) the segregation of Sn solutes at the interface of Mg17Al12 via Sn partitioning induced during the growth of Mg17Al12 and (ii) high interfacial energy at the edge-tip of growing Mg17Al12. According to the hardness profile and detailed microstructural analyses of ATZ821 cast samples artificially aged at 453 K for different times, it was confirmed that the initial precipitation of Mg17Al12 was delayed due to Sn partitioning at the interface, and all Mg2Sn without exception was nucleated at the edge-tip of pre-existing Mg17Al12 precipitates on the basal planes. In addition, a selected area diffraction pattern analysis confirmed that α-Mg, Mg17Al12, and Mg2Sn had the following orientation relationship: (0001)α//(110)Mg17Al12, [12¯10]α//[1¯11]Mg17Al12 and (0001)α//(022)Mg2Sn, [12¯10]α//[11¯1]Mg2Sn.

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide.

The role that grain boundaries (GBs) can play on mechanical properties has been studied extensively for metals and alloys. However, for covalent solids such as boron carbide (B4C), the role of GB on the inelastic response to applied stresses is not well established. We consider here the unusual ceramic, boron carbide (B4C), which is very hard and lightweight but exhibits brittle impact behavior. We used quantum mechanics (QM) simulations to examine the mechanical response in atomistic structures that model GBs in B4C under pure shear and also with biaxial shear deformation that mimics indentation stress conditions. We carried out these studies for two simple GB models including also the effect of adding Fe atoms (possible sintering aid and/or impurity) to the GB. We found that the critical shear stresses of these GB models are much lower than that for crystalline and twinned B4C. The two GB models lead to different interfacial energies. The higher interfacial energy at the GB only slightly decreases the critical shear stress but dramatically increases the critical failure strain. Doping the GB with Fe decreases the critical shear stress of at the boundary by 14% under pure shear deformation. In all GBs studied here, failure arises from deconstructing the icosahedra within the GB region under shear deformation. We find that Fe dopant interacts with icosahedra at the GB to facilitate this deconstruction of icosahedra. These results provide significant insight into designing polycrystalline B4C with improved strength and ductility.

The Effect of Methylammonium Iodide on the Supersaturation and Interfacial Energy of the Crystallization of Methylammonium Lead Triiodide Single Crystals

AbstractIt is very important to study the crystallization of hybrid organic–inorganic perovskites because their thin films are usually prepared from solution. The investigation on the growth of perovskite films is however limited by their polycrystallinity. In this work, methylammonium lead triiodide single crystals grown from solutions with different methylammonium iodide (MAI):lead iodide (PbI2) ratios were investigated. We observed a V‐shaped dependence of the crystallization onset temperature on the MAI:PbI2 ratio. This is attributed to the MAI effects on the supersaturation of precursors and the interfacial energy of the crystal growth. At low MAI:PbI2 ratio (&lt;1.7), more MAI leads to the supersaturation of the precursors at lower temperature. At high MAI:PbI2 ratio, the crystal growing plans change from (100)‐plane dominated to (001)‐plane dominated. The latter have higher interfacial energy than the former, leading to a higher crystallization onset temperature.

The Effect of Methylammonium Iodide on the Supersaturation and Interfacial Energy of the Crystallization of Methylammonium Lead Triiodide Single Crystals.

It is very important to study the crystallization of hybrid organic-inorganic perovskites because their thin films are usually prepared from solution. The investigation on the growth of perovskite films is however limited by their polycrystallinity. In this work, methylammonium lead triiodide single crystals grown from solutions with different methylammonium iodide (MAI):lead iodide (PbI2 ) ratios were investigated. We observed a V-shaped dependence of the crystallization onset temperature on the MAI:PbI2 ratio. This is attributed to the MAI effects on the supersaturation of precursors and the interfacial energy of the crystal growth. At low MAI:PbI2 ratio (<1.7), more MAI leads to the supersaturation of the precursors at lower temperature. At high MAI:PbI2 ratio, the crystal growing plans change from (100)-plane dominated to (001)-plane dominated. The latter have higher interfacial energy than the former, leading to a higher crystallization onset temperature.