Dilatometry Experiments Research Articles

Optimized NMC622 electrodes with a high content of the active material: A comprehensive study

The composition of lithium-ion battery positive electrodes, incorporating an active material, conductive carbon additives, and a binder, fundamentally influences the electrode physical and electrochemical characteristics. In this study, the properties of positive electrodes with a high amount of an active material (LiNi0.6Mn0.2Co0.2O2 98 wt-%), were tested with different ratios of carbon nanotubes (CNTs) and carbon black (CB) additives, along with varying amounts of a PVDF binder. Consequently, the electrode rate capability improves with the increase of CNTs up to 30 wt-% in the total conductive carbon share and increasing the binder amount to 1 wt-%, attributed to the optimal balance of inactive material amount. The optimal composition is determined to be 98 wt-% NMC622, 1 wt-% PVDF, and 1 wt-% total conductive carbons, out of which CNT shares accounting for 30 wt-%. Furthermore, this study continues by comparing the optimal composition with the reference electrode (CNT-free) to assess the impact of CNTs on electrochemical performance. With CNTs present, the electrode attains higher energy density and specific capacity owing to uniform conductive network. Operando XRD and dilatometry experiments also reveal that CNTs reduce irreversible height change during cycling and minimize anisotropic lattice changes, thus enhancing capacity retention.

Phenomenological sintering model and experimental validation of gravity-induced distortions in binder-jetted stainless steel components

Sintering is an important consolidation step employed in sinter-based metal additive manufacturing processes. Binder Jetting (BJT) starts with green components with low green density (40–60 %) that results in large sintering shrinkages and geometrical shape distortions caused by external forces (e.g. gravity). Consequently, the prediction of the final sintered geometry is crucial during the design process. In this work, a novel sintering simulation framework for gravity-affected sintering of stainless-steel components is presented, including the Rios-Olevsky-Hryha sintering model and the methodology for the identification of the required material parameters. The constitutive law includes material constants to account for the powder packing effects and the delta-ferrite transformation occurring at high temperatures. The material shear viscosity was explicitly related to the equilibrium phase fraction of austenite and delta-ferrite during sintering temperatures. Dilatometry experiments were conducted and followed by the data postprocessing for the model calibration. The calibrated model was incorporated in a FEM code and validated against experimental data from BJT sintered components, showing the remarkably accuracy of the numerical simulations, with small geometric deviations (0.56 mm) related to the assumption of isotropic shrinkage in the model proposed. In parallel, other alternative models were implemented based on different normalized bulk viscosity formulations, which underestimate/overestimate the sintered distortions.

(Invited) Coordinatively Cross-Linked Binders for Silicon-Based Electrodes for Lithium Ion Batteries

We have proposed a simple and versatile preparation of Cu(II)- or Zn(II)-poly(carboxylates) reticulated binders by the addition of Cu(II) or Zn(II) precursors into a pre-optimized carboxymethyl cellulose / citric acid binder solution. These binders lead systematically to a significantly improved electrochemical performance when used for the formulation of silicon-based negative electrodes [1,2]. Mechanical characterizations reveal that the coordinated binders offer a better electrode coating cohesion and adhesion to the current collector, as well as higher hardness and elastic modulus, which are even preserved in presence of a carbonate solvent (i.e. in battery operation conditions). Ultimately, as shown from operando dilatometry experiments, the electrode expansion during lithiation is reduced, mitigating electrode mechanical failure [2]. In complement, we used scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy to probe the nanoscale morphology of such electrodes. This technique reveals the homogeneous coordination of carboxylated binder with Zn cations and its layering on the silicon surface. The SEI formed after the first cycle is denser with Zn-coordinated binder and preferentially observed on binder-depleted zones [3]. In summary, the superiority of coordinated binders can be attributed to their capacity to better stabilize the electrode and the SEI layer due to improved mechanical properties. This resulted in a lower SEI impedance, a higher first cycle coulombic efficiency, and a 40% improvement of capacity retention after 60 cycles for highly loaded electrodes of over 6 mAh.cm-2. Noteworthy, this formulation principle allows for better reproducibility and manufacturing quality of the electrodes [4].[1] D. Mazouzi, R. Grissa, M. Paris, Z. Karkar, L. Huet, D. Guyomard, L. Roué, T. Devic, B. Lestriez, Electrochimica Acta, 304 (2019) 495-504[2] L. Huet, D. Mazouzi, P. Moreau, N. Dupré, M. Paris, S. Mittelette, D. Laurencin, T. Devic, L. Roué, B. Lestriez, ACS Applied Materials & Interfaces, 15 (2023) 15509-15524[3] L. Huet, P. Moreau, N. Dupré, T. Devic, L. Roué, B. Lestriez, Small Methods, 2022, 2200827[4] L. Huet, H. Houisse, N. Herkendaal, T. Devic, L. Roué, B. Lestriez, Energy Technology, 2023, 2201483 Figure 1

Monitoring the ion population at a carbon electrode/aqueous electrolyte interface at various pHs using electrochemical dilatometry

Changes in the electrode thickness in electrochemical capacitors depend strongly on the electrolyte pH. Hence, different ions (or ions with various solvation shells) participate in electrical double-layer formation. In this study, operando electrochemical dilatometry experiments incorporating various electrochemical techniques, including cyclic voltammetry, large amplitude sinusoidal voltammetry, and step potential electrochemical spectroscopy, were performed on ECs operating in 1 mol L−1 Li2SO4 with different pHs (6, 9, and 12) and 1 mol L-1 LiOH (for comparative purposes). A microporous carbon (Kuraray YP-80F) was used as the electrode material. Comparable trends for the cell behaviour were observed for electrolytes with pHs of 6 and 9; however, the cell containing the pH 12 solution exhibited similar behaviour to that containing the LiOH solution, suggesting that during positive polarization, the primary role was played by OH−, because the same salt concentration was used in all cases. This result raises an essential concern regarding the actual ion population at the electrode/electrolyte interface, which affects the water decomposition potentials and triggers various parasitic reactions impacting long-term electrochemical capacitor performance.

Determination of single crystal thermal expansion in Uranium-6wt%Niobium shape memory alloy using in-situ diffraction and modeling of textured polycrystalline samples

In-situ neutron diffraction and ex-situ dilatometry experiments were performed on a chemically banded, quenched uranium-6wt% niobium shape memory alloy to study the impact of deformation-(detwinning-) induced texture on the evolution of thermally induced strains (and associated stresses). Thermal heating and cooling cycles between 5K and 473K were performed in-situ with neutron diffraction, and the lattice strain evolution is reported for the observed monoclinic α″ phase. Comparisons between the measured diffraction strains and macroscopic dilatometry experiments reveal relationships between micro- and macro-level thermal expansion. Softening of the texture during heating suggests that twin boundary motion can accommodate the large internal thermal strains which are approximately 2% greater than that typically observed during the 175K heating interval used to age more randomly oriented polycrystalline material. Assuming weak constraint of neighboring grains in randomly textured polycrystals, the single crystal thermal expansion tensor is extracted from measurements of lattice strains over the range 5K to 473K. Predictions of polycrystalline thermal expansion, based upon this single crystal thermal expansion tensor, are shown to compare favorably with bulk thermal expansion observations of the as quenched microstructure. However, such a lower-bound estimate is insufficient to explain all aspects of the behavior of the textured material, where the matrix is not isotropic. It is hypothesized that relaxation processes which occur within the quenched microstructure during heating are responsible for the distinct thermal expansion behavior observed during the initial heating cycle compared to cooling and subsequent cycling.

Experimental and numerical investigation of the thermal properties and related microstructural influences of an interpenetrating metal ceramic composite at elevated temperatures

An interpenetrating metal-ceramic composite (IMCC), consisting of an open-porous alumina preform (26vol%), infiltrated with an AlSi10Mg alloy is investigated for its thermal properties and the microstructural impact on the thermal cycling behavior. Specific heat capacity, thermal conductivity and the coefficient of thermal expansion are investigated experimentally. Next to dilatometry experiments, an in-situ SEM setup with digital image correlation of the natural microstructure of the composite is used as a recognizable pattern on the sample surface to evaluate strain and microstructural changes during heating and cooling. The interpenetrating phase composite is also modelled based on reconstructed and generated microstructures. Extensive numerical studies are conducted with varying boundary conditions, interface properties, initial cooling temperatures, temperature dependent material properties and inclusion of pores. Microstructural investigations show phenomena of plasticity, creep, crack formation and interface detachment which is supported by numerical findings. Microstructural changes during heating and cooling in form of crack formation occur in the metallic phase and metallic precipitation. The influence of the microstructural processes on the thermal expansion behavior are discussed in comparison to existing hypotheses from literature.

Coordinatively Cross-Linked Binders for Silicon-Based Electrodes for Li-Ion Batteries: Beneficial Impact on Mechanical Properties and Electrochemical Performance.

A simple and versatile preparation of Zn(II)-poly(carboxylates) reticulated binders by the addition of Zn(II) precursors (ZnSO4, ZnO, or Zn(NO3)2) into a preoptimized poly(carboxylic acids) binder solution is proposed. These binders lead systematically to a significantly improved electrochemical performance when used for the formulation of silicon-based negative electrodes. The formation of carboxylate-Zn(II) coordination bonds formation is investigated by rheology and FTIR and NMR spectroscopies. Mechanical characterizations reveal that the coordinated binder offers a better electrode coating cohesion and adhesion to the current collector, as well as higher hardness and elastic modulus, which are even preserved in the presence of a carbonate solvent (i.e., in battery operation conditions). Ultimately, as shown from operando dilatometry experiments, the electrode expansion during lithiation is reduced, mitigating electrode mechanical failure. Such coordinatively reticulated electrodes outperform their uncoordinated counterparts with an improved capacity retention of over 30% after 60 cycles.

Densification Study of Pr6O11 as a Limiting Step for the Determination of Its Oxygen Transport Properties

This study describes the successful sintering of Pr6O11, which is recently developed as a promising oxygen electrode for Solid Oxide Cells (SOCs). Using dense pellets or thin films is mandatory prior to an accurate measurement of the ionic transport properties via the isotopic oxyen exchange method here involved. Dilatometry experiments performed under different atmospheres (argon, air, oxygen) and sintering tests with different thermal cycles allowed overcoming the detrimental phase changes of Pr6O11 and densifying this oxide with a sintered relative density of 95%. Dense pellets of large sizes were prepared. In a second part, the ionic transport properties of Pr6O11 have been determined in the range 400 < T °C < 800 thanks to Isotopic Exchange Depth Profiling (IEDP) measurements.

Thermal expansion behavior and elevated temperature elastic properties of an interpenetrating metal/ceramic composite

The thermal and elastic behavior of an interpenetrating metal ceramic composite (IMCC), consisting of ceramic foam with 74 % open porosity and an AlSi10Mg light-weight aluminum alloy was investigated at elevated temperatures. The elastic properties of the IMCC and its individual components were determined by ultrasonic phase spectroscopy and resonant frequency damping analysis (RFDA) at RT, showing a highly isotropic behavior for the IMCC. The directional elastic modulus measured at elevated temperature by RFDA decreased from about 110 GPa at room temperature to 80 GPa at 500°C. The elastic modulus temperature curve shows a clear hysteresis for the IMCC, but not for the individual components. Dilatometry experiments revealed the onset of a hysteresis effect in the CTE curve between 260 and 285°C. The hysteresis behavior could be explained by internal stress relaxation, reduction of micro voids and interfacial detachment and assigned to characteristic areas of the hysteresis curve. The associated behavior of the elastic modulus over the temperature range was investigated in detail, and the hysteresis behavior, observed for the first time in the literature was assigned and explained.

Sintering behavior of the Ti(C,N)‐based cermets with graphite or diamond additives

AbstractCombining DSC/TG–QMS analysis and dilatometry experiments at constant heating rates, the sintering behaviors of the Ti(C,N)‐based cermets with carbon additives were studied. It is found that the additives of diamond or graphite could promote the interactions among raw powders during solid‐state sintering. The outgassing behavior and endothermic effect were enhanced, thereby resulting in the increasing densification activation energy. The negative activation energy during the liquid phase sintering indicates that the dissolution–precipitation process occurs easily and provides a rapid densification path. The dissolution–precipitation process for cermets with .6‐wt% graphite or .6‐wt% diamond additive became more efficient than for cermets without additional carbon additive. The white‐core/gray‐rim grains were clustered together in the cermets with .6‐wt% graphite additive, whereas they were distributed evenly in the cermets with .6‐wt% diamond additive. Moreover, the average sizes of ceramic grains in the cermets without additional carbon additive, and with .6‐wt% graphite or .6‐wt% diamond additives, were .453, and .517, or .525 μm, respectively.

(Digital Presentation) The Role of the Electrolyte in the Charge Storage Mechanism of TiS2 in Sodium-Ion Batteries

The development of high-performance energy storage devices has recently attracted much attention for applications such as electrical vehicles, grid storage and portable devices. In this sense, sodium-ion batteries (SIBs) has appeared as an alternative to traditional lithium-ion batteries as a result of the availability, lower environmental impact and reduced cost of the battery due to the typical SIB chemistry.1 Even though graphite is a well-established and highly commercialized anode material, its application in SIBs suffers from several drawbacks, such as the practical impossibility of using traditional carbonates-based electrolytes due to unfavorable thermodynamic behavior – resulting in low specific capacities. Despite this, certain solvents (such as ethers) allow the use of graphite in SIBs through the formation of ternary graphite intercalation compounds by a co-intercalation reaction, showing excellent cyclability and kinetics. However, its capacity at 100-150 mAh g-1 is still low compare to other anode materials, in addition to showing large volume expansion. 2, 3 Transition metal dichalcogenides (TMDs) have emerged as promising anode materials owing to their low cost, high electric conductivity, good thermal stability and environmental friendliness. Among them, titanium sulphide (TiS2), with a two-dimensional framework, exhibits several advantages such as a high conductivity (compare to other metal oxides), a larger interlayer distance (0.569 nm) compared to graphite (0.335 nm) and high stability. 4 Several papers have reported on the use of TiS2 as an anode material for SIBs, and observed that the voltage profiles and electrochemical behaviour of the system is highly dependent on the choice of electrolyte, yet this has seldomly been explicitly stated, nor the cause of the electrolyte dependence investigated.Here, we demonstrate that depending on the electrolyte employed, an electrochemical co-intercalation reaction, similar to those reported with graphite as active material can also occur. Galvanostatic charge-discharge experiments were first performed to assess differences between different electrolytes (linear ethers, cyclic ethers and carbonates). Here, differences were found on the voltage profiles among the linear ethers and the rest of the solvents employed. By using in-situ and ex-situ techniques, a huge expansion on the TiS2 layers was found when diglyme was the solvent used. It was concluded here that co-intercalation of the solvent with sodium was the mechanism that occurs. On the contrary, when a cyclic ether and/or a mixture of carbonates were used, a lower expansion of the layered structure occurred and remained constant during the cycling. Dilatometry experiments were used to confirmed these mechanisms. Thus, with this technique, it is possible to monitor the variation on the thickness of the electrode during cycling, i.e. operando. In this sense, a greater expansion was observed when diglyme was used as the solvent electrolyte.Finally, DFT was used to study the solvents investigated, and their interaction with the sodium cation. It was found that among the solvents, diglyme produced by far the smallest and most stable solvation shells, making them prime candidates for co-intercalation studies. Comparing the size and stability of the solvation shell, with the interlayer binding energy of TiS2, we found it was energetically favorable to expand the lattice and allow a solvation shell into the host structure, compared to forming a bare ion. Figure 1. Illustration on the variation of the layer distance from pristine to sodiated diglyme. D. Kundu, E. Talaie, V. Duffort and L. F. Nazar, Angew. Chem. Int. Ed., 2015, 54, 3431-3448.B. Jache, J. O. Binder, T. Abe and P. Adelhelm, Phys. Chem. Chem. Phys., 2016, 18, 14299-14316.M. Goktas, C. Bolli, J. Buchheim, E. J. Berg, P. Novák, F. Bonilla, T. f. Rojo, S. Komaba, K. Kubota and P. Adelhelm, ACS applied materials & interfaces, 2019, 11, 32844-32855. Q. Yun, L. Li, Z. Hu, Q. Lu, B. Chen and H. Zhang, Adv. Mater., 2020, 32, 1903826. Figure 1

Numerical simulation of shrinkage and deformation during sintering in metal binder jetting with experimental validation

Sintering, as a post-processing step in metal binder jetting (MBJ), often results in distortion. Numerical simulations can predict sintering distortion and minimize costly trial-and-error experiments. The present paper implements a numerical approach based on a phenomenological model of sintering to capture the creep deformation during free sintering. To qualify and calibrate the material model for MBJ, metallographic studies, dilatometry experiments, and viscosity measurements are carried out instead of empirical models for viscosity and sinter stress. Using the calibrated material model, final sintering distortions are predicted in two industry-relevant parts. The reproducibility of MBJ products is illustrated by manufacturing seven specimens for each geometry, and a statistical method to evaluate the simulations’ accuracy is suggested. The predictions have a good agreement with experimental results, particularly for specimens with a lower build height. As the build height increases in MBJ specimens, the number of interlayer gaps in the build direction grows, resulting in anisotropic densification. This causes a lower prediction accuracy under isotropic shrinkage assumption, especially in overhang areas. Consideration of anisotropic shrinkage and heterogeneous density distribution of green parts in sintering simulation is essential to improve the accuracy of sintering predictions for MBJ components.

Study of one-step and two-step quench and partition heat treatments on a medium carbon high silicon alloy using dilatometry

This study evaluated the microstructural evolution in a medium carbon high silicon steel during one-step, and two-step quench and partition (Q&amp;P) processes using dilatometry experiments. The two-step Q&amp;P process was carried out using different quench temperatures ranging from 180 to 260 °C. In the one-step process, Q&amp;P heat treatment samples were held isothermally for ten minutes after quenching at specified temperatures ranging between 200 and 4°50 C. The two-step Q&amp;P process yielded a higher fraction of retained austenite than a one-step Q&amp;P process. During the isothermal hold step, the volume expansion due to carbon partitioning and austenite decomposition behavior was interpreted by experimentally determined strain values. For the one-step Q&amp;P process, the austenite decomposition kinetics above and below the Ms temperature differed, as evidenced by the JMAK parameters. The TTT diagram generated for the one-step Q &amp; P process showed a “swing back” at a temperature of around 355 °C.

Reticulated Porous Perovskite Structures for Thermochemical Solar Energy Storage

AbstractThe inherent capability of concentrated solar power (CSP) plants for sensible thermal energy storage ensures their continuous operation and is considered their most crucial competitive edge versus other renewable energy sources. The storage density of air‐operated CSP plants can be significantly increased by hybridizing sensible with thermochemical storage of solar heat, exploiting reversible air–solid oxide reduction–oxidation reactions. Thermochemical storage‐relevant‐protocols testing of in‐house manufactured lab‐scale reticulated porous ceramic foams made entirely of CaMnO3 perovskite reveals fully reversible reduction‐oxidation in up to 46 cycles between 300 and 1100 °C under air, without any deterioration of the foams’ structural integrity and exploitable endothermic/exothermic heat effects between 890 and 920 °C linked to an orthorhombic‐to‐cubic phase transition. Dilatometry experiments with CaMnO3 bars under identical cyclic conditions demonstrate the correlation of this phase transition to an increase in the thermal expansion coefficient but nevertheless, complete recovery of the initial specimen dimensions upon completion of a full heat‐up/cooldown redox cycle. The possibility of shaping into sturdy reticulated porous ceramic structures which exhibit complete dimensional reversibility upon cyclic redox operation, combined with the low cost, earth abundance and environmentally benign character of the constituting elements, render such perovskite compositions extremely attractive for the manufacture of large‐scale porous structured objects for exploitation in various thermochemical processes.

Sintering anisotropy of binder jetted 316L stainless steel: part I – sintering anisotropy

ABSTRACT In Binder Jetting (BJ) Additive Manufacturing (AM), green components are usually subjected to sintering process to reach required properties. Owing to the inherent low green density, binder jetted (BJ) parts undergo shrinkages up to 20%. In addition, anisotropic dimensional evolution during sintering is characteristic for BJ, generally caused by the specifics of the arrangement of particles during the printing process. In this study, the multi-axial dimensional evolution of 316L stainless steel cubic samples (10 × 10 × 10 mm3), manufactured using BJ, was characterised by dilatometry experiments. Dilatometry tests were conducted up to sintering temperatures of 1300°C and 1370°C, with a heating rate of 10°C/min and 5°C/min, respectively. Dilatometry results and final dimension measurements showed anisotropic shrinkage behaviour during sintering with about 15% larger shrinkage along the building direction. Shrinkages along the other two orthogonal directions were relatively similar, but a slightly larger final shrinkage along the printhead movement direction was observed. Relative density of 85.0% and 96.4% was obtained after sintering tests at 1300°C and 1370°C, respectively.

Influence of Quenching and Partitioning Parameters on Phase Transformations and Mechanical Properties of Medium Manganese Steel for Press-Hardening Application

It has been proven that through targeted quenching and partitioning (Q &amp; P), medium manganese steels can exhibit excellent mechanical properties combining very high strength and ductility. In order to apply the potential of these steels in industrial press hardening and to avoid high scrap rates, it is of utmost importance to determine a robust process window for Q &amp; P. Hence, an intensive study of dilatometry experiments was carried out to identify the influence of quenching temperature (TQ) and partitioning time (tp) on phase transformations, phase stabilities, and the mechanical properties of a lean medium manganese steel. For this purpose, additional scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy dispersive X-ray spectroscopy (EDX) examinations as well as tensile testing were performed. Based on the dilatometry data, an adjustment of the Koistinen–Marburger (K-M) equation for medium manganese steel was developed. The results show that a retained austenite content of 12–21% in combination with a low-phase fraction of untempered secondary martensite (max. 20%) leads to excellent mechanical properties with a tensile strength higher than 1500 MPa and a total elongation of 18%, whereas an exceeding secondary martensite phase fraction results in brittle failure. The optimum retained austenite content was adjusted for TQ between 130 °C and 150 °C by means of an adapted partitioning.

Influence of thermomechanical processing parameters on critical temperatures to develop an Advanced High-Strength Steel microstructure

A good selection of the thermomechanical processing parameters will optimize the function of alloying elements to get the most of mechanical properties in Advanced High-Strength Steels for automotive components, where high resistance is required for passenger safety. As such, critical processing temperatures must be defined taking into account alloy composition, in order for effective thermomechanical processing schedules to be designed. These critical temperatures mainly include the recrystallization stop temperature (T5%) and the transformation temperatures (Ar1, Ar3, Bs, etc.). These critical processing temperatures were characterized using different thermomechanical conditions. T5% was determined through the softening evaluation on double hit tests and the observation of prior austenite grain boundaries on the microstructure. Phase transformation temperatures were measured by dilatometry experiments at different cooling rates. The results indicate that the strain per pass and the interpass time will influence the most on the determination of T5%. The range of temperatures between the recrystallized and non-recrystallized regions can be as narrow as 30 °C at a higher amount of strain. The proposed controlled thermomechanical processing schedule involves getting a severely deformed austenite with a high dislocation density and deformation bands to increase the nucleation sites to start the transformation products. This microstructure along with a proper cooling strategy will lead to an enhancement in the final mechanical properties of a particular steel composition.

Shrinkage and microstructure evolution during sintering of cemented carbides with alternative binders

Cemented carbides are used in the cutting tools industry thanks to their exceptional mechanical properties. Manufactured by the powder metallurgy route, they are made of a hard WC phase with a ductile metallic binder, most commonly Co. Due to the lower availability of Co and its classification as carcenogenic material by the REACH European Regulation, new metallic binders have to be considered: Fe and Ni binders are investigated in this work. Because Co is the most common binder used in the hard metal industry for decades, there is still a lack of knowledge regarding the specific effect of alternative binders on shrinkage and microstructure evolution of cemented carbides.The purpose of this work is to understand the effect of binder nature specifically, comparing classic Co binder used in the industry to pure Fe and Ni binder including the influence of carbon content. Shrinkage behaviour and microstructure evolution of WC-M alloys (M = Co, Ni, Fe) are studied from dilatometry experiments as well as qualitative and quantitative microstructural characterisations. Solid state sintering is delayed to higher temperature for WC-Fe in comparison to WC-Co and WC-Ni alloys. Densification mechanisms are discussed in relation with dilatometry results, microstructural analyses, DFT calculations and a theoretical kinetic model from the literature.

Magnetostructural coupling in ilmenite-type NiTiO3

We report the ground state magnetic structure and in-field magnetostrictive effects of $\mathrm{Ni}\mathrm{Ti}{\mathrm{O}}_{3}$ studied by means of zero-field and in-field single-crystal neutron diffraction, magnetization, and high-resolution dilatometry experiments. Zero-field neutron diffraction on $\mathrm{Ni}\mathrm{Ti}{\mathrm{O}}_{3}$ single crystals confirms an easy-plane antiferromagnet with a multidomain ground state. Upon application of external magnetic fields, neutron diffraction shows the evolution of domains with spins perpendicular to the applied field. The rotation of spins in the multidomain state exhibits pronounced lattice changes in the magnetostriction measurements. We see magnetization and magnetostriction measurements scale with each other in the multidomain state in accordance with phenomenological theories, revealing the strong coupling of spins to the lattice.

Thermal stability and thermal expansion behavior of FeCoCrNi2Al high entropy alloy

Present work reports the thermal stability and thermal expansion behavior of dual-phase FeCoCrNi2Al HEA prepared by Mechanical Activated Synthesis and consolidated by hot pressing. The thermal stability of the phases present in FeCoCrNi2Al HEA has been extensively studied using in-situ high-temperature X-ray diffraction (HT-XRD) in conjunction with dilatometry and differential scanning calorimetry (DSC). The DSC thermogram shows a single endothermic peak at 1430 °C (1703 K) which belongs to the melting point of the alloy. HT-XRD and dilatometry experiments were carried out from room temperature to 1000 °C (1273 K). HT-XRD study has shown that the room temperature FCC + BCC (face-centred cubic + body-centred cubic) phases remains stable up to 1000 °C (1273 K). Although the amount of BCC phase has increased above 800 °C (1073 K), no additional phase formation was observed in HT-XRD. The coefficient of thermal expansion (CTE) curve shows linear increment up to 1000 °C (1273 K) with a slight change in slope beyond 800 °C (1073 K). Theoretical CTE was computed using the lattice parameter of the FCC phase, obtained from HT-XRD, as a function of temperature and compared with experimental CTE. Third-order polynomial equation was fitted to the experimental CTE data and the constants were evaluated which can be used to predict the coefficient of thermal expansion of the alloy.