Search Results (173)

This paper investigates the application of non-calcined metal tartrate as a novel alternative pore former to prepare functional ceramic composites to fabricate solid oxide fuel cells (SOFCs). Compared to carbonaceous pore formers, non-calcined pore formers offer high compatibility with various ceramic composites, providing better control over porosity and pore size distribution, which allows for enhanced gas diffusion, reactant transport and gaseous product release within the fuel cells’ functional layers. In this work, nanocrystalline gadolinium-doped ceria (GDC) and Ni-Gd-Ce-tartrate anode powders were prepared using a single-step co-precipitation synthesis method, based on the carboxylate route, utilising ammonium tartrate as a low-cost, environmentally friendly precipitant. The non-calcined Ni-Gd-Ce-tartrate was used to fabricate dense GDC electrolyte pellets (5–20 μm thick) integrated with a thin film of Ni-GDC anode with controlled porosity at 1300 °C. The dilatometry analysis showed the shrinkage anisotropy factor for the anode substrates prepared using 20 wt. The percentages of Ni-Gd-Ce-tartrate were 30 wt.% and 40 wt.%, with values of 0.98 and 1.01, respectively, showing a significant improvement in microstructural properties and pore size compared to those fabricated using a carbonaceous pore former. The results showed that the non-calcined pore formers can also lower the sintering temperature for GDC to below 1300 °C, saving energy and reducing thermal stresses on the materials. They can also help maintain optimal material properties during sintering, minimising the risk of unwanted chemical reactions or contamination. This flexibility enables the versatile designing and manufacturing of ceramic fuel cells with tailored compositions at a lower cost for large-scale applications. Full article

The widespread implementation of next-generation Li metal anodes is limited, in part, due to the formation of dendritic and/or mossy electrodeposits during cycling. These morphologies can lead to battery failure due to the formation of short circuits and significant volumetric expansion at the anode. One strategy to control the electrodeposition of Li metal is to use lithiophilic materials at the anode. Here, we evaluate the impact of Ag and Au on the early stages of Li metal electrodeposition and cycling. The alloying substrates decrease the voltage for Li reduction and improve Li wetting/adhesion. We probe volumetric expansion directly through dilatometry measurements and find that the degree of volumetric expansion is less when lithium is cycled on an alloying substrate compared to a non-alloying substrate (Cu). Dilatometry experiments reveal that Au has the least amount of volumetric expansion and coin cell cycling experiments indicate that Ag yields more stable cycling compared to Au or Cu. The evaluation of in situ cross-sectional images of cycled coin cells shows that Ag has the lowest volumetric expansion in a coin cell format. Full article

High-entropy ceramics have gained wider attention due to their structural integrity and stability, which can be used in various functional applications. Especially, high-entropy oxides exhibit excellent thermal stability, particularly at high temperatures. Thermal barrier coating materials must demonstrate good thermal stability without any phase transformation or phase separation, which is critical in aerospace and energy conversion applications. To address this, we have prepared new high-entropy stannate pyrochlore oxide nanoparticles with the composition (Gd_0.2Nd_0.2La_0.2Pr_0.2Sm_0.2)₂Sn₂O₇ through a simple glycine-assisted sol–gel synthesis. The phase evolution was probed at different heat-treatment temperatures from 1000 °C to 1500 °C. Among the temperatures investigated, a single-phase pyrochlore oxide was formed from 1300 °C without any impurity or phase separation. The obtained nanoparticles were characterized using various techniques, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), nanoindentation, and dilatometry to investigate their physiochemical and mechanical properties. The Vickers hardness of high-entropy oxides is 4.2 ± 0.33 GPa, while a thermal expansion coefficient (TEC) of 8.7 × 10⁻⁶ K⁻¹ at 900 °C is calculated. The results show that the prepared high-entropy pyrochlore oxide can be a suitable candidate for thermal barrier coating. Full article

The Po Nagar Towers (Thap Ba) complex, an iconic heritage site of Cham culture and a nationally recognized special relic, has stood in Nhatrang, Vietnam, for over a thousand years. We report here a preliminary analysis of original ancient Cham bricks from the Po Nagar Towers using a combination of appropriate characterization techniques, including X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman micro-spectroscopy, thermal dilatometry, compressive strength testing, and water sorption. Mechanical properties and firing temperatures of the ancient bricks have been determined to support the discussion on the likely technology used to make them. Specifically, they were made from clay, sand, plagioclases/feldspar, and grog mixed with intentionally added carbon precursor (charcoal powder), then fired at temperatures between 800 °C and 1000 °C to form lightweight bricks with a mass density of 1.3–1.6 kg/dm³ and an open porosity of 18–25%. The ancient Cham bricks have their texture and porosity to meet the requirements of the thin rubbing joint technique in tower construction and to contribute to the carvability and durability of Cham towers. A comparison is made with the bricks for tower restoration during the 2000s. Full article

Low-carbon steels, such as ER70S-6, are typically considered resistant to phase transformations due to their high critical cooling rate. However, this study investigates how the manufacturing process and specimen geometry influence heat dissipation, potentially leading to localized grain size variations that impact mechanical properties. To analyze these effects, samples were fabricated using Laser Wire-Feed Additive Manufacturing (LWAM) with different geometries, and their hardness and microstructural characteristics were evaluated. Vickers microhardness tests were performed along the specimens to assess local variations, while dilatometry measurements were conducted to determine thermal expansion coefficients for future integration into finite element models (FEMs) of residual stress distribution. The results reveal that differences in heat dissipation during fabrication lead to grain size heterogeneity, affecting hardness at a microscopic scale and overall mechanical performance. These findings highlight the importance of considering thermal history and geometry in LWAM-fabricated components to ensure consistent material properties. Full article

This work investigated changes in the microstructure and local mechanical properties after the application of selected heat treatments to EN-GJL-300 grey cast iron. The main goal was to optimize heat treatment to achieve increased mechanical properties and subsequently wear resistance. The heat and heat–mechanical treatment were investigated by using a dilatometer as a physical simulator of treatment on real samples. Continuous cooling with three different rates and two other non-continuous treatments (austempering and ausforming) were used to treat the experimental samples. The research was focused on modification of the matrix microstructure, initially pearlitic. No change in the shape or morphology of the graphitic lamellae was required to preserve the damping properties. The results showed that, in terms of the specified conditions, heat treatment with continuous cooling at a rate of 10 °C s⁻¹ appeared to be optimal. This variant showed the presence of bainite and martensite in the microstructure with high hardness measured by nanoindentation as well as the optimal value of general Brinell hardness. Full article

In the present work, the effect of quenching and partitioning cycles on the microstructure, hardness, and corrosion behavior of SAE 9254 spring steel was investigated. Initially, the critical phase transformation temperatures were analyzed by dilatometry. The samples were then treated by four routes of quenching and partitioning in a dilatometer with quenching stop temperatures of 250 and 220 °C. The partitioning temperatures were 300 and 400 °C. The partitioning time was 480 s. Quantitative characterization of austenite and martensite volume fractions was carried out by X-ray diffraction. Qualitative characterization was carried out by optical microscopy and scanning electron microscopy in addition to quantitative assessments of the chemical composition of segregations by EDS. The formation of martensite, retained austenite, and bainite was observed. The dilatometric curves displayed the occurrence of volumetric expansion in the partitioning step, indicating the formation of secondary martensite (fresh martensite) during the final cooling process (final quenching). The mechanical properties were evaluated by Vickers microhardness and nanoindentation tests. There was heterogeneity of hardness inside and outside the banding regions. The electrochemical properties were evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization tests in a 0.1 M H₂SO₄ solution. The best corrosion resistance was achieved for samples quenched at 250 °C and partitioned at 400 °C due to the higher volume fraction of retained austenite when compared to the other heat treatment conditions. Full article

Dilatometry was used to simulate and analyze martensite formation in the grain-coarsened heat-affected zone (GCHAZ) of P91 steel for high inter-pass temperatures during multi-pass welding. The inter-pass temperature of 360 °C was within the dual-phase temperature range (~400 °C to 240 °C), but because of the unexpected formation of isothermal martensite, the microstructure at the inter-pass temperature was substantially martensitic and similar in microstructure and hardness to those obtained using lower, conventional inter-pass temperatures (about 250 °C). The results for martensite formation indicate that kinetic classifications for transformation in carbon and alloyed steels should take into account the overlapping effects of the diffusionless transformation and thermally activated processes associated with dislocation motion and the diffusion of interstitial elements. Furthermore, the M_S temperature was found to be highly sensitive to the microstructural state of the austenite and the availability of nucleating sites for martensite formation. The data for the kinetics of martensite formation were inconsistent with the widely used Koistinen and Marburger (KM) equation for predicting the volume fraction of martensite as a function of quench temperature. It is concluded that the KM equation has limited applicability Full article

This study introduces a methodology for characterizing and modeling the viscosity and specific volume–pressure–temperature (pvT) behavior of sheet molding compound (SMC) materials, based on the use of specialized testing equipment. Conventional rheometers are inadequate for such materials due to the presence of long fibers, necessitating the use of specialized equipment like squeeze flow rheometers and pvT dilatometers. Our findings demonstrate that traditional oscillatoric rheometer measurements underestimate the viscosity of CF-SMCs, highlighting the need for advanced, albeit non-standardized, testing methods. Additionally, we found that standard Tait models failed to capture the temperature-dependent porosity of CF-SMCs at low pressures, whereas models based on thermodynamic state variables (TSVs) provided accurate predictions across a broader range of conditions. The study also addressed the complexities introduced by fiber–flow coupling and the fiber orientation in measuring the viscosity, revealing limitations in conventional modeling approaches. The numerical analysis showed that a power law-based anisotropic viscosity model (PL-IISO) combined with a TSV model offered the best predictive performance in finite volume flow simulations, especially for thick-walled regions. However, the current modeling approaches have limited predictive capabilities for the fiber orientation in thin-walled regions. This research underscores the challenges in accurately modeling CF-SMC materials in terms of the fiber orientation, whereas the compression forces needed from the pressing machine could be predicted accurately within an average error of 6.5% in the squeeze flow experiments. Full article

A Si/SiC/SiO₂ (53/44/3 wt.%) composite is evaluated as an anode material for Li-ion batteries. This material, a result of the high-energy ball-milling of a by-product of the carbothermal reduction of silica (Si slag), is predominantly made up of micrometric particles of amorphous or short-range order Si in which submicrometric SiC inclusions are dispersed. Its capacity is 860 mAh g⁻¹ (1.7 mAh cm⁻²) after 200 cycles in half-cell configuration and 1.6 mAh cm⁻² after 70 cycles in full-cell. The SiC component is not electroactive for lithiation but plays a key role in the electrode stability by preventing the formation of the c-Li₁₅S_i4 phase, known to accelerate electrode degradation. It is shown that capacity decay with cycling mainly originates from solid electrolyte interphase (SEI) growth rather than particle disconnections. Complementary wide angle X-ray scattering (WAXS) analyses confirm the SEI grows alongside cycling and allows for the highlighting of its major components, namely, Li₂CO₃ and LiF. The morphological evolution of the electrode upon cycling is studied by electrochemical dilatometry, operando optical microscopy, and focused ion beam (FIB) and broad ion beam (BIB) scanning electron microscopy (SEM). No particle cracking is observed. However, reconstructed 3D imaging of the electrodes before and after 10 and 200 cycles clearly shows that the particles progressively evolve a dendritic structure. The SEI grows on and within the particles and induces a significant decrease in the electrode’s porosity and an increase in its thickness. Full article

The aim of this work is to perform a detailed dilatometric analysis of the decomposition of austenite during the cooling process using experimentally derived continuous cooling transformation (CCT) diagrams for two specific tool steels, X153CrMoV12 Bohdan Bolzano, Bratislava, Slovakia and 100MnCrW4. The dilatometric curves were compared with metallographic evaluations using scanning electron microscopy (SEM). In addition, hardness measurements were performed to obtain additional information about the mechanical properties of the materials. All experimental work was performed using a DIL 805A. The accuracy of the resulting CCT diagrams was verified by comparing them with those calculated with the JMatPro software v12.4. The cooling rates ranged from 20 °C/s to 0.01 °C/s, depending on the specific type of steel tested. The novelty of this research is the combination of experimental and simulation methods to analyze the influence of alloying elements on the kinetics of phase transformations in tool steels. It was found that one of the most significant factors affecting the CCT diagrams is the weight percentage of alloying elements in the steels. These results clearly show that increasing the weight percentage of the content of alloying elements has a significant impact on the accuracy of the simulation results derived from the JMatPro software. Full article

This work investigates the fabrication of Ti6Al4V composites manufactured by powder metallurgy through pressureless infiltration. Porous Ti6Al4V alloy compacts with different particle sizes were fabricated by sintering and then, liquid Ag was infiltrated to obtain composites. Computed microtomography was used to analyze the samples before and after infiltration. Numerical flow simulations and dilatometry tests evaluated the kinetics of Ag infiltration into porous Ti6Al4V compacts. Microstructure was observed by SEM and mechanical strength was evaluated by compression tests. Results showed that the pore properties play a crucial role in the infiltration timing and the distribution of the Ag’s liquid. In particular, large pores allowed the infiltration to start a few °C degrees earlier than samples with smaller pores. Three-dimensional images after infiltration showed that most of the pores were filled and the remaining ones were isolated. The resulting microstructure was composed of Ti₂Ag, α-Ti and Ag phases, indicating that the Ag diffusion occurred. Furthermore, the mechanical strength depends on the interparticle neck sizes and the Ag improves the plastic deformation reached during compression tests. The best results were obtained for the samples with larger pore sizes because the resulting mechanical properties (E = 23 GPa and σ_y = 403 MPa) are close to that of human bones, making it the best candidate as an antibacterial material for biomedical use. Full article

A modified carbide-free bainite (CFB) steel has been developed, building on existing alloys for compatibility with commercial continuous annealing lines (CALs), featuring a low austenitization temperature and short overaging time. The microstructural features of such candidate CFB sheets are compared with those of conventional CFB steel sheets that require higher reheating temperatures and longer overaging times. The effects of annealing parameters such as reheating temperatures and overaging temperatures on phase transformation kinetics and microstructure evolution are presented. The annealing process was simulated in a Gleeble thermomechanical processing simulator, and the microstructural characterization was carried out using XRD, SEM, and EBSD. Reconstruction of parent austenite grains from EBSD data did not reveal any variant selection, regardless of changes in the austenitization temperature, overaging temperature, or carbon content. It was observed that the V1–V2 variant pairing is the most common at the lower overaging temperature for reheating at 950 °C; however, this pairing decreases as the isothermal overaging temperature increases, with variant pairings involving low misorientation boundaries—such as V1–V4 and V1–V8—becoming more frequent. Steels with higher carbon content exhibit no significant changes in their variant pairing, regardless of variations in the austenitizing or isothermal temperatures. The XRD results show that the retained austenite fraction is reduced by increasing the isothermal transformation temperature. Full article

We report on a series of SrMo_1−xMn_xO_3−δ perovskite oxides designed as potential anode materials for solid oxide fuel cells (SOFCs). These materials were synthesized using a citrate method, yielding scheelite-type precursors with nominal SrMo_1−xMn_xO₄ compositions, which were further reduced to obtain the active perovskite oxides. Their structural evolution was examined through X-ray diffraction (XRD) and neutron powder diffraction (NPD). These techniques provided insights into the crystallographic changes upon Mn doping, revealing key factors influencing ionic conductivity. Whereas the oxidized scheelite precursors are tetragonal, space group I4₁/a, the reduced perovskite specimens are cubic, space group Pm-3m, and show the conspicuous absence of oxygen vacancies, even at the highest temperature of 800 °C. The transport properties were analyzed through electrical conductivity measurements, exhibiting a metallic-like behavior. Thermogravimetric analysis (TGA) and dilatometry give insights into the thermal stability and expansion behavior, essential for SOFC operation. Test single SOFCs were built in an electrolyte-supported configuration, on LSGM pellets of 300 μm thickness, assessing the performance of the title materials as anodes. This work emphasizes the critical relationship between the crystal structure and its electrochemical behavior, providing a deeper understanding of how doping strategies can optimize fuel cell performance. Full article

Nowadays, metallic bone replacement is in high demand due to different issues, like sicknesses and accidents. Thus, bone implants are fabricated with tailored properties and microstructure for long-term use in the human body. To improve such implants, 3D printing is the most promising technique. Therefore, this work aims to evaluate the fabrication of porous materials by extrusion 3D printing of Ti6Al4V. Cylindrical samples were fabricated from pellets for metal injection molding of Ti6Al4V powders, creating hexagonal channels with three different sizes. The densification kinetics was evaluated by dilatometry tests, which enabled following the densification of the samples during the sintering cycle. Subsequently, the samples were characterized by scanning electron microscopy and X-ray computed tomography to analyze their microstructure. Compression tests evaluated the mechanical strength of sintered samples. It was found that the hexagonal shape during printing is better defined as the channel size increases. The results show similar behavior for each of the channel sizes during sintering; however, greater densification is obtained as the channel size decreases. Additionally, microporosity is obtained at the particle level, which is completely interconnected, ensuring the passage of fluids through the entire sample. On the other hand, as the channel size increases, Young’s modulus and yield strength are considerably reduced. The main conclusion is that parts with two scales of porosity can be designed by the 3D printing extrusion process. Full article