Search Results (63)

Proton-conducting ceramics have gained significant attention in various applications. Yttrium-doped barium cerium zirconate (BaCe_xZr_1−x−yY_yO_3–δ) is the state-of-the-art proton-conducting electrolyte but poses a major challenge because of its high sintering temperature. Sintering aids have been found to substantially reduce the sintering temperature of BaCe_xZr_1−x−yY_yO_3–δ. This work evaluates, for the first time, the impact of NiO and ZnO addition in three different loadings (1, 3, 5 mol%), via wet mechanical mixing, on the sintering and electrical properties of a low cerium-containing composition, BaCe_0.2Zr_0.7Y_0.1O_3–δ (BCZY). The sintering temperature remarkably dropped from 1600 °C (for pure BCZY) to 1350 °C (for NiOBCZY and ZnOBCZY) while achieving > 95% densification. In general, ZnO gave higher densification than NiO, the highest being 99% for 5 mol% ZnOBCZY. Dilatometric studies revealed that ZnOBCZY attained complete shrinkage at temperatures lower than NiOBCZY. Up to 650 °C, ZnO showed higher conductivity compared to NiO for the same loading, mostly due to a higher extent of Zn incorporation inside the BCZY lattice as seen from the BCZY peak shift to a lower Bragg’s angle in X-ray diffractograms, and the bigger grain sizes of ZnO samples compared to NiO captured in scanning electron microscopy. At any temperature, the variation in conductivity as a function of sintering aid concentration followed the orders 1 mol% > 3 mol% > 5 mol% (for ZnO) and 1 mol% < 3 mol%~5 mol% (for NiO). This difference in conductivity trends has been attributed to the fact that Zn fully dissolves into the BCZY matrix, unlike NiO which mostly accumulates at the grain boundaries. At 600 °C, 1 mol% ZnOBCZY showed the highest conductivity of 5.02 mS/cm, which is, by far, higher than what has been reported in the literature for a Ce/Zr molar ratio <1. This makes ZnO a better sintering aid than NiO (in the range of 1 to 5 mol% addition) in terms of higher densification at a sintering temperature as low as 1350 °C, and higher conductivity. Full article

The continuous cooling transformation (CCT) curves of undercooled austenite serve as crucial references for obtaining desired microstructures and properties in metallic materials (particularly deformed metals) through heat treatment. In this study, static and dynamic CCT curves were constructed for experimental steels micro-doped with rare earth element Ce by combining temperature-dilatometric curves recorded after austenitization at 900 °C with microstructural characterization and microhardness measurements. Comparative analyses were conducted on the microstructures and microhardness of three experimental steels with varying Ce contents subjected to sizing (reducing) diameter deformation at 850 °C and 950 °C. The CCT experimental results revealed that the microhardness of the tested steels increased with cooling rates. Notably, dynamic CCT specimens cooled at 50 °C/s to room temperature following superheated deformation exhibited 56.7 HV5 higher microhardness than static CCT specimens, accompanied by increased martensite content. The reduction of deformation temperature from 950 °C to 850 °C resulted in the expansion of the bainitic phase region. The incorporation of trace Ce elements demonstrated a significant enhancement in the microhardness of 30MnNbRE steel. This research proposes an effective processing route for improving strength-toughness combination in microalloyed oil well tubes: introducing trace Ce additions followed by sizing (reducing) diameter deformation at 950 °C and subsequent ultra-fast cooling at 50 °C/s to room temperature. This methodology facilitates the production of high-strength/toughness steels containing abundant martensitic microstructures. Full article

This paper presents the results of research on the kinetics of transformations in the two-phase (α + β) Ti-6Al-4V alloy. The transformation start and end temperatures during heating at different rates were determined using a dilatometer. A modified dilatometer was employed, equipped with an acoustic emission measurement apparatus and software enabling the assessment of sample dimensional changes during heating and cooling. The results were obtained in the form of dilatometric curves. Additionally, the occurrence of the transformation was confirmed by acoustic emission signals. In the study of the Ti-6Al-4V alloy, acoustic emission refers to the application of this non-destructive technique to monitor the alloy’s behavior during thermal processes. As the temperature increased, regardless of the heating rate, the α→β transformation was observed to occur after exceeding 900 °C. Within the transformation range, acoustic emission signals were recorded. Moreover, it was found that the applied research methods enabled the identification of signal components originating from the transformation. The application of acoustic methods in the analysis of phase transformations opens new possibilities for their use in industry. Full article

Titanium boride (TiB₂) is a material classified as an ultra-high-temperature ceramic. The TiB₂ structure is dominated by covalent bonds, which gives the materials based on TiB₂ very good mechanical and thermal properties, making them difficult to sinter at the same time. Obtaining dense TiB₂ polycrystals requires a chemical or physical sintering activation. Carbon and molybdenum disilicide (MoSi₂) were chosen as sintering activation additives. Three series of samples were made, the first one with carbon additives: 0 to 4 wt.%; the second used 2.5, 5 and 10 wt.% MoSi₂; and the third with both additions of 2 wt.% carbon and 2.5, 5 and 10 wt.% MoSi₂. On the basis of the dilatometric sintering analysis, all additives were found to have a favourable effect on the sinterability of TiB₂, and it was determined that sintering TiB₂ with the addition of carbon can be carried at 2100 °C and with MoSi₂ and both additives at 1800 °C. The polycrystals were sintered using the hot-pressing technique. On the basis of the studies conducted in this work, it was found that the addition of 1 wt.% of carbon allows single-phase TiB₂ polycrystals of high density (>90%) to be obtained. The minimum MoSi₂ addition, required to obtain dense sinters with a cermet-like microstructure, was 5 wt.%. High density was also achieved by the materials containing both additives. The samples with higher MoSi₂ content, i.e., 5 and 10%, showed densities close to 100%. The mechanical properties, such as Young’s modulus, hardness and fracture toughness (K_Ic), of the polycrystals and composites were similar for samples with densities exceeding 95%. The Vickers hardness was 23 to 27 GPa, fracture toughness (K_IC) was 4 to 6 MPa·m^0.5 and the Young’s modulus was 480 to 540 GPa. The resulting TiB₂-based materials showed potential in high-temperature applications. Full article

The paper presents a reliable technology combining sol–gel synthesis and spark plasma sintering (SPS) to obtain SrTiO₃ perovskite-type ceramics with excellent physicomechanical properties and hydrolytic stability for the long-term retention of radioactive strontium radionuclides. The Pechini sol–gel method was used to synthesize SrTiO₃ powder from Sr(NO₃)₂ and TiCl₃ (15%) precursors. Ceramic matrix samples were fabricated by SPS in the temperature range of 900–1200 °C. The perovskite structure of the synthesized initial SrTiO₃ powder was confirmed by X-ray diffraction and thermal analysis results. Scanning electron microscopy revealed agglomeration of the nanoparticles and a pronounced tendency for densification in the sintered compact with increasing sintering temperature. Chemical homogeneity of ceramics was confirmed by energy dispersive X-ray analysis. Physicochemical characteristic studies included density measurement results (3.11–4.80 g·cm⁻³), dilatometric dependencies, Vickers microhardness (20–900 HV), and hydrolytic stability (10⁻⁶–10⁻⁷ g·cm⁻²·day⁻²), exceeding GOST R 50926-96 and ISO 6961:1982 requirements for solid-state matrices. Ceramic sintered at 1200 °C demonstrated the lowest strontium leaching rate of 10⁻⁷ g/cm²·day, optimal for radioactive waste (RAW) isolation. The proposed approach can be used to fabricate mineral-like forms suitable for RAW handling. Full article

The paper presents the results of studies on the viscosity of the glass mass in various temperature ranges, determining the basic technological parameter, very important from the point of view of melting and forming. For this purpose, six sets based on natural raw materials such as basalt, dolomite, and amphibolite, modified with different amounts of float glass cullet, were melted. The melting process was carried out in an electric furnace at the temperature of 1450 °C for 2 h. Using the dilatometric method, high-temperature microscopy and theoretical calculation methods, the viscosity of the produced glasses was determined in various temperature ranges. Comparative analyses of the employed methods were carried out. The significance of the applied calculation methods for aluminosilicate glasses depending on the basic chemical composition of the glasses was presented. The relationship between the manner of incorporating amphoteric ions Al³⁺, Fe³⁺ and Mg²⁺ into the glass structure and the change in viscosity in the temperature range corresponding to the working point range at 10⁴ [dPa·s] viscosity and the relaxation range—T_g temperature at 10¹³ [dPa·s] viscosity was justified. It was justified that in order to plot the viscosity curve with the correct slope in the forming range for aluminosilicate glasses, it is appropriate to use the two-point method based on the fixed viscosity points of 10⁴ [dPa·s] and 10¹³ [dPa·s]. Full article

Quenching and partitioning (Q&P) heat treatments of low-alloy steels with exceptional property combinations are particularly promising. In this study, we characterize for the first time a new low-alloy steel to be processed using Q&P heat treatments. In combined experimental and numerical studies, we design a novel approach that effectively combines the short cycle times of press hardening with the excellent property profiles of Q&P-treated steels. We identify an appropriate austenization temperature of 950 °C and a portioning temperature of 250 °C for Q&P heat treatments through dilatometric studies. We adjust a number of reference conditions with fractions of 2.1 to 6.3 wt.% of retained austenite, resulting in tensile strengths up to 1860 MPa and elongations to failure up to 7%. Initial numerical designs of the process can identify varying temperature profiles and cooling rates depending on the position in the die. The results show that the geometry of the part plays a minor role, but the die temperature of 200 °C is the dominant factor for successful partitioning directly in the press hardening process. Full article

Thermal expansion measurements were used to characterize phase transformations in metastable β-Ti alloys (Ti15MoxSi) without and with various Si additions (where x = 0, 0.5, 1.0, 1.5, and 2 in wt.%) during linear heating at two heating rates of 5 and 10 °C/min up to 850 °C. For this study, five alloys were developed and examined in terms of their presence phases, microstructures, and starting and final transformation temperatures. According to the results, all of the as-cast samples primarily include an equiaxed β-Ti phase. The influence of phase transformation on the material dimensions was discussed and compared with the variations in Si contents. The transformation was investigated using a dilatometric technique for the developed alloys during continuous heating and cooling. The dilatometric curve of heating revealed two distinct reflection points as the heating temperature increased. The starting transformation temperature (T_s) to obtain the ω-phase was reported at 359 °C without Si addition; whereas the final transformation temperature (T_f) of the dissolution of α-phase was obtained at 572 °C at a heating rate of 10 °C/min. At 2 wt.% Si, the first derivative curves reported T_s and T_f transforming temperatures of 314–565 °C (at a 5 °C/min heating rate) and 270–540 °C (at a 10 °C/min heating rate), respectively. The T_s and T_f transforming temperatures were significantly decreased with Si additions, which decreased the β-transus temperature. Moreover, the thermal expansion coefficient curves of the investigated alloys without and with 2 wt.% Si were studied. The transformation heating curves have an S-shaped pattern, according to the results. Full article

This study investigates the sintering behaviour and properties of WC-based composites in which WC was mixed with W5vol%Ni in concentrations of 10vol% and 20vol%. Colloidal processing in water and spark plasma sintering were employed to disperse the WC particles and facilitate sintering. The addition of W5vol%Ni improved the sintering process, as evident from a lower onset temperature of shrinkage determined through dilatometric studies. All samples exhibited the formation of tungsten monocarbide (W₂C), with a more pronounced presence in the WC/20(W5vol%Ni) composite. Sintering reached its maximum rate at 1550 °C and was completed at 1600 °C, resulting in a final density exceeding 99.8%. X-ray diffraction analysis confirmed the detection of WC and W₂C phases after sintering. The observed WC content was higher than expected, which may be attributed to carbon diffusion during the process. Macro-scale mechanical characterisations revealed that the WC/10(W5vol%Ni) composite exhibited a hardness of 18.9 GPa, while the WC/20(W5vol%Ni) composite demonstrated a hardness of 18.3 GPa. Increasing the W5vol%Ni binder content caused a decrease in mechanical properties due to the formation of W₂C phases. This study provides valuable insights into the sintering behavior and properties of WC/W5vol%Ni composites, offering potential applications in extreme environments. Full article

The paper deals with the dilatometric study of high-alloy martensitic tool steel with the designation M398 (BÖHLER), which is produced by the powder metallurgy process. These materials are used to produce screws for injection molding machines in the plastic industry. Increasing the life cycle of these screws leads to significant economic savings. This contribution focuses on creating the CCT diagram of the investigated powder steel in the range of cooling rates from 100 to 0.01 °C/s. JMatPro^® API v7.0 simulation software was used to compare the experimentally measured CCT diagram. The measured dilatation curves were confronted with a microstructural analysis, which was evaluated using a scanning electron microscope (SEM). The M398 material contains a large number of carbide particles that occur in the form of M₇C₃ and MC and are based on Cr and V. EDS analysis was used to evaluate the distribution of selected chemical elements. A comparison of the surface hardness of all samples in relation to the given cooling rates was also carried out. Subsequently, the nanoindentation properties of the formed individual phases as well as the carbides, where the nanohardness and reduced modulus of elasticity (carbides and matrix) were evaluated. Full article

Elastic properties of materials and their changes with temperature are important for their applications in engineering. In the present study the influence of phase composition and temperature of AISI 4130 alloy on Young’s modulus (E_d), shear modulus (G_d), and damping (Q⁻¹) was carried out by the impulse excitation technique (IET). The material characterization was performed using confocal microscopy, XRD, SEM, HV, and dilatometry. A stable structure, composed of ferrite (BCC) and pearlite (α-Fe + Fe₃C), was obtained by annealing. Metastable structure of martensite (BCT) was obtained by quenching. The E_d, G_d, and Q⁻¹ were measured by varying the temperature from RT to 900 °C. The values of E_d and G_d, at RT, were determined as 201.5 and 79.2 GPa (annealed) and 190.13 and 76.5 GPa (quenched), respectively. In the annealed steel, the values E_d and G_d decrease linearly on heating up to 650 °C, with thermal expansion. In the quenched steel, weak changes occurred in the dilatometric curve, E_d, G_d, and Q⁻¹, in the range of 350–450 °C, which indicated decompositions of the martensitic phase. A sharp decrease in the moduli and high peak of Q⁻¹ were observed for both samples around 650–900 °C, revealing low lattice elastic stability of the phases during transformations α(BCC) + Fe₃Cγ(FCC). Full article

The rheological properties of the Zr-2.5Nb alloy by the strain rate range of 0.5–15 s⁻¹ and by the temperature range of 20–770 °C was studied. The dilatometric method for phase states temperature ranges was experimentally determined. A material properties database for computer FEM simulation regards the indicated temperature-velocity ranges were created. Using this database and DEFORM-3D FEM-softpack, the radial shear rolling complex process numerical simulation was carried out. The contributed conditions for the ultrafine-grained state alloy structure refinement were determined. Based on the simulation results, a full-scale experiment of Zr-2.5Nb rod rolling a on a radial-shear rolling mill RSP-14/40 was carried out. It takes in seven passes from a diameter of 37–20 mm with a total diameter reduction ε = 85%. According to this case simulation data, the total equivalent strain in the most processed peripheral zone 27.5 mm/mm was reached. Due to the complex vortex metal flow, the equivalent strain over the section distribution was uneven with a gradient reducing towards the axial zone. This fact should have a deep effect on the structure change. Changes and structure gradient by sample section EBSD mapping with 2 mm resolution were studied. The microhardness section gradient by the HV 0.5 method was also studied. The axial and central zones of the sample by the TEM method were studied. The rod section structure has an expressed gradient from the formed equiaxed ultrafine-grained (UFG) structure on a few outer millimeters of the peripheral section to the elongated rolling texture in the center of the bar. The work shows the possibility of processing with the gradient structure obtaining and enhanced properties for the Zr-2.5Nb alloy, and a database for this alloy FEM numerical simulations are also presents. Full article

Ruddlesden-Popper La_2−xBa_xNiO_4±δ (x = 0–1.1) nickelates were prepared by a glycine-nitrate combustion route combined with high-temperature processing and evaluated for potential application as electrocatalysts for solid oxide cells and electrochemical NO_x elimination. The characterization included structural, microstructural and dilatometric studies, determination of oxygen nonstoichiometry, measurements of electrical conductivity and oxygen permeability, and assessment of chemical compatibility with other materials. The formation range of phase-pure solid solutions was found to be limited to x = 0.5. Exceeding this limit leads to the co-existence of the main nickelate phase with low-melting Ba- and Ni-based secondary phases responsible for a strong reactivity with Pt components in experimental cells. Acceptor-type substitution of lanthanum by barium in La_2−xBa_xNiO_4+δ is charge-compensated by decreasing oxygen excess, from δ ≈ 0.1 for x = 0 to nearly oxygen-stoichiometric state for x = 0.5 at 800 °C in air, and generation of electron-holes (formation of Ni³⁺). This leads to an increase in p-type electronic conductivity (up to ~80 S/cm for highly porous La_1.5Ba_0.5NiO_4+δ ceramics at 450–900 °C) and a decline of oxygen-ionic transport. La_2−xBa_xNiO_4+δ (x = 0–0.5) ceramics exhibit moderate thermal expansion coefficients, 13.8–14.3 ppm/K at 25–1000 °C in air. These ceramic materials react with yttria-stabilized zirconia at 700 °C with the formation of an insulating La₂Zr₂O₇ phase but show good chemical compatibility with BaZr_0.85Y_0.15O_3−δ solid electrolyte. Full article

This study aims to use natural carbonated Tunisian clay as an aluminosilicate precursor for the elaboration of phosphate-based geopolymers, which yields to the valorization of this common material in Tunisia. In addition, the presence of calcium carbonate in this clay allows the investigation of this associated mineral’s effect on the properties of geopolymeric materials. To achieve these purposes, several experimental techniques were used, namely fluorescence (FX), particle size analysis, thermogravimetric analysis (TGA), differential thermal analysis (DTA), dilatometric analysis, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The mechanical strength and the open porosity of the obtained geopolymeric samples were tested by the compression test and the standard test method for water absorption, respectively. The findings of this work show that the used Tunisian clay can present an attractive aluminosilicate precursor for the synthesis of phosphate-based geopolymers. It also shows that the chosen calcination temperature of the raw clay considerably modifies the reactivity of minerals during geopolymerization and, consequently, strongly affects the properties and structure of the geopolymeric samples. These effects were attributed essentially to the formation of new calcium crystalline phases in the obtained geopolymeric samples. In fact, the anorthite (CaAl₂Si₂O₈) phase appears in all the samples but in greater abundance in those obtained from the clay calcined at 550 °C, and the brushite phase (CaHPO₄·2H₂O) appears only in the samples obtained from the clay calcined at 950 °C. All these new crystalline phases are strongly dependent on the state of the calcite present in the calcined clay. Full article

Although highly developed countries are trying to diversify away from coal-based energy, many economies rely on this resource. Its consumption results in the production of carbon dioxide, which promotes global warming, necessitating its sequestration. This paper presents the sorption–dilatometric relationships of hard coal samples differing in vitrinite and inertinite content. The studies were carried out under isothermal conditions (298 K) at a free pressure drop complemented by measurements under non-isothermal conditions (298 K to 323 K). The tests were performed on an original apparatus, based on the operation of an Arduino microcontroller. For the natural porosity to be preserved and for a better representation of the behaviour of the coal–gas system, samples in the form of cuboidal blocks were used, making this apparatus unique worldwide. Based on the study, it appears that the difference in petrographic composition affects the behaviour of the coal structure, influencing differences in the sorption–dilatometric properties. In the case of the sample with higher vitrinite content, the amount of adsorbed gases is higher. Full article