High Temperature Applications Research Articles

Design and Manufacturing of Shear Stress Sensor for High-Temperature Applications With Embedded Capacitive Floating Unit

Design and Manufacturing of Shear Stress Sensor for High-Temperature Applications With Embedded Capacitive Floating Unit

Oxidation kinetics and electrical properties of oxide scales formed under exposure to air and Ar–H2-H2O atmospheres on the Crofer 22 H ferritic steel for high-temperature applications such as interconnects in solid oxide cell stacks

A 100 h isothermal oxidation kinetics study for Crofer 22H was conducted in air and the Ar–H2-H2O gas mixture (p(H2)/p(H2O) = 94/6) in the range of 973–1123 K. The parabolic rate constant was independent of oxygen partial pressure in the range from 6.2 × 10−24 to 0.21 atm at 1023 and 1073 K, while at 973 and 1123 K it was higher in air than in Ar–H2-H2O. The scales consisted of Cr2O3 and manganese chromium spinel with an Mn:Cr ratio dependent on the oxidation conditions. Cross-scale resistance was evaluated with regards to the application of the steel in solid oxide fuel cells using a number of methods, including X-ray diffraction, scanning electron microscopy, confocal Raman imaging and area-specific resistance measurements.

Microstructural Aspects on Brazing Stainless Steels for High Temperature Applications

A wide range of applications request components that work in an environment where they are subject to high temperatures, combined with a corrosive action of the same environment. The components with a complex geometry can be obtained only using some assembling processes, among which are welding and brazing. One of the most important advantages of these processes is the possibility to obtain a sealed joint, that guarantees it to be waterproof. In comparison with welding process, brazing process has also an important technological advantage: it is a process that is able to produce a quality joint in a very small, narrow and tight places., where is very difficult or almost impossible to reach with other welding processes (e.g. GMAW/MIG – Gas Metal Arc Welding, GTAW/TIG – Gas Tungsten Arc Welding, SMAW – Shield Metal Arc Welding, FCAW - Flux Cored Arc Welding, SAW – Submerged Arc Welding). The research in this direction carried out in University Politehnica Timisoara, was focused on using brazing as a joining process to obtain a complex geometry part working in these environments. The brazed joint will create a dissimilar joint, putting in contact stainless steel with a Ag-Cu brazing alloy, which creates diffusion processes at microstructural level as well as phase transformations (due to thermal cycle and diffusion) which have a large impact on operating behavior of these joints. This paper presents some results on investigation phase and microstructural constituents transformations that took place in these brazed joints.

Irradiation damage evolution dependence on misorientaton angle for ∑ 5 grain boundary of Nb: An atomistic simulation-based study

Abstract Niobium as refractory element holds ability to arrest the primary radiation damage in reactor's fissionable conditions and can withstand high temperature applications. We have inclined the investigation of irradiated Nb ∑ 5 symmetric tilt angled-grain boundary (STGB) models at two high-angled grain boundary misorientation: 53.13 ° (∑ 5(2-10)/ (120)) and 36.87 ° (∑ 5(3-10)/ (130)) respectively. A hybrid of Ziegler-Biersack-Littmark (ZBL) and embedded atom method (EAM) potentials were superimposed to simulate radiation damage. Statistical averaging of the displacement cascades were conducted to study dynamic evolution of the point defects and interstitial clusters at varying magnitudes of primary knock-on atom (PKA) energies, irradiation temperatures and PKA directions respectively. The irradiated GB models were compared with a irradiated bulk Nb specimen and the results of the study indicate that the irradiated Nb system with greater misorientation angle i.e., Nb ∑ 5 (θ = 53.13 ° ) survived with lower number Frenkel pair defects as well as the population small-sized interstitial clusters. The cluster analysis indicated the highest population of interstitial clusters survived in Nb STGB models were irradiated along <1 3 5> PKA direction and 100 keV recoil energies respectively.

Scratch-Induced Wear Behavior of Multi-Component Ultra-High-Temperature Ceramics

Multi-component ultra-high-temperature ceramics (MC-UHTCs) are promising for high-temperature applications due to exceptional thermo-mechanical properties, yet their wear characteristics remain unexplored. Herein, the wear behavior of binary (Ta, Nb)C, ternary (Ta, Nb, Hf)C, and quaternary (Ta, Nb, Hf, Ti)C UHTCs synthesized via spark plasma sintering (SPS) is investigated. Gradual addition of equimolar UHTC components improves the wear resistance of MC-UHTCs, respectively, by ~29% in ternary UHTCs and ~49% in quaternary UHTCs when compared to binary UHTCs. Similarly, the penetration depth decreased from 115.14 mm in binary UHTCs to 73.48 mm in ternary UHTCs and 44.41 mm in quaternary UHTCs. This has been attributed to the complete solid solutioning, near-full densification and higher hardness (~up to 30%) in quaternary UHTCs. Analysis of the worn-out surface suggests pull-out, radial, and edge micro-cracking and delamination as the dominant wear mechanisms in binary and ternary UHTCs. However, grain deformation and minor delamination are the dominant wear mechanisms in quaternary UHTCs. This study underscores the potential of MC-UHTCs for tribological applications where material experiences removal and inelastic deformation under high mechanical loading.

Characterization of Palm Kernel Shell Ash Nanoparticles as Coating Material for High Temperature Applications

The kernel shell of oil palm (Elaesis guineensis) was milled, calcinated and synthesized into nanoparticles (np) with a view to analyzing and ascertaining its high temperature strength. The synthesized particles were characterized to reveal their elemental composition and temperature of maximal decomposition/destruction, with the solgel method employed in the nanoparticle synthesis. The morphology of the Palm Kernel Shell Ash nanoparticles (PKSAnp) viewed from Transmission Electron Microscope (TEM) revealed that the nanoparticles were solid in nature but vary in sizes with some spherical particles visible, and an average particle size found to be 39.17nm. The Electron Dispersion Spectroscope (EDS) result shows that only elements such as C, O, Si, Al, Ca, and K are present in the PKSAnp, with silicon (Si) found to be dominant. Oxides of Silicon and Aluminum (SiO2 and Al2O3) were identified as the key chemical compounds in PKSAnp from X-Ray Fluorescence (XRF) investigation whereas K2O, CaO and Na2O were among the other oxides present in traces. The Thermogravimetric analysis (TGA) curve shows a lower proportion of breakdown and a residual weight stability at temperatures above 1000oC, coinciding with the silica content in PKSAnp. This is comparable and consistent with known high temperature coating materials in previous literature.

Microstructure instability of additively manufactured alloy 718 fabricated by laser powder bed fusion during thermal exposure at 600–1000 ℃

Microstructure and precipitation behavior of alloy 718 produced by laser powder bed fusion (L-PBF) and its recrystallized counterpart were evaluated after thermal exposure at a temperature range of 600–1000 ℃ for up to 1000 h. The as-built 718 featured a microstructure of columnar grains, and dislocation cell structures (DCSs) with chemical segregations (rich in Nb, Ti, Mo and depleted in Cr, Fe) and precipitates (Laves phase and carbonitride). The DCSs remained thermally stable for up to 1000 h at 600 ℃ or 100 h at 700 ℃, but only 10 h at 800 ℃. With the temperature increasing to 900 ℃ and 1000 ℃ for 1 h duration, the DCSs tended to partially disassemble, and the chemical segregations were removed. The chemical segregations at cell boundaries of the as-built 718 promoted the formation of γ′, γ″ and δ phases during aging, leading to a spatially heterogeneous distribution of γ′ and γ″ phases between the cell boundaries and interiors during short exposure time or at lower temperatures. Meanwhile, the coarsening of γ′ and γ″ phases and the phase transformation of γ″ to δ at 700–800 ℃ were facilitated in the as-built 718 compared to the recrystallized ones. A unique precipitation distribution was observed at 700 ℃ that γ′ and γ″ phases precipitated both at the cell boundaries and within cell interiors, while only γ′ formed in the vicinity of cell boundaries. Time-temperature-transformation curves for additively manufactured and recrystallized 718 were constructed based on the microstructure analyses. This study indicates that conventional heat treatment procedures may be suboptimized for additively manufactured 718 in high temperature applications.

Techno-Economic analysis of ceramic matrix composites integration in remaining useful Life Aircraft Engine Hot Section Components

AbstractCeramic Matrix Composites (CMCs), specifically SiC/SiC composites, represent a significant innovation in aerospace material technology, offering superior performance over traditional nickel-based superalloys in high-temperature turbine blade applications. This study presents a novel techno-economic assessment, filling a critical gap in the literature by directly comparing the economic and technical viability of CMCs versus superalloys. Unlike previous studies, which primarily focus on technical performance or cost analysis independently, this work integrates both aspects, providing a holistic comparison across key economic metrics, including acquisition, machining, maintenance, and recycling costs. The results demonstrate that SiC/SiC blades offer a 15–20% higher Net Present Value (NPV) and a 17% greater Internal Rate of Return (IRR) over a 20-year lifecycle than superalloys. Despite higher initial costs, CMCs achieve an estimated 2 to 3 years reduction in payback period, mainly due to their superior thermal and creep resistance, leading to fewer maintenance interventions and longer operational lifetimes. Although machining costs for CMCs are higher, these are more than offset by the long-term savings achieved through improved fuel efficiency and lower maintenance costs. A comprehensive sensitivity analysis, incorporating fluctuations in discount rates and material costs, further validates the economic robustness of CMCs in various operational scenarios. This study is the first to compare CMCs and superalloys, offering new insights into the financial implications of material selection in aerospace manufacturing. The findings present critical engineering recommendations that empower aerospace manufacturers and decision-makers to optimise material selection for improved efficiency and cost-effectiveness in high-performance turbine applications.

Structural, Elastic, Electronic, Dynamic, and Thermal Properties of SrAl2O4 with an Orthorhombic Structure Under Pressure

Its outstanding mechanical and thermodynamic characteristics make SrAl2O4 a highly desirable ceramic material for high-temperature applications. However, the effects of elevated pressure on the structural and other properties of SrAl2O4 are still poorly understood. This study encompassed structural, elastic, electronic, dynamic, and thermal characteristics. Band structure calculations indicate that the direct band gap of SrAl2O4 is 4.54 eV. In addition, the Cauchy pressures provide evidence of the brittle characteristics of SrAl2O4. The mechanical and dynamic stability of SrAl2O4 is evident from the accurate determination of its elastic constants and phonon dispersion relations. In addition, a comprehensive analysis was conducted of the relationship between specific heat and entropy concerning temperature variations.

Effect of different heat treatment on thermal and electrical conductivity, and microhardness of Erbium-reinforced in-situ processed (ZrB2/Al2O3) 7085 AA nanocomposites for high temperature applications

High structurally stable 7085 aluminium alloy (7085 AA) is increasingly gaining more attention in industries such as automotive, electrical and high-temperature applications due to its demand for prolonged usage. The performance potential of conventional 7085 AA properties can be enhanced by reinforcing it with appropriate ceramic nanoparticles (AZ), namely, Aluminium oxide (Al2O3), Zirconium diboride (ZrB2), and rare earth metals, i.e. Erbium (Er), which makes it to be utilized for high-temperature industrial applications. Thus, the primary objective of the present study is to develop 7085 AA/AZ-Er composites having enhanced thermal, electrical and mechanical properties. The composites was synthesized through an In-situ process, followed by homogenization, solution treatment and artificial ageing (T6 and T74 heat treatment). The results obtained through T6 and T74 heat treatment were compared. The concentration of AZ was maintained at 1.0 wt.%, whereas Er was varied by 0.1. 0.3 and 0.5 wt.% in the 7085 AA/AZ composites. The superior properties of 7085 AA/AZ- Er composites achieved in this study are as follows: Thermal conductivity- 153.5 ± 0.7 W/m·K, Electrical conductivity- 21.99 ± 0.08 MS/m, and Hardness- 217.12 ± 3.2 Hv. The hardness and thermal conductivity of T6 heat-treated Er-based composites are found to be superior, while T74 heat-treated composites exhibited significant improvements in electrical conductivity. It is concluded that the appropriate addition of Er concentration plays a vital role in enhancing mechanical, electrical and thermal properties irrespective of the heat treatment process.

Improved thermoelectric performance of α- and β- Cu2Se through suppression of hole density using extrinsic copper vacancies

Modulating Cu+ ion disorder in Cu2Se can enable control over the polymorphism and the carrier density leading to enhanced thermoelectric properties for both α- and β-Cu2Se. Here we report that the incorporation of Cr3+ into the Cu2Se crystal lattice facilitates the stabilization of α-Cu2Se at 300 K leading to a large (∼140%) reduction in the carrier density both below and above the phase transition. This is attributed to the reduction in the density of intrinsic copper interstitials (Cui∙) within the Cu(2-δ-λ)(CrCu..)λ(VCu′)δ(Cuix)δ-2λ(h∙)δ-2λSe crystal lattice. Such optimization of the carrier density led to a large (63%) increase in the thermopower and a drastic (46%) reduction in the total thermal conductivity for both α- and β-Cu2Se matrices. Consequently, a significant enhancement of the thermoelectric performance is observed in the entire temperature range from 300 K to 773 K. This results in high average ZT values for both α-Cu2Se (ZTave = 0.60) and β-Cu2Se (ZTave = 0.97), which paves the way for both near room temperature and high temperatures applications. This work provides a new approach to optimize the thermoelectric performance of Cu2Se-based materials by leveraging the interaction between mobile intrinsic Cui. and extrinsic VCu′ to suppress the hole density.

Spark plasma sintering of high-TC calcium bismuth niobate with superior piezoelectric performance

Calcium bismuth niobate (CaBi2Nb2O9) is a promising ceramic material for high-temperature piezoelectric applications due to its high Curie temperature (TC) of 940 °C. However, its practical use is limited by poor piezoelectric performance and low direct-current (DC) electrical resistivity at elevated temperatures. In this study, we introduced pseudo-tetragonal distortion into CaBi2Nb2O9 by substituting rare-earth thulium ions, which reduced domain wall energy, facilitated domain switching, and decreased the presence of oxygen vacancies. These enhancements significantly improved both the piezoelectric performance and DC electrical resistivity of the material. To further enhance piezoelectric performance, we prepared textured thulium-substituted CaBi2Nb2O9 ceramics with a Lotgering factor (f) of up to 77.4% using a two-step spark plasma sintering method. The resulting textured CaBi2Nb2O9 ceramics exhibited superior piezoelectric performance, with a piezoelectric constant d33 of 25.2 pC/N, four times higher than that of non-textured CaBi2Nb2O9. Importantly, these textured ceramics maintained excellent electrical properties at elevated temperatures, suggesting their suitability for high-temperature piezoelectric device applications.

A near-single-ion conducting polymer-in-ceramic electrolyte for solid-state lithium metal batteries with superior cycle stability and rate capability

Composite solid-state electrolytes (CSE) represent a promising alternative to conventional porous separators and organic liquid electrolyte systems in commercialized lithium metal battery (LMBs), offering effective dendrite suppression, high interfacial compatibility and enhanced cycle life. This study introduces a polymer-in-ceramic electrolyte, which is synthesized by blending perovskite-type inorganic electrolyte Li1.5La1.5TeO6 (LLTeO) with polymethyl methacrylate (PMMA) and polyvinylidene fluoride (PVDF), denoted as PMMA/PVDF-LLTeO. The resulting CSE features a dense, non-porous structure, high mechanical strength, excellent thermal stability, and a broad electrochemical window. Notably, with the incorporation of a high ceramic filler content (up to 70 %), the CSE promotes a hybrid ion transport mechanism, yielding a near-single-ion conducting behavior with an ion transference number of 0.833, and a high elastic modulus of approximately 1 GPa. These attributes collectively contribute to the suppression of dendrite growth, as analyzed through multiphysics-based simulations. Li//Li symmetric cells using PMMA/PVDF-LLTeO-70 exhibit robust lithium stripping-plating stability, with a critical current density of 0.45 mA cm−2. Furthermore, the corresponding Li//LiFePO4 cells exhibit superior rate performance and cyclic stability, achieving over 150 cycles with a capacity retention rate of 92.2 % at high temperatures (60 °C). This research highlights the potential of the proposed CSE with high-temperature applications, significantly improving the safety and performance of LMBs

Effectiveness-MTU modeling approach for hydrogen separation with dense metallic membranes

As hydrogen gains interest as energy vector, so it happens for its purification techniques. In particular, dense metallic membranes are a promising technology for many high-temperature applications. Modeling of hydrogen permeation is a fundamental support to their commercial development. Permeation through metallic membranes, in particular Pd-alloys, is regulated by a generalized form of the Richarson’s equation, where driving force for permeation is due to the difference in hydrogen partial pressure at the membrane surfaces. From the flux expression it is possible to develop a model for a mass exchanger, in analogy with the mathematical description of heat exchangers. For the latter, a well-known method, called , is used to simplify heat transfer problem. The same approach applies to mass exchangers, where the method had already been transferred to reverse osmosis. In this article, method is applied to ideal mass exchangers for hydrogen separation. Effectiveness showed to be influenced by inlet hydrogen fraction, exponent of partial pressures and pressure ratio. Moreover, a procedure to include concentration polarization losses is presented. A rule-of-thumb approach is proposed for an estimation of hydrogen recovery, validated to reproduced an experimental result with less that 7% relative error. shows to be a fundamental support to membrane module design.

High-entropy engineering improved the corrosion resistance of rare earth tantalates

High-entropy RETa3O9 ceramics have garnered significant interest in materials science due to their impressive high melting points and lower thermal conductivity. This study focuses on three types of these ceramics: (La0.2Ce0.2Nd0.2Sm0.2Dy0.2)Ta3O9, (La0.2Ce0.2Nd0.2Sm0.2Tm0.2)Ta3O9, and SmTa3O9.The results indicate that the coefficient of thermal expansion (TEC) for RETa3O9 ceramics remains in the range of approximately 5.94×10-6 K-1 to 6.05×10-6 K-1 when subjected to temperatures from room temperature up to 1400°C. This TEC is notably similar to that of silicon carbide ceramic matrix composites (SiC-CMC), which is essential for compatibility in applications where these materials are used together.Moreover, the study highlights an important finding: after 20 hours of exposure to a CMAS (calcium-magnesium-alumino-silicate) environment at 1300°C, the high-entropy tantalates exhibit significantly reduced susceptibility to corrosion compared to traditional single-component tantalate ceramics. While single-component materials, including SmTa3O9, showed greater degradation, the high-entropy RETa3O9 ceramics maintained their original morphology, free from porosity and cracking.This impressive resistance to CMAS corrosion indicates that the high-entropy design is beneficial in enhancing the durability of tantalates in extreme environments. Consequently, these findings suggest that high-entropy RETa3O9 ceramics hold promise for use as thermal/environmental barrier coating (T/EBC) materials in applications involving SiC-CMCs, potentially leading to improved performance and longevity in high-temperature applications.

Fluorinated Polyimides incorporated with heterogeneous ZrO2@KNbO3 as multiple carrier transport barriers for Ultra-High energy storage

Advanced electronic devices and electrical power systems require high capacitor energy storage, fast charge–discharge speed and high temperature stability. Inorganic and organic nanocomposite film can achieve this great goal, but the major obstacle is the easy failure of breakdown in harsh environments. Here, we report a seires of inorganic–organic composite films prepared by blending a novel core–shell heterogeneous ZrO2@KNbO3 with fluorinated polyimide (FPI). The ZrO2@KNbO3 forms a distinctive sandwich-like microstructure, which delivers the p-n-p heterojunction interfaces. Multiple energy barriers, arisen at the interfaces, block the charge carrier transport. As a result, the 0.3 ZrO2@KN/FPI nanocomposite film achieves ultrahigh energy densities of 11.62 J cm−3 and 7.9 J cm−3 under electric fields of 665.6 MV m−1 and 550 MV m−1 at 25 °C and 150 °C, respectively, giving rise to a concurrent enhancement in breakdown strength and electrical displacement. Additionally, the 0.3 ZrO2@KN/FPI composite film exhibits superior charge–discharge cycling stability, enduring up to 100,000 cycles. This research provides a cutting-edge perspective to regulate the charge transport path, especially to inhibit charge transport at the interfaces, demonstrating a great potential for high-temperature dielectric capacitor applications.

Tribological investigation of new self-fluxing nickel alloys for high temperature application: the effect of silicon distribution on glaze layer formation

The objective of this study is to investigate the tribological performance of new nickel-based self-fluxing alloys for replacing cobalt-based alloys in aircraft components. Two new NiCrSiFeB alloys, manufactured by gravity casting and laser metal deposition processes, having different microstructures, are submitted to fretting loadings and tested at temperatures ranging from ambient to 650 °C. Their wear behavior is compared to a reference Stellite 6 cobalt- based alloy. Although the two NiCrSiFeB alloys have the same chemical composition, the alloy having a coarse microstructure rich in silicates was able to form a protective glaze layer at high temperature as Stellite 6. On the other hand, the alloy having a fine microstructure underwent severe adhesive wear. This highlights the crucial effect of the microstructure and the silicon distribution in activating the formation of a protective glaze layer at high temperatures.

In situ high-temperature emissivity measurements of heat-treated, silicon coated stainless steel for solar thermal applications

Understanding thermal emissivity at high temperatures is crucial for developing efficient materials for solar thermal applications. We present a new approach for creating an efficient material for solar absorber by developing a nano structured surface on stainless steel substrate through Si deposition and annealing. We prepare five samples by annealing them at five temperatures between 700 °C and 1100 °C. Afterwards, we perform a systematic study of the spectral emissivity at elevated temperatures, focusing on different parameters: angle dependence, wavelength dependence, and temperature dependence. The spectral directional emissivity experiments performed in the mid-infrared range reveal a dielectric behavior of the samples in the short wavelength region (λ < 6 μm) and metallic behavior in the long wavelength region (λ > 12 μm). The results indicate an increase in hemispherical and total normal emissivity with measurement temperature (from 200 °C to 700 °C), influenced by oxide/silicide formation due to interdiffusion, and by surface roughness. Notably, samples annealed at 900 °C and 1000 °C demonstrate enhanced thermal stability at 700 °C, showcasing promising characteristics for high-temperature applications. Consequently, this study presents a viable method for developing cost-effective silicon-based solar absorber coatings on stainless steel with tailored properties for solar thermal applications along with its real time high temperature emissivity details.

Deep Learning Accelerated Phase Prediction of Refractory Multi-Principal Element Alloys

The tunability of the mechanical properties of refractory multi-principal-element alloys (RMPEAs) make them attractive for numerous high-temperature applications. It is well-established that the phase stability of RMPEAs control their mechanical properties. In this study, we develop a deep learning framework that is trained on a CALPHAD-derived database that is predictive of RMPEAs phases with high accuracy up to eight phases within the elemental space of Ti, Fe, Al, V, Ni, Nb, and Zr with an accuracy of approximately 90%. We further investigate the causes for the low out of domain performance of the deep learning models in predicting phases of RMPEA with new elemental sets and propose a strategy to mitigate this performance shortfall. While our proposed approach shows marginal improvement in prediction accuracy of RMPEAs with new elemental sets, we should emphasize that overcoming the out-of-domain problem remains largely challenging, particularly in materials science where missing elements or absent material classes in training data hinder predictions, thus slowing the discovery of new potential materials. Predicting phase competition is inherently difficult due to the very small differences in free energies (on the order of meV/atom) that govern competing phases. Current deep learning models, including ours, face significant limitations in capturing these subtle energy differences. Accordingly, more substantial future work is needed to fully address this challenge and achieve robust out-of-domain predictions in complex alloy systems.

Analysis of bio-based epoxy resins: Impact of amine hardeners on thermal, thermomechanical, optical and electrical properties of epoxidized resveratrol with high Tg

Epoxidized resveratrol (RES) has been cured with different amines in order to compare their possibilities to obtain high-temperature resistance of bio-based epoxy resins. Materials obtained from the bio-based monomer present glass transition temperatures (Tg) among the highest ever reported for an epoxy-amine curing system, with extremely high char residue, making them excellent candidates for extremely high-temperature applications. Particularly, epoxidized RES stoichiometrically cured with 4,4′-sulfonyldianiline (DDS) reached 297 °C, measured as the tan δ peak by DMTA, and two other materials, using 4,4′-methylenedianiline (DDM) and 4,4′-diaminodicyclohexylmethane (CAA) as curing agents, exceeded 300 °C. In fact, the material begins to degrade before the chains are fully relaxed, so they are thermosetting that never go completely into the rubbery state. Additionally, this resin improves the direct current (DC) insulating character (~1015 Ωcm) while decreasing the optical band gap (~2 eV) when compared to other epoxy resins available, which is of great interest for photovoltaic applications. Moreover, some of the materials presented a very high char residue proportion when heated (>40 wt% at 800 °C under nitrogen atmosphere), presenting good fire-retardant properties.