Key Engineering Materials

Preface

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062

Elastic Anomalies in the 2D Van Der Waals Ti3C2Tx MXene: Possible Sliding Ferroelectricity and Ordering of Intercalated Halides

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Francesco Cordero, Hanna Pazniak, Thierry Ouisse, Jesus Gonzalez-Julian, Aldo Di Carlo, Viktor Soprunyuk, Wilfried Schranz
MXenes are 2D carbides and nitrides of transition metals whose layers are kept by van derWaals forces. These materials are generally metallic and easily intercalate several types ofmolecules and ions, so that they are studied for various types of applications, from energystorage to corrosion resistance. We measured the dynamic Young’s modulus of self-standingfilms of Ti3C2Tx with the free flexural resonance and with the DMA, finding evidence of a previouslyunnoticed phase transition at TC = 350 K. In a previous paper it is argued that the transition should be related to the onset of sliding ferroelectricity. This is a new type of ferroelectricity known in bilayers of graphene, BN and few chalcogenides, with which ultrafast andstable ferroelectric memories have already been realized. If confirmed, Ti3C2Tx would the firstMXene exhibiting sliding ferroelctricity and metallic conduction. The present work is focusedon the effect of the intercalatation of molecules, mainly water, in the intralayer space. Theinterlayer nature of the transition at 350 K is demonstrated by suppressing it through intercalationof H2O. Preliminary results are also presented on composite Ti3C2Cl2-KBr, where giantsoftening upon heating up to 800 K and a final stabilization with elastic anomalies around250 K might be due to intercalation of K and its subsequent ordering/disordering. This mightopen new perspectives in the study of the behaviour of intercalated ions in electrodes forsupercapacitors and batteries.

Study of the Thermoelastic Effect in GaN

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Iva Tkalcec-Vaju, Nicolas Grandjean, Daniele Mari
Young’s modulus and internal friction of bulk GaN single crystal samples were measured as a function of temperature in 100 K to 700 K range. The internal friction strongly depends on sample dimensions and measurement frequency (3 – 10 kHz). The experimental values are compared to the theoretical model for thermoelastic damping. The model and the experimental data match very well in the whole temperature range and for different frequencies indicating that the thermoelastic damping is the main energy dissipation mechanism.

Solid Solution of Metal Dopants in Semiconducting β-FeSi2 Matrix

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Sopheap Sam, Kosuke Yamazaki, Hiroshi Nakatsugawa
Metal dopants are commonly used to improve the transport properties of semiconducting iron silicide (β-FeSi2). However, the formation of metallic phases is sensitive to the addition of dopants, especially when they reach their solubility limits. Those secondary phases negatively impact on the transport properties of the materials. In this study, the strategy to investigate the metal solubility in β-FeSi2 matrix based on crystal structure transition, phase fraction, and microstructural evolution was established. The X-ray diffraction results show that the peak intensity of the metallic phases (ε-FeSi and α-Fe2Si5) increases with increasing doping level. For Mn-doped β-Fe1−xMnxSi2, phase fraction analysis shows that the semiconducting β phase remains the dominant phase (>95%) up to x = 0.08, whereas metallic phases become dominant for x > 0.08. Although the β-phase persists up to x = 0.08, local compositional analysis reveals that the solubility of Mn within the β-phase decreases with increasing formation of secondary phases. The local elemental distribution analysis shows that Mn and Co, respectively, have a solid solution limit of ~6.3±0.1 % and ~8.8±0.7 % in β-FeSi2. It is found that Mn and Co have higher solubility than Ni. Our study provides insights into the strategy to probe the solubility of dopants, which could be beneficial for performance enhancement in semiconducting iron silicide systems.

Fabrication of ZnO-NiO Nanocomposite/ Nano-Crystalline Silicon Thin Film Solar Cell

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Soumour Thamri, Mohamed Haythem Raouadi
This work aims to investigate efficient ZnO-NiO (zinc oxide-nickel oxide) nanocomposite/nanocrystalline silicon µc-Si solar cells. The µc-Si film was fabricated by annealing hydrogenated amorphous silicon α-Si: H deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD), and the nanocomposite ZnO-NiO thin film was manufactured using the sol-gel spin coating technique. The experimental study highlights the physical properties of the device’s thin films. The enhancement of structural properties is confirmed by Raman spectroscopy. The crystalline fraction is estimated to be 60% for µc-Si. The XRD results show sharp peaks for ZnO-NiO and µc-Si, indicating good crystallinity, which is crucial for solar cell efficiency. The association of µc-Si/ZnO-NiO considerably enhances the optical properties, reducing the reflectivity to 5% when compared with the amorphous silicon/ZnO-NiO association. The conductivity is also improved from 50 to 1 (Ω cm)-1. The solar cell is then theoretically investigated using the Solar Cell Capacitance Simulator (SCAPS-1D). The parameters used in the simulation, including the effective density of states, electron and hole mobilities, and the band gap energy, and their impact on device performance were analyzed. The amorphous silicon/ZnO-NiO device was also theoretically investigated for comparison purposes. The simulated nanocrystalline solar cell displayed a theoretical efficiency of 28% using SCAPS-1D, an open-circuit voltage (Voc) of 0.8 V, and a short-circuit current density (Jsc) of 42 mA/cm². The theoretical electrochemical study reveals improved charge transport and a high effective lifetime, in agreement with the high-power conversion efficiency. The simulation of external quantum efficiency yields good results in the UV-vis-NIR range, surpassing those of the amorphous silicon/ZnO-NiO solar cell, particularly for wavelengths exceeding 600 nm. The SCAPS-1D investigation significantly reduces manufacturing costs and energy losses by optimizing the solar cell design and validates these results with theoretical findings that highlight the potential of this solar cell as a highly efficient and cost-effective device.

In-Flight Investigation of Floating Beads for Sloshing Mitigation for Liquid-Fueled Rockets

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Maxime Christophe Nicolas Roux, Benjamin Arthur Hugo Meunier, Loup Cordey, Daniele Mari
Sloshing, characterized by free-surface wave formation in partially filled tanks under forced excitation, remains a major challenge in aerospace engineering, particularly for propellant tanks in launch vehicles. Laboratory studies have demonstrated that a granular layer placed at the liquid surface can significantly attenuate sloshing waves, provided that the granular medium remains compact. However, the performance of this mitigation strategy under real flight conditions has yet to be assessed. In this work, we investigate sloshing mitigation using a granular surface layer through an in-flight experiment conducted aboard a supersonic sounding rocket. The results show that granular surface damping is effective under realistic launch conditions as long as sufficient apparent gravity preserves the cohesion of the granular layer. Conversely, under near-microgravity conditions, loss of granular compactness leads to a breakdown of the damping mechanism. These findings indicate that granular-based sloshing mitigation is well suited for first-stage launch vehicles and sounding rockets, but is unlikely to remain effective during extended microgravity phases.

Acoustic Insulation of Panels Made from Recycled Plastics and Resin

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Rosana Gaggino, Laura Gaetan, Lucas Peisino
In social housing are commonly used panels made with wood particles like partitioning walls, because of its low cost and ease of assembly, dry way. One problem with these panels is their low acoustic insulation. In the Experimental Economical Housing Center of Cordoba, Argentina, a research team has developed panels for housing made from recycled plastics and polyester resin, more ecological than the traditional ones made with wood particles, and with technical advantages. They are manufactured with recycled various plastics from food, perfumery or cleaning packaging, waste production from factories due to failures in sheet thickness or ink application. These panels contribute to the environmental decontamination, because they are made from plastic residues. Most of this waste is buried, accumulated or burned in municipal garbage dumps without any use, causing environmental degradation. The technical advantages of these panels are that they have higher acoustic insulation than conventional panels made with wood chips or fibers. They are also water resistant, and they have higher flexural resistance. This paper presents the study about the acoustic insulation property of this panel, comparatively with other conventional panels made with wood particles. Besides, different designs of multilayer panels for housing enclosures are presented, with steel frame structure, and the corresponding Sound Reduction Index of each alternative was calculated. The results were compared with the regulations in force in our country (IRAM Standard 4044 - 2014) regarding acoustic requirements, to verify its compliance.

From the Maxwell’s Equations of Lattice Deformations to the Description of the Universe by a « Crystalline Ether »

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Gerard Gremaud
Using Eulerian coordinates to describe solid lattice deformations, it has been shown that the set of equations known as Maxwell’s equations—typically applied to electromagnetic phenomena in vacuum or matter—can also describe the elastic, anelastic, and plastic deformations of isotropic solid lattices containing topological defects such as dislocations and disclinations, under conditions of constant and homogeneous expansion. The analogy between the two physical systems is complete: it extends beyond one of the two Maxwell equation pairs in vacuum to both pairs, and includes analogues to dielectric polarization, magnetization, electric charges, and currents. In the Eulerian approach, Maxwell’s equations emerge as a special case derived from a tensor theory of lattice deformation, reducible to a vector formulation only for constant and homogeneous expansion. When dynamic and non-homogeneous expansions are considered, the tensorial nature of the theory becomes essential. This generalization naturally leads to a new conceptual framework for the Universe based on the existence of a crystalline ether. This framework offers a simple, unified, and coherent description of all major theories of modern physics—including electromagnetism, relativity, gravitation, quantum physics, cosmology, and the Standard Model of particle physics.

Dynamics of Full Skyrmions in a Chiral Liquid Crystal

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Clémence Bachmann, Daniele Mari, Sylvain Brechet
We investigate the dynamics of full skyrmions in chiral liquid crystals using an Eulerian formalism originally developed for topological defects in crystals. We show how this approach can be extended to liquid crystals and related to the Frank–Oseen description. Within this framework, skyrmions are characterised by their associated distortion charges, and their dynamics are derived from a generalised Peach–Koehler force combined with Newton’s second law. We demonstrate that the resulting equations of motion recover the behaviour reported in previous studies, in particular those of Alvim et al., while providing a purely analytical perspective. This approach offers a unified and conceptually transparent description of skyrmion dynamics and suggests possible extensions to interacting skyrmions and other topological defects.

Optimization Studies on Machining of Boron Nitride Reinforced with Al Hybrid Composite in WEDM Process Using Taguchi – Dear Based Optimization

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Murugadoss Palanivendhan, Thangaraj Muthuramalingam
Increasing demand for improving the strength of Aluminium Alloy (AMCs), which are widely used in the aerospace, automobile, and defence industries, has been seen in recent years. Aluminum 7075 (Al-7075) is a widely used aluminium alloy because of its high wear opposition and process-ability. By dispersing a suitable combination of Boron Nitride in the aluminium alloy, new techniques are being developed to im-prove the hardenability, strength and hardness of the composite. However, these hard-reinforced composites pose a number of difficulties during the machining process using WEDM process. The performance measures and surface topography acquired and input process parameters are also need to be observed and explained with aid of Taguchi-DEAR methodology. The material removal rate and kerf width have been checked and evaluated using Taguchi-DEAR methodology. The proposed method can efficiently enhance the cutting process with les tool wear and heat affected zone. 32 µs (Ton), 36 µs (Toff), 3.5 A (I), and 4.74 m/min (WF) were discovered to be the optimal arrangement of input factors in the WEDM process, with an error accuracy of 1.6%.

Design and Manufacturing of Defect-Free PumpCasings: A Numerical and Experimental Approach

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Nguyen Dang Khoa, Tran Ba Trung Nam, Pham Quang Trung
Internal shrinkage defects often occur in sand-cast gray cast iron pump casings, particularly in areas with abrupt thickness variations where heat dissipation is limited. These defects form during the final stage of solidification when isolated liquid metal cannot be properly fed. In this study, the solidification behavior of an industrial pump casing is investigated through coupled thermal–flow simulation to analyze temperature gradients and feeding paths. The results show that delayed solidification at the flange–root junction leads to isolated liquid zones that develop into shrinkage cavities. By modifying the feeding layout, heat extraction and directional solidification toward the riser are improved. Experimental casting with the optimized design shows no visible shrinkage defects and achieves an average hardness of 42.3 HRA. These findings highlight the importance of maintaining solidification continuity to eliminate defects in gray cast iron pump casings [1].

Development and Validation of a Cost-Effective Rotary Friction Welding Machine by Repurposing a J23 Mechanical Press Frame

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Nguyen Dang Khoa, Pham Quang Trung, Dinh Duy Khoa
This study presents the comprehensive design and fabrication of a bespoke laboratory-scale Rotary Friction Welding (RFW) machine, developed by repurposing a J23 mechanical press frame to provide a cost-effective research platform. The system integrates a 7.5 kW motor with VFD control for precise rotational speeds up to 1500 RPM and a two-stage hydraulic circuit to manage friction and forging pressures. To validate the machine's efficacy, twenty experimental runs were conducted on similar-material joints, specifically AISI 304 stainless steel, AA1050 aluminum, and AISI 1030 structural steel. Mechanical testing and microstructural analysis demonstrated that the system consistently produces high-integrity bonds, with AISI 1030 steel joints achieving 100% joint efficiency and AISI 304 samples reaching ultimate tensile strengths exceeding 800 MPa. The results confirm that the reoriented horizontal frame maintains the necessary axial alignment for high-quality solid-state joining, making it a reliable and accessible tool for academic investigation into RFW process optimization.

Theoretical and Analytical Methods for Determining Heat Transfer Coefficients in Evaporation Processes

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Tibor Poós, Hamza Abu-Zienah
In open-surface evaporation systems, the simultaneous transfer of heat and mass is vital for establishing the interrelated exchange of energy and mass between liquid and gas phases. This research offers a comprehensive examination of the physical mechanisms that control evaporation in both natural and forced convection scenarios. It also assesses different theoretical and empirical approaches for calculating the heat transfer coefficient. It has been shown through experiments and numerical analyses conducted in the past that the precision of predictions regarding heat and mass transfer is greatly influenced by factors such as geometrical configurations, convection regimes, and measurement accuracy. Various analytical methods are examined, such as the heat balance equation method that connects heat flux to temperature difference and evaporation rate through interfacial energy balance, and the dimensional analysis method that formulates general correlations based on important dimensionless numbers like Nusselt, Prandtl, Reynolds, and Rayleigh. Moreover, the heat–mass transfer analogy offers a practical framework for estimating one coefficient based on the other by taking advantage of the similarity between temperature and concentration fields. Furthermore, the Ackermann correction factor is implemented to consider the effect of vapor flow on the heat transfer, thereby improving estimations of the heat transfer coefficient during evaporation and diffusion. This research creates an extensive framework for the analysis of open-surface evaporation and the enhancement of heat and mass transfer coefficient predictions. This is achieved through a combination of theoretical, experimental, and analogy-based methods, leading to improvements in the design and functioning of thermal and evaporative systems.

Selecting Thermal Pipe Insulation via Discrete Optimization

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Márton Szokody, Tibor Poós
Industrial pipe insulation is almost always selected from discrete catalog steps of material, thickness, and jacket/cladding, yet a large share of the literature optimizes a continuous thickness. This paper develops a directly implementable, catalog-based method that outputs the globally optimal insulation choice for each operating temperature and summarizes it as temperature bands with explicit transition points. The approach combines a physically transparent heat-loss model with a simple, robust optimization over the finite decision set.

Experimental Investigation and Effective Numerical Modeling of Heat Transfer in Phase Change Materials

Fri, 14 Aug 2026 00:00:00 +0200

Publication date: 14 August 2026
Source: Key Engineering Materials Vol. 1062
Author(s): Dávid Illés, Róbert Kovács, Mátyás Szücs
Environmental regulations, fluctuating energy prices, and uncertainties in the international energy markets motivate consumers to ensure their security of energy supply. One method to achieve this goal is to use heat storage equipment, which is scalable and applicable in both industrial and residential environments. The present study focuses on latent heat energy storage utilizing paraffin as a phase-changing material. A cube-shaped heat storage test device was investigated both experimentally and numerically. We used the obtained experimental data to validate our effective numerical modeling approach based on the enthalpy method. We proposed an effective numerical approach to take into account the material nonlinearities and the effect of convective flow phenomena on heat transfer processes, while neglecting the exact flow field and spatial distributions.