Dear readers,
Summer break 2025 is going to start soon, which gives us all a nice opportunity to find more time to read. It could be the right moment to dive into the second EMMR issue of the year! Our readers know that materials are present in everything we do every day. They are our friends as they improve our lives by most often being the initiator of new technologies. They help us in solving issues related to health, clothing, mobility, comfort, energy production, energy harvesting and saving, and so on. However, as researchers, we know that there is still room for material optimization in many applications. It is in our DNA to always try to design better materials. The present issue focuses on strategies applied to improve the properties of various materials by adjusting interface properties at various scales: at granular scale, on material surface, at the interface within an assembling of materials, in an alloy or compound. The readers of this issue will have an insight into how to improve the strength of assembled metals or assembled polymers as well as how to improve the performance of compounds, alloys or composite materials. A focus will also be given on material surface treatment possibilities toward improving the interfacing properties with the environment of use.
First, Reyes-Mayer and Romo-Uribe1 compare the performances of various monolayer composites made either from carbon woven fabric (twill and satin) or from nonwoven glass fiber fabric. It explores the fibers/resin interface and cohesion. Tensile as well as flexure tests performed on composite samples bring out that a one-layer composite structure provides sufficient interfacial adhesion, with efficient stress transfer between matrix and fibers. No costly pre- and posttreatment of the fibers are necessary in that configuration, where a single layer of fabric is sufficient to enhance the thermal and tensile mechanical properties of the final material. When comparing woven and nonwoven materials under tension, it is observed that the woven reinforcement is twice as performant in terms of mechanical properties due to its isotropic structure.
Ismail et al.2 also studied material cohesion, particularly material blends. The authors assess the effect of additives such as metakaolin (MK) and palm oil fuel ash (POFA) on the durability of concrete. Samples were prepared and tested for chloride penetration and compressive stress. Results show that MK accelerates the hydration process, while POFA minimizes the grain size in the material. The interface modifications obtained at crystal level allow to obtain a less porous concrete, which prevents chloride capillary penetration. The durability of the material is thus increased. Moreover, with smaller grains, the concrete is also more compression resistant.
The properties of blend materials are further explored in Thakur and Rahman,3 which demonstrates that glass ceramic tiles manufactured from cupola furnace slag (byproduct of pig iron and steel production) are viable for industrial applications, using powder metallurgy techniques. The authors produce tiles from powder sintering at various temperatures. Samples are then characterized for various properties: physical, mechanical, and X-ray shielding. It comes out that these properties depend highly on the interface between sinter grains. Basically, higher sintering temperatures improve density and water absorption while fostering the formation of crystalline phases that enhance flexural strength and Vickers hardness. However, temperature should stay below 1000°C to prevent microcracking, which degrades the mechanical properties. In addition, the X-ray shielding also decreases with higher energy levels.
Material layers and grain bonding is also the purpose of Wang et al.,4 who explore the properties of an additively manufactured high entropy alloys (HEAs). FeCoCrNi HEA samples were produced, the internal crystal structure was observed, and mechanical properties of the obtained samples were assessed. The longitudinal section of the sample reveals the typical ‘fish-scale’ melt pool structure common in additively manufactured samples. Each melt pool exhibits uniform size and shape, with smooth fusion lines between adjacent pools, indicating a well-bonded structure with densely packed substructures. This dense interface pattern between material layers allows to get high mechanical properties. Uniaxial compression test results bring out a hardening behavior. This behavior is typical for HEAs due to the high degree of atomic mixing, which stabilizes a single-phase solid solution.
Compound properties enhancement is also the purpose of Liu et al.5 The work shows how optimized ligands are crucial to synthesize lanthanide compounds. These do have an impact on the crystal structure and photophysical properties of the resulting materials. Two novel compounds were synthesized in this work with specific structural architectures based on supramolecular frameworks. Photoluminescence analysis was conducted, and notable up-conversion emissions could be identified due to the specific electronic obtained configurations.
Both Selvaraj et al.6 and Mahabubadsha and Anandavelu7 present strategies toward parts assembling optimization and particularly toward metallic material grain refinement in welding joints. The goal is to increase the mechanical properties of the heat affected welded zone. In the first work, the authors study the effect of forging pressure on the microstructural evolution, mechanical properties, and fracture behavior of rotary friction welded low-alloy steel joints. At 0.84 MPa/s, the weld interface exhibited fine bainitic structures, leading to improved mechanical properties. Above and below this value, grain coarsening was obtained, reducing strength and hardness. Similar results are obtained in the second work, which analyses the effect of a postwelding heat treatment on the mechanical properties of stir welded aluminum alloy joints. The experimental results revealed that the joints subjected to postweld heat treatment presented greater strength (412MPa) than did the joints subjected to as-welded heat treatment. The strength enhancement can be attributed to grain refinement and uniform distribution of precipitates.
The performance of an assembling joint is further studied in Zhu et al.,8 who investigate this time the failure level in a glass fiber reinforced polymeric T joint. Three-point bending experiment was conducted on T-shaped samples and compared with in silico tests. The orientation of the composite reinforcement varied in the study and the strength level was assessed. Results bring out that the optimization of the layup angles significantly impacts structural strength. In particular, the incorporation of 45° and −45° layers allows to disperse stress concentration and enhances the performance of the interface.
Surface adhesion enhancement is studied in Guo et al.9 and Ergün.10 In the first study, the effect of a polyvinyl alcohol (PVA)/graphene oxide (GO) coating on an optical fiber–based humidity sensor is evaluated. The goal is to prevent the detachment of the highly moisture-sensitive GO material from the fiber. PVA has good adhesion properties and the combination of the two makes the composite material adhere stably to the surface of the optical fiber. The experimental results indicate that the sensor exhibits a linear relative humidity (RH) response within the 55%–75% range, with a sensitivity of up to 0.003/%RH. The second study focuses on titanium implants coated with hydroxyapatite (HA) bioactive material for orthopedic applications. In order to improve the adhesion and the wear resistance of the HA coating, compounds based on boron (B), fluorine (F), and zirconium (Zr) were spin-coated onto hydrogen-sputtered titanium substrates. The adhesion strength of the coatings was evaluated and highest bond strength was found to be 139.75 MPa for F/B-doped HA samples. Coatings containing F always had a higher bond strength than those without.
Based on the description of the papers I presented above, I hope you will enjoy the content of this issue, and you will find the scientific and technical information that you need to make your research go forward.
