Search Results (18)

Lignin, an abundant and renewable biopolymer, has gained significant attention as a sustainable modifier and building block in polymeric materials. Recent advancements highlight its potential to tailor mechanical, thermal, and barrier properties of polymers while offering a greener alternative to petroleum-based additives. This review provides an updated perspective on the incorporation of lignin into various polymer matrices, focusing on lignin modification techniques, structure–property relationships, and emerging applications. Special emphasis is given to recent innovations in lignin functionalization and its role in developing high-performance, biodegradable, and recyclable materials such as polyurethanes, epoxy resins, phenol-formaldehyde resins, lignin-modified composites, and lignin-based films, coatings, elastomers, and adhesives. These lignin-based materials are gaining attention for potential applications in construction, automated industries, packaging, textiles, wastewater treatment, footwear, supporting goods, automobiles, printing rollers, sealants, and binders. Full article

CoCrFeNi high-entropy alloys represent a novel structural material with considerable application potential in a variety of fields, including aerospace, automobiles, ships, machining, energy, soft magnetic materials, and hydrogen storage materials. The present study investigates the impact of the Al element on the structure and properties of the alloy. The preparation of the Al_xCr_1−xCoFeNi (x = 0.1, 0.2, 0.3, 0.4, 0.5) powders involved the use of a variety of elemental metal powders as raw materials and a mechanical alloying process at 350 rpm for 40 h. The sintering of the alloy powders was subsequently conducted using spark plasma sintering at 1000 °C. The microstructure of the alloys was analyzed using XRD, SEM, and EDS, and the properties were analyzed using a universal testing machine, a hardness measurement, friction and wear measurement, and an electrochemical workstation. The study shows that when x = 0.1, the crystal structure of Al_0.1Cr_0.9CoFeNi consists of a double FCC phase and a trace amount of σ phase. As the aluminum content increases, part of the FCC phase begins to transform to BCC. When x = 0.2~0.5, the alloy consists of a double FCC phase and a BCC phase and a trace amount of a sigma phase. As the BCC phase in the alloy increases, the tensile strength of the alloy increases, the ability to deform plastically decreases, and the hardness increases. The highest ultimate tensile strength of 1163.14 MPa is exhibited by Al_0.5Cr_0.5CoFeNi, while the minimum elongation is 26.98% and the maximum hardness value is 412.6 HV. In the initial stage of friction measurement, the wear mechanism of Al_xCr_1−xCoFeNi is adhesive wear. However, as the test time progresses, an oxide layer begins to form on the alloy’s surface, leading to a gradual increase in the friction coefficient. At this stage, the wear mechanism becomes a combination of both adhesive and abrasive wear. Once the oxidation process and the wear process have reached a dynamic equilibrium, the friction coefficient stabilizes, and the wear mechanism transitions to a state of abrasive wear. The Al_0.1Cr_0.9CoFeNi alloy demonstrates the lowest friction coefficient and wear rate, exhibiting values of 0.513 and 0.020 × 10⁻³ mm³/Nm, respectively, while the Al_0.5Cr_0.5CoFeNi alloy demonstrates the highest performance, with a self-corrosion voltage of 0.202 V in a 3.5 wt.% NaCl solution. The experimental findings demonstrate that, in the presence of a decline in the Cr element within a high-entropy alloy, an augmentation in the Al element can facilitate the transition of the FCC phase to the BCC phase within the alloy, thereby enhancing its mechanical properties. However, in the Al_xCr_1−xCoFeNi HEAs, the presence of the Cr-rich and Cr-poor phases invariably results in selective corrosion in a neutral NaCl solution. The corrosion resistance of this alloy is weaker than that of a single-phase solid solution alloy with a similar chemical composition that only undergoes pitting corrosion. Full article

Due to the recurrent starting and stopping operations of automobiles during service, their engines’ hot ends are continually subjected to high-temperature cyclic oxidation. Therefore, it is crucial to develop ferritic stainless steels with better high-temperature oxidation resistance. This study focuses on improving the high-temperature cyclic oxidation performance of 18Cr-Mo (444-type) ferritic stainless steel by alloying with high-melting-point metal W and the rare earth element Ce. For this purpose, a high-temperature cyclic oxidation experiment was designed to simulate the actual service environment and investigate the high-temperature cyclic oxidation behavior and microstructure evolution of 444-type ferritic stainless steel alloyed with W and Ce. The oxide structure and composition formed during this process were analyzed and characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS) and electron probe X-ray micro-analyzer (EPMA), in order to reveal the mechanism of action of W and Ce in the cyclic oxidation process. The results show that 18Cr-Mo ferritic stainless steel alloyed with W and Ce exhibits an excellent resistance to high-temperature cyclic oxidation. The element W can promote the precipitation of the Laves phase between the matrix and the oxide film, and the small-sized Laves phase can inhibit the interfacial diffusion of oxidation reaction elements and prevent the inward growth of the oxide film. The element Ce can refine oxide particles and reduce the thickness of the oxide film. CeO₂ particles within the oxide film can serve as nucleation sites for the formation of oxide particles from reactive elements, and they also contribute to pinning the oxide film, thereby enhancing its adhesion. Full article

Magnesium alloys are the lowest-density structural metals with a wide range of applications, such as aircraft skins, engine casings and automobile hubs. However, its low surface hardness and non-corrosion resistance in natural environments limit its wide range of applications. In this work, Si-DLC coatings (Si: 15 at.%) are fabricated on AZ91 alloy using a hollow cathode discharge combined with a DC bias voltage from 0 to −300 V to increase the deposition rate and modulate the structure and properties of the coatings. The Si interlayer with a thickness of around 0.6 µm is deposited first to enhance the adhesion. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy are used to investigate the effect of DC bias on the microstructure evolution of Si-DLC coatings. Meanwhile, corrosion and wear resistance of the coatings at various bias voltages have been investigated using electrochemical workstations and pin-on-desk wear testers. It is shown that the bias-free coating has a loose structure and is less resistant to corrosion and wear. The bias coating has a compact structure, small carbon cluster size, high chloride ion corrosion resistance, and high wear resistance against Al₂O₃ spheres. The corrosion potential of the coating bias at −300 V is −0.98 V, the corrosion current density is 1.35 × 10⁻⁶ A·cm⁻², the friction coefficient is 0.08, and the wear rate is 10⁻⁸ orders of magnitude. The formation of SiC nanocrystals and high sp³-C, as well as the formation of transfer films on the surface of their counterparts, are the main reasons for the ultra-high wear resistance of the bias coatings. The wear rate, coefficient of friction, and corrosion rate of the coating are 0.0069 times, 0.2 times, and 0.0088 times that of the AZ91 alloy, respectively. However, the bias coating has only short to medium-term protection against the magnesium alloy and no long-term protection due to cracks caused by its high internal stress. Full article

Laminated metal-composite structures, also known as fibre metal laminates (FMLs), have emerged as prominent engineering materials in various industries, particularly in the domains of aircraft and automobile manufacturing. These materials are sought after due to their enhanced impact and fatigue resistance capabilities. The machining of FMLs plays a crucial role in achieving near-net shapes for the purpose of joining and assembling components. Delamination is a prevalent issue encountered during the process of conventional machining, thus rendering FMLs are challenging materials to machine. This study aims to investigate the cutting process of novel fibre intermetallic laminates (FILs) using the abrasive water jet (AWJ) cutting technique. The FILs consists of carbon and aramid fibers that are adhesively bonded with a resin matrix filled with reduced graphene oxide (r-GO) nano fillers. Moreover, these laminates contain embedded Nitinol shape memory alloy sheets as the skin materials. Specifically, the study aims to investigate the impact of different factors, such as the addition of reduced graphene oxide (r-GO) in the laminates (ranging from 0 to 2 wt%), traverse speed (ranging from 400 to 600 mm/min), waterjet pressure (ranging from 200 to 300 MPa), and nozzle height (ranging from 2 to 4 mm), on the material removal rate (MRR), delamination factor (FD), and kerf deviation (KD). ANOVA was used in the statistical analysis to determine the most influential parameters and their effects on the selected responses. The optimal AWJC parameters are determined using a metaheuristic-based moth–flame optimization (MFO) algorithm in order to enhance cut quality. The efficacy of MFO is subsequently compared with similar well-established metaheuristics such as the genetic algorithm, particle swarm algorithm, dragonfly algorithm, and grey-wolf algorithm. MFO was found to outperform in terms of several performance indices, including rapid divergence, diversity, spacing, and hypervolume values, among the algorithms compared. Full article

iron-based coatings have exhibited good mechanical properties, such as high hardness and good wear resistance, which are desirable properties in applications such as automobile brake rotors. iron-based coatings are also good replacements for Co- and Ni-based coatings, which are costly and could have health and environmental concerns due to their toxicity. In this research, three different iron-based coatings were deposited using the Detonation Gun Spraying (DGS) technology onto aluminum substrates, including the steel powders alone (unreinforced), and steel powders mixed with Fe₃C and SiC particles, respectively. The microstructural characteristics of these coatings and mechanical properties, such as hardness and wear resistance, were examined. The morphology and structure of the feedstock powders were affected by the exposure to high temperature during the spraying process and rapid solidification of steel powders that resulted in the formation of an amorphous structure. While it was expected that steel particles reinforced with hard ceramic particles would result in increased hardness, instead, the unreinforced steel coating had the highest hardness, possibly due to a higher degree of amorphization in the coating than the other two. The microstructural observation confirmed the formation of dense coatings with good adhesion between layers. All samples were subjected to ball-on-disk wear tests at room temperature (23 °C) and at 200 °C. Similar wear resistances of the three samples were obtained at room temperature. At 200 °C, however, both ceramic reinforced composite samples exhibited higher wear rates in line with the reduction in their hardness values. This work explains, from the microstructural point of view, why adding hard particles to steel powers may not always lead to coatings with higher hardness and better wear resistance. Full article

Aluminum alloys have been widely utilized in automobiles, aircraft, building structures, and high-speed railways industries due to their excellent structural and mechanical properties. Surface oxide film removal prior to aluminum alloy welding and old paint removal prior to repainting aluminum alloy surfaces are critical factors in ensuring the welding quality and service life of aluminum alloy products. Because of its unique advantages, such as environmental protection and precision control, laser-controlled cleaning has great application potential as a surface cleaning technology in removing oxide films and paint layers on aluminum alloy surfaces. In this paper, the mechanism of laser cleaning of oxide films and paint layers on aluminum alloy is discussed. Furthermore, the impact of various processing parameters such as laser beam power, energy density, scanning speed, and so on is analyzed in detail. After laser cleaning, the corrosion resistance, welding performance, adhesive performance, and other properties of the aluminum alloy are optimized. This paper also discusses several real-time detection technologies for laser cleaning. A summary and the development trend are provided at the end of the paper. Full article

With an increased demand for the combination of different material classes in lightweight applications like automobiles, aircraft construction, etc., the need for simple and energy-efficient joining technologies to join these different material classes has been extensively researched over the last decades. One such hybrid material combination is the metal–plastic hybrid structure, which offers the combinational characteristics of high strength and stiffness of the metal part along with characteristic elasticity and low density of the plastic part. In this research work, the focus is laid on generating a graded property transition at the interface of metal–plastic joints by brazing a three-dimensional (3D) macroscopic transition wire structure (TWS) strucwire^®, over the metal part before being molded with plastic at a later stage using an injection over-molding process. This helps in providing a mechanical interlocking facility and thereby achieving a higher load transfer at the interface of metal–plastic hybrid joints. The graded steel wire structures with different carbon content were brazed onto the galvanized steel sheets using the hotplate brazing technique. In addition to the Zinc layer on the galvanized steel sheets, electroplated Zinc coatings were fabricated on the wire structures to provide better brazing quality. The microstructural, mechanical, and intermetallic phase characteristics of the resulting brazed joints were evaluated using light microscopy, adhesion tests, and scanning electron microscopy, respectively. Full article

Carbon fiber-reinforced polymer (CFRP) composites are used in a variety of applications such as aircraft, automobiles, body armors, and the sports sector owing to their ultra-strong and lightweight characteristics. However, the incorporation of an untreated pristine carbon fiber surface leads to a weak interfacial interaction with the polymeric matrix, thus triggering catastrophic failure of the composite material. Graphene oxide, a 2D-macromolecule consisting of several polar functional groups such as hydroxyl, carboxyl, and carbonyl on the basal planes and edges, tends to increase the surface area and has thus been applied between the fiber and matrix, helping to improve CFRP properties. Herein, we condense different routes of functionalization of GO nanosheets and their incorporation onto a fiber surface or in a carbon fiber-reinforced epoxy matrix, helping to improve the interfacial adhesion between the fiber and matrix, and thus allowing effective stress transfer and energy absorption. The improvement of the interfacial adhesion between the fiber and carbon fiber-reinforced epoxy matrix is due to the peculiar structure of GO nanoparticles composed of polar groups, especially on the edges of the nanosheets, able to provide strong interaction with the hosting cured epoxy matrix, and the “core” part similar to the structure of CFs, and hence able to establish strong π-π interactions with the reinforcing CFs. The article also covers the effect of functionalized graphene oxide incorporation on the mechanical, thermal, electrical, and viscoelastic properties of composite materials reinforced with carbon fibers. Full article

The present work aims to study the impact of O and N addition on Cr-sputtered coatings on plastic (polycarbonate, PC) used in automobile parts, as a promisor alternative for auto part metallization, while eliminating the usage of toxic hexavalent chromium. The coatings were deposited using DC magnetron sputtering from a single pure Cr target in a reactive atmosphere (N₂ and/or O₂). The deposition of the coatings was performed maintaining the total pressure constant and close to 1 Pa by tuning Ar pressure while reactive gases were added. The target current density was kept at J_W = 20 mA·cm⁻². Structural characterization revealed a mixture of α-Cr, δ-Cr, β-Cr₂N, and CrN crystalline structures as well as amorphous oxides. The coating hardness ranged from 9 GPa for the CrON coating to 15 GPa for the CrN coating. All deposited coatings showed a particularly good interface adhesion; adjusting the amount of O and N made it possible to tune the optical properties of the Cr-based coatings as desired. The promising results open future industrialization of sputtered Cr-based coatings for automotive industries. Full article

It is a well-known fact that to manufacture an automobile tire more than 200 different materials are used, including high-carbon steel wire. In order to withstand the affecting forces, the tire tread is reinforced with steel wire or other products such as ropes or strands. These ropes are called steel cord. Steel cord can be of different constructions. To ensure a good adhesive bond between the rubber of the tire and the steel cord, the cord is either brass-plated or bronzed. The reason brass or bronze is used is because copper, which is a part of these alloys, makes a high-strength chemical composition with sulfur in rubber. For steel cord, the high carbon steel is usually used at 0.70–0.95% C. This amount of carbon ensures the high strength of the steel cord. This kind of high-quality, unalloyed steel has a pearlitic structure which is designed for multi-pass drawing. To ensure the specified technical characteristics, modern metal reinforcing materials for automobile tires, metal cord and bead wire, must withstand, first of all, a high breaking load with a minimum running meter weight. At present, reinforcing materials of the strength range 2800–3200 MPa are increasingly used, the manufacture of which requires high-strength wire. The production of such wire requires the use of a workpiece with high carbon content, changing the drawing regimes, patenting, and other operations. At the same time, it is necessary to achieve a reduction in the cost of wire manufacturing. In this context, the development and implementation of competitive processes for the manufacture of high-quality, high-strength wire as a reinforcing material for automobile tires is an urgent task. Full article

Joining large and complex polymer–matrix composite structures is becoming increasingly important in industries such as automobiles, aerospace, sports, wind turbines, and others. Ultrasonic welding is an ultra-fast joining process and also provides excellent joint quality as a cost-effective alternative to other joining processes. This research aims at investigating the welding characteristics of novel methyl methacrylate Elium^®, a liquid thermoplastic resin. Elium^® is the first of its kind of thermoplastic resin, which is curable at room temperature and is suitable for mass production processes. The welding characteristics of Elium^® composites were investigated by optimizing the welding parameters with specially designed integrated energy directors (ED) and manufactured using the Resin transfer molding process. The results showed a 23% higher lap shear strength for ultrasonically welded composite joints when compared to the adhesively bonded joints. The optimized welding time for the ultrasonic welded joint was found to be 1.5 s whereas it was 10 min for the adhesively bonded joint. Fractographic analysis showed the significant plastic deformation and shear cusps formation on the fractured surface, which are typical characteristics for strong interfacial bonding. Full article

Six new rugged, high-temperature tolerant phosphine oxide-containing poly(4,4′-(p-phenylene)-bis(2,6-diphenylpyridinium)) polymers P-1, P-2, P-3, P-4, P-5, and P-6 are synthesized, characterized, and evaluated. Synthesis results in high yield and purity, as confirmed by elemental, proton (¹H), and carbon 13 (¹³C) nuclear magnetic resonance (NMR) spectra analyses. High glass transition temperatures (T_g > 230 °C) and high char yields (>50% at 700 °C) are determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. These new ionic polymers exhibit excellent processability, thin-film forming, high-temperature resistance, fire-resistance and retardation, coating, adhesion, mechanical and tensile strength, and n-type (electron transport) properties. The incorporation of phosphine oxide and bis(phenylpyridinium) moieties in the polymer backbones leads to high glass transition temperatures and excellent fire retardant properties, as determined by microcalorimetry measurements. The use of organic counterions allows these ionic polymers to be easily processable from several common organic solvents. A large variety of these polymers can be synthesized by utilizing structural variants of the bispyrylium salt, phosphine oxide containing diamine, and the counterion in a combinatorial fashion. These results make them very attractive for a number of applications, including as coating and structural component materials for automobiles, aircrafts, power and propulsion systems, firefighter garments, printed circuit boards, cabinets and housings for electronic and electrical components, construction materials, mattresses, carpets, upholstery and furniture, and paper-thin coatings for protecting important paper documents. Full article

Epoxy resins are widely applicable in the aircraft, automobile, coating, and adhesive industries because of their good chemical resistance and excellent mechanical and thermal properties. However, upon external impact, the crack propagation of epoxy polymers weakens the overall impact resistance of these materials. Therefore, many impact modifiers have been developed to reduce the brittleness of epoxy polymers. Polyurethanes, as impact modifiers, can improve the toughness of polymers. Although it is well known that polyurethanes (PUs) are phase-separated in the polymer matrix after curing, connecting PUs to the polymer matrix for enhancing the mechanical properties of polymers has proven to be challenging. In this study, we introduced epoxy functional groups into polyol backbones, which is different from other studies that focused on modifying capping agents to achieve a network structure between the polymer matrix and PU. We confirmed the molecular weight of the prepared PU via gel permeation chromatography. Moreover, the prepared material was added to the epoxies and the resulting mechanical and thermal properties of the materials were evaluated. Furthermore, we conducted tensile, flexural strength, and impact resistance measurements. The addition of PU to the epoxy compositions enhanced their impact strength and maintained their mechanical strength up to 10 phr of PU. Furthermore, the morphologies observed with field emission scanning electron microscopy and transmission electron microscopy proved that the PU was phase separated in the epoxy matrix. Full article

Epoxy foam adhesives are widely used for weight reduction, watertight property, and mechanical reinforcement effects. However, epoxy foam adhesives have poor impact resistance at higher expansion ratios. Hence, we prepared an epoxy composite foam adhesive with core–shell rubber (CSR) particles to improve the impact resistance and applied it to automotive structural adhesives. The curing behavior and pore structure were characterized by differential scanning calorimetry (DSC) and X-ray computed tomography (CT), respectively, and impact wedge–peel tests were conducted to quantitatively evaluate the resistance to cleavage of the CSR/epoxy composite foam adhesives under impact. At 5 and 10 phr CSR contents, the pore size and expansion ratio increased sufficiently due to the decrease in curing rate. However, at 20 phr CSR content, the pore size decreased, which might be due to the steric hindrance effect of the CSR particles. Notably, at 0 and 0.1 phr foaming agent contents, the resistance to cleavage of the adhesives under the impact wedge–peel condition significantly improved with increasing CSR content. Thus, the CSR/epoxy composite foam adhesive containing 0.1 phr foaming agent and 20 phr CSR particles showed high impact resistance (E_C = 34,000 mJ/cm²) and sufficient expansion ratio (~148%). Full article