Effect of reinforcement particle size on the corrosion and mechanical properties of spark plasma sintered aluminium matrix composites.

In this study, the effects of different sizes of reinforcing particles on the corrosion behaviour and mechanical properties of aluminium (Al)-based composites produced by spark plasma sintering (SPS) are analysed. In the study, the effects of SPS parameters, including electrical power, applied pressure and sintering temperature, on the consolidation process and microstructure evolution of the composite are closely investigated. The results reveal a nuanced relationship between the sintering conditions and the properties of the particles, which in turn determine the sintering dynamics and the formation of the microstructural features. The evaluation of mechanical properties indicates a remarkable influence of particle size distribution on the hardness of the composites, showing an initial improvement with the introduction of nanoparticles, followed by a slight decrease as the balance between nano- and micron-sized Al2O3 particles shifts. A scanning electron microscopy (SEM) study demonstrates the influence of particle dimensions on the change of grain boundaries and the spatial arrangement of the composite matrix. Electrochemical experiments in a 0.1 M NaCl solution show a consistent corrosion potential (Ecorr) across all samples, while the current densities associated with corrosion (icorr) show considerable variation. The presence of nano-sized Al2O3 particles was found to increase corrosion resistance, in contrast to the detrimental effects observed with larger microparticles. In particular, composites with a bimodal distribution of particle sizes showed a 3.5-fold increase in corrosion resistance compared to pure Al. The specific Al-2n8mAl2O3 composite that exhibited active electrochemical properties at elevated potentials without a defined passivation range emphasises the significant role of particle size. This study draws attention to bimodal microstructures as a promising route to achieving uniformity and improved corrosion resistance in Al matrix composites, while pointing to the need for further research to fully elucidate the operative mechanisms.

Thermal-Mechanical and Microstructural Simulation of Rotary Friction Welding Processes by Using Finite Element Method.

Rotary friction welding is one of the most crucial techniques for joining different parts in advanced industries. Experimentally measuring the history of thermomechanical and microstructural parameters of this process can be a significant challenge and incurs high costs. To address these challenges, the finite element method was used to simulate thermomechanical and microstructural aspects of the welding of identical superalloy Inconel 718 tubes. Numerical simulation results were used to compute essential mechanical and metallurgical parameters such as temperature, strain, strain rate, volume fraction of dynamic recrystallization, and grain size distribution. These parameters were subsequently verified using experimental test results. The Johnson-Avrami model was utilized in the microstructural simulation to convert thermomechanical parameters into metallurgical factors, employing a FORTRAN subroutine. The calculated thickness of the recrystallization zone in the wall was 480 and 850 µm at the tube wall's center and edge, respectively. These values were reported from experimental measurements as 500 and 800 µm, respectively. The predicted grain size changes from the center to the edge of the wall thickness, near the weld interface, ranged from 2.07 to 2.15 µm, comparable to the experimental measurements ranging from 1.9 to 2.2 µm. Various curves are also presented to explore the correlation between thermomechanical and microstructural parameters, with the experimental results revealing predictable microstructure evolutions correlated with thermomechanical changes.

Advancing High-Performance Metal Matrix Composites: Uniting Nature's Design and Engineering Innovation.

We are pleased to present this Special Issue entitled "Advanced High-Performance Metal Matrix Composites (MMCs)," which explores promising materials science that will change everything from aerospace to automotive technology [...].

Reviewing the Integrated Design Approach for Augmenting Strength and Toughness at Macro- and Micro-Scale in High-Performance Advanced Composites.

In response to the growing demand for high-strength and high-toughness materials in industries such as aerospace and automotive, there is a need for metal matrix composites (MMCs) that can simultaneously increase strength and toughness. The mechanical properties of MMCs depend not only on the content of reinforcing elements, but also on the architecture of the composite (shape, size, and spatial distribution). This paper focuses on the design configurations of MMCs, which include both the configurations resulting from the reinforcements and the inherent heterogeneity of the matrix itself. Such high-performance MMCs exhibit excellent mechanical properties, such as high strength, plasticity, and fracture toughness. These properties, which are not present in conventional homogeneous materials, are mainly due to the synergistic effects resulting from the interactions between the internal components, including stress-strain gradients, geometrically necessary dislocations, and unique interfacial behavior. Among them, aluminum matrix composites (AMCs) are of particular importance due to their potential for weight reduction and performance enhancement in aerospace, electronics, and electric vehicles. However, the challenge lies in the inverse relationship between strength and toughness, which hinders the widespread use and large-scale development of MMCs. Composite material design plays a critical role in simultaneously improving strength and toughness. This review examines the advantages of toughness, toughness mechanisms, toughness distribution properties, and structural parameters in the development of composite structures. The development of synthetic composites with homogeneous structural designs inspired by biological composites such as bone offers insights into achieving exceptional strength and toughness in lightweight structures. In addition, understanding fracture behavior and toughness mechanisms in heterogeneous nanostructures is critical to advancing the field of metal matrix composites. The future development direction of architectural composites and the design of the reinforcement and toughness of metal matrix composites based on energy dissipation theory are also proposed. In conclusion, the design of composite architectures holds enormous potential for the development of composites with excellent strength and toughness to meet the requirements of lightweight structures in various industries.

Ag doped Sn3O4 nanostructure and immobilized on hyperbranched polypyrrole for visible light sensitized photocatalytic, antibacterial agent and microbial detection process.

Ag doped Sn3O4 Nanostructure and immobilized on hyperbranched polypyrrole is investigated in this project. The product was synthesized by the hydrothermal synthesis method. The surface and structural characteristics of the product was studied by different instrumental analysis. The fabricated nanocomposites was utilized as a nano photocatalyst in the removal of methylene blue dye. The crystallography results depicts the triclinic phase of Sn3O4 with the crystallite size 36.3 nm. The band gap of the Ag-Sn3O4/hyperbranched polypyrrole was found 1.50 eV from kubelka-munk measurements. The specific surface area was increased in the presence of the hyperbranched polypyrrole as compared to Ag-Sn3O4 samples. The photo-catalytic activity of composites was found 100.0% degradation of CR in 30 min under visible light irradiation. The catalytic kinetic was followed from the first kinetic model. Moreover, the Ag/Sn3O4/hyperbranched polypyrrole was applied as a bactericidal agent against Streptococcus pneumoniae, and Pseudomonas aeruginosa bacteria. Determination of Streptococcus pyogenes as a pathogenic bacteria was investigated by using aptamer/Ag/Sn3O4/hyperbranched polypyrrole in peroxidase activity. The detection limit of S. pyogenes was 71.0 CFU/mL by using the nano-aptamer.

Hot deformation behaviour of bimodal sized Al2 O3 /Al nanocomposites fabricated by spark plasma sintering.

The deformation behaviour of bimodal sized Al2 O3 /Al nanocomposites were investigated by hot compression tests conducted in the temperature range 350-500°C and strain rates of 0.001, 0.01 and 0.1 s-1 . The dynamic recrystallisation behaviour of the nanocomposites strongly depended on the forming parameters. The bimodal sized Al2 O3 particles played a crucial role in the recrystallised microstructure. The addition of bimodal sized Al2 O3 particles led to a significant increase of activation energy of plastic deformation, corroborating the enhanced resistance of the nanocomposite to hot deformation. This was also reflected by the increased compressive yield strength in the nanocomposite due to both dislocation strengthening caused by n-Al2 O3 and preventing the grain growth due to the presence of µ-Al2 O3 at grain boundaries. It was found that with the decrease of Z values, local strain induced by deformation was released and the grain size of aluminium matrix gradually increased, indicating that the main softening mechanism of the bimodal sized Al2 O3 /Al nanocomposites was dynamic recrystallisation (DRX). The lower the Z value was, the easier the DRX occurred. The highly beneficial role of the bimodal sized Al2 O3 reinforcement in improving the high-temperature performance of aluminium matrix nanocomposite was discussed.

Adaptive nonsingular terminal sliding mode controller for micro/nanopositioning systems driven by linear piezoelectric ceramic motors.

In the field of nanotechnology, there is a growing demand to provide precision control and manipulation of devices with the ability to interact with complex and unstructured environments at micro/nano-scale. As a result, ultrahigh-precision positioning stages have been turned into a key requirement of nanotechnology. In this paper, linear piezoelectric ceramic motors (LPCMs) are adopted to drive micro/nanopositioning stages since they have the ability to achieve high precision in addition to being versatile to be implemented over a wide range of applications. In the establishment of a control scheme for such manipulation systems, the presence of friction, parameter uncertainties, and external disturbances prevent the systems from providing the desired positioning accuracy. The work in this paper focuses on the development of a control framework that addresses these issues as it uses the nonsingular terminal sliding mode technique for the precise position tracking problem of an LPCM-driven positioning stage with friction, uncertain parameters, and external disturbances. The developed control algorithm exhibits the following two attractive features. First, upper bounds of system uncertainties/perturbations are adaptively estimated in the proposed controller; thus, prior knowledge about uncertainty/disturbance bounds is not necessary. Second, the discontinuous signum function is transferred to the time derivative of the control input and the continuous control signal is obtained after integration; consequently, the chattering phenomenon, which presents a major handicap to the implementation of conventional sliding mode control in real applications, is alleviated without deteriorating the robustness of the system. The stability of the controlled system is analyzed, and the convergence of the position tracking error to zero is analytically proven. The proposed control strategy is experimentally validated and compared to the existing control approaches.