Influence of Normal-to-High Anodizing Voltage on AAO Surface Hardness from 1050 Aluminum Alloy in Oxalic Acid.

Anodic aluminum oxide (AAO) has been widely applied for the surface protection of electronic component packaging through a pore-sealing process, with the enhanced hardness value reaching around 400 Vickers hardness (HV). However, the traditional AAO fabrication at 0~10 °C for surface protection takes at least 3-6 h for the reaction or other complicated methods used for the pore-sealing process, including boiling-water sealing, oil sealing, or salt-compound sealing. With the increasing development of nanostructured AAO, there is a growing interest in improving hardness without pore sealing, in order to leverage the characteristics of porous AAO and surface protection properties simultaneously. Here, we investigate the effect of voltage on hardness under the same AAO thickness conditions in oxalic acid at room temperature from a normal level of 40 V to a high level of 100 V and found a positive correlation between surface hardness and voltage. The surface hardness values of AAO formed at 100 V reach about 423 HV without pore sealing in 30 min. By employing a hybrid pulse anodization (HPA) method, we are able to prevent the high-voltage burning effect and complete the anodization process at room temperature. The mechanism behind this can be explained by the porosity and photoluminescence (PL) intensity of AAO. For the same thickness of AAO from 40~100 V, increasing the anodizing voltage decreases both the porosity and PL intensity, indicating a reduction in pores, as well as anion and oxygen vacancy defects, due to rapid AAO growth. This reduction in defects in the AAO film leads to an increase in hardness, allowing us to significantly enhance AAO hardness without a pore-sealing process. This offers an effective hardness enhancement in AAO under economically feasible conditions for the application of hard coatings and protective films.

Application of synchronized tandem welding to high-hardness armor steel.

Several studies have been conducted to improve combat vehicle capabilities, such as the bulletproof performance of armor and fuel efficiency through weight reduction. Titanium alloys and ceramic materials are expensive and difficult to process; therefore, they can be applied only in specific locations. In addition, arc welding, which is relatively inexpensive compared with other welding processes, is widely used in industrial fields; however, because welding is often performed in multiple passes to join one part, the productivity is reduced. Therefore, in this study, mechanical properties were investigated according to production time and heat input by applying tandem pulse gas metal arc welding (GMAW) to increase productivity. The experimental data were obtained by varying the wire feeding speed. In addition, the current-voltage waveforms were measured, and the volume shift was analyzed by comparison with images captured using a high-speed camera. To analyze the mechanical properties of the tandem weld for the welding of high-hardness armor plates, the appearance (top bead and back bead), cross-section, hardness, tensile test, impact test, and spatter generation of the welded part were analyzed. The results show that all Tank-automotive and Armaments Command (TACOM) standards for the base material were met when the tandem wire feeding speed was 11 + 11 m/min, and the single-pass process increased production speed by a factor of more than 10. Tandem pulse GMAW is shown to be a viable option for improving productivity and maintaining high-quality welds for high-hardness materials.

Preliminary Study of New Low-Temperature Hard Abrasion Resistant Fe-P and Fe-P-X (X = C or/and B) Casting Alloys.

This article analyses the as-cast state of practically unknown Fe-P-based cast alloys with or without an addition of carbon and/or boron, cast into a grey cast iron mould. The melting intervals of the alloys were determined by DSC analysis, and the microstructure was characterized by optical and scanning electron microscopy with an EDXS detector. The hardness and microhardness of the alloys were also measured. Their hardness reached values between 52 and 65 HRC depending on chemical composition and microstructure, showing their high abrasion resistance. The high hardness is a consequence of the eutectic and primary intermetallic phases of Fe3P, Fe3C, Fe2B or mixed type. By increasing the concentration of metalloids and combining them, the hardness and brittleness of the alloys were increased. The alloys with predominantly eutectic microstructures were the least brittle. Depending on the chemical composition, the solidus and liquidus temperatures ranged from 954 °C to 1220 °C and were lower than those of the well-known wear-resistant white cast irons.

Neutron-Absorption Properties of B/Cu Composites.

Copper has high electrical and thermal conductivity, which is frequently employed in structural and functional materials. In this research, powder metallurgy was used to incorporate boron nanosheets into metal matrix composites to create boron dispersion-enhanced copper matrix composites. The neutron-absorption characteristics of composite materials were investigated, as well as the link between neutron-absorption cross-section and neutron energy. The results told us that the morphology of the second phase on the particle surface is closely related to the size of Cu-B particles, copper and boron correspond atomically to each other on the interface without dislocation or lattice distortion, forming a completely coherent interface, and that the neutron absorption cross-section decreases exponentially as neutron energy increases. In low-energy neutrons with energies less than 0.1 eV, the increase of boron content and 10B abundance in Cu-B alloy will enhance the neutron-absorption capacity of the alloy. Boron dispersion-strengthened copper matrix composites have good neutron-absorption capacity, and the microstructure and size of boron do not affect the neutron-absorption performance of composites with the same content of boron. The hardness of the B-dispersion-strengthened Cu matrix composite obtained by nanoindentation test is about 3.04 GPa. Copper matrix composites with boron dispersion reinforcement exhibit high hardness and neutron-absorption characteristics.

Supercritical Fluid Microcellular Foaming of High-Hardness TPU via a Pressure-Quenching Process: Restricted Foam Expansion Controlled by Matrix Modulus and Thermal Degradation.

High-hardness thermoplastic polyurethane (HD-TPU) presents a high matrix modulus, low-temperature durability, and remarkable abrasion resistance, and has been used in many advanced applications. However, the fabrication of microcellular HD-TPU foam is rarely reported in the literature. In this study, the foaming behavior of HD-TPU with a hardness of 75D was investigated via a pressure-quenching foaming process using CO2 as a blowing agent. Microcellular HD-TPU foam with a maximum expansion ratio of 3.9-fold, a cell size of 25.9 µm, and cell density of 7.8 × 108 cells/cm3 was prepared, where a high optimum foaming temperature of about 170 °C had to be applied with the aim of softening the polymer's matrix modulus. However, the foaming behavior of HD-TPU deteriorated when the foaming temperature further increased to 180 °C, characterized by the presence of coalesced cells, microcracks, and a high foam density of 1.0 g/cm3 even though the crystal domains still existed within the matrix. The cell morphology evolution of HD-TPU foam was investigated by adjusting the saturation time, and an obvious degradation occurred during the high-temperature saturation process. A cell growth mechanism of HD-TPU foams in degradation environments was proposed to explain this phenomenon based on the gas escape through the defective matrix.

Novel polymeric phases proposed by cold-pressing SiC tubes.

A detailed structural evolution behavior of SiC single-wall nanotubes (SiC SWNTs) under high-pressure is studied by using density functional theory. We proposed four new polymeric phases (hP4-SiC, hP48-SiC, oI32-SiC and oA40-SiC), which possess the high stability, outstanding electronic and mechanical properties. The hP4-SiC, hP48-SiC and oA40-SiC are indirect band gap semiconductors, while the oI32-SiC is direct band gap semiconductor. The exhibited suitable band gap (∼3.1 eV) allows hP4-SiC, hP48-SiC, oI32-SiC and oA40-SiC as the potential blue-laser diodes materials. The Si-C bond in four new structures is the strong covalent bond in sp3hybridization, which results in their high stability and hardness. The exhibited high decomposition temperature and high hardness make them as the potential high temperature abrasive materials. The stacking way of different rings in structures and atomic arrangement configurations of C and Si atoms in rings induce the anisotropic stiffness of polymeric structures. The analysis of x-ray diffraction, Raman and infrared radiation spectra is performed for a guideline of their synthesis in experiment. These results would help to understand the structural evolution of SiC SWNTs under high pressure and contribute to develop the high hardness and temperature materials.

Rational Design of Durable Anti-fouling Coatings with High Transparency, Hardness, and Flexibility.

Highly transparent, durable, flexible and smooth coatings with excellent anti-fouling properties have broad applications on cars, windows, and touch screens. However, the coexistence of these multi-functions is difficult to achieve in a single coating material. Here, a coating is developed with excellent performance of high transparency (98.8%), anti-fouling, high hardness (8H), and flexibility simultaneously (TAHF coating). In the material design, methyl etherified melamine formaldehyde resin, hexamethylene diisocyanate trimer, and mono-aminopropyl terminated polydimethylsiloxane (NH2-PDMS) were used as a polymer matrix to provide surface hardness, a cross-linker was used to provide toughness, and omniphobic groups from NH2-PDMS were used to provide anti-fouling performance. The TAHF coating has excellent liquid repellence even after six months of outdoor exposure, 260 h of UV light exposure, and 1500 wear and 2000 bending cycles, and its chemical shielding performance is superior to that of a commercial anti-corrosive coating. This strategy would provide a new route for the design of multifunctional anti-fouling coatings for practical applications.

Dual-Laser PBF-LB Processing of a High-Performance Maraging Tool Steel FeNiCoMoVTiAl.

As part of an international research project (HiPTSLAM), the development and holistic processing of high-performance tool steels for AM is a promising topic regarding the acceptance of the laser powder bed fusion (PBF-LB) technology for functionally optimized die, forming and cutting tools. In a previous work, the newly developed maraging tool steel FeNiCoMoVTiAl was qualified to be processed by laser powder bed fusion (PBF-LB) with a material density of more than 99.9% using a suitable parameter set. To exploit further optimization potential, the influence of dual-laser processing strategies on the material structure and the resulting mechanical properties was investigated. After an initial calibration procedure, the build data were modified so that both lasers could be aligned to the same scanning track with a defined offset. A variation of the laser-based post-heating parameters enabled specific in-situ modifications of the thermal gradients compared to standard single-laser scanning strategies, leading to corresponding property changes in the produced material structure. An increase in microhardness of up to 15% was thus obtained from 411 HV up to 471 HV. The results of the investigation can be used to derive cross-material optimization potential to produce functionally graded high-performance components on PBF-LB systems with synchronized multi-laser technology.

Experimental and Numerical Study on the PG-7VM Warhead Performance against High-Hardness Armor Steel.

Analyses presented in the article were carried out in order to characterize the main parameters of the shaped charge jet formed due to detonation of the PG-7VM warhead. As opposed to the previously published studies in which rolled homogeneous armored steel was mainly used as a target, in the current work the warhead penetration capability was determined against more contemporary high-hardness (500 HB) ARMSTAL 30PM steel armor with precisely determined mechanical properties. The research included experimental depth of penetration tests and their numerical reproduction in the LS-Dyna software. Special attention was paid to factors that could perturbate the shaped charge jet formation process and under- or overestimate its penetration capability. For this reason, warheads were X-ray inspected for structural discrepancies (voids or air inclusions in explosive, misalignment between the body, explosive, and liner, or lack of contact between the explosive and the liner) and properties of materials (explosive, targets, and most important warhead components) were analyzed before the experiments. The numerical model of the warhead was defined more accurately than in previously published studies, since it was based on the real grenade dimensions and its technical documentation. Thanks to this, the depth of penetration of the target made of ARMSTAL 30PM armored steel plates by the shaped charge jet formed from the PG-7VM warhead obtained by numerical simulation was consistent with the experimental results and equaled 278 mm and 280 mm, respectively. The difference between the experimental and numerical value was smaller than 1%, which confirms that the developed methodology of modeling allows users to properly reproduce the PG-7VM shaped charge jet formation and target penetration processes. A verified numerical model of the shaped charge jet penetration into a steel target was used to determine depth of penetration in function of stand-off distance for the PG-7VM warhead. A maximum depth of penetration of about 317 mm was obtained for the stand-off distance of 360 mm, which may indicate the potential direction of modernization of warheads.

Effect of a nanofiltration combined process on the treatment of high-hardness and micropolluted water.

The quality of raw water and the current high level of pollution presents a phenomenon of high hardness and micropollution. An experimental study was conducted of the nanofiltration (NF) pilot-scale process combined with biological contact oxidation precipitation and ultrafiltration (UF) as the pretreatment process to treat this water. The study investigated the removal efficiency and membrane fouling of the NF process under the continuous and stable operating conditions of the combination process and studied the influence of high-hardness water on the membrane pollution of the combination process. The results showed that the combined process had a positive removal effect on conventional pollutants and characteristic pollutants, and the removal rates of conventional pollutants, such as turbidity, UV254 and CODMn, were 95%, 90% and 85%, respectively. The removal efficiency of total hardness, total alkalinity and soluble total solids reached 98%, 86% and 91%, respectively, and that of total desalination was above 95%. The removal rates of fluorescent organic substances, such as tryptophan, tyrosine, soluble microbial products (SMPs), fulvic acid and humus-like substances, as well as the precursors of disinfection byproducts reached over 88% and 50%, respectively. The pollutant removal efficiency of the combined process was mainly concentrated in the NF unit. The pretreatment process had certain removal effects on turbidity and macromolecular organic substances in the raw water, which provided a perfect operating environment for the NF process. Under long-term operation, the main elements of scaling on the surface of the NF membrane included C, O, Na, Mg, Al, Si, S, Cl, Ca, Ti and Fe, which were mainly concentrated at the outlet of the membrane and mainly came from monomers or compounds composed of inorganic salts in the raw water and some organic compounds. High-hardness water accelerated the change in membrane process parameters, and the surface of the membrane had abundant inorganic scaling. The inorganic scale on the surface of the NF membrane increased noticeably when filtering water with high hardness. Regular cleaning of the UF and NF membranes could effectively restore the parameters of the process and prolong the service life of the membrane process.

Strong Graphene 3D Assemblies with High Elastic Recovery and Hardness.

The rational design and construction of 3D graphene assemblies is a crucial step to extend the graphene properties for practical applications. Here, a novel interfacially reactive self-assembling process is reported to prepare well-organized 3D honeycomb-like graphene assemblies with unique polygonal nanopores interconnected by silicon-oxygen chemical bonds. The newly developed silicate-bridged graphene assembly (SGA) exhibits an exceptionally high hardness of 13.09 GPa, outperforming all existing 3D graphene materials, while maintains high Young's modulus (162.96 GPa), elastic recovery (75.27%), and superb thermal stability (600 °C in air). The observed unusual merits are resulted from unique pore structure combining the mechanical stability of the trihedral-nanopore structure and the deformability of the other polygonal nanopores. As a filling material, a merely 0.05% (w/w) addition of SGA could double the impact resistance of unsaturated resins (e.g., polyester). While SGA is attractive for various applications, including body armors, wearable electronics, space elevators, and multifunctional reinforcement fibers for automobiles, and aerospace vehicles, the novel liquid sodium-water interfacial reactive self-assembling developed in this study could open avenues for further development of various well-defined 3D assemblies from graphene and many other materials.

Tailoring Building Blocks and Their Boundary Interaction for the Creation of New, Potentially Superhard, Carbon Materials.

A strategy for preparing hybrid carbon structures with amorphous carbon clusters as hard building blocks by compressing a series of predesigned two-component fullerides is presented. In such constructed structures the building blocks and their boundaries can be tuned by changing the starting components, providing a way for the creation of new hard/superhard materials with desirable properties.

A new carbon phase constructed by long-range ordered carbon clusters from compressing C70 solvates.

An ordered amorphous carbon cluster (OACC) structure with building blocks of highly deformed/collapsed C70 is synthesized by compressing C70 *m-xylene, which exhibits an exceptionally high hardness. Different from compressing C60 *m-xylene, a new structure transition is observed in C70*m-xylene at above 30 GPa, indicating the formation of a new OACC structure under pressure.