Crack resistance of carbonized layer of multilayer polyurethane with nanofillers. Combination of casting, solution, carbonization by ion implantation technologies

The paper describes the results of an experimental study of a polyurethane material treated by ion implantation technology. The problems of crack growth in the near-surface layer carbonized by ion treatment were investigated using digital optical microscopy. The methods of atomic force microscopy allowed studying the possibility of carbonized layers delamination from the substrate. As a result, the technology for the production of a multilayer polyurethane material with nanofillers (nanotubes, nanodiamonds, fullerenes, graphenes) and its optimal modification by ion implantation treatment was developed, which makes it possible to improve the biocompatibility of polyurethane implants with human tissues

Regional Models for High-Resolution Retrieval of Chlorophyll <i>a</i> and TSM Concentrations in the Gorky Reservoir by Sentinel-2 Imagery

The possibilities of chlorophyll a (Chl a) and total suspended matter (TSM) retrieval using Sentinel-2/MSI imagery and in situ measurements in the Gorky Reservoir are investigated. This water body is an inland freshwater ecosystem within the territory of the Russian Federation. During the algal bloom period, the optical properties of water are extremely heterogeneous and vary on scales of tens of meters. Additionally, they vary in time under the influence of currents and wind forcing. In this case, the usage of the traditional station-based sampling to describe the state of the reservoir may be uninformative and not rational. Therefore, we proposed an original approach based on simultaneous in situ measurements of the remote sensing reflectance by a single radiometer and the concentration of water constituents by an ultraviolet fluorescence LiDAR from a high-speed gliding motorboat. This approach provided fast data collection including 4087 synchronized LiDAR and radiometric measurements with high spatial resolutions of 8 m for two hours. A part of the dataset was coincided with Sentinel-2 overpass and used for the development of regional algorithms for the retrieval of Chl a and TSM concentrations. For inland waters of the Russian Federation, such research was performed for the first time. The proposed algorithms can be used for regular environmental monitoring of the Gorky Reservoir using ship measurements or Sentinel-2 images. Additionally, they can be adapted for neighboring reservoirs, for example, for other seven reservoirs on the Volga River. Moreover, the proposed ship measurement approach can be useful in the practice of limnological monitoring of inland freshwater ecosystems with high spatiotemporal variability of the optical properties

Laser Powder Bed Fusion of Chromium Bronze Using Recycled Powder

Laser powder bed fusion (LPBF) of Cu-0.5Cr was carried out using recycled powder taken out from the LPBF machine after previous printing. Various volumetric defects characterized the powder wherein particle size distribution was the same as virgin powder. Using recycled powder resulted in extra spherical pore formation after the LPBF process. Despite that, a relative density of 99.2% was achieved by LPBF parameters optimization. Solidified microstructure with a small volume of defects consisted of an oversaturated dendritic Cu matrix and nano-sized Cr precipitations providing strengthening mechanism occurrence. The possibility of a satisfactory level of mechanical properties with σ0.2 = 136.8 MPa, UTS = 187.4 MPa, along with 15.5% of elongation achieving, was shown

Synthesis of Al–Al₂O₃–CNF Composite by Cold Spray Method: Powder Preparation and Synthesized Objects Characterization

This paper is devoted to studying the composite material of the aluminum–alumina–carbon nanofiber (CNF) system. The paper considers in detail the process of preparation of the specified composite by ball milling, as well as the process of synthesis of a solid object (coating) by the cold spray method. The synthesized objects were studied using optical and electron microscopy, and the hardness of objects of various compositions was measured. The processes of interaction of composite particles are discussed in detail. The influence of CNF on the distribution of particles in a solid object and on the hardness of objects has been considered and discussed

Selective Laser Melting of Al-Based Matrix Composites with Al2O3 Reinforcement: Features and Advantages

Aluminum matrix composites (AMC) are of great interest and importance as high-performance materials with enhanced mechanical properties. Al2O3 is a commonly used reinforcement in AMCs fabricated by means of various technological methods, including casting and sintering. Selective laser melting (SLM) is a suitable modern method of the fabrication of net-shape fully dense parts from AMC with alumina. The main results, achievements, and difficulties of SLM applied to AMCs with alumina are discussed in this review and compared with conventional methods. It was shown that the initial powder preparation, namely the particle size distribution, sphericity, and thorough mixing, affected the final microstructure and properties of SLMed materials drastically. The distribution of reinforcing particles tends to consolidate the near-melting pool-edges process because of pushing by the liquid–solid interface during the solidification process that is a common problem of various fabrication methods. The achievement of an homogeneous distribution was shown to be possible through both the thorough mixing of the initial powders and the precise optimization of SLM parameters. The strength of the AMCs fabricated by the SLM method was relatively low compared with materials produced by conventional methods, while for superior relative densities of more than 99%, hardness and tribological properties were obtained, making SLM a promising method for the Al-based matrix composites with Al2O3

X-ray Fluorescence Spectroscopy Features of Micro- and Nanoscale Copper and Nickel Particle Compositions

The study is devoted to X-ray fluorescence spectroscopy (XRF) features of micro- and nanosized powder mixtures of copper and nickel. XRF is a high accuracy method that allows for both qualitative and quantitative analysis. However, the XRF measurement error due to the size of the studied particles is not usually taken into account, which limits the use of the method in some cases, such as analysis of Ni-Cu mixtures and coatings. In this paper, a method for obtaining copper and nickel nanoparticles was investigated, and the XRF of powder compositions was considered in detail. The initial micro- and nanoparticles of copper and nickel were studied in detail using SEM, TEM, XRD, and EDX. Based on experimental data, calibration curves for copper-nickel powder compositions of various sizes were developed. According to the results, it was experimentally established that the calibration curves constructed for nanoscale and microscale powders differ significantly. The presented approach can be expanded for other metals and particle sizes

Characterization of Multiphase Oxide Layer Formation on Micro and Nanoscale Iron Particles

The article presents a detailed study and characterization of the oxide layers on the surface of iron particles of various sizes. Ten iron samples with a size range from a few nm to 50 &micro;m were studied in detail using SEM, TEM, XRD, and TGA analysis. The composition of the multiphase oxide layers on the powder surface was investigated. The main components of the oxide layer were FeO, Fe3O4, and Fe2O3. By the obtained data, a model for the calculation of a multiphase oxide layer thickness on the surface of iron particles was proposed. The proposed model was validated and can be used for the characterization and certification of micro&ndash; and nanoscale iron particles

AlSi10Mg/AlN Interface Grain Structure after Laser Powder Bed Fusion

Details and features of the grain structure near the interface region between the AlN ceramic phase and AlSi10Mg matrix after the laser powder bed fusion (LPBF) were investigated. Aluminum nitride particles were obtained through self-propagating high-temperature synthesis and mechanically mixed with aluminum matrix powder. Optimization of the LPBF process parameters resulted in synthesized material free of pores and other defects. Optical microscopy analysis of etched cross-section and more detailed EBSD analysis revealed regions with relatively coarse grains at melting pool boundaries and fine grains in the melt pool core and near the AlN particles. Moreover, a pronounced orientation of fine elongated matrix grains towards the center of the ceramic particle was obtained. The such formed microstructure is attributed to directional heat sink during crystallization due to the higher thermal conductivity of aluminum nitride compared to the AlSi10Mg matrix. On the contrary, poor wettability of AlN by melt partly prevented the formation of such features, thus a combination of these factors determines the final microstructure of the interface in the resulting material

AlSi10Mg/AlN Interface Grain Structure after Laser Powder Bed Fusion

Details and features of the grain structure near the interface region between the AlN ceramic phase and AlSi10Mg matrix after the laser powder bed fusion (LPBF) were investigated. Aluminum nitride particles were obtained through self-propagating high-temperature synthesis and mechanically mixed with aluminum matrix powder. Optimization of the LPBF process parameters resulted in synthesized material free of pores and other defects. Optical microscopy analysis of etched cross-section and more detailed EBSD analysis revealed regions with relatively coarse grains at melting pool boundaries and fine grains in the melt pool core and near the AlN particles. Moreover, a pronounced orientation of fine elongated matrix grains towards the center of the ceramic particle was obtained. The such formed microstructure is attributed to directional heat sink during crystallization due to the higher thermal conductivity of aluminum nitride compared to the AlSi10Mg matrix. On the contrary, poor wettability of AlN by melt partly prevented the formation of such features, thus a combination of these factors determines the final microstructure of the interface in the resulting material

Laser powder bed fusion of AlSi10Mg-based composites with graphene and nanodiamond additions

Laser powder bed fusion (LPBF) processing of aluminum matrix composites (AMC) with blends of AlSi10Mg powder and nanodiamond and graphene additives was investigated. AMC with 0.5 wt% nanodiamonds addition was prepared by mechanical mixing, while AMC with 0.5 wt% of multi-layered graphene was prepared by electrochemical deposition. Initial powders for LPBF were thoroughly characterized and optimal LPBF parameters were found based on the relative density analysis and optical microscopy. Processing windows of both AMCs moved towards lower energy density possibly due to the increased total absorptivity of the powders. Raman spectroscopy results, SEM and HRTEM studies of samples after LPBF demonstrated the absence of nano-diamond in the structure after processing which is explained by graphitization of the nanodiamond particles during laser melting. In case of AMC with graphene additives, carbon-containing particles remained in the structure with partial in situ formation of Al4C3, along with a noticeable strengthening effect, which increased material’s microhardness by more than 40% compared to the initial AlSi10Mg alloy. The strengthening effect is explained by the presence of a network of graphene and Al4C3 particles across the solidified melt-pool promoting the Orowan strengthening mechanism.ISSN:0925-8388ISSN:1873-466