Metallic iron or a Fe-based glassy alloy to reinforce aluminum: reactions at the interface during spark plasma sintering and mechanical properties of the composites

The microstructural features and mechanical properties of composites formed by spark plasma sintering (SPS) of Al + 20 vol.% Fe and Al + 20 vol.% Fe66Cr10Nb5B19 (glassy alloy) mixtures composed of micrometer-sized particles are presented. The interaction between the mixture components was studied by differential thermal analysis and through examining the microstructure of composites sintered at two different SPS pressures. When the pressure was increased from 40 MPa to 80 MPa, the thickness of the reaction products formed between the iron particles and aluminum increased due to a more intimate contact between the phases established at a higher pressure. When the metallic glass was substituted for iron, the pressure increase had an opposite effect. It was concluded that local overheating at the interface in the case of Al + 20 vol.% Fe66Cr10Nb5B19 composites governed the formation of the product layers at 40 MPa. The influence of the nature of reinforcement on the mechanical properties of the composites was analyzed, for which sintered materials with similar microstructural features were compared. In composites without the reaction products and composites with thin layers of the products, the hardness increased by 13–38% relative to the unreinforced sintered aluminum, the glassy alloy and iron inclusions producing similar outcomes. The effect of the nature of added particles on the hardness and compressive strength of composites was seen when the microstructure of the material was such that an efficient load transfer mechanism was operative. This was possible upon the formation of thick layers of reaction products. Upon compression, the strong glassy cores experienced fracture, the composite with the glassy component showing a higher strength than the composite containing core-shell structures with metallic iron cores

Computer-Controlled Detonation Spraying: Flexible Control of the Coating Chemistry and Microstructure

This article is a focused review aimed to describe the potential of the computer-controlled detonation spraying (CCDS) for producing and designing coatings with variable chemical and phase compositions and microstructure and promising properties. The development of the detonation spraying method is briefly analyzed from a historical perspective and the capabilities of the state-of-the art facilities are presented. A key advantage of the CCDS is the possibility of using precisely measured quantities of the explosive gaseous mixtures for each shot of the detonation gun and different oxygen to fuel ratios, which can create spraying environments of different chemical properties—from severely oxidizing to highly reducing. The significance of careful adjustment of the spraying parameters is shown using material systems that are chemically sensitive to the composition of the spraying environment and temperature. Research performed by the authors on CCDS of different materials—metals, ceramics, intermetallics and metal-ceramic composites is reviewed. Novel applications of detonation spraying using the CCDS technology are described

Nanoscale Detonation Carbon Demonstrates Biosafety in Human Cell Culture

The production method of nanoscale detonation carbon (NDC) has recently been developed at Lavrentyev Institute of Hydrodynamics SB RAS. This method uses the reaction of acetylene with oxygen conducted in the detonation mode in fuel-rich acetylene–oxygen mixtures. The morphology and structural features of the NDC particles can be varied by changing the concentration of oxygen in the gaseous mixtures. The particles of NDC can serve as reinforcements in metal matrix composites and additives imparting electrical conductivity to polymer matrix composites. Before NDC can be considered for industrial applications, it is necessary to address the related biological safety concerns. The present work was aimed at determining the cytotoxicity of NDC. The NDC powders with two morphologies (obtained using different acetylene/oxygen ratios) were tested on HEK293A human cells. The NDC powder was added to the culture medium in concentrations ranging from 10 ng/mL to 400 μg/mL. The cell viability was determined by a colorimetric EZ4U test and a real-time cell analyzer xCELLigence. None of the NDC samples showed a cytotoxic effect. The results of this study allow us to recommend NDC as a safe and useful product for the development of advanced carbon-based and composite materials

Formation of Composite Coatings during Detonation Spraying of Cr₃C₂

In the current practice of applying carbide-based coatings by thermal spraying, the starting material usually contains a metal binder. However, it is important to study the possibility of spraying binder-free carbides, since the metal components usually reduce the operating temperature and corrosion resistance of cermet coatings. In this work, a powder of chromium carbide, Cr3C2, was sprayed using a CCDS2000 detonation gun. Acetylene–oxygen mixtures C2H2 + kO2 with k varying from 0.8 to 3.0 were used as an energetic material. Due to chemical reactions between Cr3C2 and the detonation products, the coatings were of composite nature (multi-phase materials) with a composition depending on k. At k values in the range from 0.8 to 1.1, along with Cr3C2, the coatings contained chromium carbonitride Cr3N0.4C1.6. In the k range from 1.3 to 2.0, Cr7C3 and Cr were the main components of the coatings. As k was increased to 3.0, along with Cr7C3 and Cr, the CrO and Cr2O3 oxides formed in the coatings. The mechanical properties and wear resistance of the coatings were found to depend on their phase compositions. Coatings produced by detonation spraying of Cr3C2 powder may be useful for increasing the corrosion resistance of machine parts to mineral acids and high-temperature oxidation resistance

Fabrication of High-Entropy Alloys Using a Combination of Detonation Spraying and Spark Plasma Sintering: A Case Study Using the Al-Fe-Co-Ni-Cu System

The use of pre-alloyed powders as high-entropy alloy (HEA) coating precursors ensures a predetermined (unaltered) elemental composition of the coating with regard to the feedstock powder. At the same time, it is interesting to tackle a more challenging task: to form alloy coatings from powder blends (not previously alloyed). The powder-blend-based route of coating formation eliminates the need to use atomization or ball milling equipment for powder preparation and allows for the introduction of additives into the material in a flexible manner. In this work, for the first time, a HEA was obtained using detonation spraying (DS) followed by spark plasma sintering (SPS). A powder mixture with a nominal composition of 10Al-22.5Fe-22.5Co-22.5Ni-22.5Cu (at.%) was detonation-sprayed to form a multicomponent metallic coating on a steel substrate. The elemental composition of the deposited layer was (9 ± 1)Al-(10 ± 1)Fe-(20 ± 1)Co-(34 ± 1)Ni-(27 ± 1)Cu (at.%), which is different from that of the feedstock powder because of the differences in the deposition efficiencies of the metals during DS. Despite the compositional deviations, the deposited layer was still suitable as a precursor for a HEA with a configurational entropy of ~1.5R, where R is the universal gas constant. The subsequent SPS treatment of the substrate/coating assembly was carried out at 800–1000 °C at a uniaxial pressure of 40 MPa. The SPS treatment of the deposited layer at 1000 °C for 20 min was sufficient to produce an alloy with a single-phase face-centered cubic structure and a porosity of 0.3). The hardness of the coatings measured in two perpendicular directions did not differ significantly. The features of the DS–SPS route of the formation of HEA coatings and its potential applications are discussed

Formation of Metallic Glass Coatings by Detonation Spraying of a Fe66Cr10Nb5B19 Powder

The present work was aimed to demonstrate the possibility of forming Fe66Cr10Nb5B19 metallic glass coatings by detonation spraying and analyze the coating formation process. A partially amorphous Fe66Cr10Nb5B19 powder with particles ranging from 45 µm to 74 µm in diameter was used to deposit coatings on stainless steel substrates. The deposition process was studied for different explosive charges (fractions of the barrel volume filled with an explosive mixture (C2H2 + 1.1O2)). As the explosive charge was increased from 35% to 55%, the content of the crystalline phase in the coatings, as determined from the X-ray diffraction patterns, decreased. Coatings formed at explosive charges of 55–70% contained as little as 1 wt.% of the crystalline phase. In these coatings, nanocrystals in a metallic glass matrix were only rarely found; their presence was confined to some inter-splat boundaries. The particle velocities and temperatures at the exit of the barrel were calculated using a previously developed model. The particle temperatures increased as the explosive charge was increased from 35% to 70%; the particle velocities passed through maxima. The coatings acquire an amorphous structure as the molten particles rapidly solidify on the substrate; cooling rates of the splats were estimated. The Fe66Cr10Nb5B19 metallic glass coatings obtained at explosive changes of 55–60% showed low porosity (0.5–2.5%), high hardness (715–1025 HV), and high bonding strength to the substrate (150 MPa)