Specific surface, crystalite size of AlB12-nano of products of interaction "BN-Al" in vacuum

Boron carbide (BC, B15-xCx B4C) has a unique combination of properties. This makes it a material for priority applications for a wide range of engineering solutions. The high melting point and heat resistance of the compound contribute to its use in refractory conditions. Due to its extreme abrasion resistance, B4C is used as an abrasive powder and coating. Due to its high hardness and low density, B15-xCx has ballistic characteristics. It is usually used in nuclear programs as an absorbent of neutron radiation Boron carbide ceramics (B15-xCx or BC) may lose strength and toughness due to the amorphization effect under high shear stresses. Aluminum dodecaboride AlB12 or B12Al, as well as boron carbide B12 [(CCC) x (CBC) 1-x] have common structural units B12 family of boron-icosahedral structures. The bond between icosahedrons is mainly due to atoms (Al, Si, O) or chains (CMC), where M is Al, Si, B, C. Doping BC powder with a small amount of AlB12, in cases of shock-shear stress, triggers the mechanism of "micro-cracking". Micro cracks and pores are formed in ceramics. The breakdown voltage decreases. AlB12 synthesis is associated with known difficulties. On the other hand. The production of metal-ceramic materials for several decades is associated with the interaction of liquid aluminum and boron nitride. The calculation of this reaction shows that it is exothermic. Avoiding oxidation in vacuum, the reaction occurs through the formation of aluminum nitride and aluminum dodeca-boride. In contrast to the liquid state, the process continues until the end, at conditional temperatures of evaporation of aluminum with slight changes in vacuum. The reaction product is a mixture of nanosized AlN/AlB12 powders with a weight ratio of 3/1 ready for baking without grinding. The acid-base properties of the nanosized powder mixture AlN + AlB12, the products of the interaction BN + Al in vacuum, which are used optionally, emit separate in pure phases of aluminum nitride and aluminum dodeca-boride. The yield of AlB12 is ~ 25%, boron reaches ~ 100%. The average particle size of the AlB12 powders according to TEM and ACS X-rays (area of coherent X-rays scattering), L (nm) is LTEM=110-150nm, LACS=51-70nm. The average specific surface area of the powder according to BET, TEM and ACS, SBET.m2/g=21,0-15,0; STEM.m2/g=21,4-15,4; SACS.m2/g=46,1-33,6; (at 1460 and 1640K, respectively).

Performance of TiB2 Wettable Cathode Coating

A TiB2 wettable cathode coating was deposited on a graphite carbon cathode material via atmospheric plasma spraying (APS). The microstructure and phase composition of the TiB2 coating were analyzed via scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The wettability and corrosion resistance of the coating were studied in a molten-aluminum electrolytic system. The results showed that the surface of the TiB2 coating prepared via plasma spraying was flat and that the main phase of the coating was TiB2. The wettability between the TiB2 coating and liquid aluminum was better than that between graphite cathode carbon block and liquid aluminum. The abilities of the TiB2 coating and graphite cathode carbon block to resist sodium (Na) penetration and prevent molten salt corrosion were compared through a corrosion test. The TiB2 coating was found to have better resistance to Na penetration and better refractory cryolite corrosion resistance than graphite cathode carbon block.

Modeling the Filler Phase Interaction with Solidification Front in Al(TiC) Composite Produced by the In Situ Method

This paper presents simulation results of the interaction of TiC nanoparticle in liquid aluminum. The behavior of the TiC particle in the frontal interaction region stems from the operation of a system of such forces as gravity, viscous flow drag force, and Saffman force. The difference in density between the TiC and the aluminum matrix makes the particle fall, regardless of the radius dimension; while the Saffman force—which accounts for the local velocity gradient of the liquid aluminum—causes that particles with the smallest radii considered in the calculations 6.4 × 10−8 m; 7 × 10−8 m; 7.75 × 10−8 m; 9.85 × 10−8 m are repelled from the solidification front and the particles with 15.03 × 10−8 m are attracted to it. The viscosity growth in the course of casting caused by the lowering temperature reduces this effect, though the trend is maintained. The degree to which the particle is attracted to the front clearly depends on the velocity gradient of the liquid phase. For a very small gradient of 0.00001 m/s, the particle is at its closest position relative to the front.

Effect of Electric Pulse Treatment on Hot-Dip Aluminizing Coating of Ductile Iron

In this paper, hot-dip aluminizing of ferrite nodular cast iron was carried out after treating liquid aluminum with different electrical pulse parameters. Compared with that of conventional hot-dip aluminizing, the coating structure of the treated sample did not change, the surface was smooth and continuous, and the solidification structure was more uniform. When high voltage and large capacitance were used to treat the liquid aluminum, the thickness and compactness of the coating surface layer increased. The thickness of the alloy layer decreased, and, the compactness and the micro hardness increased, so the electric pulse had a certain inhibition on the formation of the alloy layer. The growth kinetics of the alloy layer showed that the rate-time index decreased from 0.60 for the conventional sample to 0.38 for the electric pulse treated sample. The growth of the alloy layer was controlled by diffusion and interface reaction, but only by diffusion. The AC impedance and polarization curves of the coating showed that the corrosion resistance of hot-dip coating on nodular cast iron was improved by electric pulse treatment.

Sn-Aided Joining of Cast Aluminum and Steel Through a Compound Casting Process

Obtaining a strong bond between aluminum and steel is challenging due to poor wettability between aluminum melt and steel and brittle intermetallic phases forming in the interface. In this research, a novel coating method, namely hot dipping of Sn, has been developed to treat the steel insert surfaces. Results show that without preheating the mold or Sn-coated insert, a thin, crack-free, and continuous metallurgical bonding layer was achieved in the A356 aluminum/steel compound castings. Intermetallic structures forming in the interface have been characterized in detail. The Sn-coating layer completely melted and mixed with the liquid aluminum during the casting process. The reaction layer at the aluminum/steel interface is composed of ternary Al–Fe–Si particles and a thin layer of binary Al5Fe2 phase with thickness less than 1 µm. A small fraction of dispersed Sn-rich particles was observed distributing in the reaction layer and adjacent to eutectic Si particles in the A356 alloy. A sessile drop wetting test showed that Sn-coated steel substrates can be well wetted by aluminum melt. The improved wettability between A356 alloy melt and steel was attributed to the penetration and breaking of the aluminum oxide layer at the surface of the aluminum droplets by liquid Sn. Graphic Abstract

Using High-Speed Imaging and Machine Learning to Capture Ultrasonic Treatment Cavitation Area at Different Amplitudes

The ultrasonic treatment process strengthens metals by increasing nucleation and decreasing grain size in an energy efficient way, without having to add anything to the material. The goal of this research endeavor was to use machine learning to automatically measure cavitation area in the Ultrasonic Treatment process to understand how amplitude influences cavitation area. For this experiment, a probe was placed into a container filled with turpentine because it has a similar viscosity to liquid aluminum. The probe gyrates up and down tens of micrometers at a frequency of 20 kHz, which causes cavitations to form in the turpentine. Each experimental trial ran for 5 seconds. We took footage on a high-speed camera running the UST probe from 20% to 35% amplitude in increments of 1%. Our research examined how the amplitude of the probe changed the cavitation area per unit time. It was vital to get a great contrast between the cavitations and the turpentine so that we could train a machine learning model to measure the cavitation area in a software called Dragonfly. We observed that as amplitude increased, average cavitation area also increased. Plotting cavitation area versus time shows that the cavitation area for a given amplitude increases and decreases in a wave-like pattern as time passes.

Features of Al-10Mo electron-beam produced master-alloy assimilation in liquid aluminum and AlSi9Cu3 alloy

The work is devoted to the Al-10Mo electron-beam prepared master-alloy modifying phases dissolution and assimilation features determination. It is shown that the obtained master-alloy is characterized by uniform distribution and high dispersion of molybdenum aluminide particles. When studying the process of dissolving the master-alloy in pure aluminum, it was determined that the time of modification of the melt more than 20 minutes at a temperature of 740 ± 10 ° C leads to the most complete destruction of the original intermetallics Al22Mo5 and Al17Mo4 and the formation of smaller and evenly distributed particles Al5Mo and Al12Mo with dimensions about 2 μm. As the molybdenum content decreases, the dispersion of the modifying phases and the uniformity of their distribution increase. Increasing the temperature and exposure time do not improve the assimilation of the modifier. The Al-10Mo master-alloy, obtained in the conditions of electron-beam casting technology, has a number of characteristics that allow to consider it as more efficient and cost-effective, compared to known analogues. This is due to the much higher concentration of molybdenum in the modifier (10% wt.), as well as fine dispersion and uniform distribution of the modifying phases. The nonequilibrium composition of aluminides inherent in the ligatures obtained under these conditions contributes to their significant grinding and refining after addition into aluminum melts. The stoichiometry of the phases from Al22Mo5 and Al17Mo4 changes to Al12Mo, which serve as crystallization centers and have a size of about 1 μm, dissolves and changes. The example of industrial casting alloy AlSi9Cu3 shows complete and effective assimilation of the master-alloy in a short time of 5 minutes at a temperature of 740 ± 10 ° C. Such indicators are more economic, in comparison with standard industrial ones, for which both higher temperature of melt preparing ant longer lifetime in liquid state after modification are necessary. Keywords: master-alloys, Al-Mo, modifications, aluminum alloys, AlSi9Cu3, resource saving.

Thermodynamics of solid and liquid aluminium

Based on thermodynamic calculations, it is shown that in the temperature range of 298–1273 K, heating and cooling of aluminum are thermodynamically equilibrium processes. When aluminum is heated, the molar volume energy of Gibbs decreases and the molar boundary energy of nanocrystals increases. When aluminum is cooled, the molar volume energy of Gibbs increases and the molar boundary energy of nanocrystals decreases. Liquid aluminum is a nanostructured system. Dendritic microcrystals are formed from nanocrystals. They play a large role in the processes of changing the structure of aluminum during its heating and cooling.