Capillary behavior of gallium droplets on porous Cr2AlC was studied during heating to 1200 degrees C in high vacuum. High-speed thermal and video cameras were used for temperature and form capturing. At 1195 +/- 5 degrees C gallium began to spread abruptly and being absorbed in tenths of a second. The microstructure and composition of crosssection was analyzed by scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. Gallium was dissolved in Cr2AlC and it formed Cr2(Al1-xGax)C, with a maximum x value of 0.2. The infiltration rate, temperature of "non-wetting-wetting" transition, contact angles, and thermal effects were obtained. As a result of Ga impregnation, the porous Cr2(Al1-xGax)C exhibited increased mechanical strength.

The study proposes a direct method for studying capillary infiltration of porous media using high-speed measurements of the shape of an imbibited droplet of finite size. The method assumes isotropic infiltration, and the change in the droplet volume on the surface is equated to the volume of imbibited liquid. The shape of the imbibited volume in the case of a droplet of finite volume is assumed to be a flattened spheroid. In the mathematical model, the rate of change of the apparent volume obtained in the experiment is reduced to the rate of movement of the liquid front in the porous media. Measurements of capillary processes in the silver (melt)-iron (porous or dense solid) system were carried out at various temperatures in a vacuum of 10-3 Pa to verify the model. Time dependencies of the wetting contact angle and the contact diameter of pure silver melt on the surface of dense solid iron, the imbibition rate of silver melt into porous iron, and the kinetics of sintering of iron powder were measured. All measurements were conducted using direct methods of high-speed video and thermal imaging. As a result, in addition to the application of the proposed imbibition model, kinetic dependencies of the mentioned processes at various temperatures in the range from 1000 to 1150 degrees C were obtained and their activation energies were determined.

Plasma-facing components for thermonuclear fusion reactors require the introduction of new materials due to outstanding demands in mechanical, thermal, and thermal cycle fatigue resistivity properties. One promising solution is the W-Cu composite material or multimaterial that combines the properties of both components. In the present work, W-Cu samples were obtained by laser powder bed fusion (LPBF) consolidation of a tungsten porous matrix followed by copper infiltration. A design of structures with ordered porosity was achieved by translation of skeletal gyroid unit cell (triply periodic minimal surface). A relative density of 96.7% was achieved for solid pure tungsten samples with optimized LPBF process conditions. As-built W gyroid samples had a 15-20% ultimate compressive strength (UCS) of the solid sample. After the infiltration with copper, the ductility of W-Cu composites increased drastically, i.e. the samples did not fracture at a strain of 35%. It was found that UCS, yield strength (YS), and thermal diffusivity were sensitive to gyroid unit cell size. The sample with the smallest cell size of 2 mm had superior YS of 626 MPa and thermal diffusivity of 76.4 mm2/s. The obtained results will shed light on the possibilities for further development of W-Cu manufacturing technology based on the LPBF method combined with subsequent infiltration.

Synthesis of the MAX phase is most often conducted at high temperatures, and the synthesized mixture contains many contaminant phases that require removal. The discovery of efficient low -temperature methods for the synthesis of MAX phases and MXenes is the key to their mass application. This work reports a method for obtaining pure MAX -phase with composition of Cr2GaC using a microwave reactor without additional heating. Synthesis was performed under 2 torr vacuum in hydrogen and methane flows of 80 and 20 sccm, respectively. The power of the microwave generator was 500 W at a frequency of 4.5 GHz. The synthesis process consists of creating conditions for capillary interaction (contact angle much lower than 90 degrees, tends to zero), dissolution of chromium substrate in liquid gallium and dissolution of carbon directly from the gas phase (H2-CH4 plasma). The synthesized MAX phase does not contain any phase contaminations and has a thickness of several atomic layers and submicron lateral dimensions. Characterization of the phases was carried out using the transmission electron microscopy (TEM), energy -dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), atomicforce microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy methods. Diffraction methods show high purity of Cr2GaC phase synthesized by this method, which can be a good precursor for MXenes production.

The interaction of nitinol melt with Al2O3, ZrO2, BeO and Y2O3 oxides used as crucible materials has been studied. Capillary interaction has been monitored directly using the method of sessile drop with video and thermal imaging in 10-3torr vacuum at 1350 °C. Nitinol melt drops have been formed in a high-density graphite dispenseror directly on the substrate surface. The contact angleson the surface of polished oxides have been obtained. The contact angles established within 30 sec increase in the sequence Al2O3, ZrO2, BeO and Y2O3 from 30° to 70°. The corrosion resistance of the oxides has been studied for cross-sections using scanning electron microscopy with energy dispersion analysis. The phase composition at the ceramic/melt boundary has been studied using transmission electron microscopy. Thermodynamic analysis of melt chemical interaction with oxides has been conducted within equilibrium concentration calculation.

In this study, we experimentally investigated the interaction of a pure copper melt with dense MAX phase (Cr,Mn)2AlC obtained as a result of sintering by the spark plasma method and with a porous phase compacted by room temperature pressing. The porous phase (porosity 20

The specific feature of Cu(Co) solid solutions with a sub-solidus composition involves the formation of submicron-sized cobalt particles on the free surface. In this work, Cu(Co) substrates with cobalt particles on the surface were produced through the annealing of a series of copper-based cobalt solid solutions con-taining 1-3 at% Co in a hydrogen atmosphere at 1050 degrees C, leading to the formation of a family of cobalt-based submicron-sized particles with a similar orientation within one grain on the surface. The wetting and spreading of lead and copper-based liquid alloys on the surfaces of these substrates were compared to the wetting of pure copper and pure cobalt. Experiments were conducted via the high-speed video recording of droplet transfer onto the Cu, Co, and Cu(Co) substrates at 400 degrees C (melt: pure lead), at 850 degrees C (Pb + 10.3 at% Cu), and at 1070 degrees C (Cu + 2.5 at% Ag) in a vacuum. The contact angle of the Pb melt on cobalt (46 degrees) differed significantly from the contact angle on copper at 400 degrees C (32 degrees), while at 850 degrees C, the wetting for both metals was almost complete (the wetting angles for Cu and Co were 5 degrees and 7 degrees, respectively). The wetting angle for the Cu(Co) solid solution surface with cobalt particles was almost equal to that for pure copper, and the spreading rates were comparable for the two cases. The wetting of the Cu, Co, and Cu(Co) surfaces by the Cu (Ag) melt did not demonstrate any significant differences between the equilibrium contact angles (tending to zero), while the spreading rate differed only slightly. The surface area covered by the particles reached 20%, despite the presence of the particles, which exerted no impact on the contact angle, due to two possible effects: (i) the formation of an adsorbed copper layer on the surface of the cobalt phase confirmed by room-temperature Auger electron spectroscopy, and (ii) the compensation of wetting deterioration by an increase in roughness. (c) 2023 Elsevier B.V. All rights reserved.

Experiments were carried out on the wetting and spreading of the nitinol melt over the polished surface of high-density pure graphite. The furnace heater and the dispenser from which the melt was extruded were also made of graphite of the same quality. The measurements were carried out in vacuum of 10-3 Pa at a temperature close to the melting point and higher, up to 1430 degrees C. High-speed filming of the transferred drop was used simultaneously with high-speed thermal imaging. As a result, the kinetics of the spreading of the nitinol melt over the graphite surface was obtained, and the surface tension was also measured by the pendant drop method. The dissolution of carbon in the melt prevents the formation of a barrier layer of titanium carbide. Electron microscopic studies confirmed the formation of a dense layer of titanium carbide on the contact surface. An experiment was carried out on the melting of nitinol on carbon felt at a temperature of 1350 degrees C. It is shown that nitinol's drop on felt with a density of about 100 kg/m3 (porosity 93%) does not impregnate into the felt, retains volume and shape for more than 15 min. This indicates that carbon felt or cloth may be good candidates for lining materials.

High-entropy carbides (HECs) are paid great attention owing to superior properties, and various fabrication methods have been used to date to produce high-quality material. Here, a novel approach, in the case of HECs, is used to prepare powder and bulk (Ti,Zr,Hf,Nb,Ta)C: the calcium-hydride reduction (CHR) of oxides, followed by pressureless sintering (PS) and spark plasma sintering (SPS). The material obtained is characterized via TEM, SEM, and XRD. It has been shown that the CHR provides the formation of the nano-sized powder with a multiphase structure consisting of binary carbides. Subsequent PS and SPS lead to the formation of a single-phase structure; however, porosity differs significantly. As a bulk state, (Ti,Zr,Hf,Nb,Ta)C exhibits typical high hardness (20.4 GPa) and good fracture toughness (4.2 MPa.m(1/2)). The results have shown that calcium-hydride reduction process, with proper development, can provide a new cost-effective technology for the synthesis of nano and submicron powders of high-entropy carbides.

The wetting and spreading of Cu(0.8 at.% Cr) melt over Cr2AlC MAX phase were measured in 10(-3) Pa vacuum at 1150 ?. The measurements were carried out in-situ, by the dispensed drop method from a graphite dispenser. The contact angle established during 1 s was 35 and the alloy is found to be suitable for brazing of Cr2AlC MAX-phase. Studies of the chemical and phase compositions near the contact surface showed an intense chemical interaction during the spreading, associated with the dissolution of aluminum in the penetrated copper melt.

A direct measurement of the surface energy polytherm in Ag + 0.5 at.% Fe alloy and first-principles calculations of segregation energy in silver-based systems with iron, cobalt and nickel were performed. The surface energy was measured in situ on silver foils with 16 mu m thickness in the temperature range (0.8 0.95) T-m(Ag) in Ar+10% H-2 atmosphere. Iron was introduced by electrolytic deposition and annealing. The segregation energy calculations were performed using density functional theory (DFT). DFT calculations were used to obtain the segregation energies of Fe, Co and Ni on the (100), (110), and (111) surfaces of Ag. It was shown that alloying of silver with Ni, Co and Fe (similar to 0.5 at.%) leads to a significant increase in the surface energy and this effect increased with decreasing temperature. The alloys behaved in a similar way with decreasing temperature: the surface energy of the alloys increased to values close to the surface energy values of the second components in their standard reference states. DFT calculations of the segregation energy showed a strong "anti-segregation" behavior of Ni, Co and Fe in Ag; the segregation energy took positive values of about 0.4 eV/atom for all solute atoms. Surface studies by AFM and AES methods showed that the surface was two-phase, a silver phase and a small fraction of the second bcc-Fe phase particles coated with a thin silver layer. These observations indicated a quite pronounced desorption of iron on silver on one hand and the adsorption of silver on iron on the other hand. The positive segregation energies of Ni, Co and Fe to Ag surfaces, experimentally observed desorption behavior of these solutes as well as an increase of the surface energy with the increasing concentration of the second component, point at the fundamental reversibility of the Gibbs adsorption equation. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Abstract—The bulk and grain-boundary diffusions of copper in pure silver and a silver-copper alloy containing 3.6 at % Cu are studied. Diffusion experiments are conducted on coarse-grained samples with a diffusant source (Cu) of constant concentration at average homological temperatures (0.4–0.7$$T_{m}^{{{\text{Ag}}}}$$). Measurements of the grain-boundary diffusion indicate that diffusion along the grain boundaries is slower than self-diffusion in Ag. Averaged over the ensemble of grains, the diffusion rate of Cu along the grain boundaries slightly exceeds the bulk diffusion rate. The grain-boundary diffusion in the alloy is close to that in pure Ag. These effects are discussed in light of experiments to determine the surface energy in Ag–Cu solid solutions.

The effect of nickel on surface energy of the solid/gas interface of silver was studied. The measurements were taken using foils according to the previously developed in situ method in an atmosphere of Ar + 10% H-2 at high temperatures. This method simultaneously allows one to determine the surface energy and diffusion creep rate. The solubility of nickel in silver is very low, so the measurements were taken for the alloys in the two-phase region with 0.45 at.% Ni and 1.5 at.% Ni, as well as for pure nickel. Nickel is shown to significantly increase the surface energy of silver and slow down the diffusion creep rate.

We analyzed the changes in diffusional creep in polycrystalline copper depending on the impurities dissolved therein. The data on strain rate at high temperatures (> 0.85 Tm) and low stresses (< 0.5 MPa) obtained in zerocreep experiments were used. In dilute solutions the creep rate falls at low concentrations of surface-active impurities In, Sn, Sb, Pb and Bi. The increasing concentration of the second component increases the rate of bulk diffusion of solid solution, as a results, the viscosity decreases. So, the diffusion creep in dilute solid solutions with surface-active impurities In, Sn, Sb, Pb and Bi have extreme behavior with the concentration. (C) 2020 Elsevier B.V. All rights reserved.

The present study focuses on the interaction between copper melts and porous tantalum plates (purity, 99.99 wt% Ta). The samples were prepared by sintering tantalum powder with different grain size and were characterized by 65% porosity. A procedure to perform direct observations of the interaction between the melt and plates was developed. Equipment for high-speed recording of dipping of the samples into the melt was designed. The frame rate was up to 5000 fps. A high-vacuum furnace with a graphite heater was used. Wetting experiments were performed in the temperature range of 1100-1400 degrees C. As expected, at temperatures near 1150 degrees C the tantalum cake coated with an oxide layer is not wetted by pure copper and does not imbibe it. Rising temperature slightly improves wetting. Doping the copper melt with 2 at.% B at 1150 and 1275 degrees C reduced the contact angle to 60 degrees it dropped below 25 degrees at 1400 degrees C. The reason for the observed phenomenon was that doping with boron results in reactive wetting and formation of tantalum boride. Wetting of the porous samples was compared to wetting of cast tantalum plates. The kinetics of imbibition with Cu(B) melt were recorded. The imbibition dependence changed from power-law to linear one as temperature increased from 1275 to 1400 degrees C. This behavior is associated with degradation of the tantalum boride layer. (C) 2020 Elsevier B.V. All rights reserved.

The surface energy of Ag-Co alloys in a gaseous atmosphere of Ar + 10% H-2 in the temperature range from 1050 K to 1160 K was measured using the zero creep method. The alloys (0.2 at.% Co, 0.8 at.% Co, 2.1 at.% Co) and pure Ag were used as samples. The measurement results are presented as surface energy polytherms. The polytherms for the Ag + 0.2 at.% Co solid solution and two phase alloys have a noticeable jump, which can be interpreted to be a surface phase transition. An increase in surface energy with decreasing temperature occurs to values corresponding to pure cobalt (about 3 J/m(2)). (C) 2019 Elsevier B.V. All rights reserved.

Surfaces are key elements of nanomaterials and catalysts. The main thermodynamic properties of surfaces are their chemical composition and energy. To determine the composition of the surface, there are a number of effective methods such as AES, XPS, TEM. Direct measurements of the interfacial free energy of “solid–gas” interface are practically not carried out. This is related to experimental difficulties. We have developed a method for in situ measurements of the surface energy of solid metals and alloys. We conducted the experiments on two-component Cu-based systems in an inert or reducing gas atmosphere. The measurements on Cu [Ag] and Cu [Co] solid solutions show the presence of phase transitions on the surfaces. The isotherms of the surface energy have singularities (the minimum in the case of copper solid solutions with silver and the maximum in the case of solid solutions with cobalt). In both cases, the surface phase transitions lead to the surface miscibility gap: a monolayer (multilayer) formation (Cu–Ag) or formation of nanoscale particles (Cu–Co). In accordance with the bulk phase diagrams, the concentration and temperature of the surface phase transitions correspond to the solid solution in the bulk. Experiments on similar systems (Cu–Fe, Cu–Pb) lead to the conclusion that in all peritectic systems, an increase in the surface energy by adding a component with a higher melting point and surface phase transitions “surface solid solution—two-phase surface with particles” should be expected. In eutectic systems, the component with a lower melting point decreases the surface energy and forms continuous layers.

New magnesium-substituted bone cements containing MgO as a separate phase have been developed and demonstrated enhanced mechanical properties and cytological compatibility.

In this article new experimental evidences of anomalous grain boundary diffusion (GBD) of Fe and Co in Cu were describe. To demonstrate that the brief describing of results of grain boundary diffusion in Cu with following formulation of rules which can be established on the base of the analysis of the results is presented. Experimental results which are described here concern the attempt to change the effect negative segregation by microalloying by sulfur which did not change the situation and the diffusion through foil which allowed to demonstrate the absence of accelerated GB diffusion without specific sample preparation. It is shown that GBs do not give the additional effect to the flux of Fe and Co through the foil. The extended model of surface tension gradient as an additional driving force is described.