About evaporation–condensation coefficients on the vapor–liquid interface of high thermal conductivity matters

The paper is devoted to study of interface matter transfer during evaporation and condensation. At the beginning different definitions of evaporation and condensation coefficients are analyzed. Then brief history of study development about mass flux density determination at evaporation and condensation is presented. The possibilities of molecular dynamics simulation concerning these processes are discussed. Then interpretation of Furukawa and Murakami (1999) [16] experimental data about determination of evaporation and condensation coefficients on helium vapor and its condensed superfluid phase (HeII) interface has been done. As a resume conclusion is made that at weak evaporation of high thermal conductivity matters as evaporation and as condensation coefficients are close to unit approximately.     

On the application of SHS-electrode materials for the electrospark hardening of rolls for hot rolling mill

The structure, composition, and properties of electrospark coatings formed on substrates of white cast iron with the use of a STIM-40NA self-propagating high-temperature synthesis (SHS) electrode material (TiC-NiAl composition) are studied. The roughness of the produced coating is investigated. The application of the electrospark-alloying (ESA) process favored enhancing the mill roll durability more than twice at the Oskolsky Electrometallurgical Works.     

Composite SHS materials based on titanium carbide and nikelide doped with a refractory component

This study is devoted to the synthesis and investigation of composite ceramic materials based on titanium carbide and nickelide with the use of the effect of dispersion strengthening by force of the dedicated alloying of reactionary mixtures with a nanodispersed refractory component. The influence of nanodispersed particles on the main combustion parameters in conditions of quasi-isostatic compression is shown. The phase composition and the structure of compact synthesis products, in which the main phase components are TiC and the Ti _x Ni _y intermetallic compound, are investigated. It is established that doping with a nanocomponent does not vary the phase composition qualitatively but leads to a substantial modification of the structure of the materials, at which the average grain size of the main refractory component decreases by a factor of 1.5–3.5. In addition, a similar effect is observed with a decrease in the TiC concentration in the composition of the samples. Complex investigations into the physicomechanical properties and heat resistance of fabricated materials are performed. The effect of the positive influence of refractory nanoparticles on such characteristics of alloys as hardness, strength, Young modulus, and durability to high-temperature oxidation are shown.     

Mechanical Properties and Heat Resistance of Ta–Zr–Si–B–C–N Coatings Obtained upon the Magnetron Sputtering of the TaZrSiB Target in Ar,N2, and C2H4 Atmosphere

Russian Journal of Non-Ferrous Metals - Ta–Zr–Si–B–C–N coatings are obtained by magnetron sputtering in argon, nitrogen, and ethylene atmosphere. The structure of the...     

Combustion synthesis of high-temperature ZrB2-SiC ceramics

The work is dedicated to researching into combustion kinetics and mechanism as well as the stages of the chemical transformations during self-propagating high-temperature synthesis of ZrB₂-SiC based ceramics. Dependences of the combustion temperature and rate on the initial temperature (T₀) have been studied. It has been shown that the stages of the chemical reactions of ZrB₂ diboride and SiC carbide formation do not change within the range of T_0?=?298–700?К. The effective activation energy of the combustion process amounted to 170–270?kJ/mol, from which it has been concluded that chemical interaction through the melt plays a leading role. The stages of the chemical transformations in the combustion wave have been studied by dynamic X-ray diffraction. First, ZrB₂ phase forms from Zr-Si melt saturated with boron, and SiC phase is registered later. The SHS method has successfully been used in order to obtain ZrB₂-SiC composite powders and compact ceramics with a silicon carbide content of 25–75%. The ceramics are characterized by a residual porosity of 1.5%, hardness up to 25?GPa, the elastic modulus of 318?±?21?GPa, elastic recovery of 36% and thermal conductivity of 54.9?W/(m?×?K) at T_room.     

Self-propagating high-temperature synthesis of nanocomposite ceramics TaSi2-SiC with hierarchical structure and superior properties

This study focuses on the investigation of the combustion kinetics and mechanisms, as well as the phase and structure formation processes, during elemental self-propagating high temperature synthesis of ceramics in Ta-Si-C system.Thermodynamic and kinetic features of SHS are discussed. Thermodynamic calculations, time-resolved XRD and investigation of stopped combustion front suggest the following chemical reactions sequence in combustion wave for the Ta-Si-C system: Ta + Si_solid + C → TaC + Si_solid + C → TaC + SiC + Si_liquid + C → TaC + TaSi₂ + Ta₅Si₃ + SiC + Si_solid + C → TaSi₂ + SiC.Significant microstructure refinement occurs due to the formation of SiC within the TaC, Ta₅Si₃ and TaSi₂ particles during the SHS. Combustion products consist of agglomerated SiC and TaSi₂ particles with the size of individual grains equal to 15–50 nm. Hot pressing of TaSi₂-SiC powders at 1600 °C produces the bulk nanocomposites with a relative density of 97%. In comparison to similar materials reported in the literature, bulk SHS composite TaSi₂-30%SiC exhibits superior hardness (19.1 GPa) as well as fracture toughness (6.7 MPa m^1/2) and shows a great potential for application as a structural material and as a precursor for ion-plasma deposition of high-temperature tribological coatings.     

Fabrication of Narrow-Fraction Micropowders of NiAl-Based Refractory Alloy CompoNiAl-M5-3

Powders of new CompoNiAl M5-3 heat-resistant alloy were prepared by mechanoactivated SHS from (Ni–Al–Cr–Co–Hf)–NaCl mixtures. Ni dissolution in Al melt was found to be the motive force of combustion. Unlike the binary Ni–Al system, NiAl is formed not in the melt but in the post-combustion zone as a result of diffusion-controlled processes. Conditions for MASHS were optimized toward fabrication of a superalloy with homogeneous composition/structure and low content of gas impurities. As-prepared combustion product was disintegrated into a powder and the latter was subjected to plasma spheroidization, keeping in mind the needs of additive manufacturing. The attained degree of spheroidization was 98%. The structure and phase/chemical compositions of spherical powders did not differ from those of the synthesized powders. After plasma treatment, the content of gas impurities (О₂ and N₂) decreased.     

Structure and Magnetic Properties of WC–50% Co Model Alloys Containing TaC Additives

The structure and magnetic properties of model high-cobalt WC–50% Co alloys with different carbon contents and TaC additions in the amount of 1.6–5.6 wt % are studied. Model alloys are fabricated by the liquid-phase sintering of powder mixtures at 1420°C, and their composition is described by the formula 50% Co + 50% WC + x% TaC + y% C, where x = 0, 1.6, 2.6, 3.6, 4.6, and 5.6 wt %; y = 0, 0.2, and 0.5 wt %. It is shown that precipitations of the (Ta,W)C phase are present in all studied alloys and (Ta,W)C precipitations are needle-shaped at a TaC concentration up to 3.6 wt %, while the (Ta,W)C grains become spherical at =3.6 wt %. The (Ta,W)C precipitations are arranged both in a binding phase and along the WC grain boundaries. The lattice parameter of the (Ta,W)C phase in alloys with a low carbon content lies in a range from 0.4438 nm for the alloy with 1.6% TaC to 0.4451 nm for the alloy with 4.6% TaC. It is established by the EDX analysis that the concentration of dissolved tungsten in a cobalt phase is independent of the TaC content and strongly depends on the total carbon content; it is 7, 12, and 17 wt % for alloys with high, elevated, and low carbon contents, respectively. The TaC addition in alloys with a low and elevated carbon content leads to an increase in the coercive force up to 875 A/m and a decrease in the magnetic saturation by 5–10 G m³/g. The experimental results made it possible to put forward a hypothesis on the possibility of formation of dispersed tantalum-containing precipitates in a binder phase.     

Synthesis of Ceramic Materials Based on Titanium Carbide with a Cobalt Binder for the Pulsed Electrospark Deposition of Bioactive Coatings with an Antibacterial Effect

The goal of this study was to produce biocompatible ceramic materials in the Ti–C–Co–Ca₃(PO₄)₂–Ag–Mg system by combustion mode synthesis. The influence of cobalt on combustion parameters of the mixture, structure, and properties of the products was investigated. Compact ceramics consist of a combined grain frame of nonstoichiometric titanium carbide (TiC_0.5–TiC_0.6) with the titanium phosphate (Ti₃PO_x) phase homogeneously distributed along grain boundaries and local isolations of calcium oxide (CaO). The introduction of cobalt promotes the formation of a complex phosphide CoTiP and TiCo intermetallic compound. Alloying with silver and magnesium leads to the formation of a silver-based solid solution.