卷 60, 编号 1 (2019)

The phase formation of Ti–Al–C powder mixtures with compositions close to MAX phases during self-propagating high-temperature synthesis (SHS) is investigated using time-resolved X-ray diffraction. It is found that the formation of the material during combustion in air under low heat-removal rates is a staged process. At the first stage, the dominant reaction is titanium carbide formation, providing major heat release and combustion front propagation. This reaction leads to the formation of TiC crystals surrounded by the Ti–Al melt. Titanium carbide is dissolved in the surrounding melt behind the combustion front with the subsequent crystallization of the Ti₂AlC ternary compound. No TiC formation is observed during synthesis in helium, which provides rapid heat removal. The first phase appearing in the diffraction field is Ti₂AlC. The TiC life cycle of 5–10 s for the mixtures synthesized in air substantially decreases when performing the process in helium and does not exceed 1 s. SHS leads to the formation of the composite material based on Ti₂AlC phase containing less than 20 wt % TiAl and 2 wt % TiC. The material structure is characterized by lamellar Ti₂AlC grains surrounded by the TiAl matrix. The microhardness of synthesized materials is 4.0–4.5 GPa and corresponds to the microhardness of the Ti₂AlC phase. The dispersity of Ti₂AlC grains during the synthesis in helium is lower than during the synthesis in air. Lamellar MAX-phase grains grow to 8–15 μm in length and 2–5 μm in width during slow cooling in air. The dispersity of Ti₂AlC grains grown in helium is lower, being no larger than 8 and 1 μm, respectively.

Comprehensive investigations into Cu–ZnO (nano) and Cu–TiN (nano) copper-based materials by standard methods in combination with metallographic and electron microscopy investigations using energy-dispersive and thermal analyses make it possible to identify stable correlation relations between the content of nanoparticle additives, microstructural parameters, and mechanical-and-physical properties of pseudoalloys. Process procedures of increasing the distribution uniformity of modifying additives of ZnO and TiN nanoparticles over the pseudoalloy bulk excluding their conglomeration are developed and substantiated. Novel original methods of nanoparticle introducing into a matrix material in the form of a master alloy made of Cu–Al–ZnO or copper powders coated with TiN nanoparticles are proposed. A high specific surface and reactivity of nanopowders make it possible to lower the ceramic phase in electrocontact materials (down to 2.0–3.0% instead of 10–15% when compared with known commercial brands). This results in the conservation of the main properties characteristic of the matrix material (copper) such as thermal and electrical conductivity at a rather high level, while the general level of physicomechanical characteristics (hardness, strength, and wear resistance) and operational properties of composite pseudoalloys simultaneously increases. The main characteristics of copper-based composite materials are as follows: electrical resistance (ρ = 0.025 μΩ m), bonding strength to the contact support material (σ ~ 2 MPa), and dispersed ceramic phase inclusions. They reduce the electroerosive wear (up to a factor of 2.5) when compared with conventional materials.

An analysis of modern scientific-and-technical information evidences great prospects for using composite materials (CMs) based on the Al–Al₂O₃ system. It is shown in works of the Materials Science Department of the Moscow Aviation Institute that one promising method of fabricating aluminum-based CMs is the reaction sintering in air of blanks made of highly dispersed powders of the PAP-2 brand. However, to implement the proposed method in practice, it is necessary to solve a series of problems, in particular, associated with their low manufacturing properties, such as a lack of fluidity and extremely low apparent density. To granulate the PAP-2 aluminum powder, various process approaches are applied. They are based on process operations such as powder heating in air with subsequent isothermal holding at 350°C, introducing water-diluted sodium silicate glass into its composition, mechanical processing of the powder in a high-energy planetary mill, its heat treatment in vacuum at 650°C, and initiating the stearin saponification reaction on the surface of the PAP-2 flaked particles with the formation of the organic plasticizer component. It is found that the proposed granulation methods of the industrial PAP-2 powder make it possible to improve and vary the process characteristics of the initial powder, as well as modifying its composition and structure. The highest apparent density (up to 1.25 g/cm³) is attained when using the mechanical treatment of the initial powder in a high-energy planetary mill with the formation of rounded granules 50–150 μm in size. The most producible and cost-effective method is based on the initiation of the chemical reaction of stearin saponification on the surface of powder particles (the apparent density is ~0.4 g/cm³).

The direct laser deposition of metal powders is one additive method of producing functional materials. It consists of the melting of metallic powders by a laser beam in inert gas. The main process parameters are the laser-beam power, laser-beam speed and scanning trajectory, and powder consumption. Each parameter is selected depending on the alloy type, which in totality affects the structure and defect formation in products. In this study, experimental rectangular samples of 316L austenitic steel are fabricated by the direct laser deposition of the powder. The microstructure and fractures of samples are investigated using scanning electron microscopy in order to determine the structural features and reveal the defects (pores, holes, crystallization cracks, and oxide inclusions). Uniaxial tension tests and hardness tests are performed. The analysis of the influence of the laser beam scanning trajectory on the microstructure and properties of samples during melting is performed. It is found that a dispersed structure with an average crystallite size of 1.3–1.9 μm is formed at a laser power of 250 W and scanning rate of 16 mm/s, which results in a high level of mechanical properties of experimental samples. It is shown that, when using the lengthwise laser-beam trajectory (along the largest sample size), the tensile strength reaches 730 MPa with a relative elongation of 25%, which exceeds the level of mechanical properties of 316L steel by 110 MPa.

Abstract—The aggregation and sedimentation of ultradispersed diamonds (UDDs) in a citrate copper-plating electrolyte (CCPE) used to fabricate composite electrochemical coatings are investigated. The sedimentation and aggregation stability is investigated in order to select the UDD concentration in the CCPE. This is necessary to fabricate composite copper coatings with improved operational characteristics (increased hardness, wear resistance, and corrosion resistance), as well as impart them new properties (antifriction and catalytic). The UDD content in the electrolyte varies in limits from 0.2 to 2.0 g/L. The size distribution of the UDD particles in the electrolyte immediately after the suspension preparation and after the 10-day holding is determined using a Malvern Mastersizer 2000 laser diffraction analyzer. The aggregation and sedimentation stability of the UDD suspension in the CCPE is investigated by the gravimetric method with the continuous weighing of a quartz small cap immersed into this suspension. The quartz cap is associated with a Sartorius R200D analytical balance with the help of a quartz wire. The experimentally determined time dependence of the weight of settling UDD particles is Q = f(t). The relative size distribution of the particles is determined from this dependence. It is established that the sedimentation stability is substantially affected by the aggregation of the particles, the intensity of which increases with an increase in the UDD concentration. The results satisfying the requirements on the aggregation and sedimentation stability are found for the UDD suspension in the CCPE with a concentration of 1.0 g/L. In this case, the high content of the dispersed phase is combined with aggregation and sedimentation stability, which makes it possible to fabricate copper composite coatings with improved operational properties.

Titanium-based alloys are widely used in various industries due to their combination of high mechanical properties and low density. These properties are most effectively used when fabricating aircraft components and medical implants. Shape-memory alloys based on titanium nickelide (nitinol) are promising materials for the fabrication of superelastic medical implants and tools, as well as thermomechanical elements in aerospace technology. The joint application of these materials as elements of hybrid structures or composites is promising for the development of products with a unique set of properties such as high mechanical properties, superelasticity, and damping capacity; increased wear resistance; and thermal shape memory. The basic properties of alloys based on titanium nickelide and the most widely used VT6 titanium alloy (Ti–6Al–4V) are analyzed. It is shown that the combination of functional properties of nitinol and structural properties of titanium alloys in an integrated structure makes it possible to fabricate various products, especially for aerospace and medical industries. To fabricate such structures, various welding (mainly laser and diffusion welding) and soldering methods are currently investigated, and the best prospects are associated with the use of intermediate layers that eliminate the formation of brittle intermetallic phases in permanent joints.