Cobalt–Niobium-Carbide Eutectic Alloys for Increasing the Service Life of Gas Turbine Engines

This article represents the stages of the creation of new serial wear-proof and heat-resistant (at temperatures up to 1100 °C) cobalt–Nb-carbide cast eutectic alloys of the KhTN (XTN) grade at the G.V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine, comparing them by their main properties, and use in aircraft engine engineering.

On the Jumps of Volume, Enthalpy and Entropy at the Melting Point, the Thermal Conductivity and Thermal Diffusivity for F.C.C. Au: the Temperature- and Pressure-Dependences

The melting temperature, the jumps of volume, enthalpy and entropy at the melting point, the isothermal compressibility, the thermal expansion coefficient, the heat capacity at constant volume, the Grüneisen parameter, the Debye temperature, the electrical resistivity, the thermal conductivity, and the thermal diffusivity for defective and perfect f.c.c. metals are studied by combining the statistical moment method (SMM), the limiting condition of the absolute stability of the crystalline state, the Clapeyron–Clausius equation, the Debye model, the Grüneisen equation, the Wiedemann–Franz law, and the Mott equation. Numerical calculations are carried out for Au under high temperature and pressure. The calculated melting curve of Au is in good agreement with experiments and other calculations. Obtained results are predictive and orient towards new experiments.

The Role of Stress–Strain State of Gas Turbine Engine Metal Parts in Predicting Their Safe Life

The influence of various factors on the workability of critical metallic parts of a gas turbine engine (GTE) is analysed and systematized. As shown, compressor blades fail as a result of foreign-objects’ damage, gas corrosion, and erosion. Compressor blade roots in most cases fail due to fretting wear caused by vibrations, while the fir-tree rim of turbine discs fails due to low-cycle fatigue (LCF) damage and creep. An increase in the radial gaps between the rotor and stator of the turbine reduces the thrust force and causes changes in the gas-dynamic loading of the engine components. Additional oxidation of metal parts is observed under the action of hot gases from the combustion chamber. The principles of material selection for manufacturing turbine blades and disks, concepts of alloying heat-resistant alloys, and modern methods of surface engineering due to applying protective oxidation-resistant coatings, in particular, chemical vapour deposition (CDV), physical vapour deposition (PVD), air plasma spraying (APS), etc., are also described. To predict the lifetime of turbine disks, it is proposed to use the modified Walker model and Miner’s rule. To specify the time before the failure of the metal blades of the turbine, it is proposed to use the finite element method. To monitor the working-surfaces’ deformations of the gas turbine engine, it is recommended to use optical-digital methods.

Microstructure Evolution of the Carbon Steels During Surface Severe Plastic Deformation

The review is devoted to the state-of-the-art views on the microstructure evolution in structural and tool carbon steels during the surface severe plastic deformation (SPD). The main focus is on the effects of the nanocrystallization in the near-surface area of the low-carbon steel (C 0.05–0.2%), medium-carbon steel (C 0.35–0.65%), and high-carbon steel (C 1.0–1.5%). It is reviewed the following advanced surface SPD methods for the metal surfaces in recent years: an ultrasonic impact peening (UIP), high-frequency impact peening (HFIP), air blast shot peening (ABSP), surface mechanical attrition treatment (SMAT), and laser shock peening (LSP). Microstructure evolution before and after SPD is studied by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effects of the SPD parameters on the nanocrystalline modification of such main phase components of the carbon steels as ferrite, pearlite, and cementite are analysed. The atomic mechanism of the nanocrystallization is presented. The strain-hardening effect induced by SPD is demonstrated by the data of the near-surface microhardness profiles.

Modelling of Phase Formation in Solid–Solid and Solid–Liquid Interactions: New Developments

Recent developments (after 2016) in modelling of phase formation during solid–solid and solid–liquid reactions by SKMF (Stochastic Kinetic Mean-Field) method, Monte Carlo simulation and phenomenological modelling are reviewed. Reasonable results of multiphase reactive diffusion modelling demonstrating distinct concentration plateau for each intermediate ordered compound and distinct concentration steps between these phases are obtained by the SKMF and Monte Carlo methods, if one takes into account interatomic interactions within two coordination shells and if the signs of mixing energies are ‘minus’ for the first coordination shell and ‘plus’ for the second one. Second possibility for reasonable modelling results is consideration of interatomic interactions depending on local concentration with maxima around stoichiometric composition. In phenomenological modelling, the generalization of Wagner diffusivity concept and respective superposition rule are introduced. New mechanism of the lateral grain growth in the growing phase layers during reactive diffusion is suggested. Anomalously fast grain growth at the final stages of soldering in sandwich-like Cu–Sn–Cu contacts is reported and explained. Simple model of Zn-additions’ influence on the Cu–Sn reaction is described.

Thermodynamic Calculation of Fe–N and Fe–Ga Melting Diagrams at Pressures from 0.1 MPa to 7 GPa

This paper presents results of melting-diagrams’ calculations for the Fe–N and Fe–Ga systems at atmospheric pressure (0.1 MPa) and at high pressures (3, 5, and 7 GPa). Thermodynamic calculations are performed within the models of phenomenological thermodynamics. As shown, the increase of pressure results in destabilization of high-temperature b.c.c.-Fe modification in Fe–N system and stabilization of Fe4N equilibrium with the liquid phase. In Fe–Ga system, the intermetallic compounds Fe3Ga, Fe6Ga5, Fe3Ga4, and FeGa3 retain their stability up to pressure of 7 GPa. The stabilization of Fe4N equilibrium with the liquid phase at high pressures indicates that the Fe4N can be a competing phase in the gallium-nitride crystallization from the Fe–Ga–N system melt.

Features of Strain Hardening of Heterogeneous Aluminium Alloys to Enhance the Fatigue Durability

Heterogeneous aluminium alloys are in demand in the aviation industry, where the ability of the material to withstand fatigue loads is important. The topic of the article is the search for the most experimentally available methods of deformation effect on such materials in order to increase fatigue life. Unfortunately, previous studies were ambiguous due to the large number of factors influencing the fatigue of metal materials under the same type of mechanical load; so, we chose a dynamic load with pulse loading. It turned out that for heterogeneous 2024-T351 and D16CzATW alloys, shock–vibration loading (SVL) applied during static straining prolongs their further fatigue life at a certain magnitude of the deformation during the action of the pulse. For example, for the 2024-T351 alloy at the maximum stress of alternating load σmax = 400 MPa, the longest fatigue life should be expected at deformations εimp = 2–4%; and at the maximum stress of alternating (fatigue) loading of 440 MPa, it is at εimp = 3–5%. In comparison with the average values of fatigue life of the D16CzAT alloy in the initial state, fatigue life after processing increases at σmax = 340 MPa alloy by 11.6%, at a stress of σmax = 370 MPa, by 18.4%, at a stress of σmax = 400 MPa, by 21.2%. The positive effect of long-term exposure after treatment on fatigue life was also noted. The influence of the strengthening phases, such as the nanosize Θ-Al2Cu and S-CuAl2Mg particles, on the separate stages of pre-treatment of alloys and the effects of their quantities on total fatigue durability is investigated by statistical methods of transmission electron microscopy. The great attention is paid to the mechanism of formation of fatigue fracture embryos in the near-surface areas of the samples, for which analytical calculations and the experimental method of ultrasonic impact treatment (UIT) are used. It is shown that the use of UIT after SVL does not affect the fatigue life of the 2024-T351 alloy at a fatigue load frequency of 15 Hz, while the single UIT increases fatigue life of the alloy. It is concluded that the use of complex deformation loads accelerates the relaxation processes, which shorten fatigue life.

Structural and Physical Properties of Ultrathin Bismuth Films

Bismuth films are interesting objects for research because of the many effects occurring when the film thickness is less than 70 nm. The electronic band structure changes significantly depending on the film thickness. Consequently, by changing the film thickness, it is possible to control the physical properties of the material. The purpose of this paper is to give a brief description of the basic structural and physical properties of bismuth films. The structural properties, namely, morphology, roughness, nanoparticle size, and texture, are discussed first, followed by a description of the transport properties and the band structure. The transport properties are described using the semi-metal–semiconductor transition, which is associated with the quantum size effect. In addition, an important characteristic is a two-channel model, which allows describing the change in resistivity with temperature. The band structure of bismuth films is the most interesting part due to the anomalous effects for which there is still no unambiguous explanation. These effects include anomalous spin polarization, nontrivial topology, and zone changes near the edge of the film.