Vol 2019, No 9 (2019)

Differential scanning calorimetry and differential barothermal analysis demonstrate that a hydrostatic pressure of 100 MPa leads to a shift in the characteristic temperatures of an aluminum-matrix Al–7 wt % Si–7 wt % Cu composite alloy to higher temperatures at pressure coefficients of 0.04–0.12 K/MPa. An increase in the solidus temperature by 6°C, which is most significant from a practical point of view, is shown to enable one to increase the hot isostatic pressing (HIP) temperature as compared to the homogenizing annealing temperature or the heating temperature for quenching. It is also shown that HIP treatment (the temperature of isothermal holding is 515 ± 5°C, the hydrostatic pressure is 100 MPa, the holding time is 3 h) leads to a more compact morphology of Al₂Cu and Si eutectic particles in the alloy structure. The results of studying the mechanical properties after HIP treatment and hardening heat treatment according to regime T6 (quenching from 505°C for 1 h + aging at 175°C for 6 h) show that the strength of the alloy increases from 335 to 360 MPa, the relative elongation increases by ~35% (from 2.0 to 2.8%) as compared to a usual specimen, and the reproducibility of the mechanical properties is noticeably improved.

The methods used for the preparation of an Al–Er master alloy as a promising addition to aluminum alloys for enhancing their physical and mechanical characteristics are analytically reviewed. Thermodynamic analysis of the processes that occur during master alloy fabrication in chloride–fluoride melts containing erbium oxide is carried out. Since the data on erbium complexes are lacking or restricted, the thermodynamic values are determined by indirect methods. The study of the phase composition of the chloride–fluoride melts shows that the melting of a salt mixture results in the fluorination of erbium oxide and the formation of the KEr₃F₁₀ complex, which is a precursor for erbium reduction and intermetallic compound Al₃Er formation. The effect of the flux composition and the technological parameters of aluminothermic reduction on the transition of erbium to the master alloy is studied.

Representative samples of the waste slime of the vanadium pentoxide V₂O₅ production from converter slags according to the lime–sulfuric acid technology are studied to develop its effective reclamation with vanadium recovery. The phase composition of the slime consists of gypsum, hematite, quartz, cristobalite, pseudo-brookite, complex ferrite, and various calcium-containing silicates. The residual vanadium content in the waste slime that is based on V₂O₅ is 2–7%, the major part of which is sealed (insoluble) vanadium and the minor part is acid-soluble vanadium. A high vanadium content in the slime is found to be related to the disadvantages of oxidizing roasting of a vanadium slag with a lime addition in a rotary kiln and sulfuric acid leaching of a cinder under industrial conditions. To study the vanadium recovery from the slime, we analyzed direct sulfuric acid leaching of the slime and its leaching after preliminary oxidizing roasting. The optimum parameters of oxidizing roasting and sulfuric acid leaching are determined. Oxidizing roasting of the slime in the temperature range 925–1050°C is shown to substantially increase the vanadium recovery during subsequent leaching of the roasting product by weak sulfuric acid solutions. To exclude the formation of aggressive compounds SO₂ and SO₃ in roasting, it is necessary to separate a fine gypsum-containing fraction from the slime before oxidizing roasting in order to perform acid leaching.

The results of low-cycle fatigue (LCF) tests of a VZh175 nickel superalloy are presented. LCF is one of the main strength characteristics of nickel superalloys subjected to cyclic loading. The LCF tests are carried out during symmetric and asymmetric loading at room and high temperatures. The experimental results are presented in the form of regression lines related the logarithm of stresses and the logarithms of the number of cycles to failure and the number of cycles corresponding to 50% failure probability and in the form of tables. A change in the testing conditions, i.e., asymmetric loading and high test temperatures, is found to decrease the LCF alternating stress amplitude significantly. As compared to an increase in the test temperature, an increase in stress ratio R more strongly affects the decrease in the alternating stress amplitude σ_a in the ranges of these parameters under study.

The structure of the welded joints of high-strength steel sheets, which were made using hydroabrasive cutting, is studied by optical microscopy, scanning electron microscopy, and electron-probe microanalysis. Uniaxial tensile and impact bending tests are performed on an instrumented pendulum impact testing machine and loading diagrams are recorded. Faulty fusion defects and slag inclusions are revealed during a fractographic investigation of the fracture surfaces of tensile and impact specimens. These defects are shown not to be related to the use of hydroabrasive cutting for cutting rolled sheets.

The magnetization losses of the (Pr_0.51Dy_0.49)_13.6(Fe_0.64Co_0.36)_79.6B_6.8 and (Pr_0.51Dy_0.49)_13.4(Fe_0.64Co_0.36)_78.8Cu_1.1B_6.7 magnets are studied. The alloying of the Pr–Dy–Fe–Co–B materials with copper is shown to cause a decrease in the magnetization losses in time, which is due to an increase in the coercive force.