Study of oxygen content in titanium alloys after exposure at elevated temperature

Isothermal oxidation testing of near α titanium alloys VT18U, VT20, Ti6Al7Nb and Ti6242S was performed in air at 560 °С for 1000 hours. Parameters of diffusion layer on the alloy surfaces were studied by microhardness indentations, optical microscopy, X-ray diffraction analysis and nuclear microanalysis. It was established that concentration of oxygen in diffusion layer of tested alloys after oxidation differs significantly. An approach was demonstrated and validated by nuclear microanalysis data that allows comparative evaluation of the total concentration of interstitial impurities in the diffusion layer by the X-ray diffraction method.

Isotope Exchange between 18O2 Gas and Mechanoactivated Oxide NdMnO3+δ

sotope exchange of oxygen 18О2 with oxides NdMnO3+δ was investigated. The oxide was obtained from oxides Nd2O3 and Mn2O3 using a ceramic technology with annealing in air at 1400°C for 90 hours followed by cooling in a furnace. A planetary mill AGO-2 with a centrifugal factor of g = 60 was used for mechanical treatment of oxides. The study of isotope exchange was carried out by nuclear microanalysis. The concentration of the isotopes 18O and 16O in oxides was determined using a Van de Graaff accelerator and 18O(p, α)15N and 16O(d, p)17O* reactions at the energies of incident beams 762 and 900 keV. Isothermal annealing of powders was carried out in oxygen, enriched to 80% by the isotope 18O. It was established that the concentration of the isotope 18O in mechanically activated powders was several times higher than in the initial micropowder under the same conditions of annealing. The effect increased with increasing of mechanical activation time (30 - 300 s). The isotope exchange parameters connected with the processes at the boundaries of the particles of mechano-activated powder and within their volume were analyzed.

Study of Distribution of Impurity Atoms in Metallurgical Macrodefects

Using nuclear microanalysis (NRA) and electron probe microanalysis (EPMA), concentrations of carbon, oxygen, nitrogen, aluminum, and vanadium were measured on a large group of macrodefects formed in the course of smelting titanium alloys. A remarkable enrichment of the defect material in oxygen and nitrogen atoms was detected; histograms of defect distribution over the concentrations of oxygen, nitrogen, aluminum, and vanadium were obtained. The above results agree with the concepts according to which the defects are formed from the particles that have the melting temperature higher then the temperature of smelting.