International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The evolution of phase composition and mechanical properties and the formation of oxide layers on Fe40–xNiCoCrAlx (x = 5 and 10 at.%) alloys in long-term oxidation at 900 and 1000 °C were studied. In the initial cast state, depending on the aluminum content and valence electron concentration, the alloys contain only an fcc solid solution (VEC = 8 e/a) or a mixture of fcc and bcc phases (VEC = 7.75 e/a). Thin continuous oxide scales containing Cr2O3 and NiCr2O4 spinel formed on the surface of both alloys oxidized at 900°C for 50 h. A further increase in the annealing time to 100 h leads to the formation of aluminum oxide Al2O3 in the scale on the Fe30Ni25Co15Cr20Al10 alloy, having high protective properties. An increase in the oxidation temperature to 1000°C results in partial failure of the protective layer on the
alloy with 10 at.% Al. Long-term holding at 900°C (100 h) + 1000°C (50 h) does not change the phase composition of the Fe35Ni25Co15Cr20Al5 alloy matrix, being indicative of its high thermal stability. In the two-phase Fe30Ni25Co15Cr20Al10 alloy, the quantitative ratio of solid solutions sharply changes: the amount of the bcc phase increases from 4 to 54 wt.% and its B2-type ordering is observed. The mechanical characteristics of the starting alloys and those after long-term high-temperature annealing were determined by automated indentation. It is shown how the hardness (HIT) and the elastic modulus (E) of alloys change after oxidation, depending on the Al content.

The protective coatings of Al2O3 and AlN on iodide titanium in initial state and after annealing in a hydrogen atmosphere were investigated by scanning electron microscopy. It was found that the coatings protect titanium from the interaction with hydrogen at a pressure of 0.6 MPa up to 650 °C. It was shown that at 700 °C and pressure 0.6 MPa cracking of the protective coatings occurred, and the process of active absorption of hydrogen started.

The microstructure and phase composition of Ti47,5Zr30,2Mn15,5V5Ho2 multiphase alloy and the phase composition of the hydrogenation product were investigated by scanning electron microscopy and X-ray phase analysis. It was established that holmium introduced into the alloy not only dissolves in the phase components of the eutectic, but also forms a new phase (oxide). The formation and further growth of crystals of holmium oxide occurs only on the surface of the crystallites of Laves phase. During the first hydrogenation the active absorption of hydrogen by the alloy occurred only when it was heated up to 520 °C, with hydrogen capacity of 2.62 wt.%. The hydrogenation product obtained after the saturation of the alloy with hydrogen contained a new phase, in addition to the hydrides based on the initial phases. After the sorption-desorption cycle, the alloy was already in the activated state and able to absorb hydrogen at room temperature and low pressure (0.21 MPa) starting from the first seconds of contact with the hydrogen medium.