DETERMINATION OF REGULARITIES OF THE INFLUENCE OF THE ELEMENTAL COMPOSITION OF NIOBIUM­BASED ALLOYS ON THEIR STRUCTURE AND PROPERTIES

The method of x-ray diffractometry was used to study the effect of the composition of two, three, four and five elemental niobium-based alloys on their phase-structural state, average crystallite size, and thermal expansion coefficient in the temperature range of +20 °С...–170 °С. As elements of filling, vanadium, tantalum, hafnium, molybdenum, zirconium, tungsten and titanium were used. These elements either in equilibrium – at room temperature (RT=+20 °С), or in high-temperature states have a bcc crystal lattice similar to Nb. It is found that in alloys based on two, three, four and five elements, for the compositions used in the work, the formation of a single-phase state with a bcc crystal lattice of a solid solution occurs. At the structural level, the alloy composition affects the ratio of the intensity of the diffraction peak from different planes. For two diffraction orders from the most closely packed {110} plane in the bcc lattice, a change in the intensity value for the second diffraction order is revealed. The greatest decrease in relative intensity occurs in binary alloys with a large discrepancy in the size of the atomic radii of the components. In multi-element alloys, a smaller drop in intensity is observed. This may be associated with a reduction in the distortion of the crystal lattice due to the ordering of the elements that make up the alloys. At the substructural level, the alloy composition affects the average crystallite size. For binary alloy compositions, the greatest effect is associated with Zr and Hf filling elements having a significantly larger atomic radius. This leads to a decrease in the average crystallite size of the alloy solid solution to the smallest value of 11 nm (NbZr alloy) and the release of the second phase (NbHf alloy). It is found that the coefficient of linear thermal expansion determined by the X-ray diffraction method at 2 temperatures (RT=+20 °С and Т=–170 °С) in multi-element alloys exceeds the values for the starting elements. The largest increase in CTE is observed in alloys containing 17–26 at. % V and W, which have the smallest atomic radiu