Neutron diffraction study of the effect of equilibrium annealing on the structure of a high-temperature TixMoyN alloy

For the first time, a neutron structural study of the crystal structure of the Ti0.90Mo0.10N alloy was carried out on bulk samples. It is shown that this alloy, obtained after homogenizing annealing at 1475 K for 24 h, has an fcc structure described within sp. gr. Fm3¯m with Ti vacancies in the metal sublattice and the structural formula becomes Ti0.86Mo0.12N. In this case, the precipitation of pure α-Ti from the alloy is observed. Lattice parameter a=4.265±0.002 Å. Nitrogen atoms are located in octahedral environments of statistically interchangeable titanium and molybdenum atoms. The crystal structure can be considered as a solid solution of nitrogen interstitial on the matrix of a solid solution of substitution of Ti and Mo atoms with vacancies of Ti atoms in the metal sublattice. After equilibrium stepwise annealing at temperatures of 1375 to 1075 K with a step of 50 K for 60 hours (at each temperature for 10 hours), the amount released of α-Ti increases significantly and the defectiveness (vacancy) in the metal sublattice becomes larger and the structural formula is as follows: Ti0.77Mo0.15N. The lattice parameter becomes equal to a=4.274±0.002 Å. It is concluded that in a cubic alloy of the Ti-Mo-N system, molybdenum atoms do not replace titanium atoms to the (1-x)Ti+xMo stoichiometry, titanium atoms are pushed out of the unit cell in accordance with the rule for the concentration of valence electrons of the components. Considering this circumstance, for this alloy, the chemical formula TixMoyN should be ascribed where x+y<1 due to the titanium vacancy in the metal sublattice.

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