Phase formation at the initial stages of synthesis of HEA from a mixture of oxides TiO2, ZrO2, V2O5 and Nb2O5

Abstract

Increased interest in the creation of materials with exceptional properties, such as high-entropy alloys, necessitates the develop­ment of production methods, one of which is aluminothermic synthesis. This study investigates the processes involved in the production of the lightweight refractory high-entropy alloy Al 1.5 TiZr 0.25 VNb, for subsequent synthesis of this alloy via the joint aluminothermic reduction from a mixture of TiO 2  , ZrO 2  , V 2 O 5 and Nb 2 O 5  . Under non-isothermal conditions, phase formation at low temperatures (heating up to 1500 °C) in the initial stages of reduction in an inert atmosphere was examined. Differen­tial thermal analysis and X -ray diffraction analysis were employed to study the interactions in the system with a reactant ratio of 30Al–18TiO 2 –14ZrO 2 –15V 2 O 5 –23Nb 2 O 5 by weight, using aluminum powders of different grain sizes (≤0.160 and ≤0.630 μm). The results indicate that during continuous heating of a powder mixture of TiO 2  , ZrO 2  , V 2 O 5  , and Nb 2 O 5 with aluminum particles sized ≤0.630 μm, the reduction process remains incomplete. The X -ray diffraction pattern of the products reveals the presence of initial charge components ZrO 2  , TiO 2  , Nb 2 O 5  , unreacted aluminum, as well as intermediate oxides TiO, V 2 O 3  , traces of NbO 2  , and the intermetallic compound Al 3 Ti. Reducing the aluminum particle size to ≤0.160 μm enhances the completeness of exothermic reactions and lowers their onset temperature. Furthermore, the interaction of reactants leads to the formation of intermetallic compounds AlTi, AlV 3  , AlNb 3  , intermediate oxides TiO, V 2 O 3  , and unreacted ZrO 2 among the heating products. Joint aluminothermic reduction going through several stages and requiring an increase in heating tempera­ture or isothermal holding to complete. An adiabatic temperature assessment demonstrated the feasibility of obtaining the high-entropy Al 1.5 TiZr 0.25 VNb alloy using self-propagating high-temperature synthesis (SHS) methods.