Influence of oxygen concentration on the formation features and thermal stability of the V–Cr–W–Zr alloy microstructure under combined treatment conditions

The results of the study of the influence of oxygen concentration on the features of formation and thermal stability of the microstructure of a low-activation vanadium alloy V–Cr–W–Zr after combined thermomechanical plus chemical-heat (internal oxidation) treatment are presented. Using scanning and transmission electron microscopy, the structural-phase state of this alloy was studied depending on the duration of internal oxidation. The regularities of propagation of the front of internal oxidation with the formation of fine ZrO2 particles are revealed. It was established that the formation of these particles is carried out by the mechanism of nonequilibrium internal oxidation. The implementation of this mechanism ensures uniform conditions for the nucleation and growth of zirconium oxides and a high dispersion of the heterophase structure. It is shown that the features of oxygen distribution at different distances from the surface determine the thermal stability of the microstructure and the level of microhardness. The analysis of thermal stability of fine-disperse heterophase structure of the V–Cr–W–ZrO2 alloy depending on chemical-heat treatment regimes was carried out. •Combined treatment was used to modify the structural-phase state of V–Cr–W–Zr alloy.•Combined treatment consists of thermomechanical and chemical-heat treatments.•Nonequilibrium internal oxidation mechanism is used in chemical-heat treatment.•Fine ZrO2 particles provide disperse strengthening and contribute to thermal stability.•Relaxation processes in the alloy microstructure are suppressed up to 1200 °С.