Effects of Nb content on solidification characteristics and hot deformation behavior of Alloy 625 plus

Using the thermodynamic calculations and the microstructural characterization, the effect of Nb content on the solidification characteristics of Alloy 625 plus was systematically investigated. Subsequently, the effect of Nb content on hot deformation behavior was examined through hot compression experiments. The results indicate that increasing Nb content lowers the alloy’s liquidus temperature by 51℃, resulting in a denser solidification microstructure. The secondary dendrite arm spacing (SDAS) of the alloy decreases from 39.09 μm to 22.61 μm. Increasing Nb content alleviates element segregation but increased interdendritic precipitates, raising their area fraction from 0.15% to 5.82%. These precipitates are primarily composed of large Laves, δ, η, γʺ phases, and trace amounts of NbC. The shapes of these precipitates change from small blocky to large, elongated forms. There is no significant change in the type or amount of inclusions within the alloy. The inclusions are predom-inantly individual Al2O3 and TiN, as well as Al2O3/TiN composite inclusions. Samples with varying Nb contents underwent hot compression deformation at a true strain of 0.69, a strain rate of 0.5 s⁻¹, and a deformation tem-perature of 1150℃. Increasing Nb content also elevates the peak stress observed in the flow curves. However, alloys with higher Nb content exhibit more pronounced recrystallization softening effects. The Laves phase precipitates do not completely re-dissolve during hot deformation and are stretched into elongated shapes. The high-strain energy storage raises the recrystallization fraction from 32.4% to 95.5%, significantly enhancing the degree of recrystallization and producing a more uniform deformed microstructure. This effect is primarily at-tributed to the addition of Nb, which refines the initial grains of the alloy, enhances solid solution strengthening of the matrix, and improves the induction of particle-stimulated nucleation.