Revealing laws of element diffusion and hot deformation characteristics during homogenization process of Alloy 625 Plus

Abstract

Based on microstructure analysis, diffusion theory, and hot deformation experiments, the solidification microstructure and element segregation of the Alloy 625 Plus ingot, the diffusion kinetics of Ti, Nb, and Mo during homogenization and the hot deformation behavior of the homogenized ingot were investigated in this study. The results indicate that: (1) the solidified ingot exhibits a typical dendritic microstructure, and significant element segregation occurs, leading to the presence of Ti, Nb, and Mo-rich precipitates in the interdendritic region; (2) Following homogenization, the degree of element segregation in the ingot is significantly reduced. The diffusion coefficients (D) of Ti, Nb, and Mo under various homogenization conditions were calculated. Subsequently, the diffusion constants (D₀) and activation energies (Q) of Ti, Nb, and Mo were obtained to be 0.01432, 0.00397 and 0.00195 cm²/s and 244.851, 230.312, and 222.125 kJ/mol, respectively. Finally, the diffusion kinetics formulas for Ti, Nb, and Mo in Alloy 625 Plus were established. After homogenization at 1220 °C for 8 h, the alloy exhibits low deformation resistance, a high degree of recrystallization, and optimal deformation coordination ability. Therefore, this represents a rational single-stage homogenization process.

Keywords

solidification microstructure / microsegregation / homogenization / diffusion kinetics / hot deformation

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Central South University