U-Nb合金相分解行为的相场模拟研究

Phase-Field Simulation Study on Phase Decomposition Behavior of U-Nb Alloys

摘要:

U-Nb合金的双相区分解随着成分、时效温度和保温时间而展现出丰富的微观组织变化。为了深入研究U-Nb合金复杂相分解行为的物理机制，开展了较为系统的相场模拟研究。结果表明，连续析出和不连续析出可能具有相同的热力学条件，当体扩散受到抑制而界面扩散起主导作用时，相分解更倾向于不连续析出。推测U-5Nb合金和U-13Nb合金连续析出产物的明显差异是由不同相变机制导致，U-5Nb合金发生典型的连续析出，而U-13Nb合金先在γ相内发生互溶间隙分解，然后形成α相析出物。γ相在中间Nb含量区间的自由能关系对是否发生互溶间隙分解以及不连续析出组织中富Nb相的成分具有重要影响。

Abstract:

The phase decomposition of U-Nb alloys exhibits significant microstructure changes with composition, aging temperature, and holding time. To study the physical mechanism of complex phase decompositions behavior of U-Nb alloys, systematic phase-field simulations were conducted. The results show that continuous and discontinuous precipitations may have the same thermodynamic condition. When the volume diffusion is inhibited and the interface diffusion plays a leading role, the phase decomposition is more inclined to discontinuous precipitation. It is speculated that the obvious difference of continuous precipitates between U-5Nb alloy and U-13Nb alloy is caused by different phase transformation mechanisms. U-5Nb alloy exhibits typical continuous precipitation, while U-13Nb alloy first undergoes miscibility gap decomposition within the γ phase, followed by the precipitate of α phase. The free energy relationship of γ phase in the middle Nb content range has an important influence on the occurrence of miscibility gap decomposition and the composition of the Nb-rich phase in the discontinuous precipitation product.