U-Nb合金低温分解机制的相场法研究

Phase-Field Study of Low-Temperature Decomposition Mechanism in U-Nb Alloys

摘要:

低温时效处理导致U-Nb合金的力学性能发生显著改变，利用相场法研究了性能变化对应的微观组织演化。结果表明，在较高温度可能发生调幅分解，但必须满足其热力学条件，而且也仅出现在初期。发生普通型析出的范围可能更广，因为合金成分接近于发生结构转变的临界成分，时效对应的母相无论是类高温立方相还是类低温正交相，稳定核胚和母相之间的Nb含量差异都可以相当小。当相界面的迁移率较大而扩散率较低时，处于长大阶段的析出物的Nb含量明显不同于平衡态成分。因此，U-Nb合金的低温时效硬化效应可能是由相分解引起的Nb再分配所导致。

Abstract:

The microstructure evolution responsible for significant change of mechanical properties during low-temperature aging of U-Nb alloys was investigated by phase-field method. Results show that spinodal decomposition may occur at the early stage only when its thermodynamic condition is satisfied. Possibilities of general precipitation widely exist at low-temperature region, where the Nb content difference between the stable nucleus and the matrix can be significantly small, no matter the matrix of aging is cubic-like phase or in the orthorhombic-like phase, because the alloy composition is close to the critical composition of structural transition. At low diffusion rate and the relatively high mobility of phase interface, the Nb content of growing precipitates is far away from equilibrium composition. It is suggested that the Nb redistribution caused by phase decomposition may be responsible for the low-temperature aging hardening effect in U-Nb alloys.