Al-Li合金中δ′相沉淀过程原子图像的计算机模拟

COMPUTER SIMULATION OF THE ATOMIC PICTUREFOR δ'(Al3Li) PRECIPITATION IN Al-Li ALLOY

利用微观Langevin方程对δ'用(Al3Li)沉淀过程的原子图像进行模拟研究．该方程不但能同时描述原子簇聚和有序化过程,将用分离和粗化在同一物理框架内考虑, 而且无须预先设定第二相结构,可观察到动力学演化过程中可能出现的瞬时相,模拟结果表明:对于Al-15Li(原子分数,%)合金,最初在无序基体中出现的L12相浓度与无序用相同,在L12相之间形成重位与阵界面;随后,L12相有序度进一步增加,重位点阵界面逐渐转变为L12结沟;最后形成被反相畴界分开的L12结构单相有序相,单相有序相一经形成,便开始分解,分解主要发生在反相畴界处,富Li区向平衡δ'相转化,贫Li区自发无序化,形成δ'相与无序基体共存的平衡结构,在沉淀过程后期,δ'相租化待证明显,大颗粒长大,小颗粒变小或消失,两相界面由不规则变为平直。

The atomic picture simulation for ' phase precipitation in Al-Li alloy was conducted using the microscopic Langevin equation. Without a prior assumption about the atomic structures of phases involved, the computer simulation technique employed could not only describe all diffusion pro cesses, including clustering, ordering, antiphase domain boundary movement and coarsening, but also show possible transient ordered phase. The results show that for the Al-15Li alloy (atom fraction.%). firstly, randomly distributed Ll2 phase with the same composition as the initial state appears firstly in the disordered matrix, and then coincidence site lattice (CSL) interfaces between L12 phases form. Secondly, the order degree of L12 phase increases and the interfaces change from CSL to L12 structure until a single ordered phase separated by the APBs is formed. Once the single ordered phase was formed it starts to decompose spinodally at APBs. The solute-rich regions evolve to equilibrium ' phase, and solute-poor region disorders spontaneously when the composition reached the disordering line. At the late stage of precipitation the coarsening of ' phase occurs, larger particles become larger, smaller particles become smaller or disappear, and the interfaces become smooth and straight.