Ni_(75)Al_xV_(25-x)合金DO_(22)到L1_2相变过程异相界面的结构及其迁移特征

STRUCTURE AND MIGRATION CHARACTERISTIC OF HETEROINTERFACES DURING THE PHASE TRANSFORMATION FROM DO_(22) TO Ll_2 PHASE IN Ni_(75)Al_xV_(25-x)ALLOYS

本文基于微观相场模型模拟了Ni_(75)Al_xV_(25-x)(x=4.2,5.0)合金中DO_(22)(Ni_3V)到L1_2(Ni_3Al)相变过程.结合微观组织原子图像演化和界面处原子占位几率演化.研究了异相间有序畴界的结构及其迁移特征,提出了DO_(22)到L1_2相变过程的机制.研究表明,L1_2与DO_(22)相间存在5种界面,DO_(22)到L1_2相变过程中,除了界面(002)_D∥(001)_L之外,其他4种界面都可以迁移;在界面迁移过程中,界面(100)_D∥(200)_L和界面(100)_D∥(200)_L·1/2[001]在迁移前后,界面结构保持不变.而界面(002)_D∥(002)_L·1/2[100]迁移后形成界面(002)_D∥(002)_L,两者交替出现;相变过程中,界面迁移总是沿着最优化的路径进行原子跃迁和替换,遵循跃迁原子数目最少、跃迁路径最短原则.

The behavior of heterointerfaces governs the evolution of microstructures during processing and heat treating, and ultimately controls the resultant morphology of transformation products and therefore the resultant physical and mechanical properties of an engineering material. Atomistic numerical simulation has been proven to be one of the most powerful methods for exploring solid interface behaviors today, especially in the case where they are hardly investigated by experimental techniques, such as atomistic interface migration mechanisms during phase transformations. The microscopic phase-field model can be used to study the microstructure evolution during phase trans- formations and to track the migration of an interface at atomic scale at the same time. In this paper, this model was used to investigate the interface migration during the phase transformation from DO22 （Ni3V） to L12 （Ni3A1） in Ni75A1,V25-x （x=4.2, 5.0） alloys. The DO22 phase is precipitated from the disordered fcc phase and then transformed to the L12 phase during aging process. Using the simulated microstructures and the occupation probabilities of alloy elements at interfaces, the structure and migration characteristics of ordered domain interfaces formed between DO22 and L12 phases are investigated and the mechanism of the phase transformation from DO22 to L12 is proposed. The results show that there are five kinds of heterointerface structures to be formed between DO22 and L12 phases, four of them are able to migrate during the phase transformation from DO22 to L12 except for （002）D//（001）L. The structures of （100）D//（200）L and （100）D// （200）L.1/2[001] themselves are kept unchanged with their migrating, only （002）D//（002）L and （002）D//（002）L·I/2[100] alternate with each other, and therefore, these two kinds of interfaces appear alternatively. Ni atoms present a site selective behavior during interface migration, they would jump to their nearest neighbor sites and substitute for V atoms with V atoms migrating to the inside of DO22 phases. Al atoms would migrate to interfaces and substitute for Ni or V atoms there. Such a jump and substitution mode of atoms may be an optimization way in thermodynamics and kinetics for interface migration during phase transformation. All possible atom jump modes inducing the interface migration would obey that the number of jumping atoms during migration must be the least and the jumping distance of atoms the shortest.