Selection and mechanical evaluation of γ/γ boundary in γ-TiAl alloy

Abstract

Simulation of lamellar boundary (γ/γ) selection during the transformation of α2’→α2+γ in γ-TiAl alloy has been investigated using an improved 3D Phase Field (PF) model, and the mechanical properties of γ/γ boundaries are evaluated by Molecular Dynamics (MD) simulation. The effects of elastic strain energy and interfacial energy difference among different types of γ/γ interfaces on the occurrence frequencies of the three types of γ/γ boundaries (i.e., true twin (TT), pseudo-twin (PT) and ordered domain (OD)) have been studied. It is found that the boundary fraction of TT increases with increasing elastic strain energy or increasing interfacial energy difference among γ/γ interfaces. Besides TT, the elastic interaction also favors OD while PT is suppressed. The relative fractions of PT and OD could be effectively controlled by elastic strain energy. Furthermore, the frequency of PT or OD can also be adjusted by their interface energy ratio. The simulation results well explain the phenomenon that boundary frequencies via experimental statistics deviate from those under random distribution without interface selection. It can also be found that one-twin-dominant zones (OTDZ) can be induced by higher elastic strain energy and larger interface energy difference among different γ/γ boundaries through the merging of adjacent small clusters with the same γ/γ boundary type under the premise of correlated and sympathetic nucleation. Through MD simulation, it is found that the strengths of the configurations with true twin boundary (TTB) and ordered domain boundary (ODB) are almost the same, while the strength of that with pseudo-twin boundary (PTB) is relatively low. The order of plasticity of the configurations with three types of γ/γ interfaces is ODB > TTB > PTB.