Selection and mechanical evaluation of gamma/gamma boundary in gamma- TiAl alloy
JH Zhang and CY Teng and ZC Meng and HS Xu and L Yang and DS Xu and R Yang, INTERMETALLICS, 126, 106946 (2020).
Simulation of lamellar boundary (gamma/gamma) selection during the transformation of alpha(2)'->alpha(2)+gamma in gamma-TiAl alloy has been investigated using an improved 3D Phase Field (PF) model, and the mechanical properties of gamma/gamma boundaries are evaluated by Molecular Dynamics (MD) simulation. The effects of elastic strain energy and interfacial energy difference among different types of gamma/gamma interfaces on the occurrence frequencies of the three types of gamma/gamma 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 gamma/gamma 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 gamma/gamma boundaries through the merging of adjacent small clusters with the same gamma/gamma 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 gamma/gamma interfaces is ODB > TTB > PTB.
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