Precipitation of γNb₅Si₃ in Nb-Si based ultrahigh temperature alloys

Hexagonal γNb₅Si₃ plates have precipitated from Nb solid solution in heat-treated Nb-Si based ultrahigh temperature alloys. The orientation relationships (ORs) and interfacial structures between γNb₅Si₃ precipitates and Nb solid solution matrix have been investigated by high-resolution transmission electron microscopy (HRTEM). The ORs have been determined as [111]_Nb//[0001]_γ and (101¯)_Nb//(11¯00)_γ with a near coherent interface. The interfacial structure has been interpreted with the Coincidence site lattice/Displacement shift complete lattice (CSL/DSC) model, forming an array of phase boundary dislocations (PBDs) on the interface. PBDs with Burgers vectors of b→=[Formula presented]<1¯21¯>_Nb on (111)_Nb plane might promote the precipitation of γNb₅Si₃.