Effects of γ-TiAl/γ Lamellar Interfaces and Grain-Boundary α₂-Ti₃Al Phase on Creep of TiAl Based Alloy

The creep behavior of a γ-TiAl based alloy at 1073 K was investigated, examining three different microstructures: equiaxed γ (Eγ), γ/γ fully lamellar (FLγ), and equiaxed γ with α₂ phase on grain boundaries (Eγα₂). The aim was to understand the influence of lamellar interfaces and grain boundary α₂ phase on creep behavior. Initially, creep rates were consistent across all specimens upon loading. However, Eγ exhibited a gradual decrease in creep rate compared to Eγα₂ and FLγ. Notably, the minimum creep rate of Eγ was one order of magnitude lower than that of Eγα₂ and FLγ. Conversely, Eγα₂ and FLγ displayed a slight acceleration and the longest rupture strain, albeit with the shortest rupture time compared to Eγ. Upon microstructural analysis of of the creep-test specimens, it was observed that numerous dynamic recrystallized grains (DXGs) and sub-grains formed along grain boundaries and interiors in Eγ, whereas they were limited to the region along grain boundaries in FLγ. In contrast, very few DXGs were formed in Eγα₂. These findings indicate that γ/γ interfaces inhibit the extension of DXGs into grain interiors, suggesting that the grain boundary α₂ phase effectively suppresses the formation of DXGs.