An experimental study of the polycrystalline plasticity of lamellar titanium aluminide

In situ fracture observations of distinct interface types within a fully lamellar intermetallic TiAl alloy

“…The amount of α 2 phase and ζ-Ti 5 Si 3 silicides may be optimized by the alloying concept in order to enlarge the number of strengthened α 2 /γ interfaces. However, macroscopically thinner lamellae within the α 2 /γ colonies would result in a strain localization along the colony boundaries and thus higher tendency for crack initiation [32,39]. Also, a change in the α 2 /γ ratio and significantly lower lamellar spacing are reported to affect coherency [19,62].…”

“…Macroscopic specimens exhibiting an FL microstructure generally attain higher fracture toughness and J-integral values. This is reasoned by the positive effect of colony boundaries and, consequently, the orientation of α 2 /γ colonies with respect to the crack path [16,21,25,26,27,28,29,30,31,32]. Crack deflection, ligament bridging, pull-outs, mechanical twinning or slip in γ lamellae and the development of microcracks in front of and parallel to the crack tip within colonies furthermore improve the fracture properties [27,31,33,34].…”

“…Furthermore, crack-tip blunting by ductile phases, shear ligament toughening, twinning, and crack-tip interface debonding are also considered to enhance the crack resistance at the micro-scale [12,35,37]. Therefore, the deformability of γ lamellae due to mechanical twinning or slip of dislocations within the plastic zone in front of the crack tip and the interaction with adjacent γ or α 2 lamellae has to be considered [19,21,23,32,38,39].…”

Review on globularization of titanium alloy with lamellar colony

“…The shortcomings of the well-known globularization mechanisms make it difficult to control globularization during hot working. The mains are follows: (a) the applicable conditions of every globularization mechanism are inconsistent (dynamic recrystallization at high temperature and low strain rate [7], shearing mechanism [8] at low temperature and high strain rate); (b) the microstructure parameters considered in every globularization mechanism are different (dihedral angle of the boundary in boundary splitting [9,10], solute concentration gradient in termination migration [11,12]); (c) multiple mechanism coexistence due to the diversity of lamellar colony and meso-scale heterogeneous deformation [13][14][15][16]. Therefore, a unified globularization mechanism of coupling multiple factors needs to be further developed.…”

“…The thermal mechanical process is very sensitive to hotworking parameters and microstructure parameters, thus resulting in the difficulty in precisely controlling globularization. The detailed characteristics are described as follows: (a) complex and diverse morphologies (initial widmanstatten alpha [4], secondary alpha [28] and fine acicular martensitic alpha [29]) lead to the difference in globularization dynamics; (b) the meso-scale heterogeneous deformation (strain localization at lamellar-scale, strain partitioning behavior at colony-scale, macro-deformation bands at polycrystal-scale [15]); (c) the complex coupling effects of hot-working parameters and microstructure parameters (flow softening due to loss of interfacial coherency [3], evolution of geometry necessary dislocation(GND) at alpha/beta interface [29], the effect of lattice rotation [14,30] on meso-scale heterogeneous deformation). In general, an in-depth understanding of the effects of hot-working parameters and microstructure parameters can allow better control globularization of titanium alloy with lamellar colony.…”