Phase transformations during creep of a multiphase TiAl-based alloy with a modulated microstructure

Ab Initio Study of the Elastic and Mechanical Properties of B19 TiAl

“…The calculated G/B ratios of B19 TiAl from the EDM is 10.03% and 14.18% lower than the theoretical data of γ-TiAl (0.62) and α 2 -Ti 3 Al (0.65) [42], respectively, indicating that B19 TiAl is more ductile than γ-TiAl and α 2 -Ti 3 Al. Experimentally, Appel et al [3,[8][9][10] have measured the mechanical properties of γ-TiAl-based intermetallics with the microstructure containing B19 phase and found that the existence of B19 structure can give the intermetallics relatively high tensile ductility. According to Pettifor's rule [12], a material has more metallic (angular) bonds and thus is more ductile (brittle) if it has a larger positive (negative) Cauchy pressure.…”

Microstructure and mechanical properties of low and heavy alloyed γ-TiAl + α2-Ti3Al based alloys subjected to different treatments

“…3) Designing of alloys with the base line composition of Tie(40e44)Al þ Nb, in which refined modulated lamellar microstructure containing ductile phases like the orthorhombic B19 phase can be produced by hot extrusion. As has been recently shown, this microstructure provided room temperature plastic elongations in the extrusion direction up to around 2.5%, high strength properties both at room and elevated temperatures and relatively good creep resistance in spite of the presence of the b(B2)/B19 phase [6,7]. 4) Preparation of refined g þ a 2 lamellar structures via thermomechanical treatment, particularly extrusion at T !…”

“…The presence of lamellar colonies in the extruded condition can be ascribed to the fact that the extrusion temperature was near T a due to lower aluminum content, whereas this temperature was significantly lower than T a for the alloy under study. An appearance of the pearlite-like microstructure can also be ascribed to lower aluminum content, which might promote the phase transformations a(a 2 ) 0 b(B2) 0 B19 in the regions enriched by niobium [6,7]. Fig.…”

“…[6,7], where two major constituents, lamellar g þ a 2 colonies and pearlite-like structure consisting of the g, a 2 and b(B2)/B19 phase, were obtained after extrusion and stress-relief annealing at 1030 C in the alloy lying in the composition range of Tie(40e44)Ale8.5Nb. The presence of lamellar colonies in the extruded condition can be ascribed to the fact that the extrusion temperature was near T a due to lower aluminum content, whereas this temperature was significantly lower than T a for the alloy under study.…”

“…In the second case, lower alloying levels were applied to avoid: i) the formation of very fine a 2 and g lamellae (with thickness of 50 nm and less), typically observed in heavy alloyed alloys [6,7,27,28] that should be favorable for low temperature ductility; ii) strong dendritic segregation, which is promoted by a high content of niobium and molybdenum; iii) undesirable b(B2) 0 u phase transformation [13,27] that can also contribute to the ductility. Reasoning from the aforesaid, the present study was aimed at considering the balance between room temperature ductility/strength properties and high temperature long-term strength in the Tie45Ale8.5Nbe0.2C alloy after hot extrusion in the (a þ g) phase field followed by heat treatment and in the cast Tie43.7Ale3.2(Nb,Cr,Mo)e0.2B alloy subjected only to heat treatment.…”