Microstructure and Processing Ability of β-Solidifying TNM-Based γ-TiAl Alloys

Abstract

Microstructure and hot workability have been considered for a number of -TiAl alloys including -solidifying TNM alloys. All TNM alloys under study showed improved hot workability in cast condition. As was shown for the Ti-45Al-5Nb-1Mo-0.2B alloy, a critical issue of TNM alloys is room temperature ductility in the conditions with lamellar structure.

A Quarter Century Journey of Boron as a Grain Refiner in TiAl Alloys

“…The crack in the microzone could be larger than the critical crack size for propagation. This hypothesis was supported by the observation of clusters of parallel facets from interlamellar cracking of fine lamellar colonies on the fracture surfaces and also by the fact that the ductility of Ti45A15NblMo0.2B was improved to 1% after forging and heat treatment which has certainly destroyed the phase transformation texture [51][52][53].…”

“…Ti44A18Nb0.1B, Ti44A14Nb4HfO. 1B and Ti45A15NblMo0.2B [51][52][53]. In those alloys the lamellar colony size was not more than lOO^m.…”

“…There were no large boride precipitates as those in the cast TiAl alloys with high boron additions. The refined microstructures gave rise to the improved hot workability [53]. However, the room temperature tensile ductility of the as-cast low boron containing alloys was much lower than expected, being only 0.3-0.5% despite the fine grain size and fine boride precipitate size.…”

Effect of hot forging in the ordered phase field on microstructure and mechanical properties of β-solidifying γ-TiAl alloys

“…Furnace cooling was used to avoid appearance of non-equilibrium phases like the ω-phase and to have the most equilibrium microstructural conditions. Note that the hot forging routes applied for the Ti45 and Ti43.7 alloys were based on the hot workability criterion and the opportunity to forge different γ-TiAl alloys in the ordered phase field [18,19]. In the case of the Ti44 alloy effect of a small strain value in the ordered phase field followed by heat treatment on the microstructure and tensile properties was evaluated.…”

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

“…Microstructure refinement in b-solidifying alloys is provided by the alloying effect on the kinetics of the b 0 a transformation and stability of a grains on passing through the (a þ b)/a phase field during cooling [19e21]. It seems that improved tensile/strength properties and appropriate creep resistance might be attained in the cast TNM based alloys [22,23].…”