Characterization of a New Microstructure in a β-Solidifying TiAl Alloy after Air-Cooling from a β Phase Field and Subsequent Tempering

Abstract

In this study, we found that well-developed α 2 martensite was formed in a Ti-40Al-10V (atomic percent or at.%) alloy after air-cooling from a β phase field, rather than the traditional α 2 /γ lamellar colonies. The martensitic laths were produced according to the Burgers orientation relationship (OR), the same as those during quenching. Local variant selection detected that three (or six) α 2 variants sharing one (or two) common [11.0] α2 axes were predominant, while no global variant selection was observed. Subsequent to the martensitic transformation, the retained β phase was decomposed mainly via a β→γ transformation. The γ laths always nucleated at the α 2 /β interface according to a Blackburn orientation relationship. In order to stabilize the microstructure, the air-cooled samples were tempered at 800-1000 • C. During tempering, the microstructure decomposed mainly via an α 2 →γ transformation. The martensite was almost completely transformed after tempering at 1000 • C for 4 h, and hence a fine β-γ microstructure was obtained. Such a treatment resembling the quenching-tempering in steels may be a new strategy for the microstructural design of TiAl alloys, while an unexpected quenching process can be avoided.

Effect of Deformation Temperature on the Microstructure Characteristics of α Phase in Ti‐40Al‐8Nb‐0.5B Alloys

“…Such a characteristic demonstrates that the dynamic recrystallization (DRX) takes place during the compression in (β+α) phase field. The occurrence of DRV in S1 and DRX in S2 is consistent with the previous researches by Chen et al . and Bieler et al., which is closely related to the crystal symmetry of the body‐centered cubic β phase and close‐packed hexagonal α phase.…”

“…It is obvious from Figure 5b that the deformed β phase presents a 〈100〉‐〈111〉 double fiber texture. Such a double fiber texture is commonly discovered in the metals with a body‐centered cubic structure under hot compression process . Figure 5c shows the IPF map of the transformed α phase, in which the α phase presents a highly preferential orientation distribution.…”

“…Chen et al. indicated that the texture components of β phase in Ti‐40Al‐10V alloys varied from a 〈111〉‐〈100〉 double fiber into a simple rotated cube orientation with the decrease of strain rate during deformation in the single β phase field . Wei et al.…”

Deformation Behavior of a β-Solidifying TiAl Alloy within β Phase Field and Its Effect on the β→α Transformation

“…Accordingly, various α morphology can be produced, such as martensitic α, massive α, and Widmanstatten α [22]. As for the present alloy, after air-cooling from the β phase field, martensitic transformation is predominant, according to our previous study [23]. This is confirmed by the extensive formation of martensitic laths as shown in a local IPF map ( Figure 5) which is performed inside of one single β grain.…”

Effect of Microstructure on the High-Cycle Fatigue Behavior of Ti(43-44)Al4Nb1Mo (TNM) Alloys

“…Gamma TiAl-based alloys have been successfully applicated in aerospace and automotive industries after decades of developments [1][2][3]. In recent years, TiAl alloys containing a large amount of β-stabilizing elements, such as Nb and Mo, have attracted much more attentions due to their excellent elevated temperature properties [4][5][6][7]. Among them, the TNM alloy, which contains a balanced concentration of Nb and Mo, was recognized as the representative third generation TiAl alloy [8,9].…”