The Directional Solidification, Microstructural Characterization and Deformation Behavior of β-Solidifying TiAl Alloy

The microstructural evolution and deformation behavior of titanium aluminide alloys remain active research areas. Prior research has shown that directional solidification can influence phase alignment and mechanical properties. However, the role of the β phase in such processes is not fully understood. No prior work had resolved how the β phase interacts with γ/α₂ lamellae during solidification. This gap motivated the investigation of the β phase's influence on microstructure and deformation. The study aimed to clarify whether the β phase can be directionally solidified alongside γ/α₂ lamellae. It was already known that γ/α₂ lamellae exhibit anisotropic deformation behavior. Yet, the impact of the β phase on this behavior was unclear. The study focused on a specific TiAl alloy composition to address these uncertainties.

The researchers aimed to investigate the directional solidification behavior of a β-solidifying TiAl alloy. They focused on the γ/α₂ lamellar microstructure and the role of the β phase. The study sought to determine whether the β phase could be directionally solidified. The motivation was to understand how the β phase affects microstructural alignment. The researchers also wanted to analyze the deformation behavior of the resulting microstructure. They were particularly interested in the anisotropic characteristics of the lamellae. The study aimed to identify the mechanisms behind microstructural decomposition during deformation. The ultimate goal was to provide insights into the deformation mechanisms of TiAl alloys.

The researchers used the optical floating zone melting method for directional solidification. They selected a Ti-43Al-2Cr-2Mn-0.2Y alloy for the experiments. The microstructure was analyzed using imaging techniques to observe γ/α₂ lamellae. They examined the orientation and boundary characteristics of the lamellae. The β phase distribution was studied to determine its alignment during solidification. Hot compression tests were conducted to assess deformation behavior. The loading axis was varied to evaluate anisotropic deformation resistance. Microstructural observations were made to identify decomposition mechanisms during deformation.

The γ/α₂ lamellae exhibited straight boundaries with specific orientations. The β phase was randomly distributed, indicating no directional solidification. The presence of the β phase did not affect the directional solidification of the lamellae. Hot compression tests revealed anisotropic deformation behavior in the lamellar microstructure. The lowest deformation resistance occurred when the loading axis was at 45° to the lamellar interface. Microstructural observations showed decomposition initiated near the β phase. The β phase acted as a soft zone that promoted deformation in the lamellar structure. The main coarsening mechanisms included γ phase boundary bulging and α₂ lamellar decomposition.

The β phase does not undergo directional solidification in the studied TiAl alloy. The γ/α₂ lamellae solidify directionally regardless of β phase presence. The deformation behavior of the microstructure is anisotropic and influenced by lamellar orientation. The lowest deformation resistance occurs at a 45° loading angle to the lamellar interface. The β phase promotes microstructural decomposition during deformation. The decomposition begins around the β phase, which acts as a soft region. The coarsening mechanisms include γ phase boundary bulging and α₂ lamellar breakdown. These findings provide insights into the deformation behavior of β-solidifying TiAl alloys.