Abstract
A crack-free Ti-43Al-9V-0.2Y alloy sheet was successfully fabricated via hot-pack rolling at 1200 °C. After hot-rolling, the β/γ lamellar microstructure of the as-forged TiAl alloy was completely converted into a homogeneous duplex microstructure with an average γ grain size of 10.5 μm. The dynamic recrystallization (DRX) of the γ phase was systematically investigated. A recrystallization fraction of 62.5% was obtained for the γ phase in the TiAl alloy sheet, when a threshold value of 0.8° was applied to the distribution of grain orientation spread (GOS) values. The high strain rate and high stress associated with hot-rolling are conducive for discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), respectively. A certain high-angle boundary (HAGB: θ = 89° ± 3°<100>), which is associated with DDRX, occurs in both the recrystallized and deformed γ grains. The twin boundaries play an important role in the DDRX of the γ phase. Additionally, the sub-structures and sub-boundaries originating from low-angle boundaries in the deformed grains also indicate that CDRX occurs. The mechanical properties of the alloy sheet were determined at both room and elevated temperatures. At 750 °C, the alloy sheet exhibited excellent elongation (53%), corresponding to a failure strength of 467 MPa.
Highlights
TiAl-based alloys with low density and excellent high-temperature properties are considered promising light high-temperature structural materials for aerospace applications, such as inlet flaps, nozzle sidewalls for turbine engines, and thermal protection systems for scramjets [1,2,3,4,5].Several studies have focused on improving the mechanical properties of these alloys by breaking down the lamellar colonies and refining the grains via alloying-element additions [6,7], heat treatment [8,9], and thermomechanical processing
Studies based on the transmission electron microscopy (TEM) analysis method have reported that the γ phase with tetragonal L10 structure has low stacking fault energy
Ti-43Al-9V-0.2Y sheet was fabricated via hot pack-rolling after ingot casting and subsequent canned forging
Summary
TiAl-based alloys with low density and excellent high-temperature properties are considered promising light high-temperature structural materials for aerospace applications, such as inlet flaps, nozzle sidewalls for turbine engines, and thermal protection systems for scramjets [1,2,3,4,5]. Several studies have focused on improving the mechanical properties of these alloys by breaking down the lamellar colonies and refining the grains via alloying-element additions [6,7], heat treatment [8,9], and thermomechanical processing (e.g., hot-forging [10], extrusion [11], rolling [12,13,14]). Using the ingot metallurgical (IM) method, TiAl alloy sheets are fabricated via hot isostatic pressing of the ingots and subsequent forging for pore elimination and break-down of the coarse lamellar colonies (prior to hot-rolling), respectively These processing procedures usually lead to quite complex microstructural evolution. Studies based on the transmission electron microscopy (TEM) analysis method have reported that the γ phase with tetragonal L10 structure has low stacking fault energy For these alloys, DRX is generally the main dynamic softening mechanism during thermomechanical processing. The microstructural evolution and DRX behavior during hot-rolling are systematically investigated, and the mechanical properties at room and elevated temperatures are determined
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