Microstructural Evolution and Refinement Mechanism of a Beta–Gamma TiAl-Based Alloy during Multidirectional Isothermal Forging
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School of Materials Science and Engineering, Tongji University, Shanghai 201804, China
2
Shanghai Key Laboratory of Development and Application for Metal-functional Materials, Tongji University, Shanghai 201804, China
3
Shanghai Spaceflight Precision Machinery Institute, Shanghai 201600, China
4
College of Mechatronics and Control Engineering, Shenzhen University, Shenzhen 518060, China
*
Author to whom correspondence should be addressed.
Materials 2019, 12(15), 2496; https://doi.org/10.3390/ma12152496
Received: 29 May 2019
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Revised: 2 August 2019
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Accepted: 2 August 2019
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Published: 6 August 2019
Multidirectional isothermal forging (MDIF) was used on a Ti-44Al-4Nb-1.5Cr-0.5Mo-0.2B (at. %) alloy to obtain a crack-free pancake. The microstructural evolution, such as dynamic recovery and recrystallization behavior, were investigated using electron backscattered diffraction and transmission electron microscopy methods. The MDIF broke down the initial near-lamellar microstructure and produced a refined and homogeneous duplex microstructure. γ grains were effectively refined from 3.6 μm to 1.6 μm after the second step of isothermal forging. The ultimate tensile strength at ambient temperature and the elongation at 800 °C increased significantly after isothermal forging. β/B2→α2 transition occurred during intermediate annealing, and α2 + γ→β/B2 transition occurred during the second step of isothermal forging. The refinement mechanism of the first-step isothermal forging process involved the conversion of the lamellar structure and discontinuous dynamic recrystallization (DDRX) of γ grains in the original mixture-phase region. The lamellar conversion included continuous dynamic recrystallization and DDRX of the γ laths and bugling of the γ phase. DDRX behavior of γ grains dominated the refinement mechanism of the second step of isothermal forging.
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Keywords:
TiAl-based alloy; microstructure characterization; refinement mechanism; multidirectional isothermal forging (MDIF)
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MDPI and ACS Style
Zhu, K.; Qu, S.; Feng, A.; Sun, J.; Shen, J. Microstructural Evolution and Refinement Mechanism of a Beta–Gamma TiAl-Based Alloy during Multidirectional Isothermal Forging. Materials 2019, 12, 2496. https://doi.org/10.3390/ma12152496
AMA Style
Zhu K, Qu S, Feng A, Sun J, Shen J. Microstructural Evolution and Refinement Mechanism of a Beta–Gamma TiAl-Based Alloy during Multidirectional Isothermal Forging. Materials. 2019; 12(15):2496. https://doi.org/10.3390/ma12152496
Chicago/Turabian StyleZhu, Kai, Shoujiang Qu, Aihan Feng, Jingli Sun, and Jun Shen. 2019. "Microstructural Evolution and Refinement Mechanism of a Beta–Gamma TiAl-Based Alloy during Multidirectional Isothermal Forging" Materials 12, no. 15: 2496. https://doi.org/10.3390/ma12152496
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