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Article

Effect of Boron Content and Cooling Rate on the Microstructure and Boride Formation of β-Solidifying γ-TiAl TNM Alloy

1
Mechanical and Manufacturing Department, Mondragon University, Loramendi 4, 20500 Mondragon, Gipuzkoa, Spain
2
Materials and Processes Department, Industria de Turbopropulsores S.A.U, Parque Tecnológico No 300, 48170 Zamudio, Bizkaia, Spain
*
Author to whom correspondence should be addressed.
Metals 2020, 10(5), 698; https://doi.org/10.3390/met10050698
Received: 19 April 2020 / Revised: 20 May 2020 / Accepted: 23 May 2020 / Published: 25 May 2020
Boron is a unique and popular grain refiner element in cast titanium aluminide (TiAl) alloys, as it helps to improve mechanical properties if properly alloyed. However, the formation mechanism of different types of borides in cast TiAl alloys is not yet clearly understood. This study seeks to correlate the chemical composition and cooling rate during solidification of cast TiAl alloys, with the type of boride precipitated and the resulting microstructure. Several β-solidifying γ-TiAl alloys of the TNM family were cast, alloying boron to a starting Ti-44.5Al-4Nb-1Mo-0.1B (at.%) alloy. The alloys were manufactured with an induction skull melting furnace and poured into a stepped 2, 4, 8 and 16 mm thickness mold to achieve different cooling rates. On one hand, the results reveal that boron contents below 0.5 at.% and cooling rates during solidification above 10 K/s promote the formation of detrimental ribbon borides. On the other hand, boron contents above 0.5 at.% and cooling rates during solidification below 10 K/s promote the formation of a refined microstructure with blocky borides. Finally, the formation mechanisms of both ribbon and blocky borides are proposed. View Full-Text
Keywords: titanium aluminide; casting; boride; cooling rate; chemical composition titanium aluminide; casting; boride; cooling rate; chemical composition
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MDPI and ACS Style

Bernal, D.; Chamorro, X.; Hurtado, I.; Madariaga, I. Effect of Boron Content and Cooling Rate on the Microstructure and Boride Formation of β-Solidifying γ-TiAl TNM Alloy. Metals 2020, 10, 698. https://doi.org/10.3390/met10050698

AMA Style

Bernal D, Chamorro X, Hurtado I, Madariaga I. Effect of Boron Content and Cooling Rate on the Microstructure and Boride Formation of β-Solidifying γ-TiAl TNM Alloy. Metals. 2020; 10(5):698. https://doi.org/10.3390/met10050698

Chicago/Turabian Style

Bernal, Daniel, Xabier Chamorro, Iñaki Hurtado, and Iñaki Madariaga. 2020. "Effect of Boron Content and Cooling Rate on the Microstructure and Boride Formation of β-Solidifying γ-TiAl TNM Alloy" Metals 10, no. 5: 698. https://doi.org/10.3390/met10050698

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