High-temperature oxidation behaviour of TiAl alloys with Co addition
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High-temperature oxidation behaviour of TiAl alloys with Co addition Yu Pan1, Xin Lu1,*, Tailong Hui1, Chengcheng Liu2, Bowen Liu1, Wei Xu1, Ce Zhang1, Jianzhuo Sun1, Xuanhui Qu1, and Jiazhen Zhang1 1
State Key Laboratory for Advanced Metals and Materials, Beijing Advanced Innovation Center for Materials Genome Engineering, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China 2 Beijing Xinghang Electro-mechanical Equipment Co Ltd, Beijing 100074, China
Received: 10 May 2020
ABSTRACT
Accepted: 26 August 2020
The challenge of enhancing the high-temperature oxidation resistance of TiAl alloys is hereby addressed by Co addition. Isothermal oxidation tests were conducted on the newly designed TiAl-Co alloys in laboratory air at 900 °C up to 100 h. Sintered microstructure, oxidation kinetics, scale structure, spallation resistance and oxidation mechanisms were systematically investigated. Results show that the original sintered microstructure of TiAl alloys mainly consists of matrix phases a2-Ti3Al/c-TiAl lamellae, while the Co addition leads to the formation of the two additional Co-rich phases of CoAl2Ti and Ti (Al, Co, Cr and Nb) at grain boundaries. The Co-doped TiAl alloys exhibit an improved high-temperature oxidation resistance compared with the Co-free alloy. The presence of the Co-rich phases network along the grain boundaries and Co-rich layer at the scale/substrate interface can hinder the inward diffusion of oxygen and the outward diffusion of Ti and Al, thereby suppressing the growth of oxide scale and improving the spallation resistance of TiAl alloys. As a result, the TiAl-3Co alloy possesses excellent oxidation resistance, with the minimum mass gain of 4.08 mg/ cm2, thinnest scale thickness of 17.8 lm and without surface spallation or crack formation after isothermal oxidation for 100 h. This result would pave the way for designing high-temperature oxidation-resistant TiAl-based alloys.
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Springer Science+Business
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Introduction TiAl alloys are commonly used as high-temperature structural materials in aerospace engineering because of their lightweight, high specific strength and
Handling Editor: David Balloy.
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https://doi.org/10.1007/s10853-020-05269-z
superior creep resistance [1–5]. They drew considerable attention due to the first application of Ti-48Al2Cr-2Nb alloy low-pressure turbine blades on the GEnX jet engine to power the Boeing 787 and 747-8 airplanes [6, 7]. However, the development of TiAl
J Mater Sci
alloys remains a great challenge due to their limited ductility, poor machinability and insufficient hightemperature oxidation resistance. Powder metallurgy (PM) offers an attractive near-net shaping route to fabricate the TiAl alloys with fine grain size and chemically homogenous microstructure, which effectively simplifies the machining process of the brittle materials [8–11]. Nevertheless, improving the high-temperature oxida
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