Abstract
Requirements and strict regulations for high-performance racing applications involve the use of new and innovative lightweight structural materials. Therefore, intermetallic γ-TiAl-based alloys enable new opportunities in the field due to their lower density compared to commonly used Ni-base superalloys. In this study, a β-solidifying TiAl alloy was examined toward its use as structural material for inlet and outlet valves. The nominal composition of the investigated TNM alloy is Ti–43.5Al–4Nb–1Mo–0.1B (in at%), which enables an excellent formability at elevated temperatures due to the presence of bcc β-phase. Different hot-extrusion tests on an industrial scale were conducted on the cast and hot isostatic pressed material to determine the ideal microstructure for the respective racing application. To simulate these operation conditions, hot tensile tests, as well as rotational bending tests, at room temperature were conducted. With a higher degree of deformation, an increasing strength and fatigue limit was obtained, as well as a significant increment of ductility. The fracture surfaces of the rotational bending test specimens were analyzed using scanning electron microscopy, revealing the relationship between crack initiation and microstructural constituents. The results of this study show that the mechanical performance of extruded TiAl material can be tailored via optimizing the degree of hot-extrusion.
Highlights
Engineering intermetallic γ-TiAl-based alloys are commonly used for high-performance applications, such as racing and aviation, due to their excellent specific mechanical and thermal properties [1,2,3,4]
Γ-TiAl alloys are able to meet the aim of a higher efficiency of propulsion systems, which results in a reduction of fuel consumption and further, a decrease of CO2 emissions [9]
The TNM material was processed by GfE Metalle und Materialien GmbH, Nuremberg, Germany, using double vacuum arc remelting (VAR) followed by induction skull melting (ISM) [20]
Summary
Engineering intermetallic γ-TiAl-based alloys are commonly used for high-performance applications, such as racing and aviation, due to their excellent specific mechanical and thermal properties [1,2,3,4]. Γ-TiAl alloys exhibit good oxidation resistance and microstructural stability during long-term thermal exposure up to service temperatures of 750 ◦ C and, depending on their microstructure, a good creep behavior [5,6,7]. Materials 2020, 13, 4720 against competing materials [10,11,12]. Beneficial response behavior of engines equipped with high-temperature lightweight TiAl components can be achieved [11]. In the case of racing applications, second generation TiAl alloys were the first to achieve commercial success.
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