An Advanced TiAl Alloy for High-Performance Racing Applications

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.

A review on isothermal rotating bending fatigue failure: Microstructural and lifetime modeling of wrought and additive manufactured alloys

“…On the other hand, the behavior of fatigue at the microscopic scale is dependent on the behavior of the microstructure under high temperatures. Both Burtscher et al 98 and Wu et al 33 have demonstrated that in Ti‐alloys with a high amount of Al (40%) the colonies and β , γ phases play a significant effect in the start and propagation orientation of cracks. The microstructure is mostly made up of lamellar colonies, as seen in Figure 17.…”

“…(A) Schematic of micro‐cracks initiation and propagation in the presence of colonies in Ti‐Al alloy (wrought) under RBF test in high temperature 98 ; (B) fracture surface of AM'd material under RBF test in room temperature (red circles are showing crack initiation from porosities) 79 . [Colour figure can be viewed at wileyonlinelibrary.com]…”

Structural Change of TiAl Alloy under Uniaxial Tension and Compression in the <001> Direction: A Molecular Dynamics Study

“…This material can be found in modern airplane jet engines because of its resistance to high temperatures [10]. It is also used in high-performance vehicle engines [11]. This alloy material has excellent oxidation resistance and good structural stability during long-term thermal exposure [12,13].…”

Practical Use of Hot-Forged-Type Ti-42Al-5Mn and Various Recent Improvements

“…The turbine wheel in this product was cast TiAl alloy, which was manufactured by precision casting and joined to a low-alloy steel shaft to form the turbine rotor. Even in recent research on the practical application of TiAl alloys, small blades [2,3] and engine valves [4] manufactured by casting, isothermal forging, and extrusion are targeted, and there are no development examples of parts weighing 0.5 kg or more. The TiAl alloy is currently mostly used in the low-pressure turbine blades of jet engines [5] Parts manufactured by precision casting were initially used for practical applications; however, because the TiAl alloy is poorly castable, casting a near-net into a blade shape was difficult, with very large surplus materials required, leading to large amounts of machining that effectively negated the merits of precision casting.…”