Key Takeaways & Executive Findings
- •• High Al/Nb content in Ti-46Al-8Nb alloy suppresses B2 phase formation, enhancing creep resistance. • The alloy exhibits power-law creep with activation energy 274 kJ/mol and stress exponent 1.97, indicating grain boundary sliding as the dominant mechanism. • Irregular serrated grain boundaries improve creep resistance by hindering dislocation movement, while smooth boundaries are prone to crack initiation. • Cracks initiate within lamellar structures under stress concentration and propagate along boundaries perpendicular or at 45° to the stress axis, leading to failure.
Abstract
High Al content inhibits the formation of B2 phase, which improves creep resistance in high Al/Nb-containing TiAl alloys. In this work, the microstructure evolution and creep behavior of TiAl based alloy Ti-46Al-8Nb (at.%) with a high Al/Nb content, produced by the vacuum consumable electrode melting technology and the electromagnetic cold crucible melting technology, were studied. The microstructure of the Ti-46Al-8Nb alloy is composed of α2/γ phases arranged in layers with different orientations, which possesses smooth grain boundaries due to small-blocky segregation and irregular serrated grain boundaries caused by large-blocky segregation. Under conditions of 780-820 °C and 125-175 MPa for 200 h, it exhibits typical power-law creep characteristics. The apparent activation energy of creep (Q) and apparent stress exponent (n) of the Ti-46Al-8Nb alloy are Q=274 kJ·mol-1 and n=1.97, respectively. The creep deformation mechanism is grain boundary sliding. Cracks easily form at the smooth boundary. The irregular serrated boundaries with small specific surface area hinder the dislocation movement, thereby improving the boundary creep resistance. When the stress concentration reaches a certain degree, the cracks will initiate between the lamellar structures within the grain. The crack usually propagates along the boundary perpendicular to or at an angle of 45° with the stress axis until creep failure occurs.
1. Introduction
Due to the long-term operation of aero-engine components under high-temperature and high-pressure conditions, increasing stringent requirements are proposed on the high temperature performance of materials. The advanced intermetallic TiAl-based alloy is considered the most promising in terms of development high-temperature structural material in the aerospace industry field by reason of its outstanding overall mechanical properties [1-3], such as low density, high specific strength, and outstanding oxidation resistance [4-6]. So far, with the unremitting efforts of scientists, some systems of TiAl-based alloys have been successfully applied to low-pressure turbine blades in aero-engines [7,8]. However, the insufficient creep resistance and poor room temperature plasticity of TiAl-based alloys hinder their widespread applications [2].
Adding high melting point elements such as Nb to the alloy system is an effective method to improve the high-temperature performance of TiAl-based alloys. The rapid development of high-Nb TiAl-based alloy has become the possibility to solve the problem of its limited applications [9], with the ultimate service temperature being 60-100 °C higher than that of traditional TiAl alloy [10-12]. In addition, it has been reported that the creep properties of TiAl-based alloys are quite susceptible for the change of microstructure [13-15]. In general, the full lamellar (FL) and near lamellar (NL) structures have good high-temperature creep resistance. Through heat treatment [16], directional solidification [6], thermal mechanical processing [17], and other methods, the microstructure of the alloy can be controlled to improve the creep resistance.
With the introduction of high-melting point elements, the requirements for alloy melting are higher. Electromagnetic cold crucible melting technology has been widely used in the melting and preparation of materials because of its advantages of melting high-melting point, active materials and uniform composition of prepared materials. Electromagnetic cold crucible technology is often used to prepare high-temperature active metals such as Ti-based alloys [18], TiAl-based alloys [19-21], and monocrystalline silicon [22,23] by melting. Therefore, in this work, a fully lamellar high-Nb TiAl alloy was prepared using electromagnetic cold crucible solidification technology to obtain good creep resistance.
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Yan Wang, Qi Wang, Rui-run Chen, Yan-qing Su, Heng-zhi Fu (2026). Creep behavior and fracture mechanism of high Al/Nb-containing TiAl alloy. China Foundry. https://doi.org/10.1007/s41230-026-5097-2
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Frequently Asked Questions
What is the creep mechanism of Ti-46Al-8Nb alloy?
The creep mechanism is grain boundary sliding, as indicated by the stress exponent of 1.97 and activation energy of 274 kJ/mol.
How does high Al/Nb content affect the creep resistance?
High Al/Nb content inhibits the formation of B2 phase, which improves creep resistance.
What are the key microstructural features influencing creep?
The alloy has lamellar α2/γ phases with smooth and serrated grain boundaries; serrated boundaries hinder dislocation movement, improving creep resistance.
Where do cracks initiate and propagate during creep?
Cracks initiate between lamellar structures within grains under stress concentration and propagate along boundaries perpendicular or at 45° to the stress axis.
What is the significance of using electromagnetic cold crucible melting?
It allows uniform melting of high-melting-point active materials, producing a fully lamellar structure with good creep resistance.
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