Key Takeaways & Executive Findings
- •• The creep resistance of HT2 exceeds that of HT3, highlighting a significant precipitation strengthening effect of α2 phase. • At temperatures and stresses lower than or equal to 570 °C and 200 MPa, respectively, the creep resistance of HT1 is close to that of HT3, suggesting that silicide precipitated before creep attenuates the strengthening of creep deformation caused by the coarsening of αs phase. • At 600 °C and 250 MPa, the creep resistance of HT1 is significantly higher than that of HT3, indicating that when the dynamic precipitation of silicide in HT1 is adequate, it also resists the creep deformation of the alloy. • The stress exponent for HT1, HT2 and HT3 ranges 1.7−1.9 (550 °C) and 3.7−4.4 (600 °C), indicating that the amount of silicide and α2 phase doesn’t affect the creep mechanism.
Abstract
In TC25G alloy, Ti3Al (α2 phase) and silicide were precipitated during long-term aging. To access the effect of precipitates, three heat treatment processes were designed. The effects of these heat treatments on the creep behavior of alloy were compared and analyzed. The results show that the creep resistance of HT2 exceeds that of HT3, highlighting a significant precipitation strengthening effect of α2 phase. Furthermore, at temperatures and stresses lower than or equal to 570 °C and 200 MPa, respectively, the creep resistance of HT1 is close to that of HT3, suggesting that silicide precipitated before creep attenuates the strengthening of creep deformation caused by the coarsening of αs phase. At 600 °C and 250 MPa, the creep resistance of HT1 is significantly higher than that of HT3, indicating that when the dynamic precipitation of silicide in HT1 is adequate, it also resists the creep deformation of the alloy. The stress exponent for HT1, HT2 and HT3 ranges 1.7−1.9 (550 °C) and 3.7−4.4 (600 °C), indicating that the amount of silicide and α2 phase doesn’t affect the creep mechanism. The increase in creep activation energy is attributed to the enhanced inhibition caused by lots of precipitates on phase boundary migration and dislocations motion.
1. Introduction
TC25G (Ti−6.5Al−1.8Sn−4Zr−4Mo−1W−0.2Si) alloy belongs to the Ti−Al−Sn−Zr−Mo−W−Si series of multi-component composite strengthened α+β type high-temperature titanium alloy, and is an ideal candidate structural material for high-temperature titanium alloys for engines. It can be mainly used to manufacture important hot end parts such as compressor rotor discs, blades, and casings. It is well known that when titanium alloys are subjected to long-term high-temperature service, they will undergo creep failure under the influence of temperature and stress, resulting in the dimensional and performance of the material failing to meet the requirements [1,2]. Therefore, researchers often consider creep performance as one of the main criteria for evaluating the application of high-temperature titanium alloys, as it affects the service life and safety reliability of the alloy [3].
The creep properties of high-temperature titanium alloys are significantly influenced by the α-stabilizing element Al and the β-stabilizing element Si. During long-term high-temperature service, the alloy is prone to the formation of two types of precipitates [4,5]: silicide and Ti3Al phase (α2 phase). According to the literature [6−9], the existence state of Al and Si elements in the alloy has three effects on the alloy: the first is the strengthening effect of dissolved atoms, the second is the strengthening effect of precipitates, and the third is the dynamic precipitation diffusion effect during the precipitation process. The first and second states of existence can improve the creep resistance of the alloy, while the third state of existence is unfavorable for the creep resistance of the alloy.
PATON and MAHONEY [6] in their studies on Ti−5Zr−0.5Si alloy, Ti-11 alloy and IMI-685 alloy found that the creep properties of titanium alloys are closely related to the presence of Si, and the best creep properties can be achieved when Si elements are completely dissolved in the matrix. The creep properties of the alloy
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Zhuo-meng LIU, She-wei XIN, Yong-qing ZHAO, Kun QIAN, Chi-cheng LUO, Si-yuan ZHANG (2025). Influence of existence mode of silicide and α2 phase on creep behavior of TC25G alloy at 550−600 °C. SinoTechIntel Verified Research. https://doi.org/10.1016/S1003-6326(25)67020-8
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Frequently Asked Questions
What is the effect of α2 phase on creep resistance of TC25G alloy?
The α2 phase significantly enhances creep resistance through precipitation strengthening, as evidenced by the higher creep resistance of HT2 compared to HT3.
How does silicide precipitation affect creep behavior at different temperatures?
At lower temperatures (≤570 °C) and stresses (≤200 MPa), silicide precipitated before creep attenuates the strengthening from αs coarsening, while at 600 °C and 250 MPa, dynamic precipitation of silicide provides additional creep resistance.
What are the stress exponent values for TC25G alloy at 550 °C and 600 °C?
The stress exponent ranges from 1.7 to 1.9 at 550 °C and from 3.7 to 4.4 at 600 °C, indicating that the creep mechanism is not affected by the amount of silicide and α2 phase.
What is the role of precipitates in increasing creep activation energy?
The increase in creep activation energy is attributed to the enhanced inhibition caused by lots of precipitates on phase boundary migration and dislocations motion.
What is the significance of this study for high-temperature titanium alloys?
This study provides insights into optimizing heat treatment processes to control the existence mode of silicide and α2 phase, thereby improving the creep resistance of TC25G alloy for high-temperature applications.
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