γ-TiAl-based intermetallics (hereinafter referred to as TiAl alloys) have broad application prospects in aero-engine blade materials due to their high-temperature properties and lightweight characteristics. However, the insufficient creep performance and oxidation resistance of traditional TiAl alloys above 700-750 °C limit their application at higher temperatures. To improve the creep performance and oxidation resistance of TiAl alloys at 800-850 °C, V.M. Imayev et al. from the Russian Academy of Sciences studied the effect of tin (Sn) addition on the microstructure and creep properties of a β-solidifying TiAl alloy.
Methods
The researchers prepared two TiAl alloys: TNZ (Ti-44Al-6(Nb,Zr,Hf)-0.15B) and TNZ-Sn (Ti-44Al-6(Nb,Zr,Hf)-2Sn-0.15B). Two microstructures, duplex and fully lamellar/near lamellar, were obtained by thermomechanical processing and heat treatment. The microstructures of the alloys were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). In addition, creep tests were carried out to evaluate the creep properties of the alloys at 800 °C and 850 °C.
Key Findings
Compared with the Sn-free alloy, the creep performance of the Sn-added TiAl alloy was significantly improved. The minimum creep rates of the TNZ-Sn alloy were 1.6×10⁻⁸ s⁻¹ and 7.7×10⁻⁸ s⁻¹ at 800 °C/250 MPa and 850 °C/200 MPa, respectively. The addition of Sn increased the γ phase solvus temperature of the TiAl alloy. The addition of Sn promoted more pronounced dendritic segregation and coarse grain structure formation under as-cast conditions. The Sn-containing alloy was characterized by the presence of a small amount of Sn, Zr, and Hf-rich phases (0.5-1.5 vol%) distributed along grain/lamella boundaries. The addition of Sn significantly improved the creep performance, which may be attributed to solid solution strengthening and stronger interatomic bonding.
This study found that the addition of Sn can significantly improve the creep performance of β-solidifying TiAl alloys, which provides a new approach for the development of TiAl alloys with higher operating temperatures.
Fig. 1. BSE images of the (a,b) TNZ and (c,d) TNZ-Sn alloy in microstructural conditions 1–4: (a) upset forging + HT1 (1), (b) upset forging + HT2 (2), (c) upset forging + HT3 (3) and (d) upset forging + HT4 (4). The arrows show γ grains and the bright phase (BP). In the corners, TEM images obtained from the lamellar constituent in edge-on orientation and characterizing the lamellar spacing are represented.
Authors
This work is from the Russian Academy of Sciences, with Denis Mikhailovich as the first author and Valery M. Imayev as the corresponding author.
D.M. Trofimov, V.M. Imayev, R.M. Imayev, Preliminary study of the effect of Sn addition on microstructure and creep resistance of a β-solidifying TiAl alloy, Intermetallics 169 (2024) 108310. https://doi.org/10.1016/j.intermet.2024.108310
Editor's comment:
Figures 2b and 2d clearly show that the addition of Sn can significantly reduce the creep rate and improve the creep performance of TiAl alloys.
Editor: Dr. Jun-Jing He
