Abstract
Understanding of the creep behavior Nb and Ta-rich γ-TiAl alloys plays a crucial role towards realization of their potential applications. The present article reports the evolution of microstructural features in the crept γ-TiAl-based Ti-5Al-8Nb-2Cr-0.2B and Ti-45Al-8Ta-0.2C-0.2B-0.2C alloys. Structural characterizations have been carried out using automated crystal orientation mapping (ACOM) along with precession electron diffraction (PED) in a transmission electron microscope, in conjunction with electron back-scattered diffraction (EBSD) in a scanning electron microscope (SEM) and transmission electron microscopy (TEM). Creep behavior of the fourth generation γ-TiAl-based alloys has been comparatively investigated under constant load tensile creep tests performed in the temperature range from 800–850 °C and applied stresses range of 125–200 MPa. It has been demonstrated that the ACOM with PED technique has accurate and reliable diffraction pattern recognition and higher spatial resolution, and supplements effectively the conventional EBSD technique for characterization of complex microstructural features evolved during creep of multiphase (γ + α2 + β)-based TiAl alloys. The results show that the Nb and Ta additions have distinctly different effects on the microstructural instability and phase transformation during the creep deformation. The formation of the Ta-rich intermetallic phase (Ti4Al3Ta, the so-called τ phase) has been detected preferentially along the colony and the γ-α2 interphase boundaries in the Ta-rich alloy, whilst its isomorph, Ti4Al3Nb intermetallic, has hardly been detected in the Nb-rich alloy. Implications of τ-phase formation and related microstructural instabilities have been discussed with respect to the creep behavior of the two alloys.
Highlights
IntroductionIntroduction γTiAl based alloys have the potential to replace the existing high-temperature materials used in the structural application of gas turbine and automotive industries
Introduction γTiAl based alloys have the potential to replace the existing high-temperature materials used in the structural application of gas turbine and automotive industries
The alloying addition to the γ-TiAl alloys significantly modifies the microstructure in terms of singlephase, two-phase, or multiphase combinations, which further control the high-temperature mechanical properties such as creep
Summary
Introduction γTiAl based alloys have the potential to replace the existing high-temperature materials used in the structural application of gas turbine and automotive industries. The alloying addition to the γ-TiAl alloys significantly modifies the microstructure in terms of singlephase, two-phase, or multiphase combinations, which further control the high-temperature mechanical properties such as creep. To improve the creep resistance and structural stability of γ-TiAl based alloys for aerospace and automotive applications, the alloys are required to be modified by the addition of alloying elements such as Nb, Ta in the range of (5–10 at %) and Cr, Mo, and V (2–4 at %) and B, C (0.1–0.2 at %) which reduce the diffusion rate, provide solid solution hardening, and refine the microstructure [1,4]. Investigations have been reoriented toward Nb-based and Ta-based γ-TiAl alloys, the so-called third-generation, and fourth-generation alloys These alloys show improvement in mechanical strength and creep resistance.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
