Abstract
To investigate the high-cycle fatigue (HCF) behavior of TNM alloys, three different microstructures were designed and obtained by different heat treatments. Staircase tests and fatigue tests in a finite life-region were performed to evaluate the fatigue properties. Then, the fracture surfaces were analyzed to study the fracture behavior of TNM alloys with different microstructures. Results showed that the TNM alloys with duplex microstructure possesses the highest fatigue strength and fatigue life, followed by near lamellar TiAl alloys. HCF failure exhibited cleavage fracture morphologies, and multiple facets were generated in the crack initiation region of different TNM alloys. Two different crack initiation modes, subsurface crack nucleation and surface origin, were observed. Both crack initiation modes appeared in near lamellar alloys, while only subsurface crack initiation were obtained in the duplex (DP) alloy. It contributes to the high scatter of S-N data. The HCF failure of TNM alloys was dominated by crack nucleation rather than crack propagation. These findings could provide guidance for optimizing the microstructure and improving the HCF properties of TiAl alloys.
Highlights
Gamma TiAl-based alloys have been successfully applicated in aerospace and automotive industries after decades of developments [1,2,3]
If the specimen failed before reaching 107 cycles, the prior test was classified as failure, and the subsequent test would be conducted at a lower stress; otherwise, it is grouped in pass classification, and the specimen would be tested at a higher stress level
The parameters A, B and C were determined by equations i=1 where nj was the number of specimens tested at stress level σj in the up-and-down diagram, and j = 0, 1, 2, . . . . The results showed that the fatigue strengths of DP, near lamellar (NL)#1 and NL#2 alloys were 622 MPa, 594 MPa, and 542 MPa, respectively
Summary
Gamma TiAl-based alloys have been successfully applicated in aerospace and automotive industries after decades of developments [1,2,3]. The TNM alloy, which contains a balanced concentration of Nb and Mo, was recognized as the representative third generation TiAl alloy [8,9]. It has the potential for utilization as the last stage low-pressure turbine blades in advanced geared turbofan engines. As the most expected and important applications of TiAl alloys, turbine blades and exhaust valves in engines generally serve under cyclic loading conditions [10,11]. It was demonstrated that the low ductility and toughness of TiAl alloys result in a low tolerance to fatigue crack growth and a relatively steep slope of the Paris region [16,17]. Due to the rapid fatigue crack growth rate, the threshold stress intensity has been used for directing component design and predicting the fatigue life of TiAl alloys [18]
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.
