Abstract
The turbine section of aircraft engines (both commercial and military) is an example of one of the most hostile environments as the components in this section typically operate at upwards of 1650 °C in the presence of corrosive and oxidative gases. The blades are at the heart of the turbine section as they extract energy from the hot gases to generate work. The turbine blades are typically fabricated using investment casting, and depending on the casting complexity, they generally display one of the three common microstructures (i.e., equiaxed or polycrystalline, directionally solidified, and single crystal). Single crystal casting is exotic as several steps of the casting process are traditionally hands-on. Due to the complex production process involving several prototyping iterations, the blade castings have a significant cost associated with them. For example, a set of 40 single crystal turbine blades costs above USD 600,000 and requires 60–90 weeks for production. Additionally, if the components suffer from material loss due to prolonged service or manufacturing defects, the traditional manufacturing methods cannot restore the parent metallurgy at the damage locations. Hence, there is a significant interest in developing additive manufacturing (AM) technologies that can repair the single crystal turbine blades. Despite the blades’ criticality in aircraft propulsion, there is currently no review article that summarizes the metallurgy, production process, failure mechanisms, and AM-based repair methods of the single crystal turbine blades. To address this existing gap, this review paper starts with a discussion on the composition of the single crystal superalloys, describes the traditional fabrication methods for the metallic single crystal turbine blades, estimates the material and energy loss when the blades are scrapped or reverted, and provides a summary of the AM technologies that are currently being investigated for their repair potential. In conclusion, based on the literature reviewed, this paper identifies new avenues for research and development approaches for advancing the fabrication and repair of single crystal turbine blades.
Highlights
Modern aircraft engines employ a Brayton cycle, which takes inlet air, compresses it, and mixes it with fuel before expanding it through the turbine in order to generate the necessary thrust to propel the aircraft [1]
[9])times at thebefore shank, the dovetail, and the is damaged at the tip,forms it is typically repaired one3b–d) to three being scrapped where it bottom is of theeither airfoil limit the life of the turbine blades
Because the turbine blades operate at 90% melting temperature of the alloy, this cooling process is Because a criticalthe requirement of the advanced turbine blades
Summary
Modern aircraft engines employ a Brayton cycle, which takes inlet air, compresses it, and mixes it with fuel before expanding it through the turbine in order to generate the necessary thrust to propel the aircraft [1]. High-creep strength and fatigue-resistant materials are employed to fabricate the turbine blades [4]. 1960sof and, since loss resulting from the abrasion between the blade tip and engine shroud, the SX turbine blades they have successfully been used to increase the service life [8]. SX turbine blade fatigue cracks and other of damage [9])times at thebefore shank, the dovetail, and the is damaged at the tip,forms it is typically repaired one3b–d) to three being scrapped where it bottom is of theeither airfoil limit the life of the turbine blades. AsAs thethe airline industry the material materialand andthe theenergy energywaste waste will only continue to increase if suitable measures are not found towards repairing the turbine blades.
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