Application status of directionally solidified/single crystal superalloys for heavy-duty gas turbine blades

The design life of turbine blades in heavy-duty gas turbines (HDGT) typically reaches tens of thousands of hours, operating under conditions characterized by high stress, prolonged thermal exposure and coupled hot corrosion induced by complex media such as high salt and high sulfur. This paper systematically reviews the current research status and development trends of directionally solidified columnar (DS) and single crystal (SC) nickel-based superalloys for HDGT applications. Firstly, the graded material allocation strategy of “high performance for high-temperature front stages and cost-effectiveness for low-temperature rear stages” is clarified, noting that the core design logic has shifted from seeking instantaneous ultimate strength to ensuring long-term microstructural stability. Secondly, the evolution of alloy compositional design is emphasized, analyzing the “low-Re design philosophy” characterized by reduced Re content, optimized W/Mo ratios and increased Cr levels to suppress the precipitation of topologically close-packed (TCP) phases and enhance environmental resistance. Furthermore, considering the massive scale of HDGT blades, the challenges in manufacturing large-scale components are discussed, specifically the thermal-solute-stress multi-field synergistic instability induced by scale effects and the “microstructure inheritance effect” of dendritic segregation on service performance. Finally, this review elucidates the multi-mechanism coupled evolution of creep, fatigue and environmental damage under long-term service conditions, and highlights the prospective engineering applications of repair and life-extension technologies in life-cycle management. It emphasizes that the core of future development lies in reconstructing the surface protection systems of large-scale blades and efficiently restoring the degraded internal microstructures, without compromising the structural integrity of the original single crystal or directionally solidified substrates. It is pointed out that breaking through the bottleneck of casting yield for large-scale complex blades and improving hot corrosion resistance under extreme environments are the core challenges currently faced. Future research should focus on the synergistic optimization of mechanical-environmental performance and physics-based life prediction models to support the development of next-generation high-parameter gas turbines.