• Thermal exposure at 1100°C paradoxically improves the high-cycle fatigue life of PtAl-coated single-crystal superalloys at 900°C.
• The improvement is attributed to a shift in crack initiation from surface microcracks to internal micropores.
• Formation of a protective Al2O3 layer within microcracks and γ′ rafting near the interdiffusion zone hinder surface crack growth.
• Findings provide critical insights for refining HCF life prediction models for coated superalloys in turbine blade applications.