What are the three stages of blade creep?

• A. Secondary, Tertiary, Primary
• B. Primary, Tertiary, Secondary
• C. Primary, Secondary, and Tertiary
• D. Tertiary, Secondary, Primary

Answer: (C)

Blade creep under high-temperature service follows a sequence: primary, secondary, and tertiary in that order. First, primary creep appears right after the load is applied; the rate is high at first but slows as the material work-hardens and recovery processes offset ongoing deformation. Next comes secondary creep, a long, steady-state phase where the deformation increases at a nearly constant rate, representing most of the material’s life and allowing for predictable creep strain. Finally, tertiary creep takes over, with deformation accelerating rapidly as microstructural damage accumulates—cavitation, grain boundary sliding, and cracks grow until failure occurs. This progression—early high rate, long steady rate, then accelerating toward failure—captures how blades age in high-temperature environments, and other orders would misrepresent how the creep rate and mechanisms evolve over time.