Which is the last stage of blade creep?

• A. Tertiary
• B. Primary
• C. Secondary
• D. Quaternary

Answer: (A)

Creep in turbine blade materials at high temperature and stress unfolds in stages as damage accumulates. In the initial stage the creep rate is high but declines because the material work-hardens and the structure begins to recover. The middle stage sees a near-constant creep rate, where hardening and recovery balance each other. The final stage, tertiary creep, is where deformation accelerates rapidly as damage accumulates—cavities form and grow, grain boundaries slide, and microstructural changes drive the rate up until rupture. This makes tertiary creep the last stage in blade creep. Some references briefly mention an additional, quaternary stage, but the standard life-limiting progression used for blades ends with tertiary creep.