Creep

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Metallurgy Fundamentals

Definition

The time-dependent, permanent deformation of a material under a constant load or stress at elevated temperatures, typically above 0.4 times the absolute melting temperature. Creep failure can occur at stresses well below the room-temperature yield strength.

Detailed Explanation

Creep occurs in three stages: primary (decreasing creep rate due to work hardening), secondary (steady-state creep rate governed by competing hardening and recovery), and tertiary (accelerating rate due to necking, grain boundary cavitation, or microstructural degradation leading to rupture). Nickel-based superalloys, cobalt alloys, and ferritic-martensitic creep-resistant steels are designed to resist creep at the operating temperatures of gas turbine blades and steam power plant components. Creep resistance is improved by solid solution strengthening, precipitation of stable second-phase particles, and single-crystal or directionally solidified microstructures.