Glossary

Creep resistance is the ability of a material to withstand time-dependent deformation under constant stress at elevated temperature. In high-temperature environments—such as in turbine blades, power plant piping, jet engines, or chemical reactors—materials experience a gradual, permanent strain called creep, even when the applied stress is well below their normal yield strength. The higher the temperature (usually above about 0.4 times the material’s melting temperature in Kelvin), the more pronounced the creep behavior becomes.

The rate at which creep occurs during long-term service is described by the Norton–Bailey power law, expressed as ε˙ = Aσⁿe^(−Q/RT). In this equation, ε˙ represents the steady-state creep strain rate, A is a material constant, σ is the applied stress, n is the stress exponent (indicating how strongly stress influences creep rate), Q is the activation energy for creep, R is the universal gas constant, and T is the absolute temperature. The exponential term, e^(−Q/RT), shows how sensitively creep rate increases with temperature—small temperature rises can dramatically accelerate deformation.

Creep typically progresses through three stages: primary creep, where deformation slows as the material strain-hardens; secondary creep, the steady-state phase where the rate is nearly constant and most design calculations focus; and tertiary creep, where damage accelerates, leading to rupture. Materials that possess high creep resistance, such as nickel- and cobalt-based superalloys, stainless steels, titanium alloys, molybdenum, and tungsten, are engineered to limit dislocation motion and grain boundary sliding—the two main mechanisms that drive creep. Techniques like solid solution strengthening, precipitation hardening, and grain boundary stabilization enhance their ability to resist this slow, temperature-driven deformation.