The stress/creep rate behaviour of precipitation-hardened alloys

Abstract

Recent experimental data of the stress/creep rate relationship for precipitation-hardened alloys have been surveyed. These materials display typically a higher stress-sensitivity of the creep rate than is observed for pure metals, and solid solutions. Furthermore, their stress/creep rate curves show pronounced breaks, with a stress-sensitivity of the creep rate, ∂ ln έ/∂ ln σ, of ∼4 below the break. The precipitation dispersion affects the creep rate such that it reaches a minimum at an intermediate interparticle spacing, with higher rates for both larger and smaller spacings. Based on the principles of recovery creep, a creep theory for precipitation-hardened alloys has been described, leading to a relationship of the type έ= A(έ-έ_p)⁴, where έ_p represents a back stress due to the particle dispersion. At high creep stresses έ_p is constant and defined by the stress to operate a particle-cutting mechanism or the Orowan mechanism. At lower stresses the dislocations are able to bypass the particles, surmounting them by climb. A theoretical analysis shows that έ_p under these conditions decreases approximately linearly with decreasing applied stress. The theory adequately explains the special features of creep in precipitation-hardened materials.