Observations, theories, and predictions of high-temperature creep behavior

Abstract

The key observations that have underpinned traditional power-law approaches to creep mechanism identification have been re-evaluated, using information obtained for aluminum, copper, and 0.5Cr0.5Mo0.25V steel. In particular, stress/creep rate plots produced over extended stress ranges for all three materials are shown to be well represented by continuous curves, contradicting the common assumption that different creep mechanisms are dominant over different stress/temperature regimes. Evidence is also introduced to demonstrate that the theoretical and practical limitations of power-law descriptions of steady-state creep rates can be overcome by quantifying the shapes of normal creep curves and the variations in curve shape with changing test conditions. In this way, the behavior patterns displayed by pure metals and particle-hardened alloys can be interpreted in terms of the deformation processes controlling creep-strain accumulation and the damage/degradation processes causing the creep rate to accelerate into the tertiary stages that usually precede fracture. Moreover, the superior predictive capabilities of curve shape analysis are then illustrated by results showing that short-term property values can be extrapolated to provide accurate long-term engineering design data.