Correct Interpretation of Creep Rates: A Case Study of Cu. Issue 11 (November 2015)

• Record Type: Journal Article
• Authors: Blum, W.; Dvořák, J.; Král, P.; Eisenlohr, P.; Sklenička, V.
• Is Part Of: Journal of materials science & technology. Volume 31:Issue 11(2015:Nov.)
• Page Start: 1065
• Page End: 1068
• Publication Date: 2015-11
• Subjects: Cu -- Creep -- Minimum creep rate -- Activation energy -- Stress exponent; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2015.09.012
• Languages: English
• ISSNs: 1005-0302

Abstract

Abstract : Traditionally the deformation resistance in creep is characterized by the minimum creep rate ε ˙ min and its sensitivity to stress (stress exponent n ) and temperature (activation energy Q ). Various values of constant n have been reported in the literature and interpreted in terms of specific mechanisms. The present case study of coarse-grained Cu at 573 K yields a stress exponent n = 9 for ε ˙ min in tension and a relatively low activation energy. The evolution of the deformation resistance with strain at constant tensile creep load and comparison with creep in compression without fracture indicates that the tensile ε ˙ min result from transition from uniform deformation to strain localization during fracture. This is confirmed by the results of creep in compression where fracture is suppressed. Both the tensile ε ˙ min and the compressive creep rate at strains around 0.3 can be described using existing equations for quasi-stationary deformation containing the subgrain boundary misorientation θ as structure parameter. While in the latter case constant θ leads to monotonic increase of n with stress, the tensile nine-power-law results from variable θ, and has no simple meaning. The result of this case study means that uncritical interpretation of minimum tensile creep rates as stationary ones bears a high risk of systematic errors in the determination of creep parameters and identification of creep mechanisms.