### 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.

Language | English (US) |
---|---|

Pages | 1065-1068 |

Number of pages | 4 |

Journal | Journal of Materials Science and Technology |

Volume | 31 |

Issue number | 11 |

DOIs | |

State | Published - Nov 1 2015 |

Externally published | Yes |

### Profile

### Keywords

- Activation energy
- Creep
- Cu
- Minimum creep rate
- Stress exponent

### ASJC Scopus subject areas

- Ceramics and Composites
- Mechanics of Materials
- Mechanical Engineering
- Polymers and Plastics
- Metals and Alloys
- Materials Chemistry

### Cite this

*Journal of Materials Science and Technology*,

*31*(11), 1065-1068. DOI: 10.1016/j.jmst.2015.09.012

**Correct Interpretation of Creep Rates : A Case Study of Cu.** / Blum, Wolfgang; Dvořák, J.; Král, P.; Eisenlohr, P.; Sklenička, V.

Research output: Contribution to journal › Article

*Journal of Materials Science and Technology*, vol 31, no. 11, pp. 1065-1068. DOI: 10.1016/j.jmst.2015.09.012

}

TY - JOUR

T1 - Correct Interpretation of Creep Rates

T2 - Journal of Materials Science and Technology

AU - Blum,Wolfgang

AU - Dvořák,J.

AU - Král,P.

AU - Eisenlohr,P.

AU - Sklenička,V.

PY - 2015/11/1

Y1 - 2015/11/1

N2 - 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.

AB - 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.

KW - Activation energy

KW - Creep

KW - Cu

KW - Minimum creep rate

KW - Stress exponent

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UR - http://www.scopus.com/inward/citedby.url?scp=84947424971&partnerID=8YFLogxK

U2 - 10.1016/j.jmst.2015.09.012

DO - 10.1016/j.jmst.2015.09.012

M3 - Article

VL - 31

SP - 1065

EP - 1068

JO - Journal of Materials Science and Technology

JF - Journal of Materials Science and Technology

SN - 1005-0302

IS - 11

ER -