DEVELOPMENT OF CYCLIC SLIP BANDS IN UFG COPPER IN GIGACYCLE FATIGUE

Lucie Navrátilová

doi:10.12776/ams.v19i2.92

Abstract

Ultrafine-grained (UFG) copper studied in this paper was produced by equal channel angularpressing (ECAP) method and tested in gigacycle fatigue region. In contrary to conventionalgrain size copper, the appearance of cyclic slip bands is quite rare and surface relief does notform well below the fatigue limit. The cyclic slip bands develop in regions of near-by orientedgrains, where the neighbouring grains have very simmilar disorientation. Length of the cyclicslip bands substantially exceeds the average grain size of UFG Cu. No grain coarsening due tocycling was observed. Development of damage, which finally results in fatigue crack initiation,was observed below the surface relief.

Highlights

Fatigue properties of conventional grain (CG) size materials in low- and high-cycle region has been studied very extensively since a long time
It was observed that cyclic slip markings appear on the surface since certain value of the stress amplitude
The specimen was loaded at first with the stress amplitude of 100 MPa for 1×1010 cycles and after observation of the polished surface by scanning electron microscope (SEM) the loading was continued at the higher stress amplitude of 120 MPa for 8.64×109 cycles

Summary

Introduction

Fatigue properties of conventional grain (CG) size materials in low- and high-cycle region has been studied very extensively since a long time. Fatigue properties in gigacycle region (alternatively called ultrahigh-cycle or very high cycle region) have been studied to substantially lesser extent, though fatigue failure of engineering components may appear after a number of cycles of 1010 or even higher [15]. To the second Type II belong materials containing microstructural heterogeneities; highstrength bearing steels are an example. These two types differ by mechanism of fatigue crack initiation. In the case of the Type I materials, fatigue loading in gigacycle region causes surface roughening and subsequent persistent slip band or cyclic slip marking formation, followed by fatigue crack initiation.

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