Abstract

The lifetime of cyclically loaded devices is often limited by the fatigue resistance of their individual phases. An advanced method is presented for measuring the high-cycle fatigue behavior of materials at the micrometer scale using a nanoindenter. It is based on the cyclic deflection of focused ion beam-fabricated microcantilevers using the continuous stiffness method (CSM). In line with experimental data on bulk nanocrystalline copper, the specimens exhibit grain coarsening followed by the formation of extrusions and a fatigue strength exponent of −0.10. The method is suitable for characterizing single phases and individual components of further complex systems

Highlights

  • Many modern alloys consist of at least two different phases, such as ferrite and cementite in steel, or a layered architecture, such as in TiAl

  • Reliable cyclic methods are available for thin film testing[8,9,10] or for custom MEMS,[11] but the knowledge obtained from these specific objects cannot be extrapolated to any 3D structure

  • The low strain-hardening trend is consistent with the literature on equal channel angular pressing (ECAP) copper.[26,27]

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Summary

Introduction

Many modern alloys consist of at least two different phases, such as ferrite and cementite in steel, or a layered architecture, such as in TiAl. The top surface of the cantilevers remains in pure tension during cyclic testing, while a stress gradient reaching from tension to compression develops throughout their thickness, see Fig. 1. The low strain-hardening trend is consistent with the literature on ECAP copper.[26,27] The postmortem micrographs [Fig. 2(c)] show that the deformation is localized at the root of the cantilever, as the highest stresses are present there [see Eq (1)].

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