Abstract
Different loading protocols have been developed in the past to investigate the creep properties of materials using instrumented indentation testing technique. Recently, a new indentation creep method was presented, in which the contact pressure is kept constant during the creep test segment, similar to the constant stress applied in a uniaxial creep experiment. In this study, the results of constant contact pressure creep tests are compared to uniaxial and constant load hold indentation creep experiments on ultrafine grained Cu and CuAl5. The constant contact pressure method yields similar stress exponents as the uniaxial tests, down to indentation strain rates of 10–6 s−1, whereas the constant load hold method results mainly in a relaxation of the material at decreasing applied pressures. Furthermore, a pronounced change in the power law exponent at large stress reductions is found for both uniaxial and constant contact pressure tests, indicating a change in deformation mechanism of ultrafine grained metals.Graphical abstract
Highlights
Creep properties have been determined for a long time with standardized, macroscopic test methods (e.g. [1,2,3])
The CCP test procedure consists of two test segments, the initial loading with a constant indentation strain rate and the subsequent creep segment where the contact pressure is kept constant
Different contact pressures have been applied by varying the ratio of P/S2, where the partial unloading at the beginning of the CCP segment was done in a single step
Summary
Creep properties have been determined for a long time with standardized, macroscopic test methods (e.g. [1,2,3]). Creep properties have been determined for a long time with standardized, macroscopic test methods Macroscopic creep testing methods require relatively large sample volumes, which is critical for the analysis of the creep response in small volumes of e.g. thin coatings [4]. The small volume probed allows the mechanical properties of individual microstructure components or thin films to be investigated [5, 6]. Various indentation creep and relaxation test procedures have been developed for investigating the local, time-dependent mechanical properties. These test procedures promise to provide results comparable to macroscopic tests [7,8,9,10,11,12,13,14]. A direct comparison of macroscopic and indentation loading protocols reveals significant differences
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