Rate-dependent indentation size effect on hardness and creep behavior of a titanium metallization film on alumina substrate

Abstract

Nanoindentation tests were performed at room temperature to investigate the indentation size effect (ISE) and creep behavior of a titanium metallization film on alumina substrate. The ISE of hardness was examined at different loading strain rate (LSR). The effects of LSR and penetrating depth on nanoindentation creep were evaluated at the steady creep state. Inverse ISE in titanium film was observed at indentation depth below 200 nm while normal ISE was observed at penetrating depth ranging from 200 nm to 1000 nm. Elastic contact theory and strain gradient plasticity theory were applied to interpret the variation trends of hardness respectively. In addition, the intrinsic hardness and characteristic length were found to be strongly dependent on LSR. Except for creep strain rate, creep displacement and creep stress exponent showed relatively conspicuous correlations to LSR and/or penetrating depths.

Keywords

• Indentation size effect
• Creep
• Strain rate sensitivity
• Film/substrate system