**Xiazi Xiao 1, Hao Liu <sup>2</sup> and Long Yu 3,\***


Received: 7 September 2020; Accepted: 2 October 2020; Published: 3 October 2020

**Abstract:** In a recent experimental study of indentation creep, the strain rate sensitivity (SRS) and activation volume *v*∗ have been noticed to be dependent on the indentation depth or loading force for face-centered cubic materials. Although several possible interpretations have been proposed, the fundamental mechanism is still not well addressed. In this work, a scaling law is proposed for the indentation depth or loading force-dependent SRS. Moreover, *v*∗ is indicated to scale with hardness *H* by the relation ∂ ln(*v*∗ /*b*3)/<sup>∂</sup> ln *<sup>H</sup>* = <sup>−</sup>2 with the Burgers vector *<sup>b</sup>*. We show that this size effect of SRS and activation volume can mainly be ascribed to the evolution of geometrically necessary dislocations during the creep process. By comparing the theoretical results with different sets of reported experimental data, the proposed law is verified and a good agreement is achieved.

**Keywords:** indentation creep; size effect; strain rate sensitivity; activation volume; geometrically necessary dislocations
