The indentation size effect of single-crystalline tungsten revisited

Jin Wang,Tillmann Volz,Sabine M Weygand,Ruth Schwaiger

doi:10.1557/s43578-021-00221-6

Abstract

In this study, we have investigated the indentation size effect (ISE) of single crystalline tungsten with low defect density. As expected, the hardness shows a pronounced increase with decreasing indentation depth as well as a strong strain rate dependence. For penetration depths greater than about 300 nm, the ISE is well captured by the Nix–Gao model in the context of geometrically necessary dislocations. However, clear deviations from the model are observed in the low depth regime resulting in a bilinear effect. The hardness behavior in the low depth regime can be modeled assuming a non-uniform spacing of the geometrically necessary dislocations. We propose that the bilinear indentation size effect observed reflects the evolution of the geometrically necessary dislocation density. With increasing strain rate, the bilinear effect becomes less pronounced. This observation can be rationalized by the activation of different slip systems.Graphic abstract

Highlights

The indentation size effect (ISE) describes the observation that the hardness of a material increases as the size of an indent decreases [1]
The effective strain rate was determined as 0.033 s− 1 [8], which results in the smaller hardness values compared to the other data at the indentation strain rate of 0.05 s− 1 [8, 9]
Nanoindentation experiments were conducted on (001) and (112) tungsten single crystals using different indentation methods to study the indentation size effect. Both crystal orientations exhibit a significant bilinear behavior of H2 versus 1/h, which was observed over a range of different indentation strain rates

Summary

Introduction

The indentation size effect (ISE) describes the observation that the hardness of a material increases as the size of an indent decreases [1]. The ISE has been known for many years, mostly noticed in crystalline materials with low defect density indented with pyramidal indenters, and becomes important at depths below 1 μm. It has been observed for a range of different materials, e.g., Cu, Ag, Ir, MgO and W [2,3,4,5,6,7,8,9,10]. We will briefly summarize its main ideas

Methods

Results

Conclusion