Investigations on indentation size effects using a pile-up corrected hardness

Abstract

Indentation size effects (ISEs) become severe in the nanoindentation regime because various influencing factors become active in a very shallow indentation regime. Additionally, the general analysis on the nanoindentation curve yields hardness overestimation because it cannot take into account material pile-up around contacts. Thus we tried to investigate intrinsic ISEs in monolithic materials by proposing a new hardness measurement method; the load-supporting contact boundary was approximated as the peak trajectory around an impression and analysed by a radial differentiation of the remnant indent morphology. Dependence of the new load-off hardness on the indentation depth was investigated for (1 0 0) tungsten single crystal and fused quartz. The contribution of the material pile-up to the new hardness was clearly modified but more significant hardness increase appeared at a very shallow indentation regime due to severe elastic recovery. These phenomena are discussed with the strain-gradient plasticity model.