Abstract
Instrumented indentation of a high purity Fe surface with unresolved surface deformation due to mechanical polishing is compared to the same grain surface annealed at increasing time and temperature. The differences in indentation size effect behavior with annealing are correlated with hardness and electron backscatter diffraction measurements as independent measures of surface layer deformation. It is found that the Nix Gao plot evolves from non-linear (bilinear) towards the predicted linear relationship as the surface deformation is removed. The experimental observations are rationalized by inclusion of a depth dependent, polishing induced forest dislocation density within the Nix-Gao model.
Highlights
The indentation size effect has been studied for variety of materials reporting significant variation in hardness as a function of depth [1,2,3]
This paper examines the effect of surface deformation induced by polishing can have on Nix-Gao non-linearity, noting that mechanical polishing introduces ‘forest dislocations’ (FD), which will be in addition to the statistically stored dislocations (SSD) and geometrically necessary dislocations (GND)’s required for accommodation of indentation plasticity
It is observed from the load-depth (P-h) curves in Fig. 1 and averaged hardness vs depth (H-h) profile plots in figure 2 that the hardness for the as polished sample is significantly greater than that for the partially or fully annealed samples
Summary
The indentation size effect has been studied for variety of materials reporting significant variation in hardness as a function of depth [1,2,3]. To explain mechanism responsible for the indentation size effect, various strain gradient plasticity [4,5] and mechanistic models [6,7,8] have been proposed. Nix and Gao [6] proposed, arguably the most widely accepted mechanistic model, based on geometrically necessary dislocations (GND) required for the indentation plastic shape change and statistically stored dislocations (SSD) due to the indentation characteristic strain [6]. To explain decreasing hardness with increasing depth, this model proposes that GND have an increase in spacing as the indentation depth increases.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
