Nanoindentation Response Analysis of Thin Film Substrates-II: Strain Hardening-Softening Oscillations in Subsurface Layer

Abstract

We have extracted stress-strain field (SSF) gradient and divergence representations from nanoindentation data sets of bulk solids often used as thin film substrates: bearing and tooling steels, silicon, glasses, and fused silica. Oscillations of the stress-strain field gradient and divergence induced in the subsurface layer by the nanoindentation have been revealed. The oscillations are especially prominent in single indentation tests at shallow penetration depths, h<100 nm, whereas they are concealed in the averaged datasets of 10 and more single tests. The amplitude of the SSF divergence oscillations decays as a sublinear power-law when the indenter approaches deeper atomic layers, with an exponent -0.9 for the steel and -0.8 for the fused silica. The oscillations are interpreted as alternating strain hardening-softening plastic deformation cycles induced in the subsurface layer under the indenter load.

Nanoindentation Response analysis of Thin Film Substrates-I: Strain Gradient-Divergence Approach

“…Perfectly smooth Si(100) sample was chosen as a material with single crystal structure and well-known mechanical properties to validate the strain gradient-divergence approach developed above. Further results on the steel samples and fused silica, as well as a quantitative treatment of the oscillations are provided in the second part of the present research [10].…”

“…Therefore, it was important to analyse single indentation test datasets prior to any smoothening and averaging. Further applications of the strain gradient-divergence analysis approach to several steel, glass and fused silica samples, which are chosen as representative materials of bulk solids commonly used as substrates for thin film deposition, are demonstrated in the second part of the present research [10].…”

“…We show the strain gradientdivergence analysis results of the nanoindentation response of a bulk solid silicon sample. Further application to bulk samples of various thin film substrates, such as different types of bearing and tooling steels as well as fused silica, is presented in the second part of the present research [10].…”

Toward an Instrumented Strength Microprobe – Origins of the Oliver-Pharr Method and Continued Advancements in Nanoindentation: Part 2

“…While Siu and Ngan continued to build upon their 2013 research elsewhere [17,18], other researchers garnered a maintained interest in the topic [19][20][21] [26].…”