Influence of indentation size and spacing on statistical phase analysis via high-speed nanoindentation mapping of metal alloys

Hossein Besharatloo,Jeffrey M Wheeler

doi:10.1557/s43578-021-00214-5

Hossein Besharatloo, Jeffrey M Wheeler

Open Access

https://doi.org/10.1557/s43578-021-00214-5

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Abstract

The development of high-speed nanoindentation has enabled the acquisition of mechanical property maps over square millimeters of area with micron-scale resolution in reasonable amounts of time. This provides rich datasets which contain morphological and statistical data on the variation of mechanical properties in a microstructure. However, the influences of the indentation size and the deconvolution method employed on the extracted phase properties remain unclear. In this work, a range of depth/spacing increments was explored on two different materials systems, an Al-Cu eutectic alloy and a duplex stainless steel, representing an ‘easy’ and a ‘hard’ case for statistical deconvolution, respectively. A total of ~ 500,000 indentations were performed. A variety of statistical analyses were then employed and compared: the 1D analysis of Ulm et al. using 2 and 3 phases, a 2D rotated Gaussian fit, K-means clustering, and a visual comparison to 2D histograms. This revealed several different sensitivities of the deconvolution methods to various types of error in phase identification.Graphic abstract

Highlights

The development of instrumented nanoindentation coupled with the Oliver and Pharr analysis [1] in the 1990s allowed a new era of automated, local mechanical property measurement
Conventional nanoindentation testing was performed on each individual phase of the investigated samples
These results are consistent with those recently observed on an Al–Cu diffusion couple investigated by the same methods [24]

Summary

Introduction

The development of instrumented nanoindentation coupled with the Oliver and Pharr analysis [1] in the 1990s allowed a new era of automated, local mechanical property measurement. Indentation mapping, or cartography, considers the variation of the measured properties over a two-dimensional surface, whereas statistical extraction assumes a number of discrete phases and fits their distributions within a property space to determine the fraction, average value, and variation of each separate, constitutive phase while ignoring the positions of the indents in the Cartesian surface. Both of these techniques required a significant amount of experimental time due to the large numbers of indents required. This makes both techniques simultaneously more accessible and more popular with numerous applications emerging in the recent literature on a variety of materials: cements [8, 9], hardmetals [6, 10, 11], Ni–Fe meteorites [12], titanium [13], duplex [14] and tool steels [15], and thermal barrier coatings [16]

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Discussion

Conclusion