Investigations of orientation and length scale effects on micromechanical responses in polycrystalline zirconium using spherical nanoindentation

Abstract

Here we investigate the elastic and plastic anisotropy of hexagonal materialsas a function of crystal orientation using a high-throughput approach (spherical nanoindentation). Using high purity zirconium as a specific example, we demonstrate the differences in indentation moduli, indentation yield strengths and indentation post-elastic hardening rates over multiple grain orientations. These results are validated against bulk single crystal measurements, as well as data from cubic materials. By varying the indenter size (radius), we are also able to demonstrate indentation size effects in © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ Scripta Materialia 2 hexagonal materials, including possible signatures of strain hardening due to twin formation in the nanoindentation stress-strain curves. Text:Nanomechanical testing techniques, such as nanoindentation [1-3], micropillar compression and tension [4,5], as well as three point bend and cantilever bend techniques [6][7][8], have been used for the past couple of decades to probe small volumes of material of the order of 1 μm 3 or smaller. In techniques other than nanoindentation, preparation of miniaturized tensile and compression samples is typically carried out in bulk materials using Focused Ion Beam (FIB) milling, a time consuming technique that runs the risk of ion beam damage to the sample [9,10]. Nanoindentation, on the other hand, provides copious amounts of mechanical data from extremely small volumes of material while only requiring a flat polished surface [11]. Much work has also been carried out over the past few years to obtain stress-strain curves using a spherical nanoindentation approach [2,[11][12][13]. This technique can transform the raw loaddisplacement data into meaningful indentation stress-strain curves that capture the local loading and unloading elastic moduli, local indentation yield strengths, and post-yield strain hardening behavior.As such, spherical nanoindentation represents a highthroughput technique that can amass enormous amounts of grain-level data from one polycrystalline sample.Early work utilizing this technique focused largely on orientation dependent local (grain-scale) mechanical responses in relatively low anisotropy cubic systems such as

High Throughput Assays for Additively Manufactured Ti-Ni Alloys Based on Compositional Gradients and Spherical Indentation

“…The indentation work hardening rate, H ind , is computed from the indentation stress-strain curve between 0.5 and 2% offset plastic strains using a linear regression fit [7,11].…”

“…If the indentation length scales are well below the typical grain size, relevant microstructure attributes would include the grain orientation and local dislocation density in the indented zone [7,10,36,37]. If the indentation zone cover several grains, the relevant microstructure features might include grain size, shape, and orientation distributions in the indented zones [7].…”

“…In this regard, recent advances in spherical indentation stress-strain protocols [6][7][8][9][10][11][12][13] offer many advantages. The conventional practices in indentation testing rely on sharp indenters and analyze the unloading segments after imposing substantial amounts of indentation loads (or depths) to arrive at estimates of modulus and hardness [14][15][16].…”

New Insights into the Microstructural Changes During the Processing of Dual-Phase Steels from Multiresolution Spherical Indentation Stress–Strain Protocols

“…An example indentation stress-strain curve extracted using the above protocols presented in Figure 3c. The spherical nanoindentation stress-strain protocols described above have been validated extensively in both experiments [53][54][55][56][57][58][59][60][61] and numerical simulations (performed using finite element models) [96][97][98][99]. As a result of these prior validations, we are now fairly confident in obtaining highly reproducible indentation stress-strain curves on a broad variety of material samples.…”

“…The large variations in the reported hardness data have hindered attempts aimed at extracting quantitative physical insights that could guide the rational design of DP process histories to achieve desirable combinations of bulk properties. In recent work [53][54][55][56][57][58][59][60][61], it has been demonstrated that indentation yield strength is a much more reproducible and reliable measure of the intrinsic plastic strength of the microscale constituents in a heterogeneous material, and could be estimated from the recently established spherical indentation stress-strain protocols [62,63]. Using this analysis method, it has been shown [57] that the indentation yield strength is very sensitive to The discussion above points out the difficulties encountered in the optimization of the processing of DP steels to meet the desired combination of properties [1,35,36].…”