In situ nanocompression testing of irradiated copper
TL;DR: It is shown that yield strengths approaching macroscopic values are measured from irradiated ~400 nm diameter copper specimens, and it is concluded that nano-scale in situ testing can determine bulk-like yield strengths and simultaneously identify deformation mechanisms.
Abstract: Increasing demand for energy and reduction of carbon dioxide emissions has revived interest in nuclear energy Designing materials for radiation environments necessitates a fundamental understanding of how radiation-induced defects alter mechanical properties Ion beams create radiation damage efficiently without material activation, but their limited penetration depth requires small-scale testing However, strength measurements of nanoscale irradiated specimens have not been previously performed Here we show that yield strengths approaching macroscopic values are measured from irradiated ~400 nm-diameter copper specimens Quantitative in situ nanocompression testing in a transmission electron microscope reveals that the strength of larger samples is controlled by dislocation-irradiation defect interactions, yielding size-independent strengths Below ~400 nm, size-dependent strength results from dislocation source limitation This transition length-scale should be universal, but depends on material and irradiation conditions We conclude that for irradiated copper, and presumably related materials, nanoscale in situ testing can determine bulk-like yield strengths and simultaneously identify deformation mechanisms
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TL;DR: In this paper, the authors summarized and analyzed the current understandings on the influence of various types of internal defect sinks on reduction of radiation damage in primarily nanostructured metallic materials, and partially on nanoceramic materials.
288 citations
TL;DR: In this paper, the challenges of instrumented micro-and nanomechanical testing at elevated temperature are summarized and a special focus is laid on the pitfalls of micro-compression testing with its stringent boundary conditions often hampering reliable experiments.
260 citations
TL;DR: A review of the recent progress made in this respect in extracting meaningful indentation stress-strain curves from the raw datasets measured in instrumented spherical nanoindentation experiments can be found in this article.
Abstract: Although indentation experiments have long been used to measure the hardness and Young's modulus, the utility of this technique in analyzing the complete elastic–plastic response of materials under contact loading has only been realized in the past few years – mostly due to recent advances in testing equipment and analysis protocols. This paper provides a timely review of the recent progress made in this respect in extracting meaningful indentation stress–strain curves from the raw datasets measured in instrumented spherical nanoindentation experiments. These indentation stress–strain curves have produced highly reliable estimates of the indentation modulus and the indentation yield strength in the sample, as well as certain aspects of their post-yield behavior, and have been critically validated through numerical simulations using finite element models as well as direct in situ scanning electron microscopy (SEM) measurements on micro-pillars. Much of this recent progress was made possible through the introduction of a new measure of indentation strain and the development of new protocols to locate the effective zero-point of initial contact between the indenter and the sample in the measured datasets. This has led to an important key advance in this field where it is now possible to reliably identify and analyze the initial loading segment in the indentation experiments. Major advances have also been made in correlating the local mechanical response measured in nanoindentation with the local measurements of structure at the indentation site using complementary techniques. For example, it has been shown that the combined use of Orientation Imaging Microscopy (OIM, using Electron BackScattered Diffraction (EBSD)) and nanoindentation on polycrystalline metallic samples can yield important information on the orientation dependence of indentation yield stress, which can in turn be used to estimate percentage increase in the local slip resistance in deformed samples. The same methods have been used successfully to probe the intrinsic role of grain boundaries in the overall mechanical deformation of the sample. More recently, these protocols have been extended to characterize local mechanical property changes in the damaged layers in ion-irradiated metals. Similarly, the combined use of Raman spectroscopy and nanoindentation on samples of mouse bone has revealed tissue-level correlations between the mineral content at the indentation site and the associated local mechanical properties. The new protocols have also provided several new insights into the buckling response in dense carbon nanotube (CNT) brushes. These and other recent successful applications of nanoindentation are expected to provide the critically needed information for the maturation of physics-based multiscale models for the mechanical behavior of most advanced materials. In this paper, we review these latest developments and identify the future challenges that lie ahead.
254 citations
TL;DR: It is observed that both frequently discussed mechanisms, truncation of spiral dislocation sources and exhaustion of defects available within the specimen, contribute to high strengths and related size-effects in small volumes, suggesting that in the submicrometer range these mechanisms should be considered simultaneously rather than exclusively.
Abstract: A unique method for quantitative in situ nano- tensile testing in a transmission electron microscope employing focused ion beam fabricated specimens was developed. Experi- ments were performed on copper samples with minimum dimensions in the 100200 nm regime oriented for either single slip or multiple slip, respectively. We observe that both frequently discussed mechanisms, truncation of spiral disloca- tion sources and exhaustion of defects available within the specimen, contribute to high strengths and related size-effects insmallvolumes.Thissuggeststhatinthesubmicrometerrange these mechanisms should be considered simultaneously rather than exclusively.
213 citations
TL;DR: In this article, a review article summarizes the results of previous studies in this rapidly-developing field, attempting to provide a new perspective in expounding the connection between macroscopic properties and micro-mechanisms.
193 citations
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TL;DR: In this paper, the authors used a Berkovich indenter to determine hardness and elastic modulus from indentation load-displacement data, and showed that the curve of the curve is not linear, even in the initial stages of the unloading process.
Abstract: The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
22,557 citations
TL;DR: Measurements of plastic yielding for single crystals of micrometer-sized dimensions for three different types of metals find that within the tests, the overall sample dimensions artificially limit the length scales available for plastic processes.
Abstract: When a crystal deforms plastically, phenomena such as dislocation storage, multiplication, motion, pinning, and nucleation occur over the submicron-to-nanometer scale. Here we report measurements of plastic yielding for single crystals of micrometer-sized dimensions for three different types of metals. We find that within the tests, the overall sample dimensions artificially limit the length scales available for plastic processes. The results show dramatic size effects at surprisingly large sample dimensions. These results emphasize that at the micrometer scale, one must define both the external geometry and internal structure to characterize the strength of a material.
2,113 citations
TL;DR: In this article, a constitutive expression for the twinning stress in BCC metals is developed using dislocation emission from a source and the formation of pile-ups, as rate-controlling mechanism.
1,366 citations
TL;DR: In this article, the effects of size on predominantly mechanical properties of materials are reviewed at a first-order level, and important aspects can be understood from the point of view of the interaction of a characteristic length (which may be as diverse as the dislocation radius of curvature at a given stress or the magnetic exchange length) with a size parameter (grain or particle size, or film thickness).
1,068 citations
"In situ nanocompression testing of ..." refers background in this paper
...It is well known that the smallest internal structural element can provide a characteristic length-scale determining the strength of a materia...
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