Elevated temperature, micro-compression transient plasticity tests on nanocrystalline Palladium-Gold: Probing activation parameters at the lower limit of crystallinity

Wehrs, Juri; Deckarm, Michael Johannes; Wheeler, Jeffrey M.; Maeder, Xavier; Birringer, R.; Mischler, S.; Michler, Johann

doi:10.1016/j.actamat.2017.02.045

Cited by 13 publications

(5 citation statements)

References 57 publications

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“…However, studies of rate sensitivity at a given temperature as well as creep/relaxation testing at the extremes of slow rates/long times are often of interest, either where not enough measurements can be taken in a specific temperature regime to extract a gradient or where creep mechanisms are of interest. [42,[73][74][75][76] Strain rate jump tests and creep/ relaxation hold segments may therefore be employed in microcompression in a similar way to macroscopic testing (Fig. 9).…”

Section: Thermal Activation Of Plasticitymentioning

confidence: 99%

Microcompression of brittle and anisotropic crystals: recent advances and current challenges in studying plasticity in hard materials

Korte‐Kerzel

2017

MRS Communications

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Recent years have seen an increased application of small-scale uniaxial testing-microcompression-to the study of plasticity in macroscopically brittle materials. By suppressing fast fracture, new insights into deformation mechanisms of more complex crystals have become available, which had previously been out of reach of experiments. Structurally complex intermetallics, metallic compounds, or oxides are commonly brittle, but in some cases extraordinary, though currently mostly unpredictable, mechanical properties are found. This paper aims to give a survey of current advances, outstanding challenges, and practical considerations in testing such hard, brittle, and anisotropic crystals.While the origin of mechanical strength, toughness, and creep resistance is well studied in most metals, much less is known about the properties of more complex crystal structuresdespite their wide use as reinforcement phases and the undiscovered potential in their sheer number and variability. A major challenge in plasticity research of the next years will therefore be to close this gap in knowledge. Small-scale testing techniques have been demonstrated as a key enabling technique for such studies. Most prominent is microcompression, which helps overcome the fundamental challenge of studying plasticity in materials, which suffer from extreme brittleness in conventional testing. [1,2] Their plastic properties may, at first glance, appear to be of only academic interest: aiming to deduce fundamental relationships of crystal plasticity and structure to enable knowledge-guided search and data mining for new structural materials. However, they are in fact essential to performance at the microstructural scale of many advanced and highly alloyed materials and to understanding the effects of alloying strategies aimed at inducing deformability as baseline or reference information. Investigating plasticity in hard crystalsA deep understanding of plasticity and dislocation motion exists in most metallic crystals and strategies to engineer different aspects, for example by adjustment of the stacking fault energy, have been very successful. [3,4] These are being applied-with great effect-to hexagonal metals [3] which in spite of their closely related atomic packing show strongly anisotropic deformation and are therefore much more difficult to deform at low temperatures. In BCC metals, fundamental aspects of dislocation core structure, stress tensor dependence, and resulting non-Schmid behavior, are also still under investigation. [5,6] However, in all of these materials, the availability of large-grained or single crystals with sufficient purity has scarcely been a problem, nor has the ability to deform such samples under carefully controlled conditions. Suitable investigations by conventional, analytical and high-resolution microscopy techniques have also been carried out whenever new methods have allowed researchers to dive deeper into the physics of their plastic deformation.In intermetallics, ceramics, and compounds we face challeng...

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Section: Thermal Activation Of Plasticitymentioning

confidence: 99%

Microcompression of brittle and anisotropic crystals: recent advances and current challenges in studying plasticity in hard materials

Korte‐Kerzel

2017

MRS Communications

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“…Typical stress-strain behavior was observed on a preliminary micropillar compression test to establish the strain necessary for plastic deformation to begin and determine how long each strain rate should be applied between the strain rate jumps. In general, the transients were not as sharp as those observed in other material systems [21,29], so at most four SRJs could be performed for a given micropillar. Strain rate sensitivity is observed for both 5-and 50-nmthick layers, though it is more pronounced in the 5nm layers.…”

Section: Mechanical Testing-micropillar Compressionmentioning

confidence: 75%

Elevated and cryogenic temperature micropillar compression of magnesium–niobium multilayer films

et al. 2019

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The mechanical properties of multilayer films consisting of alternating layers of magnesium and niobium are investigated through micropillar compression experiments across a broad range of temperatures. The data collected from the variable temperature micropillar compression tests and strain rate jump tests are used to gain insight into the operative deformation mechanisms within the material. At higher temperatures, diffusion-based deformation mechanisms are shown to determine the plastic behavior of the multilayers. Diffusion occurs more readily along the magnesium-niobium interface than within the bulk, acting as pathway for magnesium diffusion. When individual layer thicknesses are sufficiently small, diffusion can remain the dominant deformation mechanism down to room temperature. Multilayer strengthening models historically rely solely on dislocation-based arguments; therefore, consideration of diffusion-based deformation in nanolaminates with low melting temperature components offers improved understanding of multilayer behavior.

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“…Besides nanoindentation, which always represents a multiaxial loading situation, uniaxial micropillar compression experiments can also be used to examine thermally activated deformation parameters on a very local scale, using, for example, creep, 76 jump, 73 or stress relaxation tests. 77 Wehrs et al 12 , 78 demonstrated that the different protocols for the same material lead to comparable results. Finally, also bulge test techniques were modified regarding a reliable testing of SRS.…”

Section: Experimental Possibilities and Challenges: Development Of Admentioning

confidence: 99%

Advanced Nanoindentation Testing for Studying Strain-Rate Sensitivity and Activation Volume

Maier–Kiener

Durst

2017

JOM

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Nanoindentation became a versatile tool for testing local mechanical properties beyond hardness and modulus. By adapting standard nanoindentation test methods, simple protocols capable of probing thermally activated deformation processes can be accomplished. Abrupt strain-rate changes within one indentation allow determining the strain-rate dependency of hardness at various indentation depths. For probing lower strain-rates and excluding thermal drift influences, long-term creep experiments can be performed by using the dynamic contact stiffness for determining the true contact area. From both procedures hardness and strain-rate, and consequently strain-rate sensitivity and activation volume can be reliably deducted within one indentation, permitting information on the locally acting thermally activated deformation mechanism. This review will first discuss various testing protocols including possible challenges and improvements. Second, it will focus on different examples showing the direct influence of crystal structure and/or microstructure on the underlying deformation behavior in pure and highly alloyed material systems.

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Elevated temperature, micro-compression transient plasticity tests on nanocrystalline Palladium-Gold: Probing activation parameters at the lower limit of crystallinity

Cited by 13 publications

References 57 publications

Microcompression of brittle and anisotropic crystals: recent advances and current challenges in studying plasticity in hard materials

Microcompression of brittle and anisotropic crystals: recent advances and current challenges in studying plasticity in hard materials

Elevated and cryogenic temperature micropillar compression of magnesium–niobium multilayer films

Advanced Nanoindentation Testing for Studying Strain-Rate Sensitivity and Activation Volume

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