Hall–Petch revisited

Saada, G.

doi:10.1016/j.msea.2005.02.091

Cited by 85 publications

(54 citation statements)

References 17 publications

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“…The hardness, unlike the Young modulus, is more sensitive to the microstructure, as suggested by some deformation models of nanoindentation [33,34] and by the Hall-Petch relationship [35]. In 316L thin film (F0- Figure 5) the hardness is higher than the one of the bulk 316L which can be attributed to the smaller grain size [35].…”

Section: Resultsmentioning

confidence: 96%

Nanoindentation of functionally graded hybrid polymer/metal thin films

Piedade¹

2013

Applied Surface Science

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Hybrid functionally graded coatings (2D-FGC) were deposited by magnetron co-sputtering from poly(tetrafluoroethylene) (PTFE) and AISI 316L stainless steel (316L) targets. The carbon and fluorine content varied from 7.3 to 23.7 at.% and from 0 to 57 at.%, respectively.The surface modification was developed to change the surface of 316L vascular stents in order to improve the biocompatibility of the outmost layer of the metallic biomaterial. Indepth XPS analysis revealed the presence of a graded chemical composition accompanied by the variation of the film structure. These results were complemented by those of transmission electron microscopy (TEM) analysis that highlighted the nanocomposite nature of the coatings.The nanomechanical characterization of 2D-FGC was performed by nanoindentation at several loads on the thin films deposited onto two different steel substrates: 316L and AISI M2. The study allowed establishing 0.7 mN as the load that characterized the coatings without substrate influence. Both hardness and Young modulus decrease with the increase of fluorine content due to the evolution in chemical composition, chemical bonds and structure.

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Section: Resultsmentioning

confidence: 96%

Nanoindentation of functionally graded hybrid polymer/metal thin films

Piedade¹

2013

Applied Surface Science

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“…[21,22] If one assumes that in a nanocrystalline metal all macroscopic plasticity is carried by dislocations emitted from, and subsequently absorbed in, GBs, [23,24] only 4 % of the grains would have deformed plastically at the 0.2 % yield stress. [25] In other words, a nanocrystalline structure deforms more heterogeneously than a coarse-grained polycrystal.In the present work we show, through analysis of X-ray diffraction (XRD) spectra measured during in situ deformation of nanocrystalline and ultrafine-grained Ni, that the amount of strain assigned to microplasticity can significantly exceed the usual 0.2 % definition of the macroscopic yield stress when grain sizes reach the nanometer range.XRD profile analysis is a well-known technique for microstructural analysis, where the broadening of the diffraction peaks result from limitations in the spatial extent of the coherent scattering volumes (in our case, the grain size) and the presence of inhomogeneous strain. The first type of broadening is diffraction-order independent, whereas the second is order dependent.…”

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confidence: 99%

From Micro‐ to Macroplasticity

Brandstetter¹,

Swygenhoven²,

Petegem³

et al. 2006

Advanced Materials

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Early results of experimental investigations on microplasticity have been gathered into collected works and treatises. [1][2][3] The plastic events taking place at lower strains are related to short-range dislocation motion [4] and are of different origin than the dislocation mechanism occurring in the macroplastic regime.[5] Therefore, macroplasticity theories based on a mechanism involving long-range dislocation motion cannot serve to predict micro-yielding. In terms of measured stressstrain behavior, the two regimes are poorly distinguished, especially when they are characterized by positive strain-hardening, i.e., an increase in strength when the microstructure is strained. To facilitate comparison of data, metallurgists have come up with the rather arbitrary 0.2 % definition of the macroscopic yield stress. [6,7] It is one of the most frequently used engineering materials parameters and very important for the precise design of functional components ranging from construction materials down to micrometer-sized microelectromechanical (MEMS) devices. In polycrystalline materials, it is taken for granted that the majority of grains are plastically deforming at the macroscopic yield stress. However, there is no easy and suitable method to verify this assumption, and the real amount of strain that should be assigned to microplasticity is unknown. Experimental studies on granular materials have predominantly been performed by precise mechanical testing using load-unload cycles accompanied by surface-visualization techniques. The first experimental investigations on the effect of grain size on microplasticity [8,9] ascribed strain-hardening predominantly to the ability of grain boundaries (GBs) to act as barriers to dislocation motion, where the strain for a given stress varied as the cube of the grain size: large grains showed more strain than smaller grains. However, it was soon recognized that the relationship between microplastic strain and stress was not so simple. When a polycrystal is subjected to an external force, an inhomogeneous state of internal stress is developed resulting from elastic anisotropy and plastic incompatibilities arising from different resolved shear stresses within the different grains. [10] In addition to the fact that plastic yielding does not start at the same time in all grains, it was recognized that internal stresses arising from the elastic interactions of neighboring grains provide additional stresses that activate non-favored slip systems in grain interiors [11] and/or change the maximum shear direction in the vicinity of a GB. The latter may result in GBs emitting dislocations [12,13] on slip systems in the GB region that are different from the primary slip system of the grain interior. [14,15] Several plasticity models have been developed to predict the mechanical behavior in terms of stress-strain and hardening as a function of grain size. Some theories are based on the postulate that geometrically necessary dislocations account for the inherent difference in the accumulation o...

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“…The physical reason of improved mechanical properties lies in the higher grain boundary volume in fine-grained structures, which makes the dislocation motion and resulting plastic deformation more difficult. For many materials the yield stress follows the Hall-Petch equation in a very broad range of grain size between 1 μm and 1 mm (Saada, 2005). Deviations from this law are observed only for very coarse grained and for nano-grained structures.…”

Section: Ultrafine-grained Coppermentioning

confidence: 98%

Mechanical Properties of Copper Processed by Severe Plastic Deformation

Kunz¹

2012

Copper Alloys - Early Applications and Current Performance - Enhancing Processes

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Hall–Petch revisited

Cited by 85 publications

References 17 publications

Nanoindentation of functionally graded hybrid polymer/metal thin films

Nanoindentation of functionally graded hybrid polymer/metal thin films

From Micro‐ to Macroplasticity

Mechanical Properties of Copper Processed by Severe Plastic Deformation

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