Review on superior strength and enhanced ductility of metallic nanomaterials

A review of predictive nonlinear theories for multiscale modeling of heterogeneous materials

https://escholarship.org/content/qt9jj8t067/qt9jj8t067.pdf?t=mj53rl

On the effect of deep-rolling and laser-peening on the stress-controlled low- and high-cycle fatigue behavior of Ti-6Al-4V at elevated temperatures up to 550 C

As a carrier of deformation information, the speckle pattern, or more exactly the random intensity distributions, which could be naturally occurred or artificially fabricated onto test samples’ surface, plays an indispensable role in digital image correlation (DIC). It is now well recognized that the accuracy and precision in DIC measurements not only rely on correlation algorithms, but also depend highly on the quality of the speckle pattern. Considering the huge diversity in test materials, spatial scales and experimental conditions, speckle pattern fabrication could be a challenging issue facing DIC practitioners. To obtain good speckle patterns suitable for DIC measurements, some key issues of fabrication methods and quality assessment of speckle patterns must be well addressed. To this end, this review systematically presents the speckle pattern classification and fabrication techniques for various samples and scales, as well as some typical quality assessment metrics.

A Review of Speckle Pattern Fabrication and Assessment for Digital Image Correlation

http://rupert.eng.uci.edu/Publications/Acta%20Mat_nanocrystalline%20SSS_2011.pdf

Enhanced solid solution effects on the strength of nanocrystalline alloys

Nanocrystalline metals have been shown to exhibit unique mechanical behavior, including break-down in Hall-Petch behavior, suppression of dislocation-mediated plasticity, induction of grain boundary sliding, and induction of mechanical grain coarsening. Early research on the fatigue behavior of nanocrystalline metals shows evidence of improved fatigue resistance compared to traditional microcrystalline metals. In this review, experimental and modeling observations are used to evaluate aspects of cyclic plasticity, microstructural stability, crack initiation processes, and crack propagation processes. In cyclic plasticity studies to date, nanocrystalline metals have exhibited strongly rate-dependent cyclic hardening, suggesting the importance of diffusive deformation mechanisms such as grain-boundary sliding. The cyclic deformation processes have also been shown to cause substantial mechanically-induced grain coarsening reminiscent of coarsening observed during large-strain monotonic deformation of nanocrystalline metals. The crack-initiation process in nanocrystalline metals has been associated with both subsurface internal defects and surface extrusions, although it is unclear how these extrusions form when the grain size is below the scale necessary for persistent slip band formation. Finally, as expected, nanocrystalline metals have very little resistance to crack propagation due to limited plasticity and the lack of crack path tortuosity among other factors. Nevertheless, like bulk metallic glasses, nanocrystalline metals exhibit both ductile fatigue striations and metal-like Paris-law behavior. The review provides both a comprehensive critical survey of existing literature and a summary of key areas for further investigation.

A Review of Fatigue Behavior in Nanocrystalline Metals

Fatigue failure due to repetitive loading of metallic devices is a pervasive engineering concern. The present work reveals extraordinary fatigue resistance in nanocrystalline (NC) alloys, which appears to be associated with the small ( 107 cycles to failure). Postmortem examinations show that failed samples contain an aggregate of coarsened grains at the crack initiation site. The experimental data and accompanying microscopy suggest that the NC matrix undergoes abnormal grain growth during cyclic loading, allowing dislocation activity to persist over length scales necessary to initiate a fatigue crack by traditional fatigue mechanisms. Thus, the present observations demonstrate anomalous fatigue behavior in two regards: (1) quantitatively anomalous when considering the extremely high stress levels needed to drive fatigue failure and (2) mechanistically anomalous in light of the grain growth process that appears to be a necessary precursor to crack initiation.

/pdf/anomalous-fatigue-behavior-and-fatigue-induced-grain-growth-5c5v62ku6i.pdf

Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

Frictional performance and near-surface evolution of nanocrystalline Ni–Fe as governed by contact stress and sliding velocity

Nanocrystalline (NC) metals are known for having excellent strength but perceived to have poor ductility. Miniature tensile tests on NC Ni-Fe measured ultimate strengths of 2 GPa and elongations, by digital image correlation, of up to 10%. Detailed examination of the fracture surface revealed dimpled rupture and cross-section reduction up to 75%, suggesting an intrinsic ability for small grained Ni-Fe to accommodate plasticity. A survey of published studies on NC metals reveals that this behavior is quite common; despite low macroscopic elongation, NC metals often achieve extensive deformation suggesting good intrinsic ductility. Unfortunately, the common sheet-like configuration of NC tensile specimens muddies a simple evaluation of ductility based on elongation, since thin and wide geometries promote localized necking that expedites catastrophic failure. This paper presents a compact review of ductility concepts and literature to interpret the experimental ductility measurements of an electrodeposited nickel alloy.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/DF534609407D5AF0DECADCAF5D5D9C7A/S0884291413001398a.pdf/div-class-title-interpreting-the-ductility-of-nanocrystalline-metals-span-class-sup-a-href-fn2-ref-type-fn-1-a-span-div.pdf

Henry A. Padilla

Papers

A Review of Fatigue Behavior in Nanocrystalline Metals

Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

Frictional performance and near-surface evolution of nanocrystalline Ni–Fe as governed by contact stress and sliding velocity

Interpreting the ductility of nanocrystalline metals

Relating inhomogeneous deformation to local texture in zirconium through grain-scale digital image correlation strain mapping experiments