Hall-Petch relation and boundary strengthening

The morphology and crystallography of lath martensite in alloy steels

Forming alloys with impurity elements is a routine method for modifying the properties of metals. An alternative approach involves the incorporation of interfaces into the crystalline lattice to enhance the metal's properties without changing its chemical composition. The introduction of high-density interfaces in nanostructured materials results in greatly improved strength and hardness; however, interfaces at the nanoscale show low stability. In this Review, I discuss recent developments in the stabilization of nanostructured metals by modifying the architectures of their interfaces. The amount, structure and distribution of several types of interfaces, such as high- and low-angle grain boundaries and twin boundaries, are discussed. I survey several examples of materials with nanotwinned and nanolaminated structures, as well as with gradient nanostructures, describing the techniques used to produce such samples and tracing their exceptional performances back to the nanoscale architectures of their interfaces. The incorporation of structural defects, in particular of interfaces, into crystalline lattices results in enhanced material properties. In this Review, different types of boundaries and interfaces are discussed, including high- and low-angle grain boundaries, twin boundaries, nanotwinned and nanolaminated structures, and gradient nanostructures.

Stabilizing nanostructures in metals using grain and twin boundary architectures

Formation of nanostructured surface layer on AISI 304 stainless steel by means of surface mechanical attrition treatment

The microstructure in the surface layer of a pure iron plate was refined at the nanometer scale by means of a surface mechanical attrition treatment that generates repetitive severe plastic deformation of the surface layer. The subsequent nitriding kinetics of the treated iron with the nanostructured surface layer were greatly enhanced, so that the nitriding temperature could be as low as 300°C, which is much lower than conventional nitriding temperatures (above 500°C). This enhanced processing method demonstrates the technological significance of nanomaterials in improving traditional processing techniques and provides a new approach for selective surface reactions in solids.

https://science.sciencemag.org/content/sci/299/5607/686.full.pdf

Nitriding iron at lower temperatures.

Microstructural analysis by advanced and automated methods has allowed deformation microstructures to be quantified in terms of common structural parameters. This quantification has shown for a variety of materials and processing conditions that the microstructural evolution follows a universal pattern of grain subdivision from the macroscale to the nanometer scale. This microstructural evolution has been described empirically and in theoretical models based on general principles for the formation of dislocation structures during plastic deformation by slip. The similarity between the behavior of materials undergoing different deformation patterns forms the basis for future research and development encompassing traditional as well as new materials and processes.

New discoveries in deformed metals

The present report attempts to make a historical review of the progress of the study of grain-boundary relaxation since 1947 to the present time. The outcomes of scientific experiments are gathered mainly from the measurements of internal friction and the accompanying anelastic effects in polycrystalline and bicrystal metals. Emphasis is placed on the information provided about the structure of the grain boundary, especially at elevated temperatures.

Fifty-year study of grain-boundary relaxation

Small metal and semiconductor particles with a size of a few nanometers are one of the important systems in modern materials science. Nanoparticles have found applications in many fields, ranging from catalysis to magnetic storage. In the present work, we discuss some of the methods to characterize the structure of nanoparticles using electron microscopy. We also discuss some of the exciting novel applications of nanoparticles in nanoelectronics and nanophotonics. Finally, we show that nanoparticles play an important role in producing atmospheric pollutants.

The role of nanosized particles. A frontier in modern materials science, from nanoelectronics to environmental problems

Despite great differences in the physical and chemical properties of various ionic media, common methods for analyzing internal equilibrium provide useful and simple means for interpreting and predicting their behavior. The formalism of M. Pourbaix for analyzing the activities and solubilities of solutes in aqueous solutions has provided a foundation for interpreting corrosion, solubilities, and electrochemical phenomena for such solutions. Although perhaps not so obvious, the formalism of Kroger-Vink (K-V) in plotting the point defect concentrations for ionic solids derives from the same mathematical method. Likewise, the activities and solubilities for solutes in fused salts, e.g., fused sodium sulfate, can be treated by exactly the same sort of simultaneous resolution of equilibria for reactions in an ionic medium. Suggestions for extension of this analysis to cryolite-base fused salt solutions important to aluminum extraction are discussed.

Robert F. Mehl

Papers

New discoveries in deformed metals

Fifty-year study of grain-boundary relaxation

The role of nanosized particles. A frontier in modern materials science, from nanoelectronics to environmental problems

Some generalities in the analyses of equilibria in lonic solutions