Influence of grain size distribution on the mechanical behavior of materials in a wide range of strain rates

This work compares the mechanical behavior of alloys with influence of grain siz

Mechanical Behavior of Nanostructured and Ultrafine-Grained Metal Alloy under Intensive Dynamic Loading

Researches of the last years have allowed to establish that the laws of deformation and fracture of bulk ultrafine-grained (UFG) and coarse-grained (CG) materials are various both in static and in dynamic loading conditions. The influence of average grain size on the yield stress, the tensile strength, and the compression strength was established for metal alloys with a face-centered cubic (FCC), a body-centered cubic (BCC), and a hexagonal close-packed (HCP) structures. The study of the microstructure of the alloys after severe plastic deformation (SPD) by the electron backscatter diffraction (EBSD) technique showed the presence of a bimodal grain size distribution in the UFG alloys. Metal alloys with a bimodal grain size distribution possess a negative strain rate sensitivity of the yield stress and higher ductility at quasi-static strain rates. In this chapter, we will discuss the regularities of deformation at high strain rates, damage, and fracture of ultrafine-grained alloys

Effect of Grain Size on Superplastic Deformation of Metallic Materials

The superplastic deformation exhibited by metals with different grain sizes and their corresponding deformation mechanism influences the industrial metal-forming processes. The coarse-grained materials, which contain grain size greater than 20 μm, exhibited superplastic deformation at high homologous temperature and low strain rate of the order of 10−4 s−1. Fine grain materials (1–20 μm) are generally considered as favorable for superplastic deformation. They possess high-strain-rate sensitivity “m” value, approximately, equal to 0.5 at the temperature of 0.5 times the melting point and at a strain rate of 10−3 to 10−4 s−1. Ultrafine grains (100 nm to less than 1 μm) exhibit superplasticity at high strain rate as well as at low temperature when compared to fine grain materials. It is attributed to the fact that both temperature and strain rates are inversely proportional to the grain size in Arrhenius-type superplastic constitute equation. The superplastic phenomenon with nano-sized grains (10 nm to less than 100 nm) is quite different from their higher-scale counterparts. It exhibits high ductility with high strength. Materials with mixed grain size distribution (bimodal or layered) are found to exhibit superior superplasticity when compared to the homogeneous grain-sized material. The deformation mechanisms governing these superplastic deformations with different scale grain size microstructures are discussed in this chapter

Heterostructured materials: superior properties from hetero-zone interaction

Heterostructured materials are an emerging class of materials with superior performances that are unattainable by their conventional homogeneous counterparts. They consist of heterogeneous zones with dramatic (>100%) variations in mechanical and/or physical properties. The interaction in these hetero-zones produces a synergistic effect where the integrated property exceeds the prediction by the rule-of-mixtures. The heterostructured materials field explores heterostructures to control defect distributions, long-range internal stresses, and nonlinear inter-zone interactions for unprecedented performances. This paper is aimed to provide perspectives on this novel field, describe the state-of-the-art of heterostructured materials, and identify and discuss key issues that deserve additional studies

Ultrafine-Grained Metals

Ultrafine-grained metallic materials produced by severe plastic deformation methods are at the cutting edge of modern materials science. UFG-metals exhibit outstanding properties which make them very interesting for structural or functional engineering applications. Fifteen articles in this special issue address a broad variety of topics: New developments in severe plastic deformation techniques, advances in modeling and simulation of the severe plastic deformation processes, mechanical properties under monotonic and cyclic loading of homogenous and graded UFG structures, dominating deformation mechanisms in UFG materials, advances and strategies for high conductivity UFG-materials, correlation between severe plastic deformation parameters and resulting materials properties and peculiarities in the corrosion behavior of UFG materials. The book covers latest results on ultrafine-grained titanium, aluminum and copper alloys and on UFG iron and steels and thus provides a deep insight to current research activities in the field of ultrafine-grained metals

Bimodal microstructure and fatigue properties of nanocrystalline and ultrafine grained nickel

The nanocrystalline (NC) and ultrafine grained (UFG) materials show very high strength but low ductility. In this work bimodal microstructures are developed by introducing larger grains into the finer grained matrix, to combine high strength and considerably high ductility at the same time. Different bimodal microstructures are developed by heat treatment of the PED NC nickel and the ECAP UFG nickel. The grain growth kinetics is quantitatively analyzed using the JMAK model and the Burke and Turnbull model for the PED nickel. However, the annealing phenomena for the ECAP UFG nickel are difficult to be described quantitatively due to the initial severe plastic deformed state and are only qualitatively analyzed. Microhardness measurement and tensile tests show that the finer grains provide the strength and the coarser grains ensure the ductility in the bimodal microstructures. The fatigue behavior and crack growth resistance is systematically investigated for the different microstructures. The microcracks introduced by focus ion beam propagate during the fatigue experiments and induce the ultimate fracture for the PED NC, NC/UFG and UFG nickel. Among them the bimodal NC/UFG nickel shows the best fatigue performance. However, the ECAP nickel is not sensitive to the microcracks, and therefore the macro-notches are introduced to investigate the crack growth behavior. Dynamic recrystallization is found to be the main mechanism for the plastic deformation in the ECAP nickel.Nanokristalline (NK) und ultrafeinkörnige (UFG) Materialien besitzen sehr hohe Festigkeit aber niedrige Duktilität. In dieser Arbeit werden bimodale Mikrostrukturen, die gleichzeitig hohe Festigkeit und gute Duktilität haben, durch das Einbringen größerer Körner in die feinkörnige Matrix entwickelt. Verschiedene bimodale Mikrostrukturen werden durch Wärmebehandlungen von NK PED Nickel und UFG ECAP Nickel entwickelt. Die Kornwachstumskinetik des PED Nickels wird quantitativ erfolgreich nach dem JMAK Modell und Burke und Turnbull Modell analysiert. Die Kornwachstumsphänomene von ECAP Nickel können hingegen wegen ihrer komplizierten Anfangsmikrostruktur nur qualitativ beschrieben werden. Mikrohärtemessung und Zugversuche zeigen, dass in den bimodalen Gefügen die feineren Körner die Festigkeit und die gröberen Körner die Duktilität gewährleisteten. Ermüdungsverhalten und Risswachstumswiderstand der verschiedenen Gefüge werden erforscht. Die durch Focused Ion Beam geschnittenen Mikrorisse breiten sich während der Ermüdungszyklen aus und führen zum endgültigen Bruch fr das PED NK, NK/UFG und UFG Nickel. Das bimodale NK/UFG Nickel zeigt das beste Ermüdungsverhalten. Im Gegensatz zum PED Nickel wird festgestellt, dass das ECAP Nickel nicht mikrorissempfindlich ist. Daher werden Makrokerben initiiert, um die Rissausbreitung zu untersuchen. Für das ECAP Nickel ist dynamische Recrystallization der Hauptmechanismus für die plastische Verformung in den Ermüdungsexperimenten

Copper Alloys

Copper has been used for thousands of years. In the centuries, both handicraft and industry have taken advantage of its easy castability and remarkable ductility combined with good mechanical and corrosion resistance. Although its mechanical properties are now well known, the simple f.c.c. structure still makes copper a model material for basic studies of deformation and damage mechanism in metals. On the other hand, its increasing use in many industrial sectors stimulates the development of high-performance and high-efficiency copper-based alloys. After an introduction to classification and casting, this book presents modern techniques and trends in processing copper alloys, such as the developing of lead-free alloys and the role of severe plastic deformation in improving its tensile and fatigue strength. Finally, in a specific section, archaeometallurgy techniques are applied to ancient copper alloys. The book is addressed to engineering professionals, manufacturers and materials scientists

Failure by Simultaneous Grain Growth, Strain Localization, and Interface Debonding in Metal Films on Polymer Substrates

In a previous paper, we have demonstrated that a microcrystalline copper film well bonded to a polymer substrate can be stretched beyond 50% without cracking. The film eventually fails through the co-evolution of necking and debonding from the substrate. Here we report much lower strains to failure (around 10%) for polymer-supported nanocrystalline metal films, whose microstructure is revealed to be unstable under mechanical loading. We find that strain localization and deformation-associated grain growth facilitate each other, resulting in an unstable deformation process. Film/substrate delamination can be found wherever strain localization occurs. We therefore propose that three concomitant mechanisms are responsible for the failure of a plastically deformable but microstructurally unstable thin metal film: strain localization at large grains, deformation-induced grain growth and film debonding from the substrate.Engineering and Applied Science