Bulk Structural Materials Research Articles

Nanoarchitectonics: A Conceptual Paradigm for Design and Synthesis of Dimension-Controlled Functional Nanomaterials

Nanomaterials have been prepared over a wide range of length scales from nanoscopic objects to bulk structural materials. Recent investigations have been focused on the regulation and control of nanoscopic structures for the modulation of the properties of even macroscopic objects. As an emerging concept, nanoarchitectonics has been proposed as a technology system to be used for arranging nanoscale structural units--i.e., the nanostructure unit as a group of atoms or molecules--in a predesignated configuration. In this review, we summarize recent research on nanomaterials including design, synthesis, fabrication and functionalization based on the nanoarchitectonics concept. Examples are roughly classified according to their dimensionalities: (i) OD nanomaterials (quantum dots, nanocrystals, nanoparticles and nanospheres); (ii) 1D nanomaterials (nanorods, nanowires, nanobelts, nanowhiskers and nanotubes), (iii) 2D nanomaterials (nanosheets, graphene, self-assemble monolayers, Langmuir-Blodgett films, layer-by-layer assemblies and interfacial structures), and (iv) 3D nanomaterials (bulk materials with nanoscale structural control, nanohybrids, nanocomposites and mesoporous materials).

Bulk nanoscale materials in steel products

Although a number of nanoscale metallic materials exhibit interesting mechanical properties the fabrication paths are often complex and difficult to apply to bulk structural materials. However a number of steels which exhibit combinations of plasticity and phase transitions can be deformed to produce ultra high strength levels in the range 1 to 3 GPa. The resultant high stored energy and complex microstructures allow new nanoscale structures to be produced by combinations of recovery and recrystallisation.The resultant structures exhibit totally new combinations of strength and ductility to be achieved. In specific cases this also enables both the nature of the grain boundary structure and the spatial variation in structure to be controlled. In this presentation both the detailed microstructural features and their relation to the strength, work-hardening capacity and ductility will be discussed for a number of martensitic and austenitic steels.

A Semi-Empirical Atomistic Approach in Materials Research

With developments of semi-empirical interatomic potentials for realistic materials systems, atomistic approaches to a wide range of bulk and nanostructured materials become more and more feasible. This article outlines a recently developed semi-empirical interatomic potential model, the second nearest-neighbor modified embedded-atom method that shows a strong applicability to multicomponent systems. It is shown that the interatomic potentials can well reproduce fundamental physical properties of representative materials systems. Examples are used to illustrate the applications of the atomistic approach to calculation of fundamental physical properties of both nano and bulk structural materials such as thermodynamic, elastic, interface, and defect properties necessary to understand the materials behavior and to serve as input to larger-scale simulations.

Cu-Based Bulk Glass Formation in the Cu-Zr-Ga Alloy System and Their Mechanical Properties

The thermal stability, glass-forming ability (GFA) and mechanical properties of a new Cu-based glassy alloy in Cu-Zr-Ga ternary system have been investigated. The supercooled liquid region ΔT x (= T x - T g ) exceeding 40 Kand reduced glass transition temperature (T g /T l ) above 0.59 are obtained simultaneously in the composition range from 2.5 to 7.5%Ga and 37.5 to 42.5%Zr, and the highest T g /T l is 0.62 for Cu 5 2 . 5 Zr 4 2 . 5 Ga 5 and Cu 5 5 Zr 4 0 Ga 5 alloys. The Cu-based Cu-Zr-Ga glassy alloys are formed in a rod form with a diameter up to 2.0 mm by the copper mold casting. The bulk glassy alloys exhibit good mechanical properties of 550-580 for Vicker's hardness (H v ), 105-111 GPa for Young's modulus (E), 1910-2130 MPa for compressive fracture strength (σ c , f ), and 0.2-0.5% for plastic elongation. The GFA of Cu-based Cu-Zr-Ga glassy alloys is more closely related to T g /T l values rather than ΔT x . The present new Cu-based bulk glassy alloys are expected to be developed as another type of bulk structural material with higher strength combined with good ductility.

Mechanical properties of thin films

The mechanical properties of thin films on substrates are described and studied. It is shown that very large stresses may be present in the thin films that comprise integrated circuits and magnetic disks and that these stresses can cause deformation and fracture to occur. It is argued that the approaches that have proven useful in the study of bulk structural materials can be used to understand the mechanical behavior of thin film materials. Understanding the mechanical properties of thin films on substrates requires an understanding of the stresses in thin film structures as well as a knowledge of the mechanisms by which thin films deform. The fundamentals of these processes are reviewed. For a crystalline film on a nondeformable substrate, a key problem involves the movement of dislocations in the film. An analysis of this problem provides insight into both the formation of misfit dislocations in epitaxial thin films and the high strengths of thin metal films on substrates. It is demonstrated that the kinetics of dislocation motion at high temperatures are expecially important to the understanding of the formation of misfit dislocations in heteroepitaxial structures. The experimental study of mechanical properties of thin films requires the development and use of nontraditional mechanical testing techniques. Some of the techniques that have been developed recently are described. The measurement of substrate curvature by laser scanning is shown to be an effective way of measuring the biaxial stresses in thin films and studying the biaxial deformation properties at elevated temperatures. Submicron indentation testing techniques, which make use of the Nanoindenter, are also reviewed. The mechanical properties that can be studied using this instrument are described, including hardness, elastic modulus, and time-dependent deformation properties. Finally, a new testing technique involving the deflection of microbeam samples of thin film materials made by integrated circuit manufacturing methods is described. It is shown that both elastic and plastic properties of thin film materials can be measured using this technique.