There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

The method we introduced in 1992 for measuring hardness and elastic modulus by instrumented indentation techniques has widely been adopted and used in the characterization of small-scale mechanical behavior. Since its original development, the method has undergone numerous refinements and changes brought about by improvements to testing equipment and techniques as well as from advances in our understanding of the mechanics of elastic–plastic contact. Here, we review our current understanding of the mechanics governing elastic–plastic indentation as they pertain to load and depth-sensing indentation testing of monolithic materials and provide an update of how we now implement the method to make the most accurate mechanical property measurements. The limitations of the method are also discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400085800

Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology

Bulk nanostructured materials from severe plastic deformation

https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1032&context=superalloys_ii

A critical review of high entropy alloys and related concepts

High-temperature materials such as TiN have been successfully applied as wear corrosion protection, decorative coatings, electrical contacts and diffusion barriers in electronic devices. However the poor toughness and ductility have limited some of these applications. To alleviate some of these problems, reduction of grain size can enhance grain boundary sliding and grain boundary diffusion related creep phenomena. We have investigated mechanical and electrical properties of TiN as a function of microstructure varying from nanocrystalline to single crystal TiN films deposited on (100) silicon substrates. By varying the substrate temperature from 25oC to 700oC during pulsed laser deposition, the microstructure of TiN films changed from nanocrystalline (having uniform grain size of 8 nm) to a single crystal epitaxial film on the silicon (100) substrate. The microstructure and epitaxial nature of these films were investigated using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Hardness measurements were made using nanoindentation techniques. Resistivity measurements were performed by van der Pauw method. The nanocrystalline TiN contained numerous triple junctions without any presence of amorphous regions. The width of the grain boundary remained constant 1 nm as a function of boundary angle. Similarly the grain boundary structure did not change with grain size. The hardness of TiN films decreased with decreasing grain size in nanoscale. This behavior has been modeled recently involving grain boundary sliding which is particularly relevant in the case of hard materials such as TiN. The dependence of resistivity of TiN as a function of the substrate temperature is discussed and correlated with hardness results.

Mechanical and Electrical Properties of Nanocrystalline and Epitaxial TiN Films

Introduction Knowledge of the thermal stability of nanocrystalline materials is important for both technological and scientific reasons. From a technological point of view, the thermal stability is important for consolidation of nanocrystalline particulates without coarsening the microstructure. That is, many methods, as described in Chapter 2, for synthesis of nanocrystalline materials result in particulate products which must be consolidated into bulk form. Since most consolidation processes involve both heat and pressure, the thermal stability of the nanoscale microstructure is always at risk. The goal of particulate consolidation is to attain essentially 100% theoretical density and good particulate bonding while preventing or minimizing grain growth of the nanocrystalline grains. Understanding the scientific nature of stability, grain growth of nanocrystalline microstructures is a criterion for allowing strategies for minimizing grain growth to be developed. A basic scientific question with regard to nanocrystalline materials is whether their behavior involves “new physics” or is simply the expected grain-size-dependent behavior extrapolated to nanocrystalline grain sizes. Thermal stability is an important phenomenon to be addressed in this regard. The thermal stability in a broader sense involves not only the stability of the grain structure, that is the microstructure, but also the stability of the structure of the grain boundaries in nanocrystalline materials. A number of investigations on the thermal stability of nanocrystalline materials have been conducted. Grain growth in nanocrystalline materials has been reviewed by Suryanarayana (1995), Weissmuller (1996), and Malow and Koch (1996a,b).

Structural Nanocrystalline Materials: Stability of structural nanocrystalline materials – grain growth

Introduction The very early application of nanomaterials is utilized in systems where nanopowders are used in their free form, without consolidation or blending. For a simple example, nanoscale titanium dioxide and zinc oxide powders are now commonly used by cosmetics manufacturers for facial base creams and sunscreen lotions for UV protection. Nanoscale iron oxide powder is now being used as a base material for rouge and lipstick. Paints with reflective properties are also being manufactured using nanoscale titanium dioxide particles. Figure 7.1 lists some of the common current and future applications of nanomaterials. The list is not complete, however; it is a current summary and the view of the present authors. Nanostructured wear-resistant coatings for cutting tools and engineering components have been in use for several years. Nanostructured cemented carbide coatings are used on some Navy ships for their increased durability. Recently, more sophisticated uses of nanoscale materials have been realized. Nanostructured materials are in wide use in the area of information technology, integrated into complex products such as the hard disk drives that provide faster communication in today's world. Many uses of nanoscale particles have already appeared in specialty markets, such as defense applications, and in markets for scientific and technical equipment. Producers of optical materials and electronics substrates such as silicon and gallium arsenide have embraced the use of nanosize particles for chemomechanical polishing of these substrates for chip manufacturing.

Structural Nanocrystalline Materials: Applications of structural nanomaterials

This text deals mainly with the synthesis and processing of metastable and nanocrystalline materials. The subjects covered include mechanochemistry and the effect of mechanical attrition upon the chemical behaviour of solids, and encompass many classes of material including metals, polymers and ceramics. A significant fraction of the book also deals with with bulk metallic glasses - right from the fundamentals and theory of their mechanical properties, to their transformation kinetics and the development of processing techniques for improved practical applications. Another large part of the book covers the mechanical, electrochemical and magnetic properties of metastable and nanocrystalline materials. Overall, this publication provides a state-of-the-art overview of research results and technological developments in the field, and highlights the most recent achievements.

Metastable, mechanically alloyed and nanocrystalline materials : ISMANAM 2001 : proceedings of the International Symposium on Metastable, Mecanically Alloyed and Nanocrystalline Materials, University of Michigan, Ann Arbor, MI, USA, Jun 24-29, 2001

Carl C. Koch

Papers

Mechanical and Electrical Properties of Nanocrystalline and Epitaxial TiN Films

Structural Nanocrystalline Materials: Stability of structural nanocrystalline materials – grain growth

Structural Nanocrystalline Materials: Applications of structural nanomaterials

Metastable, mechanically alloyed and nanocrystalline materials : ISMANAM 2001 : proceedings of the International Symposium on Metastable, Mecanically Alloyed and Nanocrystalline Materials, University of Michigan, Ann Arbor, MI, USA, Jun 24-29, 2001

High-Throughput Combinatorial Development of High-Entropy Alloys For Light-Weight Structural Applications