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 aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

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Hallmarks of mechanochemistry: From nanoparticles to technology

3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting

A review on fundamental of high entropy alloys with promising high–temperature properties

Defect-interface interactions

Forced atomic mixing during severe plastic deformation: Chemical interactions and kinetically driven segregation

The Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation is widely used to describe phase transformation kinetics. This description, however, is not valid in finite size domains, in particular, thin films. A new computational model incorporating the level-set method is employed to study phase evolution in thin film systems. For both homogeneous (bulk) and heterogeneous (surface) nucleation, nucleation density and film thickness were systematically adjusted to study finite-thickness effects on the Avrami exponent during the transformation process. Only site-saturated nucleation with isotropic interface-kinetics controlled growth is considered in this paper. We show that the observed Avrami exponent is not constant throughout the phase transformation process in thin films with a value that is not consistent with the dimensionality of the transformation. Finite-thickness effects are shown to result in reduced time-dependent Avrami exponents when bulk nucleation is present, but not necessarily when surface nucleation is present.

/pdf/modeling-interface-controlled-phase-transformation-kinetics-1soaqt42oj.pdf

Modeling interface-controlled phase transformation kinetics in thin films

A dilute Al-0.06Sc-0.02Zr-0.005Er (at%) alloy, to which 0.09 at% Si was added, was peak-aged to create a high number density of (Al,Si)3(Sc,Er,Zr) precipitates, 3.6 nm in radius. The alloy shows a high resistance to dislocation creep, with a threshold stress of 18 MPa at 400 °C. After further aging under applied stress for ~ 1000 h at 400 °C, the threshold stress increases to 22 MPa, with the precipitates growing to a radius of 4–8 nm. This represents a very substantial improvement in creep resistance as compared to a similar alloy with one-third the Si content, 0.03 at%, whose threshold stress at 400 °C is 9–14 MPa. Atom probe tomography reveals that, for the new higher-Si alloy, the precipitates have an average Si concentration of 3.3 at% and show a broad core with uniform Sc-, Si- and Er concentrations and a thin Zr-enriched shell. By contrast, the low-Si alloy exhibits precipitates with half the average Si content, showing an Er-enriched core, a Sc-enriched inner-shell and a Zr-enriched outer-shell. A possible explanation for the higher creep resistance of the high-Si alloy is that the enhanced chemical homogeneity of Sc and Er in the core, as compared to the highly segregated core/shell/shell structure of the low-Si alloy, modifies the elastic strain field around precipitates so as to increase the repulsive force from the precipitate on the matrix dislocations climbing over them, thus enhancing the threshold creep stresses.

Effect of Si micro-addition on creep resistance of a dilute Al-Sc-Zr-Er alloy

Aluminum alloys, fabricated by a rapid solidification process, with high strength, high ductility, high corrosion resistance, high creep resistance, and good weldability.

Nhon Q. Vo

Papers

Forced atomic mixing during severe plastic deformation: Chemical interactions and kinetically driven segregation

Modeling interface-controlled phase transformation kinetics in thin films

Effect of Si micro-addition on creep resistance of a dilute Al-Sc-Zr-Er alloy

Ribbons and powders from high strength corrosion resistant aluminum alloys

Ultrafine-grained Al-Mg-Zr alloy processed by shear-assisted extrusion with high thermal stability