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

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

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

A critical review of high entropy alloys and related concepts

Additive manufacturing of metallic components – Process, structure and properties

High-entropy alloys are equiatomic, multi-element systems that can crystallize as a single phase, despite containing multiple elements with different crystal structures. A rationale for this is that the configurational entropy contribution to the total free energy in alloys with five or more major elements may stabilize the solid-solution state relative to multiphase microstructures. We examined a five-element high-entropy alloy, CrMnFeCoNi, which forms a single-phase face-centered cubic solid solution, and found it to have exceptional damage tolerance with tensile strengths above 1 GPa and fracture toughness values exceeding 200 MPa·m(1/2). Furthermore, its mechanical properties actually improve at cryogenic temperatures; we attribute this to a transition from planar-slip dislocation activity at room temperature to deformation by mechanical nanotwinning with decreasing temperature, which results in continuous steady strain hardening.

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A fracture-resistant high-entropy alloy for cryogenic applications

Ni-based single crystal (SX) superalloys with low specific weight are essential for developing aero engine turbine blades with great strength to weight ratios. To develop such alloys, numerical analysis methods for specific weight, the volume fraction of γ′ phase and elemental partitioning coefficients between γ and γ′ phases are collected and analyzed based on literature data of Ni-based superalloys. Specific weight can be well predicted based on the weight percentage of each element, and tungsten has the most significant effect. Rhenium has the greatest elemental partitioning coefficient which might provide a strengthening effect for the γ matrix. Thus, we design four model alloys with rhenium but without tungsten for experimental validation with the aid of thermodynamic calculation. It is found that after solid solution and aging treatments, four alloys all have required typical γ/γ′ two phase microstructure, and specific weight is all lower than 8.4 g/cm^3. Graphical abstract

Composition design and microstructure of Ni-based single crystal superalloy with low specific weight—numerical modeling and experimental validation

Defect energetics in structural materials has long been recognized to be affected by specific alloy compositions. Local structural distortion greatly affects the physical properties and performance of alloys. To reveal the atomic-level lattice distortion, the local structures of Ni and Fe in Ni1-xFex (x = 0.10, 0.20, 0.35 and 0.50) solid solution alloys were measured with extended X-ray absorption fine structure (EXAFS) technique. The EXAFS measurements have revealed that the bond length of Fe with surrounding atoms is 0.01–0.02 A larger than that of Ni with its neighbors in the alloys. Both the lattice constant and the interatomic distance of the nearest neighbors increase with the addition of Fe content in the solid solutions. The local bonding environments in Ni1-xFex alloys were also calculated from ab initio and compared with the experimental results.

X-ray absorption investigation of local structural disorder in Ni1-xFex (x = 0.10, 0.20, 0.35, and 0.50) alloys

Depending on the processing method, pseudoelastic NiTi alloys can have small, lenticular Ni4Ti3 precipitates; however, the mechanical properties of these precipitates are not well understood. By performing nanoindentation with a spherical indenter, Ni4Ti3 precipitates within a pseudoelastic NiTi alloy were examined. Scanning electron microscopy was used to examine the indents after nanoindentation. After unloading, the hardness and remnant depth ratios of the indents in the Ni4Ti3 precipitates, the NiTi matrix, and the “average” NiTi alloy were compared. To decouple the effects of elasticity from those of pseudoelasticity, similar nanoindentation experiments were performed on an NiAl sample and compared with results from the NiTi sample.

Hongbin Bei

Papers

Composition design and microstructure of Ni-based single crystal superalloy with low specific weight—numerical modeling and experimental validation

X-ray absorption investigation of local structural disorder in Ni1-xFex (x = 0.10, 0.20, 0.35, and 0.50) alloys

Nanoindentation of pseudoelastic NiTi containing Ni4Ti3 precipitates

Microstructure and mechanical behavior of directionally solidified Fe35Ni15Mn25Al25

The dependence of stress and strain rate on the deformation behavior of a Ni-based single crystal superalloy at 1050°C