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

Hundreds of different types of coatings are used to protect a variety of structural engineering materials from corrosion, wear, and erosion, and to provide lubrication and thermal insulation. Of all these, thermal barrier coatings (TBCs) have the most complex structure and must operate in the most demanding high-temperature environment of aircraft and industrial gas-turbine engines. TBCs, which comprise metal and ceramic multilayers, insulate turbine and combustor engine components from the hot gas stream, and improve the durability and energy efficiency of these engines. Improvements in TBCs will require a better understanding of the complex changes in their structure and properties that occur under operating conditions that lead to their failure. The structure, properties, and failure mechanisms of TBCs are herein reviewed, together with a discussion of current limitations and future opportunities.

http://science.sciencemag.org/content/sci/296/5566/280.full.pdf

Thermal Barrier Coatings for Gas-Turbine Engine Applications

1. Introduction 2. The physical metallurgy of nickel and its alloys 3. Single crystal superalloys for blade applications 4. Superalloys for turbine disc applications 5. Environmental degradation: the role of coatings 6. Summary and future trends.

The Superalloys: Fundamentals and Applications

TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.

TiO2 nanotubes: synthesis and applications.

This paper summarizes the basic properties of ceramic materials for thermal barrier coatings. Ceramics, in contrast to metals, are often more resistant to oxidation, corrosion and wear, as well as being better thermal insulators. Except yttria stabilized zirconia, other materials such as lanthanum zirconate and rare earth oxides are also promising materials for thermal barrier coatings.

Ceramic materials for thermal barrier coatings

Gas-turbine engines used in transportation, energy, and defense sectors rely on high-temperature thermal-barrier coatings (TBCs) for improved efficiencies and power. The promise of still higher efficiencies and other benefits is driving TBCs research and development worldwide. An introduction to TBCs—complex, multi-layer evolving systems—is presented, where these fascinating systems touch on several known phenomena in materials science and engineering. Critical elements identified as being important to the development of future TBCs form the basis for the five articles in this issue of MRS Bulletin. These articles are introduced, together with a discussion of the major challenges to improved coating development and the rich opportunities for materials research they provide.

https://link.springer.com/content/pdf/10.1557/mrs.2012.232.pdf

Thermal-barrier coatings for more efficient gas-turbine engines

Humankind's aerospace aspirations are placing unprecedented demands on vehicle propulsion systems. Advanced structural ceramics are playing a key role in addressing these challenges.

Advanced structural ceramics in aerospace propulsion.

The thermal conductivity of dense and porous yttria-stabilized zirconia (YSZ) ceramics has been measured as a function of temperature in the range 25 to 1000 °C The dense specimens were either single crystal (8 mol% YSZ) or sintered polycrystalline (3 mol% and 8 mol% YSZ) The porous specimens (3 mol% YSZ) were prepared using the “fugitive” polymer method, where different amounts of polymer spheres (of two different average sizes) were included in the starting powders before sintering This method yielded materials with uniformly distributed porosities with a tight pore-size distributions A theory has been developed to describe the thermal conductivity of dense YSZ as a function of temperature This theory considers the reduction in the intrinsic thermal conductivity due scattering of phonons by point defects (oxygen vacancies and solute) and by the “hopping” of oxygen vacancies It also considers an increase in the effective thermal conductivity at high temperatures due to radiation This theory captures the essential features of the observed thermal conductivity The Maxwell theory has been used to analyze the thermal conductivity of the porous materials An adequate agreement was found between the theory and experiment

Thermal conductivity of dense and porous yttria-stabilized zirconia

Rare-earth zirconates have been identified as a class of low-thermal-conductivity ceramics for possible use in thermal barrier coatings (TBCs) for gas-turbine engine applications. To document and compare the thermal conductivities of important rare-earth zirconates, we have measured the thermal conductivities of the following hot-pressed ceramics: (i) Gd 2 Zr 2 O 7 (pyrochlore phase), (ii) Gd 2 Zr 2 O 7 (fluorite phase), (iii) Gd 2.58 Zr 1.57 O 7 (fluorite phase), (iv) Nd 2 Zr 2 O 7 (pyrochlore phase), and (v) Sm 2 Zr 2 O 7 (pyrochlore phase). We have also measured the thermal conductivity of pressureless-sintered 7 wt% yttria-stabilized zirconia (7YSZ)--the commonly used composition in current TBCs. All rare-earth zirconates investigated here showed nearly identical thermal conductivities, all of which were ∼30% lower than the thermal conductivity of 7YSZ in the temperature range 25°-700°C. This finding is discussed qualitatively with reference to thermal-conductivity theory.

Nitin P. Padture

Papers

Thermal Barrier Coatings for Gas-Turbine Engine Applications

Thermal-barrier coatings for more efficient gas-turbine engines

Advanced structural ceramics in aerospace propulsion.

Thermal conductivity of dense and porous yttria-stabilized zirconia

Low‐Thermal‐Conductivity Rare‐Earth Zirconates for Potential Thermal‐Barrier‐Coating Applications