bluuebunny/crossref_metadata_2025_split huggingface dataset:
Perspective on Submicron-Resolution Three-Dimensional X-Ray Structural Microscopy to Address Mesoscale Materials Microstructure and Evolution Issues
Authors: Larson B. C. , Yang Wenge 
Published: June 2019

AbstractThis paper provides a perspective on submicron-resolution three-dimensional x-ray structural microscopy for the investigation of materials microstructure and evolution on mesoscopic length scales. Microstructure and thermal/stress induced microstructure evolution at the length scale of the local crystal grains, grain boundaries, triple junctions, and dislocation patterning are known to play critical roles in determining the physical properties of materials. Large scale computer simulations and multi-scale modeling are making significant progress on the nanoscale and detailed mesoscale computations are becoming increasingly tractable as new methods are developed. X-ray structural microscopy with submicron resolution now provides a (previously missing) direct experimental link between theory and computations and the mesoscopic behavior of materials microstructure.
Atomic-Scale Analysis of Strain Relaxation Mechanisms in Ultra-Thin Metallic Films
Authors: Gungor M. Rauf , Maroudas Dimitrios 
Published: June 2019

AbstractA comprehensive computational analysis is presented of the atomistic mechanisms of strain relaxation over a wide range of applied biaxial tensile strain in free-standing Cu thin films. The analysis is based on large-scale isothermal-isostrain MD simulations using slab supercells with cylindrical voids normal to the film plane and extending throughout the film thickness. Our analysis has revealed various regimes in the film's mechanical response as the applied strain level increases. Following an elastic response at low strain (≶ 2%), plastic deformation occurs accompanied by emission of screw dislocations from the void surface and threading dislocations from the film surfaces, in parallel with generation of vacancies due to slip of jogged dislocations. At the lower strain range following the elastic-to-plastic deformation transition (⋚ 6%), void growth is the major strain relaxation mechanism, while at higher levels of applied strain (≥ 8%), a subsequent transition leads to a new plastic deformation regime where void growth plays a negligible role in the film strain relaxation.
Residual Stresses around Indentations in Alumina/SiC Nanocomposites [Abstract + Supplemental Data]
Authors: Limpichaipanit Apichart , Todd Richard Ian 
Published: June 2019

AbstractAlumina/SiC nanocomposites are more wear resistant and have better surface finish than pure alumina of a similar grain size. Grain pullouts caused by intergranular fracture are observed on worn surfaces of alumina whereas only a few pullouts resulting from transgranular fracture and scratches caused by plastic deformation are the main features of a worn surface of the nanocomposites. Surface mechanical properties were investigated by Cr3+ fluorescence microscopy. The experiments were carried out using a variety of microstructures.
Deformation-induced Nanocomposites
Authors: Wilde Gerhard 
Published: June 2019

AbstractComposite approaches, e.g. with mutually immiscible constituents or including at least one refractory phase, present a viable and maybe even necessary route for stabilizing massive nanostructured materials against detrimental coarsening under thermal and/or mechanical loading conditions [1]. A different way for nanoscaled composite formation is presented by the nanocrystallization of marginally glass-forming amorphous alloys, such as Al-rich alloys with rare earth and transition metal additions. Such composite systems that are stabilized at nanometer-scaled structure sizes due to diffusion limitations have conventionally been processed by supplying thermal energy for initiating the nanocrystal formation [2]. New opportunities for fabricating massive nanocrystalline composites in bulk quantities and with improved microstructures from such alloys might be based on the plastic deformation of the amorphous quenching products, as indicated by the observation of nanocrystallization in shear bands [3-5].ere, different deformation methods with largely different strain and pressure levels have been applied on rapidly quenched Al-rich metallic glasses in order to investigate the strain-induced nanocrystal formation. The results indicate e.g. that shear straining under a high pressure and to large strain values can produce uniform nanocrystalline structures in bulk samples, which is essential to their functional performance. Moreover, detailed structure analyses indicate that the amorphous structure of the entire sample volume, and not only the shear band regions, might be affected by the plastic deformation. In addition to the significance concerning the understanding of the deformation of glasses, the results also indicate the applicability of the new processing routes for synthesizing massive, porosity-free nanocrystalline materials.[1]	G. Wilde, H. Rösner, J. Mater. Sci., in press. [2]G. Wilde, et al., Adv. Engr. Mater. 5 (2003) 125. [3]G. Wilde et al., Mater. Sci. Forum 503-504 (2006) 425. [4] N. Boucharat, et al., Scripta Mater. 53 (2005) 823. [5] R. Hebert, et al., Scripta Mater. 54 (2006) 25.
Microstructure and Mechanical Properties of Combinatorially Prepared Thin Film Aluminum-Silicon Nanocomposites
Authors: Olk Charles H. , Lukitsch Michael , Haddad Daad B 
Published: June 2019

Abstracte have undertaken the exploration of the AlxSi1-x systems to discover new alloys with enhanced properties. We describe the mechanical properties of thin film AlxSi1-x alloys determined through indentation experiments. Combinatorial methods were used to systematically control thin film microstructure through variations in composition and growth temperature. Discrete libraries of compositionally graded films have been sputter deposited onto silicon substrates to produce two structural phase regions: amorphous Al-Si and amorphous Si plus crystalline Al. The mechanical properties of the thin films were determined by analyzing the load-displacement traces based on the Oliver-Pharr method. X-ray diffraction was used to investigate the microstructures and determine the crystallite sizes.
Microstructure-Property Relationships in Wear Resistant Alumina/SiC 'nanocomposites' the Importance of Plastic Deformation in Ceramics
Authors: Todd Richard Ian , Limpichaipanit Apichart , Ortiz Merino Jose 
Published: June 2019

AbstractAlumina/SiC “nanocomposites" consist of a dispersion of submicron SiC particles in an alumina matrix. The resistance to severe wear of the nanocomposites and the surface finish produced by a given grinding treatment are strikingly superior to those of pure alumina with the same grain size. We have explored the reasons for this by correlating a wide range of variations in the basic microstructure with the wear behaviour observed, including both the wear rate, and quantitative surface fractography of the worn surfaces. These improved properties of the nanocomposites are shown to be a consequence of a reduction in surface grain pullout by brittle fracture. In “dilute” nanocomposites (<10% SiC), this is due largely to a reduction in size of the individual pullouts. With 10% SiC nanoparticles, however, there is also evidence that the SiC directly suppresses the nucleation of cracking by plastic deformation of the surface. The origin of these effects will be discussed.
Depth-dependent defect and residual stress distribution in magnetron sputtered MoN:Cu nanocomposite films by x-ray microdiffraction
Authors: Chen Gang , Singh Dileep , Eryilmaz Osman , Erdemir Ali , Routbort Jules , Liu Wenjun 
Published: June 2019

AbstractWe have developed a synchrotron-based x-ray microdiffraction technique for measuring depth-resolved residual stress distribution in nanocrystalline films with submicron resolution [1]. In this study, we further refined this technique and applied it to low-friction and high-hardness Cu-doped MoN films. These magnetron sputtered nanocomposites films consist of MoN, Mo2N, and Cu phases, whose ratio depends on Cu concentration. By using the microdiffraction technique, we discovered that both the deviatoric and the hydrostatic components of the residual stresses depend on the film depth (Fig.1). The former indicates depth-dependent distribution of biaxial stresses, while the latter implies depth-dependent defect distribution, which also depends on Cu concentration. Thermal annealing of the nanocomposite film partially relives the stress, significantly reduces the lattice spacing, and eliminates the defect gradients. These results suggest that interstitial N may play an important role in the lattice expansion and the defect gradients formed during the non-equilibrium sputtering process. Our study provides fresh insights into understanding the structure-property relations in the magnetron sputtered MoN:Cu nanocomposites films.
Nanoscale Strain Measurements in Polymer Nanocomposites
Authors: Chen Qi , Chasiotis Ioannis , Chen Chenggang , Roy Ajit 
Published: June 2019

AbstractThe paper describes a multiscale experimental investigation of the mechanical behavior of polymer nanocomposites with nanoscale fused silica inclusions with the objective to shed light into the effect of the hard nanoparticles on the quasistatic mechanical behavior of epoxy matrix and the implications of the latter to the effective composite properties. The main variable in this study was the nanofiller volume fraction while the particle size was either 15 nm or 100 nm. Local strain measurements indicated strain field localization in the vicinity of the nanofillers at strains that macroscopically fall in the linearly elastic regime. The matrix strains were as high as three times the applied far field strain at applied effective strains of ∼ 1%. At larger stresses the local strain fields evolved to maxima that were considerably higher than the applied strain, and they were affected by local particle density and distribution. In composites with the largest particle volume fraction, 5 vol.%, 100 nm fillers, neighboring particles located in small proximities behaved as single large particles and often resulted in matrix strain shielding thus decreasing the benefit of the large surface-to-volume ratio and the associated efficiency in load transfer. On the other hand the 15 nm fillers resulted in more uniformly distributed deformation compared to composites with 100 nm particles.
The Influence of Nanosized Molybdenum and Tungsten Fillers on the Physico-Mechanical and Tribological Properties of Polymer-based Composite Materials
Authors: Makaryan Victor 
Published: June 2019

AbstractThe problems of the creation of composite polymer-based materials with the use of nanosized molybdenum and tungsten fillers with the particle size of less than 10 nm are considered. The copolymer of formaldehyde and dioxolane (CFD) and the polyphenylene sulphide (PPS) are chosen as polymeric matrixes. A comparative analysis of the tribological properties of composite materials with fine nanosized fillers (5-10 nm) and nanosized analogues (100-200) is made. It is determined that the use of nanosized isotropic structure Mo fillers leads to improved wear-resistance up to three times for CFD-based composites and up to four times for PPS-based. The highest hardness values were observed while using isotropic nanosized tungsten fillers. The nanosized crystalline fillers also give positive results, but the bigger sized fillers decrease the polymer hardness characteristics comparatively nanosize isotropic analogues.
Power Cycling Effects on the Structural Stability of Thermal Pastes Used in Microelectronics
Authors: Nnebe Ijeoma , Feger Claudius , McGlashan-Powell Maurice 
Published: June 2019

AbstractThermal pastes are a class of soft composite materials of great importance to the microelectronics industry. The function of these pastes is two-fold: (i) to transport heat away from the chip; and (ii) to accommodate mechanical stresses in the package arising from the mismatch in the thermal expansion between the chip and the heat spreader or sink. Due to the former requirement, thermal pastes are among some of the most highly-filled composite systems in practice (solids volume fraction > 70%). These materials are expected to withstand the significant normal forces, lateral forces, and temperature variations associated with chip operations and power off/on transitions. The structural changes and degradation of various thermal pastes during power cycling have been characterized using optical microscopy and IR thermography. Correlations between the evolving structures and variables such as thermal paste inhomogeneity and binder-particle dispersability have been successfully made and will be presented.
Preferential Site Precipitation and Subcell Stability in AA6061 Sandwich Cores
Authors: Bouwhuis B. A. , Hibbard G. D. 
Published: June 2019

AbstractPeriodic cellular metal (PCM) sandwich cores can be considered hybrids of the solid and gas type. These can be designed at both the architectural and microstructural levels. PCM cores with 95% open porosity have been constructed from perforated 6061 aluminium alloy (AA6061) sheets using a perforation-stretching method. This method places planar, periodically-perforated sheet metal in an alternating-pin jig. The pins apply force out-of-plane, plastically deforming the sheet metal into a truss-like array of struts (i.e. metal supports) and nodal peaks (i.e. strut intersections). The result is a non-uniform work-hardened profile exhibiting large deformation at the nodes and small deformation at the struts.For identical PCM architectures, this study looks at the interaction of microstructural strengthening mechanisms and the resultant performance of PCM truss cores. Beginning with fabrication, work-hardening induced a subcell network of dislocation tangles within the AA6061 matrix. Following this stage, a variety of microstructures were created through recovery, recrystallization and precipitation mechanisms. Microhardness measurements and electron back-scattered diffraction (EBSD) characterization were employed through truss core cross-sections in order to study the microstructural gradients of subcell size as well as interaction between subcells and precipitates in the truss cores. To determine the effect of microstructure on mechanical performance, PCM cores were compressed to study deformation and collapse mechanisms.The present data can be used to illustrate engineering at the architectural and microstructural levels to achieve a range of mechanical properties in a hybrid sandwich core.
Threshold crack speed in dynamic fracture of silicon
Authors: Buehler Markus J. , Tang Harvey , van Duin Adri C.T. , Goddard William A. 
Published: June 2019

AbstractWe report a study of dynamic cracking of a silicon single crystal in which the ReaxFF reactive force field is used for about 3,000 atoms near the crack tip while the other 100,000 atoms of the model system are described with a simple nonreactive force field. The ReaxFF is completely derived from quantum mechanical calculations of simple silicon systems without any empirical parameters. This model has been successfully used to study crack dynamics in silicon, capable of reproducing key experimental results such as orientation dependence of crack dynamics (Buehler et al., Phys. Rev. Lett., 2006). Here we focus on crack speeds as a function of loading and crack propagation mechanisms. We find that the steady state crack speed does not increase continuously with applied load, but instead jumps to a finite value immediately after the critical load, followed by a regime of slow increase. Our results quantitatively reproduce experimental observations of crack speeds during fracture in silicon along the (111) planes, confirming the existence of lattice trapping effects. We find that the underlying reason for this behavior is formation of a 5-7-double ring defect at the tip of the crack, effectively hindering nucleation of the crack at the Griffith load. We develop a simple continuum model that explains the qualitative behavior of the fracture dynamics.
Simulation of Directed Nanocrack Patterns for the Fabrication of Nanowires [PowerPoint Submission]
Authors: Salac David , Lu Wei 
Published: June 2019

Abstract	While material fracture is generally considered undesirable, recent experimental work has indicated that cracking can be utilized to create small scale nanowire structures with diameters of 100nm and smaller. Typical nanowire fabrication techniques include the use of a scanning tunneling microscope and electrochemical deposition. Compared to fracture fabricated nanowire structures current fabrication techniques are either extremely slow or require large amounts of post-processing. To become a viable nanowire fabrication technique the cracking of materials must be directed. We propose a computational model to predict propagation paths in large scale crack systems. We utilize the level set method to investigate the creation of nanoscale crack patterns. The level set method allows for large scale simulations of many crack tips while easily accommodating large scale deformations. Unlike traditional methods such as finite elements explicit modeling of the cracks is not needed. We show that the use of multiple materials and etched regions can effectively direct the cracking of a thin film. Using these patterns nanowire structures can be constructed which would be difficult to obtain otherwise.
Modeling the Effect of Oxidation and Etching of Silicon Photonic Crystals
Authors: Thitsa Makhin , Ali Haider , Wu Feng , Peters Kurt M. , Albin Sacharia 
Published: June 2019

AbstractTuning the band-gap of photonic crystals has been a challenge because there are few parameters that can be varied to modify the band structure. In this paper we modeled the effect of well controlled complementary metal oxide semiconductor (CMOS) compatible processing techniques, viz. oxidation and oxide etching, on the band-gap and mid-gap frequency of a silicon photonic crystal (PC). By adding silicon dioxide as the third dielectric, oxide thickness serves as a new parameter that influences the band structure. In the case of a PC of Si atoms in air, if silicon is etched to reduce the original atom radius from 0.28a (a = lattice constant) to 0.1a, the band-gap and mid-gap normalized frequencies increase from 0.1 to 1.6 and from 0.28 to 0.49 respectively. During oxidation, silicon is consumed to form silicon dioxide. Thus, if the Si atom of 0.4a radius is oxidized until it reaches 0.1a, the band-gap and mid-gap vary in the range of (0.1-1.5) and (0.28-0.41) respectively. When the oxide is etched back, the band-gap can be tuned in the range of (0.1-1.6) for a new mid-gap frequency in the range of (0.41-0.49). Results are also presented for a triangular lattice of air holes in silicon.
Inelastic Behavior and Grain-Boundary Effects in Polycrystalline Materials
Authors: Shi Jibin , Zikry Mohammed , Hatem Tarek Moustafa 
Published: June 2019

AbstractDislocation-density based multiple-slip constitutive formulations and specialized computational schemes are introduced to account for grain-boundary (GB) effects in polycrystalline aggregates. New kinematically based interfacial grain-boundary regions and formulations are introduced to account for dislocation-density transmission, absorption, and pile-ups that may occur due to CSL grain-boundary misorientations.
A Procedure of Determining Parameters to Expand Applicability of Modified Embedded Atom Method to Non-bulk Systems
Authors: Tokumaru Kento , Takahashi Kunio , Saito Shigeki , Yin Yingchen 
Published: June 2019

AbstractModified Embedded Atom Method '92 (MEAM92) developed by Baskes is the most popular among researchers using Embedded Atom Method series, because MEAM92 has high reliability for bulk system, and parameters are determined consistently. However, the applicability of this method to non-bulk systems, such as surface, is still uncertain. In such background, in order to expand the applicability to non-bulk systems, Kunio Takahashi has proposed Dimer Reference Modified Embedded Atom Method (DR-MEAM). The objective of this work is to discuss the applicability to non-bulk systems by determining the DR-MEAM parameters fitted to the results of clusters and bulk calculated by MEAM92. It is suggested as one of the effective methods for lining up the candidates of optimized parameters consistently. Additionally, calculated surface properties by determined parameters for Cu suggest the valid values in comparison with the other methods, and the possibility of DR-MEAM for expanding to non-bulk systems.
Molecular Dynamics Simulation of Nanoparticle Chain Aggregate Sintering
Authors: Hawa Takumi , Zachariah Michael R 
Published: June 2019

AbstractSintering of silicon nanoparticle chain aggregates are investigated using molecular dynamics (MD) simulations at 1500 K, which is about melting temperature at the size range we tested. The straight chain aggregates consist of upto 40 particles and the primary particles of 2.5 to 5 nm sizes are considered. The sintering time increases with increase the total volume of the chain aggregate or with increase the exposed initial surface area of the chain. A mathematical model was developed to describe the dynamics of sintering of chain aggregates. The model was able to predict the sintering time with excellent agreement with the results obtained from MD simulations. We also studied the chain aggregate that has a secondary branch coming out from the edge of the primary branch (L-shape) and from the middle of the primary branch (T-shape). In general, sintering time changes as much as 30% of that of a straight chain which contains the same volume of particles.
Chromium Impurity States in Pb1-xGexTe Alloys Under Pressure
Authors: Skipetrov Evgeny , Plastun Alexey , Kovalev Boris , Skipetrova Lyudmila , Topchevskaya Tatyana , Slyn'ko Vasily 
Published: June 2019

AbstractThe galvanomagnetic effects in the n-Pb1-xGexTe:Cr (x=0.02-0.13) alloys at the temperatures 4.2≤T≤300 K and under hydrostatic compression up to 17 kbar have been investigated. The metal-insulator transition under the increase of germanium content in the alloys and insulator-metal transition, induced by pressure in Pb1-xGexTe:Cr (x=0.10) alloy, were revealed. Using the experimental data in the frame of two-band Kane dispersion relation the dependences of the free electron concentration and the Fermi level position on the matrix composition and on the pressure were calculated. The composition and pressure coefficients of chromium deep level movement were obtained and the models of the electronic structure reconstruction under varying the alloy composition and under pressure were proposed.
High Pressure-High Temperature Reactions in Xenon-Chlorine System
Authors: Somayazulu Maddury , Gramsch Steven , Mao Ho-Kwang , Hemley Russell 
Published: June 2019

AbstractWe present results of studies of the xenon-chlorine system to 60 GPa and temperature range 300 to 2000 K. Using a combination of Raman spectroscopy, infrared spectroscopy and synchrotron x-ray diffraction; we characterize the products of diamond cell experiments. In the 2-20 GPa pressure interval, we observe the formation of a deep red crystalline phase. Above 15 GPa, and at high temperature, a solid solution of Xe and Cl2 appears to form. Comparison of the ultraviolet-visible and infrared absorption measurements on the proposed alloy of Xe and Cl2 show that band edge moves into the visible range at high pressure