Centered Cubic Research Articles

Precipitation behavior and properties of aged Cu-0.23Be-0.84Co alloy

The precipitation behavior and properties of Cu-0.23Be-0.84Co alloy aging at 460 °C for 0 h, 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h were investigated systematically by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) in this study. With increase of aging time, the morphology, size, and distribution of precipitates change significantly, giving rise to the hardness and electrical conductivity change as well. It is confirmed that the phase transformation of Cu-0.23Be-0.84Co alloy during aging process follows the sequence of γ″ → γ′ → γ phase. The spherical γ″ phase has a body centered cubic (b. c. c.) structure with the lattice parameters of 0.28–0.29 nm, and the size increases from 2–5 nm to 5–7 nm after aging for 0.5 h–1 h. The γ″ phase aligns the Cu matrix according to the following orientation: (110)α//(1¯00)γ″ and [11¯2¯]α//[011¯]γ″. The ellipsoidal γ′ phase forms after aging for 3 h and has a consistent and ordered distribution on the Cu matrix. The orientation relationship between γ′ phase and the Cu matrix can be stated as (110)α//(31¯1)γ′ and [1¯13]α//[1¯14]γ′ with the lattice parameters of 0.26 nm. After aging for 4 h–6 h, the ellipsoidal γ′ phase gradually transforms into the coarse and spherical γ phase, and the orientation of precipitates is disordered. In addition, the hardness and electrical conductivity of Cu-0.23Be-0.84Co alloy have an obvious change with the aging time. The change of performance can be explained by the precipitation behavior of Cu-0.23Be-0.84Co alloy during aging. It is especially noteworthy that, due to the formation of consistent and ordered γ′ precipitates, the hardness and electrical conductivity has a peak value of 121 HB and 64.6%IACS (International Annealed Copper Standard) after aging for 3 h based on the experimental results in this study, respectively.

Effects of TiN, CrN and TiAlN coatings using reactive sputtering on the fatigue behaviour of AA2024 and medium carbon steel specimens

ABSTRACTThe effects of ceramic coatings (TiN, CrN and TiAlN films) on the fatigue behaviour of 2024 aluminium alloy (AA2024) and medium carbon steel (MCS) specimens under cyclic loading have been investigated in this study. These ceramic thin films of about 2 μm thickness were deposited on the substrates using radio frequency reactive magnetron sputtering, with metallic Ti, Cr and Al targets in an Ar/N2 gas environment. The (111), (200) and (220) and (311) peaks of a face centre cubic (fcc) structure in CrN films, and the (111), (200) and (220) peaks in TiN/TiAlN films were observed using X-ray diffraction method, respectively. Fatigue tests were performed using rotational bending conditions at a speed of 3000 rpm with five stress levels (115, 173, 231, 288 and 346 MPa for AA2024; 288, 346, 404, 462 and 519 MPa for MCS) in air. Scanning electron microscopy was used for the analysis of surface morphologies and initial failure stage. The results show that the fatigue life of coated specimens is significantly increased under lower cyclic loading, for example, from 42% at 288 MPa, to 98% at 230 MPa and up to 434% at 173 MPa, for AA2024 with TiN coatings. The improvements of mean fatigue life for MCS coated with TiN films are 88% at 519 MPa, 197% at 462 MPa and up to 597% at 404 MPa, respectively. The experimental results also depict that the coated specimens with higher surface hardness (TiAlN) tended to increase in fatigue strength and fatigue life over uncoated and TiN/CrN specimens.

Characterisation, Luminescence and Antibacterial Properties of Stable AgNPs Synthesised from AgCl by Precipitation Method

Silver nanoparticles (AgNPs) were synthesised using equimolar concentrations of reducing agent vitamin C and AgCl precursor by simple precipitation method. The synthesised AgNPs were characterised by X-ray diffraction (XRD), UV-Visible, photoluminescence and field emission scanning electron microscopy (FESEM) analysis. The formation of AgNPs was confirmed by the typical surface plasmon resonance band at 426 nm. The presence of elemental silver and pure crystalline face centre cubic (fcc) structure was confirmed by energy dispersive X-ray analysis and XRD analysis, respectively. The FESEM images showed the formation of spherical AgNPs for lower concentrations (0.1 and 0.3 mol/L) while spike and flower shaped particles were formed for higher concentration. Photoluminescence characteristic band was observed with no shift at 390 nm indicating the stable nature of AgNPs. The antibacterial property of the AgNPs was tested against gram negative bacteria Pseudomonas aeruginosa by using Cissus quadrangular as a control and the result showed that vitamin C reduced AgNPs have good antibacterial activity.

Overall thermo-magneto-electro-elastic properties of multiferroics composite materials with arbitrary heterogeneities spatial distributions

This study extends our recent work (Koutsawa, 2014) to multiferroics composite materials with temperature-independent properties. The key ingredient in this development is the computation of the so-called interaction tensors between the multiferroics inhomogeneities which are for the first time presented here for the magneto-electro-elastic coupling. The present mean field based micromechanics model is able to account for the morphological and topological textures of the multiferroics heterogeneities. Numerical examples based on the multiple site Mori–Tanaka model are used to quantify the prediction capabilities of the proposed micromechanics scheme. The predictions of the micromechanics model are compared to those of the variational asymptotic method for unit-cell homogenization (VAMUCH), a finite element based micromechanics approach. There is a good quantitative agreement between the mean field model predictions and numerical results obtained with VAMUCH. The model is then applied to three typical packing arrangements of particulate thermo-magneto-electro-elastic composites, namely, Body Centered Cubic (BCC), Face Centered Cubic (FCC) and Simple Cubic (SC) to demonstrate its capability to account for the topological texture of multiferroics composite materials microstructures.

Synthesis and electron microscopy of high entropy alloy nanoparticles

This work provides a methodology for synthesizing isolated multi-component, high entropy alloy nanoparticles. Wet chemical synthesis technique was used to synthesis NiFeCrCuCo nanoparticles. As synthesized nanoparticles were spherical with an average size of 26.7±3.3nm. Average composition of the as-synthesized nanoparticle dispersion was 26±2at% Cr, 14±2at% Fe, 10±0.6at% Co, 25±0.1at% Ni and 25±1.1at% Cu. Compositional analysis of the nanoparticles conducted using the compositional line profile analysis and compositional mapping on a single nanoparticle level revealed a fairly uniform distribution of all the five component elements within the nanoparticle volume. Electron diffraction analysis clearly revealed that the structure of as-synthesized nanoparticles was face centered cubic.

Microstructure and characterization of a novel cobalt coating prepared by cathode plasma electrolytic deposition

A novel cobalt coating was prepared by cathode plasma electrolytic deposition (CPED). The kinetics of the electrode process in cathode plasma electrolytic deposition was studied. The composition and microstructure of the deposited coatings were investigated by SEM, EDS, XRD and TEM. The novel cobalt coatings were dense and uniform, showing a typically molten morphology, and were deposited with a rather fast rate. Different from the coatings prepared by conventional electrodeposition or chemical plating, pure cobalt coatings with face center cubic (fcc) structure were obtained by CPED. The deposited coatings were nanocrystalline structure with an average grain size of 40–50nm, exhibited high hardness, excellent adhesion with the stainless steels, and superior wear resistance. The properties of the novel cobalt coatings prepared by CPED have been improved significantly, as compared with that prepared by conventional methods. It reveals that cathode plasma electrolytic deposition is an effective way to prepare novel cobalt coatings with high quality.

Effect of Metals Oxides Loading on the Modification of Microstructure and Phase Transformation of Nanocrystalline CeZrO2 Synthesized Using Water-in-oil-Microemulsion

In this paper, the microstructural and textural characteristics of a series of nanocrystalline CeZrFeO2 (CZF) loaded with different concentration of Fe were reported. Nanocrystalline CZF was synthesized at room temperature using water-in-oil microemulsion method. The microstructure and textural properties of CZF nanocrystal were investigated using dynamic light scattering, x-ray diffraction (XRD), and N2 adsorption–desorption analysis. The micelles size distribution of CZF samples, measured by dynamic light scattering, was found to be revealed almost similar trend of distribution pattern. More small size of micelles was formed at higher Fe concentration. The micelles were distributed in a narrow distribution size, in the range of 6 to 44nm. Xrd analysis proved that the face centered cubic of nanocrystalline CZF was successfully produced through the microemulsion synthesis, with the exposure of the samples at high calcination temperature for reduction was unnecessary. The influence of Fe loading on the modification of the microstructure and textural characteristics of CZF was clearly observed. Fe ions contributed in making the degree of crystal lattice shrinking and provided a larger surface area with the increasing of Fe concentration. XRD patterns of CZF tended to shift toward lower 2θ value with increasing Fe concentration which attributed to the replacement of Ce or Zr ions with the smaller Fe ions in Ce-Zr structure. The clearer effect of Fe loading was observed in modification of Ce-Zr textural. The surface area and average pores size of CZF increased with increasing Fe concentration, while the particle diameter decreased. All of CZF samples revealed the mesoporous profile (type IV) materials.

Subsurface defects structural evolution in nano-cutting of single crystal copper

In this work, molecular dynamics simulation is performed to study the subsurface defects structural distribution and its evolution during nano-cutting process of single crystal copper. The formation mechanism of chip and machined surface is interviewed by analyzing the dislocation evolution and atomic migration. The centro-symmetry parameter and spherical harmonics method are adopted to characterize the distribution and evolution of the subsurface defect structures and local atomic structures. The results show that stacking faults, dislocation loops, “V-shaped” dislocation loops, and plenty of point defects are formed during the machined surface being formed in shear-slip zone. In subsurface damage layers, stair-rod dislocation, stacking fault tetrahedra, atomic cluster defect, and vacancy defect are formed. And the formation mechanism of stair-rod dislocation is investigated by atomic-scale structure evolution. The local atomic structures of subsurface defects are icosahedrons, hexagonal close packed, body-centered cubic, and defect face center cubic, and the variations of local atomic structures are investigated.

TOPO-capped silver selenide nanoparticles and their incorporation into polymer nanofibers using electrospinning technique

Electrospinning is the most common technique for fabricating polymer fibers as well as nanoparticles embedded polymer fibers. Silver selenide nanoparticles were synthesized using tri-n-octylphosphine (TOP) as solvent and tri-n-octylphosphine oxide (TOPO) as capping environment. Silver selenide was prepared by reacting silver nitrate and selenium with tri-n-octylphosphine (TOP) to form TOP–Ag and TOP–Se solutions. Both absorption and emission spectra signify the formation of nanoparticles as well as the TEM which revealed spherical particles with an average particle size of 22nm. The polymer, PVP used was prepared at concentrations ranging from (35 to 45wt%) and the TOPO-capped silver selenide nanoparticles (0.2 and 0.6wt%) were incorporated into them and electrospun by varying the voltage from 11 to 20kV. The SEM images of the Ag2Se/PVP composite fibers revealed the fibers of diameters with average values of 425 and 461nm. The X-ray diffraction results show peaks which were identified due to α-Ag2Se body centered cubic compound. The sharp peak observed for all the samples at 2θ=44.5 suggest the presence of Ag in the face centered cubic which can be attributed to higher concentration of silver nitrate used with molar ratio of selenium to silver and the abundance of silver in the silver selenide crystal. Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA) and ultraviolet–visible spectroscopy were used to characterize the structure of the PVP/Ag2Se composite fibers.

Orientation dependences of atomic structures in chemically heterogeneous Cu50Ta50/Ta glass-crystal interfaces

Molecular dynamics simulations based on an angular-dependent potential were performed to examine the structural properties of chemically heterogeneous interfaces between amorphous Cu50Ta50 and crystalline Ta. Several phenomena, namely, layering, crystallization, intermixing, and composition segregation, were observed in the Cu50Ta50 region adjacent to the Ta layers. These interfacial behaviors are found to depend on the orientation of the underlying Ta substrate: Layering induced by Ta(110) extends the farthest into Cu50Ta50, crystallization in the Cu50Ta50 region is most significant for interface against Ta(100), while inter-diffusion is most pronounced for Ta(111). It turns out that the induced layering behavior is dominated by the interlayer distances of the underlying Ta layers, while the degree of inter-diffusion is governed by the openness of the Ta crystalline layers. In addition, composition segregations are observed in all interface models, corresponding to the immiscible nature of the Cu-Ta system. Furthermore, Voronoi polyhedra ⟨0,5,2,6⟩ and ⟨0,4,4,6⟩ are found to be abundant in the vicinity of the interfaces for all models, whose presence is believed to facilitate the structural transition between amorphous and body centered cubic.

Synthesis and characterization of alloy catalyst nanoparticles PtNi/C for oxygen reduction reaction in proton exchange membrane fuel cell

In this report, vulcan XC-72 supported PtNi alloy catalyst nanoparticles were synthesized by electroless deposition method using NaBH4 as a reduction agent. The properties of the synthesized Pt-Ni/C catalysts were investigated and evaluated. Transmission electron microscopy (TEM) results showed that PtNi alloy catalysts dispersed well on the carbon supports and their particle size was in the range of 4–8 nm. X-ray diffraction (XRD) analysis confirmed that the crystal lattice of Pt and PtNi alloy is face centered cubic. In the presence of Ni atom, an XRD pattern showed that structure of PtNi alloy crystal was contracted, which affected the catalyst’s properties. The activity of the catalyst was estimated by electrochemical methods including cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The electrochemical results indicated that the activity of PtNi/C alloy catalysts toward oxygen reduction reaction on cathode of PEMFC was higher in comparison with Pt/C catalysts.

Catalytic Reduction of 4-Nitrophenol Using Biogenic Silver Nanoparticles Derived from Papaya (Carica papaya) Peel extract

A facile and green method is described for the synthesis of Silver (Ag) nanoparticles (NPs) from the extract of Papaya Peel as capping and reducing agent. The green synthesized Ag NPs were characterized by diverse techniques such as powder X-ray diffraction (XRD), UV-visible, Fourier transform-infrared spectroscopy (FTIR) and Transmission electron microscopy (TEM) coupled with X-ray energy dispersive spectroscopy (EDS) techniques. These clearly reveal that the structure of the synthesized silver nanoparticles was face centered cubic. The nanoparticles obtained from Papaya Peel extract were spherical shape with an average diameter of 3-5 nm. Furthermore, the catalytic activity of synthesized Ag NPs in the reduction of 4-nitrophenol (4-NP) was studied by UVvis absorption spectroscopy. The synthesized Ag NPs have a good catalytic activity on the reduction of 4-nitrophenol (4-NP) by Papaya Peel extract which is confirmed by the decrease in absorbance maximum values of 4-nitrophenol (4-NP) with respect to time using UV-vis absorption spectroscopy. An efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of Ag NPs and NaBH4 was observed and was found to depend upon the nanoparticle size or the peel extract concentration used for synthesis.

Neutrons attenuation on composite metal foams and hybrid open-cell Al foam

Abstract A comprehensive investigation of monochromatic neutron attenuation effectiveness for close-cell composite metal foams (CMFs) and open-cell Al foam infiltrated with variety of second phase materials is presented using both experimental and theoretical methods. The experimental results indicated higher neutron flux reduction in open-cell Al foam with fillers compared to the close-cell CMFs due to their large percentage of low Z elements such as hydrogen, boron and carbon, with superior neutron attenuation performance, in their filler materials. The main factor controlling the shielding effectiveness of steel–steel CMFs is found to be the ratio of the thickness of the sphere wall to the sphere radius while the intermetallic phases in the matrix of Al–steel CMFs seem to have a major role on their shielding properties. Successful models that link the observed material properties and microstructure have been developed using Monte Carlo N-Particle Transport Code (MCNP) to verify the accuracy of the experimental results. Close-cell CMFs were proposed through three different sphere arrangements: simple cubic, body center cubic and face center cubic, whereas open-cell Al foam with fillers was represented by creating a three-dimensional structure using periodic unit cell through two approaches. The simulation results were found to be in good agreement with the experimental values. This research indicates the potential of utilizing light-weight close-cell CMFs and open-cell Al foam with fillers as nuclear shields replacing conventional materials to achieve a specified shielding level with additional benefits of excellent energy absorption and thermal isolation.

Effect of Manganese on the Fe-Rich Phases in Al-22Si-2Fe Alloy by Cooling Slope

Hypereutectic Al-Si alloys have low thermal expansion coefficients, excellent wear resistance, and high hardness. To replace cast iron with hypereutectic Al-Si alloys, the hypereutectic Al-Si alloys must still have the originally desired mechanical properties. The addition of Fe and Mn to the hypereutectic Al-Si alloys can form Fe-rich phases, which can improve thermal stability. In this paper, the effect of manganese (0 %, 0.99 %, and 1.36 %) on the Fe-rich phases of hypereutectic Al-22Si-2Fe (% w/w) alloys was studied. The results showed that primary Si particles (PSPs), needle-like Fe phases, a coarser fishbone-shaped α-Al15(Fe, Mn)3Si2 phases, and eutectic Si could be refined by cooling slope. With such a CS process, the intermetallic compounds in the alloys with different Mn/Fe ratios were examined with an optical microscope, scanning electron microscope, and X-ray diffraction. Moreover, the blocky α-Al15(Fe, Mn)3Si2 phases were analyzed by transmission electron microscopy. Through the analysis of the SADP, the lattice structures of α-Al15(Fe, Mn)3Si2 phases were identified with tetragonal structure and body centre cubic.

Preparation and characterization of carbopol/silver nanoparticles composites obtained by heating process for antimicrobial application

Properties such as absorption, structural and external aspect of Carbopol/silver nanoparticles composites, prepared in DMF by heating process up to 30, 60, 80, 100 and 120 °C, were investigated by UV-visible, FTIR and SEM-EDS analyses. Samples were named respectively D30 to D120, according to the temperature at which they were extracted. The results showed that instead of the appearance of silver aggregates observed by SEM microscopy, all the obtained materials present a single absorption band centred at 430 nm, attributed to the classical surface plasmon excitation of the silver nanoparticles. The presence of silver nanoparticles is also proved by the X-ray powder diffraction XRD patterns, which show the appearance of small peaks corresponding to the face centered cubic (f.c.c.) silver phase in the case of D100 and D120 samples. Additionally strong interactions between silver ions and carboxylic groups of Carbopol were identified by ATR-FTIR spectroscopy. The thermal properties of the carbopol are effectively enhanced by the presence of silver nanoparticles as evidenced by thermo-gravimetric analysis. Furthermore the water loss that generally occurs at 100 °C in acrylic acid polymer was completely avoided in these new materials since less than 2 % of weight loss is recorded up to 160 °C. Finally, the inhibiting activity of Carbopol/silver nanoparticles composites against staphylococcus Aureus micro-organisms was confirmed for all the obtained materials, suggesting their suitable uses as effective growth inhibitors of micro-organisms and making them appropriate for diverse antimicrobial control systems.

Structure and Microstructure of Binary Nitride TiN Thin Films Deposited by DC Reactive Sputtering

Titanium nitride (TiN) thin films were deposited on to unheated silicon (100) and stainless steel substrates by home-made direct current (DC) reactive magnetron sputtering method at a deposition of 60 min in an Ar-N2 gas mixture. The effects of sputtering power on structure and microstructure of these films have been studied. The films were analyzed by X-ray diffraction (XRD), Atomic Force Microscope (AFM) and Field-Emission Scanning Electron Microscope (FE-SEM). The films colors were influenced by sputtering parameter which altered from green purple to light gold and dark gold, respectively. By XRD, the polycrystalline structure of the as-deposited films was face center cubic (fcc) of TiN structure with (111), (200), (220), and (311), planes. The increasing of sputtering power transformed film from amorphous phase to crystal phase with crystal size were enhanced from 21.9 nm to 39.8 nm. The AFM scans revealed that sputtering power significantly affected surface morphologies and thicknesses of the TiN films. With increase in sputtering power, the roughness and films thickness were increased from 0.5 nm to 25.1 nm and 331 nm to 1113 μm, respectively. The microstructure combined with cross-section analysis FE-SEM revealed that the grain refinement with columnar structure were obtained for the film deposited at sputtering power of 270 W.

Icosahedral stereographic projections in three dimensions for use in dark field TEM

Thermodynamics require that rapidly cooled crystals and quasicrystals are relatively defective. Yet, without convenient 3-dimensional indexation both at crystal poles and in diffraction planes, or Kikuchi maps, it is difficult to identify the defects by dark field transmission electron microscopy. For two phase Al6Mn, these maps are derived. They relate i-Al6Mn to the standard face centered cubic, matrix crystals. An example of their usefulness in determining interfacial characteristics is described. Indices are integral powers on an irrational number.

A study of the oxidation behavior of multilayered tungsten nitride/amorphous tungsten oxide film prepared in a planar magnetron sputtering system

Abstract Tungsten nitride and tungsten nitride/amorphous tungsten oxide multilayered films were produced by a planar type reactive sputtering system on glass and stainless steel substrates. The effect of amorphous tungsten oxide top layer on oxidation behavior of tungsten nitride film has been characterized by thermal analysis using TGA and DTA. The structure of the film at different thermal-annealing temperatures was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The mechanical properties of the films at different heat-annealing states were measured by nano-indentation. It was found that the tungsten nitride film oxidized in air at 600 °C by the dissociation of face center cubic (fcc)–W 2 N to WO 3 and WO 2.92 and showed low hardness of 6 GPa. The addition of 500 nm thick amorphous tungsten oxide top layer to tungsten nitride film can further improve the oxidation resistance. Multilayered film oxidized in air at 800 °C by the dissociation of face center cubic (fcc)–W 2 N to WO 3 and WO 2.92 . The film retained a hardness of 24 GPa after annealing at 600 °C for 10 h. This indicates that this film is a good candidate for high temperature applications.

Creation of biaxial body center cubic tungsten nanorods under dynamic shadowing effect

Using a dynamic oblique angle deposition in a flipping rotation mode where the flux incident angle continuously changes during the magnetron sputter deposition, we demonstrated that a stable, biaxial (110)[11¯0] body center cubic (alpha-phase) tungsten nanorod film can be grown on amorphous substrates. In contrast, we showed that only a fiber-textured, metastable A15 (beta-phase) tungsten nanorod film was obtained using the conventional rotation mode where the oblique incident flux angle was fixed with the substrate rotating around the surface normal. Different flipping rotation speeds were performed to study the effect of dynamic shadowing on texture axis angular dispersion. The sample grown at 0.3 rotations per minute was observed to have the minimum out-of-plane and in-plane orientation dispersions characterized by the reflection high energy electron diffraction surface pole figure technique. The biaxial texture selection under the flipping rotation mode is explained qualitatively.

Coupled Thermomechanical Modeling of Small Volume FCC Metals

The mechanical and thermal behavior of small volume metallic compounds on the fast transient time are addressed in this work through developing a thermodynamically consistent nonlocal framework. In this regard, an enhanced gradient plasticity theory is coupled with the application of the micromorphic approach to the temperature variable. The yield function of the VA–FCC (Voyiadjis Abed Face Centered Cubic) model based on the concept of thermal activation energy and the dislocations interaction mechanisms including nonlinear hardening is taken into consideration in the derivation. The effect of the material microstructural interface between two materials is also incorporated in the formulation with both temperature and rate effects. In order to accurately address the strengthening and hardening mechanisms, the theory is developed based on the decomposition of the mechanical state variables into energetic and dissipative counterparts which provided the constitutive equations to have both energetic and dissipative gradient length scales for the bulk material and the interface. Moreover, the nonlocal evolution of temperature is addressed by incorporating the microstructural interaction effect in the fast transient process using two time scales in the microscopic heat equation.