Atomic structure of nanoscale quasicrystal-forming Zr–noble metal binary metallic glasses

We report the results of the local structural evaluation and mechanism of QC formation in the Zr₇₀Pd₃₀ and Zr₈₀Pt₂₀ glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr₇₀Pd₃₀. In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr₈₀Pt₂₀. It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr₇₀Pd₃₀. Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr₈₀Pt₂₀. This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase.     

Indentation behavior of metal–ceramic multilayers at the nanoscale: Numerical analysis and experimental verification

The behavior of aluminum/silicon carbide nanolayered composite in response to nanoindentation loading is studied. The effects of heterogeneity on the deformation fields, as well as the hardness and elastic modulus obtained from indentation, are investigated using finite element analysis. Attention is also devoted to correlating the numerical results with experimental deformation and damage features. The model uses an explicit layered structure within the axisymmetric framework. It is found that the nanolayered composite results in unique deformation patterns. Significant tensile stresses can be generated locally along certain directions, which offers a mechanistic rationale for the internal cracking observed experimentally. The unloading process also leads to an expansion of the tension-stressed area, as well as continued plastic flow in parts of the aluminum layers. Comparisons of hardness and indentation-derived modulus between modeling and experiments also point to the importance of incorporating the detailed geometric features when performing indentation analyses.     

Rheological properties of metal injection molding feedstock

Viscosity of a polyethylene glycol-polymethyl methacrylate (PEG-PMMA) binder and PEG-PMMA/Fe-2Ni feedstock in powder injection molding was measured and calculated. A logarithmic additivity between viscosity of the binder and that of its constituents was found. Other factors, such as temperature, powder loads, content and type of surface-active agents and those of polymers, in relation to rheological properties of feedstock were discussed as well. The results showed that with increasing viscosity of surface-active agent, polymer melt index or temperature, the feedstock viscosity decreased while higher polymer content and powder loading would lead to additional feedstock viscosity. The relationship mentioned above is expressed and effectively explained why the change rate of feedstock viscosity will slow down with the increase of shear rate.     

Rheological properties of metal injection molding fccdstock

Viscosity of a polyethylene glycol-polymethyl methacrylate (PEG-PMMA) binder and PEG-PMMA/Fe-2Ni feedstock in powder injection molding was measured and calculated. A logarithmic additivity between viscosity of the binder and that of its constituents was found. Other factors, such as temperature, powder loads, content and type of surface-active agents and those of polymers, in relation to rheological properties of feedstock were dismmsed as well. The resuits showed that with increasing viscosity of surface-active agent, polymer melt index or temperature, the feedstock viscosity decreased while higher polymer content and powder loading would lead to additional feedstock viscosity. The relationship mentioned above is expressed and effectively explained why the change rate of feedstock viscosity will slow down with the increase of shear rate.     

High temperature thermo-physical properties and thermal shock behavior of metal–diborides-based composites

The thermo-mechanical properties and thermal shock resistance of two metal diborides composites, HfB₂ with 20 vol.% SiC and HfB₂ with 20 vol.% SiC and 10 vol.% AlN, were investigated. Results showed that the composite HfB₂–SiC–AlN had a higher specific heat capacity than that of composite HfB₂–SiC. However, the occurrence of a Si–Al–O phase in the grain boundaries increased the heat flow resistance at grain boundaries, resulting in decrease thermal diffusivity and thermal conductivity. The calculated thermal shock resistance parameters indicated that the addition of AlN increased the resistance against crack initiation and crack propagation of composite, corresponding to the increase in critical thermal shock temperature difference from 400 to 600 °C.     

Influence of laser cladding process on the magnetic properties of WC–FeNiCr metal–matrix composite coatings

Metal–matrix composite (MMC) coatings were deposited by laser cladding technique with direct injection of WC–FeNiCr powder onto N1310 nonmagnetic steel matrix. Laser cladding was conducted using a Trumpf6000 CO₂ laser. The morphology of WC–FeNiCr MMC coatings was characterized using scanning electron microscopy (SEM). Magnetic properties of WC–FeNiCr MMC coatings were examined by vibrating sample magnetometer (VSM) at room temperature. The influence of laser cladding process on the magnetic properties of coatings was investigated. It was found that the content of tungsten carbide and laser power have significant effect on the magnetic properties of composite coatings. The evolution of phase constitution at different laser power was identified by X-ray diffraction (XRD). The presence of an austenitic γ-(Fe, Ni), Cr_0.19Fe_0.7Ni_0.11, Fe₃W₃C, WC and W₂C phases were confirmed by the XRD analysis in the laser clad layer.     

Synthesis of metallic copper nanoparticles using copper oxide nanoparticles as precursor and their metal–metal bonding properties

Abstract

This work proposes a method for preparing metallic Cu nanoparticles using CuO nanoparticles as a precursor, and performs metal–metal bonding by using the metallic Cu nanoparticles. Colloid solution of CuO nanoparticles with a longitudinal particle size of 13·0±3·0, a lateral particle size of 8·4±2·2 and a crystal size of 7·8 nm was prepared with salt base reaction using Cu(NO₃)₂ aqueous solution and NaOH aqueous solution. Preparation of the metallic Cu particle colloid solution was performed in water using the CuO nanoparticles, hydrazine and cetyltrimethylammonium bromide, which resulted in production of the metallic Cu nanoparticles with a particle size of 50·6 nm and a crystal size of 30·5 nm. Metallic copper discs could be bonded using the metallic Cu nanoparticles under annealing at 400°C and pressurising at 1·2 MPa for 5 min in H₂ gas. A shear strength required for separating the bonded discs was recorded as high as 39·6 MPa.     

Microstructures and strength of nanoscale Cu–Ag multilayers

Cu–Ag multilayers were found to have lower peak hardness than Cu–Ni in spite of lower misfit dislocation spacing that is expected to increase the resistance of interfaces to glide dislocation transmission. This is attributed to misfit dislocation core spreading in the interface plane in Cu–Ag.     

Effect of filler metal on microstructure and mechanical properties of manganese–aluminum bronze repair welds

The repair welding of UNS C95700 manganese–aluminum bronze plates was done using different filler metals. The microstructure and mechanical properties of welds were studied. The main microstructural constituents were α, β and κ phases with different morphologies. The addition of manganese decreased the percentage of α phase in the microstructure of weldments from 80% (Mn-free weld) to 57% (12.5% Mn weld, mass fraction). The morphology of κ phase was lamellar in high nickel specimens and it was changed to a globular morphology for high manganese welds. Although the application of high manganese filler metal yielded the higher tensile and bending strengths of weldment compared with the weld using high nickel filler material, the optimum mechanical properties of repair welds were obtained using a non-alloy filler material (ERCuAl-A2) for the underlay and high manganese filler metal (ERCuMnNiAl) for filling passes. This weld presented an increase of 39% in tensile strength compared with the base metal, and no cracking was observed after bending test.     

Influence of temper condition on microstructure and mechanical properties of semisolid metal processed Al–Si–Mg alloy A356

Abstract

The microstructures and mechanical properties of strontium modified semisolid metal high pressure die cast A356 alloy are presented. The alloy A356-F (as cast) has a globular primary grain structure containing a fine eutectic. Solution treatment results in spheroidisation of the eutectic silicon particles under the T4 and T6 temper conditions. The A356-T5 maintains the fibrous silicon morphology after artificial aging. A356-T4 has better ductility and impact strength than A356-T5 due to its spheroidised silicon morphology. The impact properties of semisolid metal high pressure die cast A356 are controlled mainly by the silicon morphology and alloy strength (hardness), whereas tensile strength is determined by the degree of solid solution coupled with precipitate formation during aging.     

Critical aspects of sinter-hardening of prealloyed Cr–Mo steel

In recent years, growing demand for greater mechanical properties of PM steel components with competitive fabrication cost has led to significant innovations in different fields of powder metallurgy. Recent research has been focused on reaching higher performance with lower cost. To this end, the possibility of combining the conventional sintering and post-sintering processes for a particular powder composition has been introduced. Sinter-hardening is a result of the research conducted along this line. Elimination of any secondary operation such as quench-hardening by incorporating it in the sintering process (i.e. sinter-hardening) is of great interest, as it will lead to lower processing costs and equal, if not higher mechanical performance. However, to ensure the desired mechanical properties of the final component and robustness of the performance, critical aspects of the sinter-hardening process should be rigorously studied.Hence with specific attention to a Cr–Mo steel powder (FL-5305), this study deals with the influence of density on cooling rate, the effect of different sintering temperatures (e.g. 1120 °C and 1250 °C) on austenite grain size and consequently, hardenability. The microstructure development in sinter-hardened FL-5305 material has been analyzed and predicted by means of the available literature for solid steel and also using the commercial software (JMatPro 5.0) for materials assessment based on thermodynamic and kinetics modeling. Finally, inaccurate carbon control and its adverse impact on excessive formation of cementite have been addressed.     

Structure,dielectric and optical properties of Nd3+-doped LiTaO3 transparent ferroelectric glass–ceramic nanocomposites

Here, we present the structural, dielectric and optical properties of neodymium ion (Nd³⁺) doped novel transparent glass-ceramics containing LiTaO₃ nanocrystals in the Li₂O–Ta₂O₅–SiO₂–Al₂O₃ (LTSA) glass system prepared by the melt-quenching technique. The precursor glasses were isothermally crystallized at 680 °C for 3–100 h, following the differential thermal analysis (DTA) data, to obtain nanostructured glass-ceramics. They were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), Fourier transform infrared reflection spectra (FTIRRS), optical absorption and luminescence spectroscopy along with dielectric constant measurements. XRD, FESEM, TEM and FTIRRS confirm the nanocrystallization of LiTaO₃ (14–36 nm) in the LTSA glass matrix. A steep increase in dielectric constant (?_r) of glass-ceramics with heat-treatment time is observed due to high dielectric constant ferroelectric LiTaO₃ formation. The measured NIR photoluminescence spectra have exhibited emission transitions of ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) from Nd³⁺ ions upon excitation at 809 nm. It is observed that the photoluminescent intensity and excited state (⁴F_3/2) lifetime of Nd³⁺ ions decrease with increase in heat-treatment time due to concentration quenching effect. The absorption spectra and fluorescence measurements reveal that the incorporation of Nd³⁺ ions in the LiTaO₃ crystal lattice in the oxide glassy matrix is important for obtaining desirable fluorescence performance of the material.     

Evolution of domain structure and frequency effect on ferroelectric properties in BIT ferroelectrics

Based on the time-dependent Ginzburg-Landau （TDGL） equation, the temporal evolution of the domain structure and hysteresis loops of polarization versus electric field were simulated by a phase-field model for Bi4Ti3O12 （BIT） ferroelectric single crystal under an applied electric field. In the static electric energy induced by an applied alternating electric field, the effects of field frequency on the ferroelectric properties of BIT ferroelectrics were investigated. The results show that the evolution of ferroelectric domain structure is a gradual process including domain nucleation, domain wall motion, domain growth and domain combination. In the boundary regions of ferroelectric domain, the new domain nucleations occur and the old domains disappear. The coercive field increases with the field frequency, and it is in good agreement with the previous experiment.     

Carbon nanotube–metal–oxide nanocomposites: microstructure,electrical conductivity and mechanical properties

Carbon nanotube–metal–oxide composites (metal=Fe, Co or Fe/Co alloy; oxide=Al₂O₃, MgO or MgAl₂O₄) have been prepared by hot-pressing the corresponding composite powders, in which the carbon nanotubes, mostly single or double-walled, are very homogeneously dispersed between the metal–oxide grains. For the sake of comparison, ceramic and metal–oxide nanocomposites have also been prepared. The microstructure of the specimens has been studied and discussed in relation to the nature of the matrix, the electrical conductivity, the fracture strength and the fracture toughness. The carbon nanotube–metal–oxide composites are electrical conductors owing to the percolation of the carbon nanotubes.     

Mechanical properties and fracture of Al–15 vol.-%B4C based metal matrix composites

The present work was performed on three aluminium metal matrix composites (MMCs) containing 15 vol.-%B₄C particles. The matrix in two of these materials is pure aluminium, whereas the matrix of the third material was an experimental 6063 aluminium alloy. All composites were homogenised at elevated temperatures for 48 h before being quenched in warm water. The quenched samples were aged in the range of 25–400°C for 10 h, at each temperature. Hardness and tensile tests performed on the aged MMCs show that the presence of Zr (with or without Ti) resulted in a noticeable hardening due to the precipitation of a Zr rich phase. Maximum strengthening was obtained from the 6063 based MMC due to the precipitation of Mg₂Si phase particles. The present technique used to produce the MMCs examined proved capable of manufacturing composites with a uniform distribution of B₄C in the matrix with a strong degree of matrix/particle bonding. When the MMC samples were deformed to failure, the B₄C was fractured transgranularly without debonding from the matrix. The addition of Zr and Ti resulted in the formation of protective layers around the B₄C particles that were retained after fracture; these protective layers were not affected by the B₄C particle size (0·15–20 μm). Stacking faults were commonly observed in fractured Al 6063/B₄C/15p samples. The precipitation of zirconium–titanium compounds during aging contributed to the composite strength.     

Influences of misch metal on hydrogenstorage properties of FeTi_(1.3) alloy

lINTRODUCTI0NItiswellknownthattheFeTialloyhasmanyfavorablecharacteristicsforhydrogenstor-ageapplication,suchashighhydrogenstoragecapacity,goodthermodynamicspropertiesandlowmaterialcost.Buttheactivati0nbehavi0r0fFeTialloyisratherpoor.Ithastobeactivatedbyheatingupto670Kinahydrogenatmosphereorinvacuumlfollowedbycoolingt0roomtem-peratureandbyapplyinghigh-pressurehydro-gen['~'].PooractivationbehaviorofFeTial1oyhasimpededitsapplications.HowtomaketheactivationbehaviorofFeTiall0ybetterbecomesa…     

Hydrogen storage properties of non stoichiometric AB_2-type metal hydride

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