Fabrication and Characterization of Plasma-Sprayed Carbon-Fiber-Reinforced Aluminum Composites

Carbon fiber (C_f)/Al specimens were fabricated by plasma-spraying aluminum powder on unidirectional carbon fiber bundles (CFBs) layer by layer, followed by a densification heat treatment process. The microstructure and chemical composition of the C_f/Al composites were examined by scanning electron microscopy and energy-dispersive spectrometry. The CFBs were completely enveloped by aluminum matrix, and the peripheral regions of the CFBs were wetted by aluminum. In the wetted region, no significant Al₄C₃ reaction layer was found at the interface between the carbon fibers and aluminum matrix. The mechanical properties of the C_f/Al specimens were evaluated. When the carbon fiber volume fraction (CFVF) was 9.2%, the ultimate tensile strength (UTS) of the C_f/Al composites reached 138.3 MPa with elongation of 4.7%, 2.2 times the UTS of the Al matrix (i.e., 63 MPa). This strength ratio (between the UTS of C_f/Al and the Al matrix) is higher than for most C_f/Al composites fabricated by the commonly used method of liquid-based processing at the same CFVF level.     

Microstructure,Phase Occurrence,and Corrosion Behavior of As-Solidified and As-Annealed Al-Pd Alloys

In the present work, we studied the microstructure, phase constitution, and corrosion performance of Al₈₈Pd₁₂, Al₇₇Pd₂₃, Al₇₂Pd₂₈, and Al₆₇Pd₃₃ alloys (metal concentrations are given in at.%). The alloys were prepared by repeated arc melting of Al and Pd granules in argon atmosphere. The as-solidified samples were further annealed at 700 °C for 500 h. The microstructure and phase constitution of the as-solidified and as-annealed alloys were studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. The alloys were found to consist of (Al), ε _n (~ Al₃Pd), and δ (Al₃Pd₂) in various fractions. The corrosion testing of the alloys was performed in aqueous NaCl (0.6 M) using a standard 3-electrode cell monitored by potentiostat. The corrosion current densities and corrosion potentials were determined by Tafel extrapolation. The corrosion potentials of the alloys were found between ? 763 and ? 841 mV versus Ag/AgCl. An active alloy dissolution has been observed, and it has been found that (Al) was excavated, whereas Al in ε _n was de-alloyed. The effects of bulk chemical composition, phase occurrence and microstructure on the corrosion behavior are evaluated. The local nobilities of ε _n and δ are discussed. Finally, the conclusions about the alloy’s corrosion resistance in saline solutions are provided.     

Normal state of metallic hydrogen sulfide

A generalized theory of the normal properties of metals in the case of electron–phonon (EP) systems with a nonconstant density of electron states has been used to study the normal state of the SH₃ and SH₂ phases of hydrogen sulfide at different pressures. The frequency dependence of the real Re Σ (ω) and imaginary ImΣ (ω) parts of the self-energy Σ (ω) part (SEP) of the Green’s function of the electron Σ (ω), real part Re Z (ω), and imaginary part Im Z (ω) of the complex renormalization of the mass of the electron; the real part Re χ (ω) and the imaginary part Imχ (ω) of the complex renormalization of the chemical potential; and the density of electron states N (ε) renormalized by strong electron–phonon interaction have been calculated. Calculations have been carried out for the stable orthorhombic structure (space group Im3?m) of the hydrogen sulfide SH₃ for three values of the pressure P = 170, 180, and 225 GPa; and for an SH₂ structure with a symmetry of I4/mmm (D4h1?7) for three values of pressure P = 150, 180, and 225 GP at temperature T = 200 K.     

Optimum Combination of Thermoplastic Formability and Electrical Conductivity in Al–Ni–Y Metallic Glass

Both thermoplastic formability and electrical conductivity of Al–Ni–Y metallic glass with 12 different compositions have been investigated in the present study with an aim to apply as a functional material, i.e. as a binder of Ag powders in Ag paste for silicon solar cell. The thermoplastic formability is basically influenced by thermal stability and fragility of supercooled liquid which can be reflected by the temperature range for the supercooled liquid region (ΔT_x) and the difference in specific heat between the frozen glass state and the supercooled liquid state (ΔC_p). The measured ΔT_x and ΔC_p values show a strong composition dependence. However, the composition showing the highest ΔT_x and ΔC_p does not correspond to the composition with the highest amount of Ni and Y. It is considered that higher ΔT_x and ΔC_p may be related to enhancement of icosahedral SRO near T_g during cooling. On the other hand, electrical resistivity varies with the change of Al contents as well as with the change of the volume fraction of each phase after crystallization. The composition range with the optimum combination of thermoplastic formability and electrical conductivity in Al–Ni–Y system located inside the composition triangle whose vertices compositions are Al₈₇Ni₃Y₁₀, Al₈₅Ni₅Y₁₀, and Al₈₆Ni₅Y₉.     

The influence of the conditions of synthesis on the composition and mechanical properties of silicon oxycarbonitride nanocomposite films

Dielectric films of hydrogenated silicon oxycarbonitride SiC _x N _y O _z :H were prepared by plasmaenhanced chemical vapor deposition using gas mixtures of 1,1,1,3,3,3-hexamethyldisilazane (HMDS) or 1,1,3,3-tetramethyldisilazane (TMDS) with oxygen and nitrogen in the temperature range of 373–973 K. The effect of the conditions of synthesis on the chemical and phase composition of the films was studied, in the amorphous part of which nanocrystals belonging to the phases of the Si–C–N system α-Si₃N₄, α-Si_3–x C _x N₄, and graphite were distributed. To measure the hardness and Young’s modulus, the nanoindentation method was used. The influence that the synthesis temperature and nitrogen-to-oxygen ratio in the initial gas mixtures HMDS + O₂ + xN₂ and TMDS + O₂ + xN₂ have on the hardness and Young’s modulus of the resulting SiC _x N _y O _z :H films was investigated. The maximum obtained values of these parameters were 20.4 and 201.5 GPa, respectively.     

Effect of Al,Si, and Cr on the thermal stability and high-temperature oxidation resistance of coatings based on titanium boronitride

The thermal stability and resistance to high-temperature oxidation of multicomponent nanostructured coatings in the Ti-X-B-N (X = Al, Si, Cr) system have been studied using X-ray diffraction analysis, X-ray photoelectron spectroscopy, secondary-ion mass spectroscopy, and transmission electron microscopy. The hardness, elastic modulus, elastic recovery, friction coefficient, wear rate, and adhesion strength of the coatings have been determined. It has been established that Ti-B-N and Ti-Cr-B-N coatings exhibit a stable nanostructure and high stable mechanical and tribological properties up to 1000°C. The coatings with an fcc structure can be also employed as barrier layers preventing diffusion of metal atoms from the substrate. It has been shown that the high resistance to high-temperature oxidation of Ti-Cr-B-N and Ti-Al-Si-B-N coatings is connected with the fact that protective oxide layers based on (Ti,Cr)BO₃ and Ti _x Al _y SiO _z are formed on their surface.     

Isothermal Section of the Al-Mn-Dy System at 500 °C

Phase relationships in the Al-Mn-Dy ternary system at 500 °C have been investigated by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, and electron probe microanalysis. From the experimental results it was concluded that the isothermal section consists of 16 single-phase regions, 26 two-phase regions and 12 three-phase regions. Two extensive solid solutions, (Al _x Mn_1?x )₁₂Dy and (Al_1?x Mn _x )₂Dy, were observed. The solid solution (Al _x Mn_1?x )₁₂Dy forms by Al replacing Mn in Mn₁₂Dy, while the continuous solid solution (Al_1?x Mn _x )₂Dy forms by Mn and Al mutually substituting in Al₂Dy and Mn₂Dy, respectively. The maximum solid solubility of Al in Mn₁₂Dy is 79.3 at.%.     

Phases and microstructures of high Zn-containing Al–Zn–Mg–Cu alloys

Phases and microstructures of three high Zncontaining Al–Zn–Mg–Cu alloys were investigated by means of thermodynamic calculation method, optica microscopy(OM), scanning electron microscopy(SEM)energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), and differential scanning calorimetry(DSC) analysis. The results indicate that similar dendritic network morphologies are found in these three Al–Zn–Mg–Cu alloys. The as-cast 7056 aluminum alloy consists of aluminum solid solution, coarse Al/Mg(Cu, Zn, Al)_2 eutectic phases, and fine intermetallic compounds g(MgZn_2). Both of as-cast 7095 and 7136 aluminum alloys involve a(Al)eutectic Al/Mg(Cu, Zn, Al)_2, intermetallic g(MgZn_2), and h(Al_2Cu). During homogenization at 450 °C, fine g(MgZn_2) can dissolve into matrix absolutely. After homogenization at 450 °C for 24 h, Mg(Cu, Zn, Al)_2 phase in 7136 alloy transforms into S(Al_2Cu Mg) while no change is found in 7056 and 7095 alloys. The thermodynamic calculation can be used to predict the phases in high Zncontaining Al–Zn–Mg–Cu alloys.     

Thermal Shock Resistance of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/h<Emphasis Type="Italic">-</Emphasis>BN Composites Prepared via Catalytic Reaction-Bonding Route

Si₃N₄/h-BN ceramic matrix composites were prepared via a catalytic reaction-bonding route by using ZrO₂ as nitridation catalyst, and the water quenching (fast cooling) and molten aluminum quenching tests (fast heating) were carried out to evaluate the thermal shock resistance of the composites. The results showed that the thermal shock resistance was improved obviously with the increase in h-BN content, and the critical thermal shock temperature difference (ΔT _c) reaches as high as 780 °C when the h-BN content was 30 wt.%. The improvement of thermal shock resistance of the composites was mainly due to the crack tending to quasi static propagating at weak bonding interface between Si₃N₄ and h-BN with the increase in h-BN content. For the molten aluminum quenching test, the residual strength showed no obvious decrease compared with water quenching test, which could be caused by the mild stress condition on the surface. In addition, a calculated parameter, volumetric crack density (N _f), was presented to quantitative evaluating the thermal shock resistance of the composites in contrast to the conventional R parameter.     

High Pressure Oxidation of Metals: Tantalum in Oxygen

The temperature and pressure dependence of the reaction of tantalum in oxygen were investigated from 500° to 1000°C at pressures from 10 mm Hg to 600 psi total oxygen pressure. Tantalum was found to oxidize linearly under the above conditions. Three distinct regions of temperature dependence were found with different energies of activation. From 500° to 600°C the rate of oxidation of tantalum was found to be essentially independent of the oxygen pressure at the pressure investigated. The oxidation rate increases rapidly with an increase in pressure from 600° to 800°C. The dependence of the oxidation rate on the bulk concentration may be expressed by V = k′θ, where k′ is the specific rate constant and \(\theta=k_1C_{\text{O}_{2}}/(1\;+\;k_1C_{\text{O}_{2}})\), where k₁is the equilibrium constant for the adsorption of oxygen on tantalum.     

Equilibrium adsorption of stilbenoids at metal oxides

The isotherms of adsorption of trans-hydroxystilbenes (stilbenoids) and hydroxybenzenes (phenols) from n-hexane-ethyl acetate (1: 1) at nanodispersed aerogels of aluminum and titanium oxides were measured under static conditions. The adsorption isotherms can be approximated well by the Freundlich equation for the model of localized adsorption at energetically heterogeneous solids. It was found that the adsorption value of both stilbenoids and phenols is improved with an increase in the number of OH groups in their molecules, being sensitive to the chemistry of the adsorbent surface. trans-Hydroxystilbenes adsorb at TiO₂ better than do the corresponding phenols. The opposite pattern was observed for Al₂ O₃. The adsorption of trans-hydroxystilbenes at TiO₂ is irreversible and accompanied by the formation of colored surface compounds.     

Effect of Si on the Formation and Growth of Intermetallic Compounds at Roll-Bonded Aluminum–Steel (Al-St) Interface

The formation and growth of intermetallic compounds (IMC) were investigated using the Al-St clad materials with additional different Si content to aluminum and steel substrate by differential scanning calorimetry, scanning electron microscopy and energy-dispersive x-ray spectroscopy, x-ray diffraction and transmission electron microscopy. The addition of Si to Al (Al-0.8Si/St) can drastically delay the formation of IMC and accelerate the growth of IMC layer. The Si (Al-0.8Si/St) segregates at the interface and inhibits the diffusion of Al atom to steel before the IMC forms, which further decreases the diffusion depth of Al in the steel layer. By contrast, the addition of Si to St (Al/St-0.8Si) has limited impact on delaying the formation and decelerating the growth of IMC layer. The Si (Al/St-0.8Si) hardly affects the diffusion of Fe atom to the aluminum layer. Among the four clad materials, the major IMC layer (η-Fe₂Al₅) always exhibits the parabolic growth phenomenon. The addition of Si cannot influence the phase compositions of IMC at the interface between the η-Fe₂Al₅ layer and the aluminum. However, we observe an extra Fe-rich phase β₁-Fe₃Al at the interface between the Fe₂Al₅ layer and steel substrate in the Al-0.8Si/St clad material.     

Magnetoresistive properties of Ni-doped La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> manganites

La_0.7Sr_0.3Mn_1?x Ni _x O₃ (x = 0, 0.025, 0.050 and 0.075) ceramics were prepared by the conventional solid-state reaction method. The partial substitution of Mn by Ni²⁺ leads to a decrease in cell volume as well as a structural transition from the rhombohedral to the orthorhombic structure. Ni²⁺ doping increases the electrical resistivity, decreases the semiconductor–metal transition temperature (T _ms) and relatively enhances the room temperature magnetoresistance (MR), especially in x = 0.025 and around T _ms. With respect to conduction mechanism, the small polaron hopping (SPH) and the variable range hopping (VRH) models were used to examine conduction in the semiconducting region.     

Radiation Stability of Metal Fe<Subscript>0.56</Subscript>Ni<Subscript>0.44</Subscript> Nanowires Exposed to Powerful Pulsed Ion Beams

The resistance of Fe_0.56Ni_0.44 alloy nanowires (fabricated by template synthesis using polymer track membranes) 60 and 100 nm in diameter to radiation with powerful pulsed 85% C⁺ + 15% H⁺ ions (E = 20 keV, j = 100 A/cm², τ = 90 ns) has been investigated. The conclusion that nanosized regions of explosive energy release, so-called thermal spikes, which are thermalized regions of dense cascades of atomic displacements heated to several thousand degrees (in which the thermal pressure can reach several tens of GPa), play an important role in the nanowire structure change is drawn. These are observed as melted nanosized regions on the nanowire surface. Calculations have shown that energy supplied by an ion beam during the action of a single pulse in the used mode (provided that thermal radiation and thermal conductivity serve as energy sinks) can be both sufficient and insufficient to completely melt nanowires depending on their orientation with respect to the ion beam. The bending and failure of nonmelted nanowires is explained by the generation and propagation of post-cascade shock waves.     

Influences of carbon and silicon on blister formation in scale surface during high temperature oxidation of carbon steels

The in-situ blistering phenomena of the scale ‘surface’ was investigated on three carbon steels with respect to carbon and silicon concentrations, such as 0.05 wt%C, 0.2 wt%C, and 0.2 wt%C-0.2 wt%Si. The oxidation and blistering kinetics and blister area fraction during high temperature oxidation were analyzed. The average thickness of the surface scale by oxidation during isothermal holding from 800 to 1200 °C in dry air was observed to decrease when the amount of carbon increased and/or when Si was inserted additionally. Thus, the blistering behavior depended primarily on a change in oxidation temperature (T _ox ) as well as amounts of carbon and silicon in the matrix. It is also revealed that such blister formation would be triggered by growth of internal stress and active generations of CO and/or CO₂ gases at the interface between the scale and matrix since carbon would result in an increase in the blister formation by generating CO and/or CO₂ gas. In addition, silicon might play an important role in preventing the blister formation at T _ox below 900 °C by reducing the thickness of the surface scale whilst silicon might enhance the blister formation by means of the appreciable micro-void formation in the scale layer at T _ox higher 900 °C.     

Evaluation of Calphad Approach and Empirical Rules on the Phase Stability of Multi-principal Element Alloys

The formation of single disordered solid solution phase in multi-principal element alloys (MPEAs) is crucial for the properties of the alloy, and thus several empirical rules have been proposed to predict the stability of disordered solid solution phase in MPEAs. Compared to these empirical rules, Calphad approach provides a more reliable and quantitative prediction. In the present work, we choose three model systems of Al _x CoCrFeNi, CoCr _x FeMnNi and Al _x LiMgSnZn to evaluate these empirical rules by comparing with the Calphad calculated results. The Calphad calculated temperature-composition sections reveal the effect of composition on the phase formation under equilibrium condition. Corresponding diagrams along these sections illustrate parameter variations from empirical rules associated with alloy compositions and highlight predictions and limitations. The impact of the different sources of atomic size data is also discussed.     

Effect of plastic deformation on disordering and ordering processes in the intermetallic compound Ti<Subscript>3</Subscript>Al

Samples of a Ti₃Al intermetallic compound have been subjected to cold plastic deformation with different logarithmic (true) strains e up to 10.3 using high-pressure torsion (HPT) under a pressure of 9 GPa. Formation of the disordered phase depending on the strain has been studied by X-ray diffraction and electron microscopy. At the degrees of deformation e = 8.7–10.3, a nanostructured disordered phase with a crystal size of mainly 5–15 nm is formed. Recovery of the ordered structure occurs in a temperature range of 400–600°C and is accompanied by the recrystallization of the deformed structure. In recrystallized grains of the ordered phase, antiphase domains appear in the form of oriented plates.     

Anisotropic Mechanical Behavior of AlSi10Mg Parts Produced by Selective Laser Melting

AlSi10Mg cylinders produced by laser powder-bed fusion have somewhat different yield behavior for cylinders with XY orientation and Z orientation. Earlier yielding for Z-oriented samples is likely related to micro-residual stress, resulting from the difference in thermal expansion of the aluminum matrix and cellular silicon. Smaller tensile reduction in area of Z-oriented samples is related to tearing along the softer region at the boundaries of melt pools, where the silicon cell spacing is larger. Indentation measurements confirmed the lower hardness at the edges of melt pools.