Microstructure and mechanical properties of nanocrystalline high strength Al–Mg–Si (AA6061) alloy by high energy ball milling and spark plasma sintering

In the present paper, the microstructure and mechanical properties of nanostructured Al–Mg–Si based AA6061 alloy obtained by high energy ball milling and spark plasma sintering were reported. Gas atomized microcrystalline powder of AA6061 alloy was ball milled under wet condition at room temperature to obtain nanocrystalline powder with grain size of 30 nm. The nanocrystalline powder was consolidated to fully dense compacts by spark plasma sintering (SPS) at 500 °C. The grain size after SPS consolidation was found to be 85 nm. The resultant SPS compacts exhibited microhardness of 190–200 HV_100 g, compressive strength of 800 MPa and strain to fracture of 15%.     

Survey of the 1997, 1998 and 1999 annual technical reports on patent information activities (part II: I to Z)

The activities of 59 intellectual property offices and organisations worldwide in the field of patent information are summarised for the period 1997–1999. The summary is presented under eight standard headings, as far as relevant, for each country. Activity varies enormously from just a handful of applications through to RU (24K), GB (30K), DE (58K), KR (80K), EP (121K), US (270K utility patents), and Japan (405K); the numbers are continuing to increase significantly in most countries. This part (second of two) covers 35 countries and organisations, with WIPO codes starting I to Z.The author concludes, inter alia, that

(i) the number of patent applications is increasing at such a rate that the granting or registration activities of many IP Offices are unable to keep up;

(ii) the development of electronic filing systems is proceeding apace;

(iii) the IPC, or derivatives such as ECLA, continue to be the primary tools for allocation, classification, and search in all IP Offices, except US and GB;

(iv) automated search systems continue to be developed and are used in tandem with manual search files, commercial and free Internet online databases; and

(v) the use of complex jukebox systems to handle the vast numbers of patent specifications on CD-ROM continues to increase.

Thin films deposition with ECR planar plasma source

The results of film deposition of pure tungsten as well as intermetallic compound of NdFeB type on various substrates using planar ECR plasma source (with multipole magnetic field) developed in our laboratory are presented. The frequency of 2.45 GHz was generated within the magnetic system by two-slot antenna. The ions of ECR argon plasma are used for target sputtering. The main plasma parameters are density 10¹⁰ cm⁻³, T_e15 eV, ions energy 20 eV, ion current density 3.5 mA/cm² at the ultimate magnetron power. Under sputtering of Nd₈Fe₈₆B₆ target the amorphous films with high adherence and thickness of 5 μm were formed on the substrate. The deposition rate of tungsten films (target biasing 900 V) was 0.59 nm/s. The fine-grained films with high adhesion were obtained. They were tested against heat loads up to 100 J/cm² produced under irradiation of coatings with plasma streams.     

Visualization of emitting sites on carbon fiber cathode by surface treatment in high-current vacuum discharge process

In this paper, a carbon fiber cathode, having robust, easily shaped, and epoxy-free properties, is constructed by squeeze casting technique that can overcome some disadvantages of conventional methods. Carbon fiber emitters on the cathode surface had a high distribution density, thus ensuring sufficient emission centers or emission uniformity. The fabricated cathode was tested in a diode powered by a 350 kV, 40 Ω, 400 ns high-voltage pulse generator. The turn-on electric field was estimated to be 50 kV/cm, and the field enhancement factor was (1.2–2.0) × 10³. It was found that the electron emission of carbon fiber cathode is initiated from the individual bright spots at a current density of up to 400 A/cm². Most notably, the X-ray images of electron beam on anode foil demonstrate the development of bright spots on the cathode surface. As a whole, this class of cathodes can endure high-current pulsed emission, and has a positive application prospect.     

Dielectric and electrostrictive properties of PMNT near MPB

The dielectric constant (ε_r), dielectric loss (tan δ) and strain induced by electric field in lead magnesium niobate–lead titanate (PMN-PT/PMNT) solid solutions in the morphotropic phase boundary (MPB) region at different sintering temperatures have been studied. ε_r and tan δ increase, whereas Curie phase transition range decreases with the increase in sintering temperature. Strain levels in the range of 0.07–0.2% were obtained. A high saturated strain% 0.19, a high d₃₃ coefficient 320 pm/V and a low strain hysteresis% 3.5 in PMNT 68/32 composition sintered at 1200 °C indicate its suitability for actuator applications.     

Environmental sensitivity and mechanical behavior of boron-doped Fe–45at.%Al intermetallic in the temperature range from 77 to 1000 K

The tensile properties and fracture behavior of a coarse-grained (grain size 420 μm) Fe–45at.%Al intermetallic doped with 0.05 at.% boron were examined at ambient temperature in air, argon and vacuum as well as in the 77–1000 K temperature range in liquid nitrogen, dry ice and air. Before testing the alloy was low temperature annealed (vacancy annealed) in order to remove all the retained vacancies. At ambient temperature ductility increases accordingly to decreasing water vapor (moisture) content in each environment. The mixed transgranular cleavage (TGC)+intergranular failure (IGF) mode in vacuum, which is associated with the highest elongation (6%), exhibits around 40% of IGF and the mixed fracture mode in argon, which is associated with the second highest elongation (3.2%), exhibits 15% of IGF. The TGC fracture mode in air is associated with the lowest elongation (1%). Elongation in the cryogenic temperature range from 77 to 213 K is very low being in the range from 0.6 to 2.8%, and is associated with a mixed transgranular+intergranular fracture mode. Elongation increases gradually from 300 to 800 K attaining a ductility peak at 800 K and then decreases rapidly with increasing temperature. At 600–800 K, the yield strength of Fe–45Al–0.05B exhibits anomalous temperature dependence with the yield strength peak at 800 K. The mode of fracture from 300 to 700 K is predominantly TGC and that at the ductility peak is ductile rupture with very deep dimples. At temperatures above 800 K the mode of fracture changes to a typical intergranular creep (fibrous) failure with numerous flat dimples (voids/cavities) at the grain boundary facets, which is associated with a tensile ductility drop. Fine particles (borides) are observed at the grain boundary facets, which assist the development of intergranular creep fracture.     

Mechanical and thermal properties of AlN–BN–SiC ceramics

Mechanical and thermal properties were characterized for two AlN:BN:SiC composite ceramics produced from BN with different particle sizes. The ceramics were hot pressed at temperatures from 1950 to 2100 °C to 97% relative density. For both materials, the matrix (90:10 vol% SiC:AlN) had a grain size of 0.4 μm, and the BN grains (10 vol%) were crystallographically aligned. Microhardness values were between 20 and 22 GPa, while fracture toughness values were between 2.5 and 3.1 MPa m^1/2. Other properties were found to be dependent on testing direction. Elastic moduli were between 260 and 300 GPa and strengths were 630 MPa for small particle BN additions. Thermal conductivity was calculated to be between 25 and 37 W/m K at room temperature and 17 and 25 W/m K at 900 °C. The low values compared to traditional SiC ceramics were attributed to AlN–SiC solid solution formation and sub-micron matrix grain sizes.     

High specific strength Mg-based bulk metallic glass matrix composite highly ductilized by Ti dispersoid

Mg-based bulk metallic glass matrix composite with hcp-Ti powders was fabricated by casting the mixtures of Mg₆₅Cu₂₅Gd₁₀ molten alloy and pure Ti powders into a copper mold. Ti powder was spherical and less than 150 μm in diameter, and its volume fraction was controlled from 5 to 40%. Thermal stability of the glassy matrix was maintanied even in the coexistence with the Ti powders. However, Ti dispersoid caused a significant improvement on compressive ductility from 0% plastic deformation for the monolithic glass to 41% plastic deformation for the composite with 40 vol.% Ti powders. This is the first success of synthesizing Mg-based alloys with high ultimate strength of 900 MPa level as well as the large plastic deformation of 40%, and suggests a novel guideline to develop Mg-based alloys having high specific strength with high ductility.     

The influence of Yb doping on the upconversion luminescence of Pr in aluminum oxide based powders prepared by combustion synthesis

The effect of ytterbium (Yb³⁺) doping on the upconversion (UC) emission of praseodymium (Pr³⁺) doped in aluminum oxide based powders prepared by combustion synthesis is reported for near-infrared excitation (λ = 980 nm). Our experimental results show that the crystalline structure and the UC emission changes with the Yb³⁺ concentration. The sample containing only Pr³⁺ (1.0 wt.%) did not show any UC signal and the UC emission profiles of the samples containing Pr³⁺ (1.0 wt.%) and Yb³⁺ (0.5, 2.0 wt.%) are quite different. The sample containing 0.5 wt.% of Yb³⁺ has five emission lines in the visible range associated to Pr³⁺ 4f–4f transitions, ³P₀ → ³H₄ (497 nm), ³P₀ → ³H₅ (525 and 550 nm), ³P₀ → ³H₆ (620 nm) and ³P₀ → ³F₂ (650 nm). We believe that the UC process has its origin in energy transfer from Yb³⁺ ions to Pr³⁺ ions in Pr_0.83Al_11.83O₁₉ phase. The sample containing 2.0 wt.% of Yb³⁺ has only one emission line in the visible range peaked at 507 nm which we believe has its origin in cooperative UC emission due to excited Yb³⁺ pairs in YbAlO₃ phase. The samples containing Yb³⁺ also present UC emission lines in the near-infrared which are assigned to intrinsic lattice defects.     

Synthesis, characterization and dielectric properties of nanocrystalline strontium zirconate prepared through a modified reverse micellar route

Nanocrystalline strontium zirconate has been synthesized using a modified reverse micellar route (avoiding Sr-alkoxide). Powder X-ray diffraction studies show the monophasic nature of the powder of SrZrO₃ after heating at 800 °C. The particle size has been obtained from X-ray line broadening studies (62 nm) and transmission electron microscopic studies (72 nm). The average grain size of 85 nm was found to be reasonably stable to sintering till 1000 °C. A dielectric constant of 19.8 is observed for nanocrystalline SrZrO₃ sintered at 1000 °C. Detailed dielectric studies have been carried out with respect to frequency and temperature.     

Effect of the extrusion conditions on microstructure evolution of the extruded Al–Mg–Si–Cu alloy rods

Hot extrusion experiment was conducted using an Al–Mg–Si–Cu alloy and the effect of the extrusion conditions on microstructure and texture changes through the radial direction was investigated by using SEM/EBSP analysis method. In the surface layer where severe frictional shear deformation is predominant, the recrystallized 1 1 0//ED grains surrounded by high angle grain boundaries are formed in spite of the existence of some peripheral overcoarse grains. Strong 1 0 0//ED and 1 1 1//ED fiber textures evolve in the center where axisymmetric deformation along the extrusion direction is intensive. As the extrusion ratio increases, number of 1 1 1//ED grains remarkably decreases while the number of 1 0 0//ED grains apparently increases. It is also found that the 1 0 0//ED grains surrounded by low angle grain boundaries form orientation colonies in the center of the extruded rods.     

Tensile deformation and fracture behaviors of high purity polycrystalline zinc

The damage and fracture behaviors of high purity polycrystalline zinc with two grain sizes during tension were investigated experimentally at different strain rates. It was found that specimens with coarse grains (1 mm) showed serrated flow behavior and failed in intermittent brittle cleavage fracture, while specimens with fine grains (70 μm) showed no cleavage crack initiation before necking even at high strain rate. It was observed that the fracture process of the fine-grained specimen was highly related to strain rates. With the strain rate increasing, the damage mechanism transformed from formation of tearing cracks along interfaces (including grain boundaries, twin boundaries and kink band boundaries) and cavity coalescence into abrupt quasi-cleavage fracture. Based on the observation, the inter-crystalline fracture of zinc was investigated, and the damage and fracture behaviors of polycrystalline zinc during tension at room temperature were discussed in general.     

One-dimensional simulation of multi pulse phenomena in dielectric-barrier atmospheric-pressure glow discharges

The dielectric-barrier configuration is commonly used to generate uniform, highly non-equilibrium atmospheric-pressure glow discharges. Although recent research has improved our understanding of these discharges, several questions relating to the structure and transient characteristics of the discharge remain to be answered. We employ a self-consistent, one-dimensional, model to simulate these discharges in helium. In particular, we address question of pulse formation and multi-pulse phenomena. The model provides excellent predictive capability for all trends concerning multiple pulse behavior. The appearance of multiple pulses with increasing external voltages is predicted accurately for the nominal operating frequency of 10 kHz. With decreasing frequencies down to 100 Hz, the weakening of the discharge pulse and the increasing number of pulses are also predicted. However, in the low frequency regime the prediction of the discharge phenomena is very sensitive to plasma chemistry model. Impurity effects appear to play an important role in this regime.     

Analysis and elimination of the distortion in electro-optic measurement of low-energy subpicosecond electron bunches

Electro-optic (EO) technique is widely used to characterize longitudinal profile of electron bunches. However, electron bunches with a low energy (MeV) and a short time duration (subpicosecond) cannot be well resolved by EO measurement, which leads to distortion. The convolution theorem is proposed to analyze this distortion in EO measurement. And the factors leading to the distortion are discussed, among which the divergent Coulomb field of electrons is the main one. Distortion elimination and reconstruction of electron bunch profiles from detected EO signals is an ill-posed inverse problem. This paper proposes an iterative Tikhonov regularization method to solve this inverse problem and to reconstruct electron bunch profiles from the EO signals detected by the EO measurement. The feasibility of our proposal is tested and numerically verified based on subpicosecond electron bunches with several MeV energy.     

From iron(III) precursor to magnetite and vice versa

The syntheses of nanosize magnetite particles by wet-chemical oxidation of Fe²⁺ have been extensively investigated. In the present investigation the nanosize magnetite particles were synthesised without using the Fe(II) precursor. This was achieved by γ-irradiation of water-in-oil microemulsion containing only the Fe(III) precursor. The corresponding phase transformations were monitored. Microemulsions (pH  12.5) were γ-irradiated at a relatively high dose rate of 22 kGy/h. Upon 1 h of γ-irradiation the XRD pattern of the precipitate showed goethite and unidentified low-intensity peaks. Upon 6 h of γ-irradiation, reductive conditions were achieved and substoichiometric magnetite (Fe_2.71O₄) particles with insignificant amount of goethite particles found in the precipitate. Hydrated electrons , organic radicals and hydrogen gas as radiolytic products were responsible for the reductive dissolution of iron oxide in the microemulsion and the reduction Fe³⁺ → Fe²⁺. Upon 18 h of γ-irradiation the precipitate exhibited dual behaviour, it was a more oxidised product than the precipitate obtained after 6 h of γ-irradiation, but it contained magnetite particles in a more reduced form (Fe_2.93O₄). It was presumed that the reduction and oxidation processes existed as concurrent competitive processes in the microemulsion. After 18 h of γ-irradiation the pH of the medium shifted from the alkaline to the acidic range. The high dose rate of 22 kGy/h was directly responsible for this shift to the acidic range. At a slightly acidic pH a further reduction of Fe³⁺ → Fe²⁺ resulted in the formation of more stoichiometric magnetite particles, whereas the oxidation conditions in the acidic medium permitted the oxidation Fe²⁺ → Fe³⁺. The Fe³⁺ was much less soluble in the acidic medium and it hydrolysed and recrystallised as goethite. The γ-irradiation of the microemulsion for 25 h at a lower dose rate of 16 kGy/h produced pure substoichiometric nanosize magnetite particles of about 25 nm in size and with the stoichiometry of Fe_2.83O₄.     

Effect of environment on fatigue crack growth in ultrafine grain Al–Mg

The fatigue crack growth rates, obtained in high vacuum and in ambient air, of ultrafine grain (UFG) Al–7.5Mg (grain size  250 nm) at various load ratios were compared to those of powder-metallurgy (P/M) Al–7Mg (grain size  2 μm) and ingot-metallurgy (I/M) Al–7Mg (grain size  100 μm). In both vacuum and ambient air, fatigue crack growth rates at all stress ratios decrease with increasing grain size. The fatigue crack growth threshold (ΔK_th) follows the reverse order, increasing with increasing grain size. These trends are interpreted in terms of fracture surface roughness effects that are correlated with grain size. In vacuum, the thresholds of all three materials exhibit no load ratio dependency at load ratios from 0.1 to 0.5. In air, the threshold of UFG Al–7.5Mg exhibits weak load ratio dependency, while P/M and I/M Al–7Mg exhibit modest load ratio dependency. The environmental effect on the fatigue crack growth rates is assessed by determining the difference in crack growth driving force (ΔK) between air and vacuum. It was found that the environmental contribution to the driving force of all three materials is similar, nearly independent of grain size.     

A study of tensile properties in Al–Si–Cu and Al–Si–Mg alloys: Effect of β-iron intermetallics and porosity

The effect of β-iron intermetallics and porosity on the tensile properties in cast Al–Si–Cu and Al–Si–Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 alloys. The results showed that the alloy ductility and ultimate tensile strength (UTS) were subject to deterioration as a result of an increase in the size of β-iron intermetallics, most noticeable up to β-iron intermetallic lengths of 100 μm in 319.2 alloys, or 70 μm in A356.2 alloys. An increase in the size of the porosity was also deleterious to alloy ductility and UTS. Although tensile properties are interpreted by means of UTS vs. log elongation plots in the present study, the properties for all sample conditions were best interpreted by means of log UTS vs. log elongation plots, where the properties increased linearly between conditions of low cooling rate–high Fe and high cooling rate–low Fe. The results are explained in terms of the β-Al₅FeSi platelet size and porosity values obtained.     

Superplastic flow in a nanostructured aluminum alloy produced using high-pressure torsion

Samples of a spray-cast Al-7034 alloy were processed by high-pressure torsion (HPT) at temperatures of 293 or 473 K using an imposed pressure of 4 GPa and torsional straining through five revolutions. Processing by HPT produced significant grain refinement with grain sizes of 60 and 85 nm at the edges of the disks for the two processing temperatures. In tensile testing at room temperature, the alloy processed by HPT exhibited higher strength and lower ductility than the unprocessed material. Good superplastic properties were achieved in tensile testing at elevated temperatures with a maximum elongation of 750% for the sample processed at 473 K and tested in tension at 703 K under an initial strain rate of 1.0 × 10⁻² s⁻¹. The measured superplastic elongations are lower than in samples prepared by equal-channel angular pressing because of the use of very thin disks in the HPT processing.     

The effect of Li on the tensile properties of cast Al–Mg2Si metal matrix composite

The effects of both Li modification and cooling rate on the microstructure and tensile properties of an in situ prepared Al–15%Mg₂Si composite were investigated. It was found that the addition of 0.3%Li reduces the average size of Mg₂Si primary particles from 30 to 6 μm. The effect of cooling rate was investigated by the use of a mold with different section test bars. The results showed an increase in both UTS and elongation values with reduction in section thicknesses corresponding to increasing cooling rates. Adding Li also raised the tensile strength and elongation values and reduced the number of decohered particles observed in fracture surfaces thereby increasing the alloy's ductility. Data scatter and unexpected low tensile values of 3 mm sections were attributed to casting defects observed in fracture surfaces. Large clusters of Mg₂Si particles and eutectic cell boundaries were found to be potential crack propagation paths in this alloy.     

Low-temperature fabrication of 0.65 PMN–0.35 PT by a mixed oxide method

Single-phase perovskite 0.65 PMN–0.35 PT was achieved at low temperature by a conventional mixed oxide method. It was prepared by ball-milling a mixture of PbO(orthorhombic), TiO₂, Nb₂O₅ and (MgCO₃)₄Mg(OH)₂·5H₂O instead of MgO and heat treatment at 800 °C for 2 h. The formation was studied by means of DSC, FT-IR, Coupled TG-Mass, XRD, and SEM. It proceeded via formation of PbO(tetragonal) and Pb₂Nb₂O₇(P₂N) intermediates to form perovskite phase. The pure perovskite PMN-PT powder was obtained in particle size of 0.5–0.8 μm, agglomerate-free, and pseudo-cube. The powder calcined at 600 °C was sintered to 97% T.D. at 900–1000 °C for 2 h and showed room temperature dielectric constant of 3200, loss of 1–2%, and specific resistance of 5 × 10¹¹ Ω cm.