A novel technique of rapid solidification net- form materials synthesis

A novel method of net-form materials synthesis that is related to spray forming has been conceived, and initial verification experiments have been successfully completed. The method uses streams of ultra-uni-form droplets of molten metal that are deposited onto a substrate in a controlled environment. The drop-lets are directed onto the substrate with measured angular dispersions as small as 2 × 10^-6 radians, and speed dispersions as small as 3.5 × 10^-7 times the average speed of the droplet, thereby facilitating the synthesis of small, detailed parts as well as large bulk parts with high resolution and a uniformly fine grain structure.     

Direct synthesis of aligned cis-rich polyacetylene films using low-temperature nematic liquid crystals

Liquid crystal polymerization method has been extended so as to cover synthesis of cis-rich polyacetylene films with high alignment. Three kinds of liquid crystal mixtures which maintain nematic phase at lower temperature than 0 °C have been developed by using a series of liquid crystals of phenylcyclohexane derivatives because of their well-confirmed inertness towards Ti(OBu)₄ - AlEt₃ catalyst. It has been implied from DSC measurements that catalyst solutions using three, five and six component systems permit low-temperature polymerizations ranging from −20 to −30 °C, from −40 to −60 °C and from −10 to −45 °C, respectively. Polyacetylene films synthesized by using five and six component liquid crystals with and without an external magnetic force have high cis contents of 85 – 94 %. High alignment of fibril morphology of the films has also been confirmed through SEM observations. Measurements of electrical conductivity of the films upon iodine doping yielded a maximum conductivity of 1.6 × 10⁴ S/cm and electrical anisotropy of 7.0.     

Rapid solidification of copper alloys with high strength and high conductivity

Rapid solidification has been employed to develop high-strength/high-conductivity copper alloys, because it offers advantages not achievable by conventional ingot metallurgy practice. The effect of rapid solidification on mechanical properties and electrical conductivity on copper alloys (with and without heat treatment) has been studied. Results indicated that alloys of the Cu-Cr-Zr type, rapidly solidified and aged, show a good combination of electrical conductivity [45.82 × 10⁶(l/Ω · m)] and microhardness Vickers (24.46 × 10⁶ Pa) values. These values are superior to those of optimally aged conventional copper alloys for resistance welding electrode applications.     

Creep of Polycrystalline Nickel

Minimum creep rates of nickel samples were measured in the stress region of 2.5×10⁷ to 2.8×10⁹ dyne per sq cm and the temperature region of 400° to 1100°C. The creep rate seems to be proportional to (stress)^4.6 at stresses below 7×10⁸ dyne per sq cm. The activation energy of creep is approximately 65,000 cal per mol.     

Modeling of Ionic Conductivity Enhancement of LiClO4-PVA-C System by TiO2 Addition Using Complex Numerical Model of PDE

PVA-TiO₂ nanocomposite polymer electrolytes (PEs) were produced with different amounts of TiO₂ (0, 5, 10, 15, and 20 wt.%) using the electrospinning process. Morphological studies of PVA-TiO₂ nanofibers were accomplished with SEM. PVA-TiO₂ membranes exhibited a high porosity of 79-91%. The impedance results showed that incorporation of TiO₂ into the nanofiber membrane improved its ionic conductivity from 0.7 × 10^?5 to 2.5 × 10^?5 S/cm at room temperature. Nanofiber PEs showed very good reversibility and electrochemical stability up to 4.7 V. Diffusion coefficient of Li ion into PVA-TiO₂ nanocomposite PEs was estimated by using a complex numerical model of partial differential equation for evaluation of ion transmission. Diffusion coefficient of PVA-TiO₂ PEs containing different amounts of TiO₂ (0, 5, 10, 15, and 20 wt.%) increased with increasing the nanoparticles content.     

The effect of ion implantation on the corrosion behaviour of pure iron—II. Chromium ion implantation

As part of a programme to investigate the effect of ion implantation on the corrosion behaviour of iron, pure iron specimens have been implanted with doses of 5 × 10¹⁴ and 2 × 10¹⁵ chromium ions/mm². Using a three-sweep potentiokinetic polarization technique the corrosion behaviour of these surface alloy layers has been compared with that of conventional binary FeCr alloys containing from 0.8 to 12.5 wt%Cr. It was found that apart from a slight thickening of the air-formed oxide film induced by the ion implantation process, the polarization behaviour of conventional alloys and of alloys produced by ion implantation was qualitatively very similar. Quantitatively the low dose chromium implanted specimens corresponded to a conventional Fe-4.9%Cr alloy while the high dose chromium implanted specimens resembled conventional alloys containing x12.5%Cr. These data provide a sound basis for the interpretation of the potentiokinetic polarization and corrosion behaviour of the novel surface alloy layers which can be produced by ion implantation.     

Transgranular Stress-Corrosion Cracking

Abstract

The rates of dissolution of atoms from steps of different widths on a metal surface are calculated. It is shown that there is a critical spacing, below which the rate of dissolution possible from a step falls rapidly. This critical spacing is related to the solution viscosity and hence the solution composition and temperature by the relationship:

l _crit = 8 παb³η10¹³ √2V₂(ε_s ? ε_∞)/ε_s²KT³ For a stainless steel immersed in 42% MgCl₂ solution at 150°, the calculated critical value of the slip line spacing is 6 × 10^?5cm. This agrees well With the experimental observations, as a steel which has a spacing of 4 × 10^?5 cm. takes fifty times longer to fail in a stress-corrosion test under these conditions than does a steel with a spacing of 7 × 10^?5 cm. The reactivities of steps of different widths on copper alloys are also calculated and it is shown that slip line spacings found in cold worked copper-zinc alloys containing between 10–30% Zn lie in the critical range where the reactivity of the step changes rapidly with step width.     

Concentration dependence of Cr for alleviating environmental embrittlement in Fe30Ni20Mn35Al15

Previously, it has been shown that Fe₃₀Ni₂₀Mn₃₅Al_15, which consists of alternating submicron B2 and f.c.c. lamellae, exhibits a room temperature yield strength of 770 MPa and an elongation of ∼10% at a strain rate of 3 × 10⁻³ s⁻¹ in air, but at the slower strain rate of 3 × 10⁻⁶ s⁻¹ the alloy exhibits an elongation <1% [1]. An addition of 6 at% Cr has been proven to not only solve this environmental problem, but also to increase the elongation to 15–18% irrespective of strain rate [2]. Since we do not know whether Cr additions less than 6 at% can suppress this environmental embrittlement, in this paper we examined the room temperature mechanical properties of several alloys based on Fe₃₀Ni₂₀Mn₃₅Al₁₅ with Cr additions ≤6 at%. We show that additions as low as 0.5 at% Cr alleviate the environmental embrittlement and that additions of ≥2 at% completely suppress the embrittlement with little change in microstructure. X-ray photoelectron spectroscopy examination suggested that the suppression is mostly due to the formation of protective oxide scales on the surface that provide rapid passivation. The lower yield strength when Cr is present may also contribute to the improved ductility, possibly by easing dislocation cross-slip in the deforming f.c.c. phase where most of the Cr resides.     

Electronic conduction mechanism in chitin–polyaniline blend

The electrical conductivity of chitin–polyaniline blend doped with HCl has been studied in the temperature range 323–373 K for various blend compositions. Conductivity of blends increases from less than ≈10^?7 S/cm to 2.15 × 10^?5 S/cm, depending on the percentage of polyaniline in the blend due to self-doping of LiCl. When these blends are doped with HCl conductivity raises to ≈9.68 × 10^?2 S/cm. Current–voltage data is analyzed using various models available. The results suggest Schottky–Richardson and one-dimensional variable range hopping mechanisms for undoped blend and one-dimensional variable range hopping mechanism in the case of doped blend.     

Nanocrystalline Nickel Deposition on the Titanium Alloys Using High Solution Flow Velocity

An innovative process has been developed for electroplating of nickel on titanium surface using fast solution flow technique. Nickel was directly deposited on a titanium alloy without using any pre-treatment process. Level of adhesion was determined using quantitative peel test and characterization of the deposition was performed by scanning electron microscopy. Results showed that the rate of nickel deposition at 60 °C was higher than that of the rate of nickel deposition at 40 °C. Moreover, Watts solution provided higher rate of nickel deposition compared to the sulfate-based nickel solution. The rate of deposition increased with increasing the solution flow velocity from 1.5 to 3 m/s and raising current density from 0.4 × 10⁴ to 1.6 × 10⁴ A/m² for both solution baths. Adhesion test indicated good level of adhesion between the deposited nickel and titanium surface. The bonding toughness increased to 4 J/m² for 1.2 × 10⁴ A/m² as a result of higher deposition rate. However, the mechanism responsible for the coating process was discussed in detail.     

Optimum conditions in the thermal passivation of aisi 430 and 304 stainless steel in controlled oxygen atmosphere

The oxidation of stainless steels AISI 304 and 430 was undertaken in the temperature range 450–600°C and oxygen partial pressure range 6.7 × 10⁷ to 1.33 × 10^?5 Pa. The composition of the oxide layer formed has been analysed by AES and ESCA. Optimum conditions were determined for the formation of a ～40 nm thick oxide layer with a high chromium content. Attention is drawn to the role of the chromium content of the bulk in the passivation process.     

Self-Diffusivity Along Edge-Dislocation Singular Lines in Silver

Use was made of a recently developed surface-accumulation diffusion technique to measure the self-diffusivity of edge-type dislocation singular lines (Burgers vector along <110>) in a bent and polygonized single crystal of silver. Two factors are involved in obtaining a number for the diffusivity. One factor, the dislocation-line density, was measured by a microscopic technique recently developed, and the value of the other parameter, the effective “diameter” of a dislocation pipe, was estimated. With these parameters equal to 7.3×10⁶ dislocations per sq cm and 10^?7 cm, respectively, it was found that the self-diffusivity along edge-type dislocation lines was a factor of about two times the average grain-boundary self-diffusivity. The dislocation-pipe diffusivity is about 7×10^?7 sq cm per sec at 450°C.     

Conversion electron Mössbauer spectroscopy on the oxidation of a (110) Fe-57 single crystal 100 Å thick

Conversion electron Mösshauer spectroscopy (CEMS) has been used to measure the initial stages of oxidation on an 100 Å thick (110) Fe-57 single crystal face at 275°C in the pressure range from 2 × 10^?4 to 8 × 10^?3 torr. Only magnetite is formed at 2 × 10^?4 and 8 × 10^?3 torr, a magnetite/haematite conversion occurs at 2 × 10^?3 torr. The various oxide phases have been investigated according to their growth behaviour and kinetics. Complicated changes in the kinetic behaviour are found with the magnetite/haematite conversion. Depth selective CEMS has been used to measure qualitatively the depth distribution of the oxide phases and the iron ion sites.     

Low cost corrosion damage mitigation and improved fatigue performance of low plasticity burnished 7075-T6

Low plasticity burnishing (LPB) has been investigated as a surface enhancement process and corrosion mitigation method for aging aircraft structural applications. Compressive residual stresses reaching the alloy yield strength and extending to a depth of 1.25 mm (0.050 in.) deeper than typical corrosion damage is achievable. Excellent surface finish can be achieved with no detectable metallurgical damage to surface and subsurface material. Salt fog exposures of 100 and 500 h reduced the fatigue strength at 2×10⁶ cycles by 50%. The LPB of the corroded surface, without removal of the corrosion product or pitted material, restored the 2×10⁶ fatigue strength to greater than that of the original machined surface. The fatigue strength of the corroded material in the finite life regime (10⁴ to 10⁶ cycles) after LPB was 140 MPa (20 ksi) higher than the original uncorroded alloy and increased the life by an order of magnitude. Ease of adaptation to computer numerical control (CNC) machine tools allows LPB processing at costs and speeds comparable to machining operations. Low plasticity burnishing offers a promising new technology for mitigation of corrosion damage and improved fatigue life of aircraft structural components with significant cost and time savings over current practices.     

Microstructural evolution of Al-20Si-5Fe alloy during rapid solidification and hot consolidation

Al-20Si-5Fe melt was rapidly solidified into particles and ribbons and then consolidated to near full density by hot pressing at 400°C/250 MPa/1 h. According to the eutectic-growth and dendritic-growth velocity models, the solidification front velocity and the amount of undercooling were estimated for the particles with different sizes. Values of 0.43−1.2 cm/s and 15–28 K were obtained. The secondary dendrite arm spacing revealed a cooling rate of 6 × 10⁵ K/s for the particles with an average size of 20 μm. Solidification models for the ribbons yielded a cooling rate of 5 × 10⁷ K/s. As a result of the higher cooling rate, the melt-spun ribbons exhibited considerable microstructural refinement and modification. The size of the primary silicon decreased from approximately 1 μm to 30 nm while the formation of iron-containing intermetallic compounds was suppressed. Supersaturation of the aluminum matrix in an amount of ∼7 at.% Si was noticed from the XRD patterns. During the hot consolidation process, coarsening of the primary silicon particles and precipitation of β-Al₅FeSi phase were observed. Evaluation of the compressive strength and hardness of the alloy indicated an improvement in mechanical properties due to the microstructural modification.     

Modeling the Gas Nitriding Process of Low Alloy Steels

The effort to simulate the nitriding process has been ongoing for the last 20 years. Most of the work has been done to simulate the nitriding process of pure iron. In the present work a series of experiments have been done to understand the effects of the nitriding process parameters such as the nitriding potential, temperature, and time as well as surface condition on the gas nitriding process for the steels. The compound layer growth model has been developed to simulate the nitriding process of AISI 4140 steel. In this paper the fundamentals of the model are presented and discussed including the kinetics of compound layer growth and the determination of the nitrogen diffusivity in the diffusion zone. The excellent agreements have been achieved for both as-washed and pre-oxided nitrided AISI 4140 between the experimental data and simulation results. The nitrogen diffusivity in the diffusion zone is determined to be constant and only depends on the nitriding temperature, which is ~5 × 10^?9 cm²/s at 548 °C. It proves the concept of utilizing the compound layer growth model in other steels. The nitriding process of various steels can thus be modeled and predicted in the future.     

Superplastic behaviour and microstructure evolution of a fine-grained TA15 titanium alloy

The fine-grained microstructure of TA15 titanium alloy was prepared through two-step forging technology combined with high and low temperatures, and a transnormal superplastic elongation of more than 2000% was obtained. The superplastic behaviour and microstructure evolution were systematically researched at different temperatures and strain rates through superplastic tensile test. The results indicate that the fine-grained TA15 alloy exhibits superplasticity at temperatures of 760–980°C and initial strain rates from 1.1 × 10⁻² to 5.5 × 10⁻⁵ s⁻¹. The optimal superplastic conditions are 940°C and 3.3 × 10⁻⁴ s⁻¹, in which the average elongation is 2526% and the maximum elongation is 2743%. During superplastic deformation, dynamic recovery and recrystallization occur obviously, and the corporate effect of strain hardening and recrystallization softening decides the superplastic ability directly.     

Study of the effect of ion-stimulated deposition assisted by a pulsed laser on the properties of zinc oxide nanocrystalline films

Nanocrystalline thin films of ZnO have been fabricated using the pulsed laser deposition method. The influence of the ion/atom ratio on the structural, morphological, and electrical parameters of these films is considered. It is established that, in the case of ion action on thin films, their crystalline structure and electrophysical properties are significantly changed. It is demonstrated that modes of ion-assisted deposition can help to control the average grain size in the range from 75.4 ± 2.0 nm to 79.1 ± 2.0 nm, the roughness in the range from 2.14 ± 1.11 nm to 7.30 ± 1.25 nm, and the resistivity and mobility in the range from (22.6 ± 2) × 10^?4 Ohm cm to (33.6 ± 2) × 10^?4 Ohm cm and from 28.21 ± 4.60 cm²/V s to 71.92 ± 2.50 cm²/V s, respectively.     

3,6-Di(diphenylamino)-9-alkylcarbazole-based hole-transporting hydrazones

The synthesis of a series of new glass-forming hydrazones containing carbazole and diphenylamine moieties is reported. The thermal, optical and photoelectrical properties of mono-, di- and tetra-substituted compounds are compared. The glass transition temperatures of the newly synthesized hydrazones range from 75 to 145 °C. The ionization potentials of the films of hydrazones, measured by the electron photoemission technique, range from 4.74 to 5.15 eV. Hole-drift mobilities of the solid solutions of hydrazones in bisphenol Z polycarbonate (50 wt.%) are in the range of 6.3 × 10⁻⁶ to 1.1 × 10⁻⁵ cm²/Vs at electric field of 6.4 × 10⁵ V/cm as characterized by the time-of-flight method.     

Influence of oxygen partial pressure on properties of N-doped ZnO films deposited by magnetron sputtering

N-doped ZnO films were radio frequency(RF)sputtered on glass substrates and studied as a function of oxygen partial pressure(OPP)ranging from 3.0×10-4 to 9.5×10-3 Pa.X-ray diffraction patters confirmed the polycrystalline nature of the deposited films.The crystalline structure is influenced by the variation of OPP.Atomic force microscopy analysis confirmed the agglomeration of the neighboring spherical grains with a sharp increase of root mean square(RMS)roughness when the OPP is increased above 1.4×10-3 Pa.X-ray photoelectron spectroscopy analysis revealed that the incorporation of N content into the film is decreased with the increase of OPP,noticeably N 1s XPS peaks are hardly identified at 9.5×10-3 Pa.The average visible transmittance(380-700 nm) is increased with the increase of OPP(from～17%to 70%),and the optical absorption edge shifts towards the shorter wavelength.The films deposited with low OPP(≤3.0×10-4 Pa)show n-type conductivity and those deposited with high OPP(≥9.0×10-4 Pa)are highly resistive(105Ω·cm)