Thin films of SiO<Subscript>2</Subscript> and hydroxyapatite on titanium deposited by spray pyrolysis

Wet spray pyrolysis of fine, well-dispersed a SiO₂ sol was used for the deposition of thin films of silicon dioxide. The sol was obtained by hydrothermal precipitation of silicon acid from a solution at pH = 10. The morphology, roughness, phase composition, chemical homogeneity and the mechanism of the films were investigated by SEM, EDS and IR spectroscopy. The obtained results show a complete covering of the titanium substrate with SiO₂ after 3 h of deposition. It was observed that the film thickness increased from 3 to 19 μm, the roughness of the film decreased from 12 to 3 μm, while the morphology of the deposit changed considerably. A hydroxyapatite film was prepared on the so-obtained SiO₂ thin film by spray pyrolysis deposition and its morphology and phase composition were investigated.     

Microstructural control by spray forming and wear characteristics of a Babbit alloy

The effect of process variables during spray forming of a commercial Babbit alloy containing Pb74–Sn12–Sb11.5–Cu1.25–NiO.75–Cd0.3–As0.2 on its microstructure and wear characteristics were investigated. Variation in atomization gas pressure from 0.6 to 1.2 MPa and nozzle to substrate distance from 0.2 to 0.4 m revealed considerable change in the nature of porosity and microstructural features of the spray deposits. The process variables during spray deposition were optimized to achieve microstructural homogeneity and refinement in second phase particles of this alloy. The wear study of both the spray formed and as-cast alloy under an applied load of 10 to 70 N and sliding velocity of 0.2 to 1.5 ms-1 indicated two distinct regimes of mild and severe wear. In both the regimes, the spray-formed alloy consistently indicated a low wear rate compared to that of the as-cast alloy. In addition, the mild wear regime of the spray-formed alloy was extended to higher load and sliding velocity. Wear characteristics of the spray formed alloy is discussed in light of its microstructural features induced during spray deposition processing.     

Microstructural stability of copper with antimony dopants at grain boundaries: experiments and molecular dynamics simulations

This study presents evidence that the microstructural stability of fine-grained and nanocrystalline Cu is improved by alloying with Sb. Experimentally, Cu_100−x Sb _x alloys are cast in three compositions (Cu-0.0, 0.2, and 0.5 at.%Sb) and extruded into fine-grained form (with average grain diameter of 350 nm) by equal channel angular extrusion. Alloying the Cu specimens with Sb causes an increase in the temperature associated with microstructural evolution to 400 °C, compared to 250 °C for pure Cu. This is verified by measurements of microhardness, ultimate tensile strength, and grain size using transmission electron microscopy. Complementary molecular dynamics (MD) simulations are performed on nanocrystalline Cu–Sb alloy models (with average grain diameter of 10 nm). MD simulations show fundamentally that Sb atoms placed at random sites along the grain boundaries can stabilize the nanocrystalline Cu microstructure during an accelerated annealing process.     

The effect of spray forming on the microstructure and properties of a high chromium white cast iron

The effect of spray forming on the structure and properties of a 17% Cr, 2.5% C white cast iron is described and compared with conventionally cast material of the same composition. Spray forming resulted in a substantial reduction in microstructural scale (eutectic (Cr,Fe)₇C₃ fields of up to 500 m in conventionally cast material were replaced by discrete carbides of typically 2–8 m diameter in the spray cast deposit). Carbide size varied as a function of position in the spray deposit, being approximately twice the size at mid section compared with either surface or interface with the collector. Carbide size was not altered by the gas to metal ratio used to atomise the spray. Spray forming increased transverse rupture stress and work of fracture by 50% compared with the conventionally cast material. Forging of the spray formed material was possible at 950°C, without inducing carbide fracture or void formation in the matrix. Quenching into iced water from 300°C induced extensive macroscopic cracking in the conventionally cast material whereas 400°C was required in the spray cast material to induce similar damage. The relationship between processing, microstructure and mechanical properties is discussed.     

Electrochemical Al2O3–Cr2O3 alloy coatings on non-oxide ceramic substrates

Aqueous solutions of xAl(NO₃)₃ + (1−x)Cr(NO₃)₃ were used for electrodeposition of ceramic Al₂O₃–Cr₂O₃ alloy coatings on TiC, TiB₂ and SiC substrates. Cell voltage and deposit weight were studied as function of deposition duration, current density and electrolyte composition. It was shown that the electrochemical parameters permit simple control of the deposition process. Optimal current densities and deposition durations were determined to obtain maximal deposit weights for different solutions and substrates. Deposits with thicknesses up to 10 μm were formed. The green deposits revealed a crystalline nature for compositions of x < 0.3, and an amorphous nature for x ≥ 0.3, independent of the substrate material. Voltage–electrolyte composition dependencies exhibited an ubiquitous minimum at x ≈ 0.3 to 0.4 independent of substrate type and deposition duration. These minima were attributed to the change in the electrical resistance of the deposit with composition and degree of crystallinity. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructure and electrical conductivity of Al-SiCp composites produced by spray forming process

Al- SiC_p composites have been synthesized by spray forming process with variation in particle flow rate, size of reinforcement particles and their volume fraction. The microstructure of composites and their electrical conductivity have been investigated. The results showed a uniform dispersion of large size particulate phase in the matrix of the primary α- phase with its equiaxed grain morphology. However, clustering of small size particles was observed at the grain boundary and grain junctions. The grain size of the composite materials was observed to be lower than that of the base Al- alloy. The composite materials invariably indicated their lower electrical conductivity compared to that of the monolithic Al- alloy. The electrical conductivity of composites decreased with increase in the volume fraction and decrease in size of the reinforcement particles. A high flow rate of particles during spray deposition resulted in a decrease in its conductivity. These results are explained in the light of thermal mismatch between the matrix and the reinforcement phases resulting in generation of high dislocation density. The droplet- particle interaction and resulting microstructure evolution during the spray deposition of the composites are discussed.     

Epitaxial growth and stabilization of the compound Ag3Sb on silver {1 1 1}

The vapour deposition of antimony on silver {1 1 1} under ultra-high vacuum conditions has been studied by means of reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). At room temperature, no evidence for sub monolayer structures was obtained and a deposit of an apparent thickness equivalent to six monolayers was necessary before any diffraction features typical of the overlayer could be detected. With increasing film thickness, the formation of islands with random rotational orientation was detected with Sb 〈100〉 normal to the substrate surface. Annealing of the deposit at 573 K led to the formation of the intermetallic compound Ag₃Sb in epitaxial relation to the substrate. Lattice parameters for pseudo-cubic antimony (a=0.613 nm) and hexagonal Ag₃Sb (a=0.295 nm andc=0.482 nm) were obtained.     

Réaction à l'état solide dans les couches minces du système binaire Cu/Sb

The formation kinetics of intermetallic compounds in Cu/Sb thin films in the temperature range 473–623 K is studied by X-ray and electron diffraction. It is established that the Cu₂Sb phase begins to form during the deposition of the second layer. In the range 473–573 K, independently of film composition, only the Cu₂Sb phase forms and grows, even though the equilibrium diagram predicts two (Cu₂Sb and Cu₉Sb₂). A supplementary annealing of these samples at 623 K in the case where we have a copper excess (N_Cu >N_Sb) leads to the complete transformation of Cu₂Sb to the Cu₉Sb₂ phase. However, in the case of an antimony excess (N_Cu < N_Sb) we do not observe any transformation. During an annealing at 623 K of as-evaporated samples, in a first reaction stage both the Cu₂Sb and the Cu₉Sb₂ phases appear simultaneously whatever the film composition. Then the Cu₂Sb changes completely to the Cu₉Sb₂ phase if N_Cu >N_Sb, whereas both phases always coexist if N_Sb >N_Cu.     

Precipitation of iron-rich intermetallic phases in Al-4.6Cu-0.5Fe-0.5Mn cast alloy

The solidification of Al-4.6Cu-0.5Fe-0.5Mn (206 type) cast alloy has been studied using Thermal Analysis, Differential Scanning Calorimeter, Scanning Electron Microscopy, Electron Back-Scattered Diffraction (EBSD), and Transmission Electron Microscopy (TEM). It is interesting to note that an iron-rich intermetallic phase, Al₃(FeMn), is experimentally observed to be dominantly present in the fully solidified cast structure of the experimental 206 cast alloy, in addition to β-Fe (Al₇Cu₂(FeMn)/Al₇Cu₂Fe) phase. Al₃(FeMn) phase is formed through a eutectic reaction approximately at 640 °C during solidification, possibly resulting from the phase selection and segregation of Fe in liquid Al. The presence of the Al₃(FeMn) phase has been confirmed by both EBSD and TEM. It is also found that both β-Fe and Al₆(FeMn) are possible to nucleate on Al₃(FeMn), as confirmed by the calculated low planar disregistries. The possible solidification reactions have been established for 206-type cast alloy at 0.5%Fe.     

Spray processing and wear characteristics of Al-Cu-Al2O3-Pb based composites

The spray deposition process has been employed in synthesis of Al-4.5Cu-10Al₂O₃ and Al-4.5Cu-10Al₂O₃-10Pb based composites. The microstructure and wear characteristics of composites were investigated. The rapid solidification inherent in spray deposition processing resulted in a uniform dispersion of Al₂O₃ and Pb particles co-existing in the matrix of the- primary α-phase. The grain size of the Al-4.5Cu-10Al₂O₃-Pb composite was observed to be higher than that of the Al-4.5Cu-10Al₂O₃ composite in various sections of the spray deposit. The wear rate of composite materials decreased with addition of Pb phase. This behavior is discussed in the light of the microstructural modification induced by spray deposition and the morphology of debris particles on the wear track surfaces. The wear characteristics of the composites are compared with that of the liquid immiscible Al-4.5Cu-10Pb alloy.     

The Influence of Temperature Distribution on YBCO Coated Conductor Deposited by Reel-to-Reel PLD Method

It is known that the tape’s temperature controlled by a close substrate heater will still deviate after the deposition process. In this work, we deposited YBa₂Cu₃O_7−δ (YBCO) films on RABiTS substrates with multilayer CeO₂/YSZ/CeO₂ buffer layers by pulsed laser deposition (PLD) under a different distribution of temperature deviation in order to improve it. Thermocouples were applied to exactly measure the temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to inspect c-axis oriented crystals and surface morphology of YBCO films. Through this work, we found that the even shape is best. Under the temperature deviation with the best shape, a transport J _c of 3.2×10⁶ A/cm² and I _c =240 A was obtained for a 0.75 μm thick YBCO film on CeO₂/YSZ/CeO₂-bufferd RABiTS Ni–W alloy.     

Magnetic properties of Fe78.4Si9.5B9Cu0.6Nb2.5 nanocrystalline alloy powder cores

The microstructure and morphology of nanocrystalline Fe_78.4Si_9.5B₉Cu_0.6Nb_2.5 alloy powders prepared by ball milling technique were characterized by X-ray diffraction and scanning electron microscopy studies. The effective permeability (μ_e), quality factor (Q), DC bias property, and core losses of the corresponding powder cores were tested using low capacitance resonator meter and B–H analyzer in the range of 1–1000 kHz. The results show that the relative density and compression strength of the powder cores increased with increasing particle size. Powder cores from large size particles (150–300 μm) were found to exhibit higher μ_e and core loss, but lower Q level when compared to samples of small size ones (5–40 μm). Moreover, the μ_e of powder cores with large particles reached a peak value with the addition of 2 wt% glass binder. The Q value was also found to be proportional to the binder content except 10 wt%, while its peak position was shifted toward higher frequency.     

Effect of dispersion and polymeric coatings on the magnetic properties of the Fe<Subscript>73.1</Subscript>Cu<Subscript>1.0</Subscript>Nb<Subscript>3.0</Subscript>Si<Subscript>15.5</Subscript>B<Subscript>7.4</Subscript> amorphous alloy

We tested Fe_73.1Cu_1.0Nb_3.0Si_15.5B_7.4 amorphous alloy for changes in the magnetic properties accompanying the transition from the strip form into a powder and after modification with polymeric coatings. It is shown that the dispersion down to particles smaller than 10 μm in size and the procedure of modification do not, in fact, worsen the magnetic properties of the alloy.     

Patterning of fine particles by means of supercritical CO2

A new method for positioning fine particles on surfaces has been developed. Supercritical CO₂-assisted printing (SCAP) was utilized to spray and deposit the prepared particles on solid substrates. By means of masks, regular arrays of the particles were successfully created in designed patterns. Typical size of the particles employed was in the range of submicrometers to micrometers. Supercritical CO₂ (sc-CO₂) acted as an effective dispersion and transportation medium in this process. Good dispersion state of the particles was achieved by stirring in sc-CO₂. Fabrications of fine patterns of solder particles and other ceramic powders on smooth plates were demonstrated. Under optimum operation conditions, fine structures of 30 μm in width can be formed in a minimal pitch of 60 μm. Ultra high yield of the patterning was obtained since the deposition rate could be as high as 100 μm per second. Main factors affecting the process were discussed. The research results indicate that the SCAP is a potential approach to the organization of fine particles into microstructures. Hopefully, it may find wide industrial applications where lithography is needed, such as solder printing in surface mounting technology for higher density electronics and thick film fabrication for miniature systems.     

Microstructural evolution during extrusion and ECAP of a spray-deposited Al–Zn–Mg–Cu–Sc–Zr alloy

The microstructural evolution of an Al–Zn–Mg–Cu–Sc–Zr alloy prepared by spray deposition via extrusion and equal-channel angular pressing (ECAP) was investigated in this study. Deformation route A for Al–11.5 wt% Zn–2 wt% Mg–1.5 wt% Cu–0.2 wt% Sc–0.15% Zr super-strength alloy was carried out at 573 K by ECAP. The microstructures of extruded and ECAP samples were investigated by means of Electron Backscatter Diffraction (EBSD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). A large amount of dislocation tangles were formed inside grains during ECAP, which further evolved into sub-boundaries and high angle grain boundaries. Microstructure analyses showed that the grain size was refined to 800 nm after 8 passes ECAP from earlier 3.5 μm of sprayed and extruded alloy. A few finer MgZn₂ and Al₃(Sc,Zr) were dispersed uniformly after ECAP. The textures of 8 passes ECAPed sample were dominated by the strong Cu orientation and relatively weak S orientation.     

Low cost synthesis of high-Tc superconducting films on metallic substrates via ultrasonic spray pyrolysis

Ultrasonic spray pyrolysis technique has been used to deposit both in situ and ex situ high temperature superconducting films (HTSC) of Y₁Ba₂Cu₃O_x(YBCO) and Bi₂Sr₂CaCu₂O_x (BSCCO) compounds over various substrates. Nitrate precursor solutions are used to deposit films of ∼10 μm thickness. Both low temperature spray with substrate temperature T_s < 500 °C and high temperature deposition with T_s = 550-900 °C are carried out. Superconducting properties of these films are observed to vary with various parameters such as concentration of spray solution, deposition temperature and nature of substrate and annealing process. Best quality films show T_c (R = 0) of 89 K and J_c of ∼4 × 10⁴ A/cm² at 77 K and ∼ 10⁵ A/cm² at 20 K. X-ray diffraction pattern reveals that the films are textured along c-axis. Successful attempt has been made to deposit in situ superconducting films over polycrystalline Ag for coated conductor applications. Various deposition and annealing conditions are optimized to control the diffusion of Ag from substrate to film, which otherwise can segregate into the grain boundaries and make the films non-superconducting.     

Investigation of mechanical,electrical, and thermal properties of a Zn–1.26 wt% Al alloy

Zn–1.26 wt% Al alloy was directionally solidified upward with a constant growth rate (V = 16.6 μm/s) in a wide range of temperature gradients (1.94–5.15 K/mm) and with a constant temperature gradient (G = 5.15 K/mm) in a wide range of growth rates (8.3–500 μm/s) with a Bridgman-type directional solidification furnace. The microhardness (HV) and tensile strength (σ) of alloy were measured from directionally solidified samples. The dependency of the microhardness, tensile strength for directionally solidified Zn–1.26 wt% Al alloy on the solidification parameters (G, V) and microstructure parameters (λ₁, λ₂) were investigated and the relationships between them were experimentally obtained using regression analysis. According to present results, the microhardness and tensile strength of directionally solidified Zn–1.26 wt% Al alloy increase with increasing solidification processing parameters and decrease with the microstructure parameters. Variations of electrical resistivity (ρ) with the temperature in the range of 300–650 K were also measured using a standard dc four-point probe technique for cast samples. The enthalpy of fusion and specific heat for same alloy was also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from solid to liquid.     

Enhanced crystal grain size by bromine doping in electrodeposited Cu2O

Extremely large crystal grains are obtained by bromine doping in electrodeposited Cu₂O on indium tin oxide (ITO) substrate through an acetate bath. The grains are as large as 10,000 μm² in area, or ~ 100 μm in linear dimension, while the film is only 1-5 μm thick. The enhanced grain size is explained by the effect of over-potential for the Cu²⁺/Cu⁺ redox couple on nucleation density of Cu₂O on ITO substrate. The over-potential is a function of several deposition conditions including solution pH, deposition potential, deposition temperature, bromine precursor concentration, and copper precursor concentration. In addition, undoped Cu₂O displays a high resistivity of 100 MΩcm. Bromine doping in Cu₂O significantly reduces the resistivity to as low as 42 Ωcm after vacuum annealing. Br-doped Cu₂O shows n-type behavior.     

Comparative analysis of oxide phase formation and its effects on electrical properties of SiO2/InSb metal-oxide-semiconductor structures

We report on the changes in the interfacial phases between SiO₂ and InSb caused by various deposition temperatures and heat treatments. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to evaluate the relative amount of each phase present at the interface. The effect of interfacial phases on the electrical properties of SiO₂/InSb metal-oxide-semiconductor (MOS) structures was investigated by capacitance-voltage (C-V) measurements. The amount of both In and Sb oxides increased with the deposition temperature. The amount of interfacial In oxide was larger for all samples, regardless of the deposition and annealing temperatures and times. In particular, the annealed samples contained less than half the amount of Sb oxide compared with the as-deposited samples, indicating a strong interfacial reaction between Sb oxide and the InSb substrate during annealing. The interface trap density sharply increased for deposition temperatures above 240 °C. The C-V measurements and Raman spectroscopy indicated that elemental Sb accumulation due to the interfacial reaction of Sb oxide with InSb substrate was responsible for the increased interfacial trap densities in these SiO₂/InSb MOS structures.     

Crystallization and thermally induced surface relief effects in a Mg<Subscript>65</Subscript>Cu<Subscript>25</Subscript>Y<Subscript>10</Subscript> bulk metallic glass

The crystallization behaviour of Mg₆₅Cu₂₅Y₁₀ bulk metallic glass (BMG) under different reheating conditions was investigated. X-ray diffraction spectrometery (XRD), differential scanning calorimetery (DSC), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to examine the crystallization of different samples and the surface relief generated on as-polished surfaces during heat treatment. Different phase constituents were found in samples that experienced different reheating stages. It is proposed that both the reheating temperature and holding time have a significant effect on the phase constituents. The BMG was found to generate surface corrugations of amplitude 1–2 μm during annealing above its crystallization temperature. Such thermally induced surface relief effects are probably a result of the development of surface stresses generated by volumetric changes associated with crystallization of the residual amorphous phase.