Function Of Process Parameters Research Articles

BE Coatings on Spherical Surface for NIF Target Development

Beryllium is one of the preferred ablators for achieving ignition in inertial confinement fusion (ICF). Thin and thick coatings of Be on CH shells have been deposited using a sputter coater established at UCSD’s PISCES facility and examined using a variety of characterization techniques. Due to the spherical nature of these substrates, shadowing effects are expected to play significant roles in film growth as well as the expected surface diffusion length of deposited atoms. Be coatings on flat surfaces and spherical surfaces have been deposited and compared to understand the material growth behaviors on different surfaces and as a function of processing parameters. On flat surfaces, Be film developed polycrystalline morphology with columnar growth. On spherical surfaces, Be film also showed columnar growth at lower powers, which then transitioned into a twisted grain structure at higher powers. Cycling of parameters has been used to investigate possible grain growth interruption during growth and improving morphology. Initial results also suggest that copper doping during deposition does not change the columnar growth morphology. Measurements of the surface roughness of beryllium-coated shells indicate roughness growth proportional to the thickness with an exponent of 0.8 to 1.2, which is consistent with shadowing dominated roughening. As ion-beam-assisted growth may improve the surface finish and micro-structure of deposited films, we have also studied the effect of process parameters on the flux and energy of the ions reaching the substrates using an offline energy dispersive mass spectrometer system.

Synthesis of nanoparticles in an atmospheric pressure glow discharge

Nanopowders are produced in a low temperature, non-equilibrium plasma jet (APPJ), which produces a glow discharge at atmospheric pressure, for the first time. Amorphous carbon and iron nanoparticles have been synthesized from Acetylene and Ferrocene/H2, respectively. High generation rates are achieved from the glow discharge at near-ambient temperature (40–80°C), and rise with increasing plasma power and precursor concentration. Fairly narrow particle size distributions are measured with a differential mobility analyzer (DMA) and an aerosol electrometer (AEM), and are centered around 30–35 nm for carbon and 20–25 nm for iron. Particle characteristics analyzed by TEM and EDX reveal amorphous carbon and iron nanoparticles. The Fe particles are highly oxidized on exposure to air. Comparison of the mobility and micrograph diameters reveal that the particles are hardly agglomerated or unagglomerated. This is ascribed to the unipolar charge on particles in the plasma. The generated particle distributions are examined as a function of process parameters.

Advances in pulsed-laser-deposited AIN thin films for high-temperature capping, device passivation, and piezoelectric-based RF MEMS/NEMS resonator applications

In this paper we report recent advances in pulsed-laser-deposited AIN thin films for high-temperature capping of SiC, passivation of SiC-based devices, and fabrication of a piezoelectric MEMS/NEMS resonator on Pt-metallized SiO2/Si. The AlN films grown using the reactive laser ablation technique were found to be highly stoichiometric, dense with an optical band gap of 6.2 eV, and with a surface smoothness of less than 1 nm. A low-temperature buffer-layer approach was used to reduce the lattice and thermal mismatch strains. The dependence of the quality of AlN thin films and its characteristics as a function of processing parameters are discussed. Due to high crystallinity, near-perfect stoichiometry, and high packing density, pulsed-laser-deposited AlN thin films show a tendency to withstand high temperatures up to 1600°C, and which enables it to be used as an anneal capping layer for SiC wafers for removing ion-implantation damage and dopant activation. The laser-deposited AlN thin films show conformal coverage on SiC-based devices and exhibit an electrical break-down strength of 1.66 MV/cm up to 350°C when used as an insulator in Ni/AlN/SiC metal-insulator-semiconductor (MIS) devices. Pulsed laser deposition (PLD) AlN films grown on Pt/SiO2/Si (100) substrates for radio-frequency microelectrical and mechanical systems and nanoelectrical and mechanical systems (MEMS and NEMS) demonstrated resonators having high Q values ranging from 8,000 to 17,000 in the frequency range of 2.5–0.45 MHz. AlN thin films were characterized by x-ray diffraction, Rutherford backscattering spectrometry (in normal and oxygen resonance mode), atomic force microscopy, ultraviolet (UV)-visible spectroscopy, and scanning electron microscopy. Applications exploiting characteristics of high bandgap, high bond strength, excellent piezoelectric characteristics, extremely high chemical inertness, high electrical resistivity, high breakdown strength, and high thermal stability of the pulsed-laser-deposited thin films have been discussed in the context of emerging developments of SiC power devices, for high-temperature electronics, and for radio frequency (RF) MEMS.

Property and microstructure evaluation as a function of processing parameters: Large HY-80 steel casting for a US Navy submarine

Processing techniques can significantly alter the properties of a material and can ultimately determine whether a component will perform its function safely. This effort involves the investigation of the processing parameters of HY-80 steel castings; specifically a large HY-80 submarine casting that failed while in service due to improper processing. Samples taken from the failed casting were evaluated in the as-received condition and after exposures to various improper quench and temper scenarios that were possible during casting production. Microstructural examination and hardness measurements were used to evaluate the condition of the high strength steel and these results were correlated to Charpy impact toughness. One important result of this work indicates that hardness alone is not a good indication of material condition: the same measured hardness values yielded very different fracture behavior. The window of favorable processing parameters as defined by heat treatment temperature was clarified based on the specification requirements set by the US Navy for HY-80 castings.

Large Area Multi-wafer MOCVD of Transparent and Conducting ZnO Films

ABSTRACTZnO thin films are of interest for an array of applications, including: light emitters, photovoltaics, sensors and transparent contacts, among others. Production routes for ZnO include sputtering, MBE and MOCVD. This paper focuses on our efforts to produce a large scale MOCVD thin film production tool and the results obtained from the reactor. Specifically, we have constructed a tool with a 16” wafer carrier that uniformly deposits ZnO films on 38×2” wafers simultaneously. The reactor operates at low pressure (<0.1 Atmosphere) and through 700°C. High quality, uniform films have been deposited on an array of substrates. Al-doped films exhibited resisitivities in the 1×10-3 ohm-cm range and transmissivity greater than 80%. Film morphology and crystallinity are a function of process parameters. The large area oxide MOCVD reactor design challenges and results are summarized. Tool performance and ZnO thin film quality are reviewed, as well as preliminary ZnO contact performance on GaN LEDs.

Spectral measurements in fruits and vegetables

Purpose of review: Colour is one of the major attributes that affect the consumer’s perception of quality. The colour of foods is objectively measured by several techniques, with much of the early works concentrating on reflectance spectrophotometry which was followed by tristimulus colourimetry. Several tristimulus colourimeters are available today in the marketplace and are benefiting from developments in digital photography. More recently, spectral techniques have re-emerged as powerful tools with the advent of hyperspectral measurements and support analytical methodology. This review details potential applications of techniques in colour measurement of fruits and vegetables. Main findings: Computer vision employing image processing techniques has been developed rapidly and can quantitatively characterise the colour of foods. Application of hyper-spectral imaging is useful in characterising the colour of fruits and vegetables and can help in maturity grading. Correlation between instrumental colour measurements and quantification of the pigment responsible for the colour is gaining in popularity. Directions for future research: Future research should focus on more accurate online instrumental techniques to replace manual colour evaluation which is tedious, laborious, costly and inherently unreliable. Modelling of colour parameters as a function of process parameters is also important.

3D computer simulation of the influence of microstructure on the cut edge corrosion behaviour of a zinc aluminium alloy galvanized steel

Abstract Recently, experimental work has been reported that demonstrates the effects of microstructural variations within Zn–Al Galfan type coatings on the corrosion behaviour of cut-edge material, i.e. those cases where both the underlying steel and the organic coated Galfan layer are simultaneously exposed to a corrosive environment [J. Elvins, J.A. Spittle, D.A. Worsley, Microstructural changes in zinc aluminium alloy galvanising as a function of processing parameters and their influence on corrosion, Corros. Sci. 47 (11) (2005) 2740–2759]. In this paper a finite difference numerical model of localized corrosion has been applied in an attempt to simulate this type of corrosion. Results from the model are compared to experimental observations.

Boundary conditions and evaporation front instabilities

The problem of evaporation front stability under the general conditions of volumetric heating of the target and an arbitrary value of the Mach number in the evaporated matter flow is discussed. The relationships of instability increments versus surface tension coefficient and versus laser intensity are analysed. The influence of different phenomena on evaporation front instability is determined. It is shown that, in the case of surface energy absorption, the evaporation front is stabilized in the initial phase with a decrease of the Mach number. Subsequently, instability increases in the long-wave and short-wave areas with a further decrease in the Mach number. As for the latter, the increment in instability strongly depends on the surface tension coefficient. Within the limits of small Mach numbers, when thermal effects in the condensed phase are neglected, the dispersion equation is transformed into the well-known Darrieus–Landau equation. In the case of volumetric energy absorption, the instability associated with the temperature profile having its peak in the depth below the surface of the condensed phase is found to be a predominant factor for the evaporation front instability. As the laser intensity increases, the evaporation front instability increments grow as well. However, the evaporation front may remain stable for a given energy input within the laser pulse duration. The values of the increments obtained as a function of process parameters allow us to identify the conditions for evaporation front stability.

Surface roughness of silicon carbide etching in a NF 3 inductively coupled plasma

Silicon carbide was etched in a NF 3/CH 4 inductively coupled plasma. Surface roughness measured by atomic force microscopy was investigated as a function of process parameters. Both etch rate and dc bias were correlated to the surface roughness. To optimize the surface roughness, a 2 4 full factorial experiment was conducted for 700–900 W source power, 50–150 W bias power, 0.80–1.60 Pa, and 20–100% NF 3 percentage. Main effect analysis revealed that the surface roughness is the most strongly affected by the bias power. For variations in the bias power or NF 3 percentage, decrease in the surface roughness was observed only as positive variations in the etch rate and dc bias are considerably large. The surface roughness with the pressure was chemically dominated as illustrated by its inverse relationship with the dc bias. For the variations in the NF 3 percentage, the radical variation was estimated to play a more dominant role. The smoothest surface roughness of 0.312 nm was obtained at 700 W source power, 150 W bias power, 1.60 Pa pressure, and 100% NF 3 percentage.

Evolution of SiO2 matrix during the formation of Ge and Si nanocrystals by ion implantation

Fourier transformed infrared spectroscopy (FTIR) has been employed to observe and understand structural variations in SiO2 matrix during the formation of Ge and Si nanocrystals by ion implantation as a function of processing parameters. The Si–O asymmetric stretching peak of absorption spectra were used to monitor the evolution of SiOx (x<2) films during the annealing process. It was shown that the recovery process in Si–O network is quite different in Ge and Si implanted samples and the deformation caused by Ge atoms in the SiO2 matrix can be recovered by annealing the implanted samples at lower temperatures than that by Si atoms. This is in agreement with the formation kinetics of the Si and Ge nanocrystals in SiO2 as observed by Raman spectroscopy and photoluminescence measurements of the same samples.

Measurements and semi-empirical model describing the onset of powder formation as a function of process parameters in an RF silane–hydrogen discharge

The transition pressure above which powder formation takes place was experimentally determined in a parallel plate RF silane–hydrogen plasma as a function of the process parameters—power, temperature, gas flow and hydrogen dilution—using the dc-bias voltage as powder formation indicator. The resulting empirical scaling law describes in what conditions powders are formed and in what conditions the plasma is powder-free. Second, a semi-empirical model was developed that treats the nano-particle density in the plasma. This model was applied to analytically describe the transition pressure above which nano-particle coagulation takes place as a function of process parameters. The resulting modelled scaling law shows good correspondence with the experimentally found scaling law. Finally, a series of amorphous silicon films was deposited. The reflection–transmission spectra of the films were measured and modelled through Tauc–Lorentz formalism. The optical analysis shows that at around the plasma transition pressure there occurs also a transition in the properties of the deposited material.

Electrical Properties of DC Sputtered Titanium Nitride Films with Different Processing Conditions and Substrates

Deposition of TiN x film was conducted with a DC sputtering technique. The effect of the processing parameters such as substrate temperature, deposition time, working pressure, bias power, and volumetric flowing rate ratio of Ar to N₂ gas on the resistivity of TiN x film was systematically investigated. Three kinds of substrates, soda-lime glass, (100) Si wafer, and 1 ㎛ thermally grown (111) SiO₂ wafer were used to explore the effect of substrate. The phase of TiN x film was analyzed by XRD peak pattern and deposition rate was determined by measuring the thickness of TiN x film through SEM cross-sectional view. Resistance was obtained by 4 point probe method as a function of processing parameters and types of substrates. Finally, optimum condition for synthesizing TiN x film having lowest resistivity was discussed.

Warpage induced in bi-material specimens: Coefficient of thermal expansion, chemical shrinkage and viscoelastic modulus evolution during cure

Processing of polymer-based composites requires deep knowledge of materials property evolution. In this paper, a comprehensive approach to account for the dimensional and mechanical property changes as function of process parameters is presented. Valid experimental results were obtained to model material properties during the curing process and good agreement has been found with proposed constitutive models. Theoretical predictions of the strip curvature are generated using commercial FEM software (ANSYS) and compared with experimental measurements.

Sheet Thinning Prediction in Single Point Incremental Forming

Incremental forming processes are characterized by a well known and particular feature: any deformation across the sheet plane determines sheet thinning, since the blank is fully clamped by means of a proper equipment. As a consequence, the availability of effective and reliable CAE tools capable to supply an accurate prediction of sheet thinning as a function of process parameters, represents a strong requirement for a wider practical application of incremental forming. The already available theoretical models (i.e. the sine law) do not provide, on the other hand, satisfactory results. Therefore in the paper a couple of numerical analysis strategies was applied to simulate simple incremental forming processes, as well as a proper experimental equipment was developed to verify the accuracy of the numerical predictions.

Microstructural properties of SiC based hardfacing on low alloy steel

The effects of tungsten inert gas arc-processing (TIG) parameters on the microstructure and microhardness of silicon carbide coatings were investigated experimentally. Coatings were developed with TIG processing on an SAE 1020 steel substrate. Depending on the processing parameters (e.g., heat input, powder content, and processing speed), silicon carbide particles completely dissolved during the processing and different microstructures were produced. At lower powder contents, the microstructures consisted of dendrites. However, at high powder contents, the microstructures consisted of M 7C 3 primary carbides, Fe 3Si, SiC, and the graphitic carbon precipitates were generated. The microhardness of the surface layer was measured as a function of process parameters. Microhardness of the surface layer was significantly improved to as high as 1135 H V as compared to 220 H V of the substrate. The highest hardness measured 1250 H V, which produced high heat input and low powder contents of 2.310 kJ mm − 1 and 1.5 g, respectively. The lower hardness of dendritic microstructure was related to the presence of primary dendrites and relatively low concentrations of Si and C.

Neural modelling of Mooney viscosity of polybutadiene rubber

Mooney viscosity is one of the important quality properties of polybutadiene rubber (PBR). It is important to implement appropriate measures to maintain and guarantee a uniform product quality required by the rubber processing industries. One major step towards quality assurance is the on line quality prediction of the product from the process parameters. This can be accomplished by developing a reliable model that predicts product quality as a function of process parameters. Artificial neural networks (ANN), which are capable of mapping highly complex and non-linear dependencies, have been adapted to develop models to predict Mooney and solution viscosity of PBR from process variables. Of the different networks trained with input–output data collected from plant history to predict Mooney and fluid viscosity (FV) from process variables, generalized regression neural networks (GRNN) mapped the input–output well compared to that of other networks. The predicted Mooney viscosity of PBR from the reactor outlet by GRNN was deviated by mean square error of 0.0252 when tested with new data.

A diffusion model for describing the bilayer growth (FeB/Fe 2B) during the iron powder-pack boriding

In this paper, a diffusion model is proposed for studying the bilayer growth kinetics (FeB/Fe 2B) on pure iron substrate during the powder-pack boriding in the temperature range of 1023–1273 K. This model based on Fick's laws was solved, under certain assumptions, considering a parabolic growth of iron borides. For this purpose, a computer simulation program was created for predicting the boride layer thickness as a function of process parameters (temperature, time and surface boron content). A fairly good agreement was observed between the simulation calculations and experimental data derived from the literature.

Microstructural changes in zinc aluminium alloy galvanising as a function of processing parameters and their influence on corrosion

The effect of cooling rate and substrate gauge upon the microstructure and corrosion resistance of Galfan (Zn–4.5 wt.%Al) coated steels is presented. The coatings, applied to steel of gauges 0.47 mm (light gauge) and 0.67 mm (heavy gauge) on a coil coating line, were subjected to three different cooling rates by increasing output from 55% to 100% of the total power from a high powered cooling rig. The increase in cooling rate did not significantly alter the volume fraction of the primary zinc, this remaining at ∼20%. However, the size and number of the primary zinc dendrites were altered. The fast cooled samples contained small but numerous (∼3000 mm −2 in the heavy gauge and ∼2850 mm −2 in the light gauge) dendrites as opposed to the slow cooled samples where there were fewer (∼1850 mm −2 for the heavy gauge and ∼1500 mm −2 in the light gauge) dendrites of greater size. Characterisation of the surface revealed a reduction in eutectic cell size (∼1.8 mm to ∼0.8 mm on the heavy gauge and ∼2.1 mm to ∼1.2 mm on the light gauge) with increasing cooling rate. This leads to an increased unit length of depressed boundary between the eutectic cells. The eutectic microstructure is also finer (with reduced inter-lamella spacing) in the fast cooled samples again reflecting the more rapid nucleation of the coating. The scanning vibrating electrode technique (SVET) has been used to quantify the effects of these microstructural changes upon the surface and cut edge corrosion performance. There is an increase in corrosion activity on the surface of the fast cooled samples (metal loss 150 μg to 260 μg on the heavy gauge and 50 μg to 80 μg on the light gauge) primarily due to the increased length of depressed boundaries. Applying the same analysis to the cut edge, a decrease in corrosion occurs upon the faster cooled specimens. Metal loss calculations show a decrease (140 μg to 75 μg on the heavy gauge and 190 μg to 115 μg on the light gauge) as the cooling rate is increased. The higher intensity long lived anodes at the cut edge in the slower cooling rate samples are directly related to the increase in zinc dendrite size within the coating as nucleation rates are reduced.

Wireless optical diagnostic apparatus for analyzing diamond thin film CVD process under high gravity conditions

A wireless optical emission diagnostic apparatus has been developed for in-situ diagnosis of the high gravity (HG) plasma properties during diamond chemical vapor deposition using H 2–CH 4 gas mixture. Optical emission spectroscopy (OES) enabled us to identify the emitting chemical species and to qualitatively investigate the plasma composition changes as a function of process parameters, including gravity, up to 100 g. During the diamond deposition process, the light emitted from the individual chemical species existing in the plasma is analyzed as overall emission spectra. The developed diagnostic system is not intrusive and allows a real-time probing of the plasma inside the reactor. The purpose of this paper is to describe the developed plasma diagnostic apparatus, including the new wireless data transfer communication system, which has been designed to improve both stability and reliability of traced plasma characteristics, together with some preliminary results.

Numerical finite element investigation on laser cladding treatment of ring geometries

A laser cladding treatment using powder blown (single track) on a ring part was analyzed adopting a numerical approach, in particular the analyses of both the temperature and the stress distributions in the laser cladding process were performed through a 3D thermo-mechanical finite element (FE) model (ABAQUS/Standard). The thermal FE model was calibrated using the measured clad profile and melt pool size in the substrate; experiments were performed with a 6kW CO2 laser beam using an Al–Si alloy as substrate and a Cu-based alloy as cladding material. The aim of the thermal analysis was determining thermal cycles, variations of the dilution and of the melt pool shape during the process. The mechanical FE model allowed evaluating stress and strain distributions at the end of the treatment. All of these variables were analyzed at the clad–substrate interface as a function of processing parameters (like laser beam power, clad thickness, processing speed), boundary conditions and geometry of the treated zone.