Spray-forming is a newly developed industrial metal forming process in which a cylindrical metal billet is produced by the incremental deposition and solidification of an atomised metal spray on a moving substrate. A mathematical model is developed to describe billet growth and heat flow within spray-formed aluminium alloy billets. In the first part of the thesis, growth dynamics of the billet are considered. Conservation of mass at the billet surface yields a single first order quasi-linear partial differential equation for the movement of the billet surface; the nonlinearity arising from the possibility of surface shadowing. The existence of two distinctly different timescales, amongst the process motions governing billet growth, prompts the use of an averaging method. The resulting averaged equations permit analysis and are shown to provide a valid asymptotic approximation to the billet surface motion on the timescale 1/∊, for a suitably defined class of billet surfaces. The parameter ∊ ≪ 1 is the ratio of the two process timescales. Conditions under which the crown profile of the cylindrical billet becomes steady are analysed, through the averaged equations, and the stability of such profiles is examined. Computed examples of single and multiple steady state crown profiles are given. The averaged equations are also solved numerically to provide a model for transient billet growth on a "slow" timescale; results are presented. The second part of the thesis considers heat flow within the growing billet. Phase change is incorporated using an enthalpy formulation of the energy equation. The resulting equation is a nonlinear heat equation that must be solved in an expanding domain, the boundary of which is determined by solution of the billet growth model equations. Conduction on the billet length-scale takes place only on the slow timescale, with more rapid heat flow taking place only close to the billet surface. Accordingly, billet heat flow is analysed through the assumption that there is a thermal boundary layer close to the billet surface, which is driven by the "rapid" timescale spray deposition, with heat flow in the remainder of the billet driven by the time-averaged growth. The boundary layer equation is a one dimensional nonlinear advection-diffusion equation, with a nonlinear boundary condition that incorporates the intermittent deposition from the spray in the form of an irregular pulse. This equation is solved numerically using an implicit finite difference method. The slow-time heat flow is two dimensional, (assuming axisymmetric slow-time billet growth), and must also be solved numerically. For this an implicit predictor-corrector method is used. The predictor stage uses a "splitting" method, adapted from the fully implicit L.O.D. method to take account of the expanding domain. The method appears to be stable and consistent. Various numerical results are presented. The model provides significant new understanding of the dynamics of billet growth and succeeds in providing a useful framework within which the transient heat flow that occurs during spray deposition, on a number of different timescales and length-scales, can be understood. Comparison of computed model predictions with real sprayed billets confirms the validity of the model. The thesis is concluded with a summary of results and a look at possible future directions for research in this area.

Incremental step load testing was used in accordance with ASTM F1940 to rank a number coating processes used in the fastener industry for their propensity to cause internal hydrogen embrittlement. The results showed that coating permeability has a first order effect, while the quantity of hydrogen introduced by the process has a second order effect. Pure zinc electroplating processes, alkaline and acid, were found to be the most embrittling, owing to the low permeability of zinc. The least embrittling processes were zinc-nickel, alkaline and acid, owing to the high permeability of Zn-Ni coatings. Non-electrolytic processes, namely phosphating, mechanical galvanising, DacrometRTM and Magni 555RTM were found to be non-embrittling. Hot dip galvanising was found to be highly embrittling, evidently due to trapped hydrogen being released by the thermal shock of up-quenching upon immersion in molten zinc. The full effect of up-quenching on the metallurgical and mechanical properties of high strength steel requires further investigation.

The overall emphasis of this doctoral dissertation is on the design, synthesis, detailed characterization and application of amphiphilic hyperbranched fluoropolymers (HBFPs) crosslinked with poly(ethylene glycols) (PEGs) in complex polymer coatings as anti-biofouling surfaces. This dissertation bridges synthetic polymer chemistry, materials science and biology to produce functional coatings capable of fouling prevention, demonstrating thermo-controlled healing and acting as a benchmark surface to understand component:property relationships prior to increasing formulation complexities. A two-dimensional array of HBFP-PEG coatings was produced by the co-deposition of uniquely composed HBFPs with varying weight percentages of PEG. Bulk and surface properties were evaluated and assigned to formulation trends. Based on these findings, the most viable candidates were replicated and their fouling responses were assessed against three marine fouling organisms. An active mode of biofouling resistance was covalently grafted onto the surface of HBFP-PEG. The presentation of the settlement-deterrent molecule noradrenaline (NA) works in tandem with the highly-complex surface, to act as a dual-mode, anti-biofouling coating NA-HBFP-PEG. Secondary ion mass spectrometry (SIMS) was employed to quantify the extent of NA substitution. Biological assays against oyster hemocytes confirmed the activity of the grafted NA and cyprid settlement assays supported that the overall anti-biofouling ability of NA-HBFP-PEG was increased by 75%. Thermally-reversible crosslinks were installed as healable units throughout the framework of the networks, with the goal of generating coatings that could possess a greater resistance to mechanical failure. Small molecule and linear polymer models were probed by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) to demonstrate the controlled reversibility of the crosslinks. Optical microscopy was employed to visualize surface scratch healing and fluorescence microscopy was used to identify the adsorption behavior of fluorescently-labeled proteins. A benchmark, anti-biofouling surface was generated through thiol-ene crosslinking of a linear fluoropolymer with pendant alkenes (LFPene) with pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). Core constituents were evaluated spectroscopically and surfaces of LFPene-PETMP, along with two model surfaces that largely expressed a single component, were analyzed to understand how individual elements and blending contributed to the physical, mechanical and anti-biofouling properties to generate a performance baseline to compare against future generations.

Thesis (PhD (Metallurgical Engineering))--University of South Australia, 1997

Pulse Pressure Metal-Organic Chemical Vapour Deposition (PP-MOCVD) is a technique for creating thin coatings. It is less dependent on the volatility of precursors than other Chemical Vapour Deposition (CVD) processes as the precursors are introduced into the reaction chamber as an aerosol; therefore sublimation of the precursor is not necessary. This allows solutions of multiple compounds to be created with a known concentration and ratio of precursors. We explored the formation of hydroxyapatite (HAp) coatings for use on bone implants, using a methanolic solution of calcium lactate and trimethyl phosphate (TMP) as a PP-MOCVD precursor solution. The thermal decomposition of the precursors and the reaction between them were investigated using Thermogravimetric Analysis (TGA). Several variables on the PP-MOCVD apparatus were varied to test their effect on the formed coating: deposition temperatures, ratio of precursors, number of pulses, precursor concentration, the use of ambient temperatures and annealing the coatings after formation. All the coatings were analysed using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and Fourier Transform Infra-Red spectroscopy (FTIR). These coatings were not uniformly smooth in appearance at the micro level. However, using higher deposition temperatures, an excess ratio of TMP to calcium lactate and annealing the coatings for short periods of time and low temperatures improved the uniformity of the coating. When vigorous annealing was performed it resulted in surface oxidation and the production of titanium dioxide (TiO2 ). The EDS results showed that both calcium and phosphorus were present in the coatings. The use of high deposition temperatures, excess TMP or gentle annealing resulted in calcium to phosphorous ratios similar to the stoichiometry of HAp. These same conditions gave improved coating uniformity.

Thesis (PhD (Metallurgical Engineering))--University of South Australia, 1997

Proefschrift Universiteit van Amsterdam. / Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

Thesis (M. App. Sc.)--University of Adelaide, Dept. of Chemical Engineering, 1994. / Includes bibliographical references (leaves 210-223).

Thesis (Ph. D.)--Ohio University, March, 1995. / Title from PDF t.p.

Thesis (Ph.D.)--University of Wollongong, 2003. / Typescript. Bibliography: leaf 288-292.