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An apparatus for use in a friction stir operation, such as friction stir welding (FSW) or friction stir processing (FSP). The apparatus may have a rotating tool adapted to be plunged into a material, where the material is susceptible to being softened by heating. The rotating tool may further be adapted to be advanced along a surface of the material. An optical energy generating subsystem may be used to heat a portion of the material using optical energy as the tool is advanced along the material.

This thesis presents research on the corrosion properties and effects of heat treatment on austenitic stainless steel coatings produced by the cold gas dynamic spray process on 316L stainless steel substrates. Previous work on the use of the low-pressure cold spray process to spray austenitic stainless steel was reproduced and validated. Heat treatment of the coatings was found to reduce porosity and evidence was found of recrystallization of the coatings. No significant changes in elemental distribution were found to occur during heat treatment. Corrosion testing was conducted by salt fog testing and anodic polarization. Coatings in the as-sprayed condition were found to be less corrosion resistant than bulk 316L stainless steel. Heat treated samples were observed to show corrosion resistance even worse than as-sprayed coatings. In fact, all heat treated samples exhibited little or no passivation behavior. Grain boundary sensitization is suspected to a probable cause for poor corrosion resistance in some samples and the presence of ferrite in the powder and coatings may also be a cause of corrosion resistance that is worse than the fully austenitic substrate.

This study examined particles created by laser-driven hydrothermal processing, an innovative technique used for the ablation of submerged materials. Two naturally occurring materials, obsidian and tektite, were used as targets for this technique. Characterization of sample materials before and after laser processing was conducted through multiple techniques such as optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. Examination of the untreated base material, in bulk and crushed form, established a baseline for comparison to particles created by laser processing of the same material. Characterization methods provided data of micron- and nano-sized particles, including their crystal structure, microstructure, and chemical composition. The bulk and crushed obsidian and tektite samples contained inclusions and particles rich in several transition elements, most notably iron and titanium. Analysis of liquid media collected after laser processing of bulk obsidian and tektite samples revealed fine particles rich in the same elements. Evidence suggests laser-driven hydrothermal processing separates heavy elements from the mostly amorphous silica matrix encountered in the materials examined.

This work aimed to produce nitrogen doped graphene from Graphite Oxide (GO) by combining the Expansion Reduction Synthesis (RES) approach, which utilizes urea as doping/reducing agent, with the use of an Atmospheric Plasma torch (Plasma), which provides the high temperature reactor environment known to thermally exfoliate it. The use of this combined strategy (Plasma-RES) was tried in an attempt to increase the surface area of the products. The amount of nitrogen doping was controlled by varying the urea/GO mass ratios in the precursor powders. X-ray diffraction analysis, SEM, TEM, BET surface areas and conductivity measurements of the diverse products are presented. Nitrogen inclusion in the graphene samples was corroborated by the mass spectral signal of the evolved gases generated during thermal programmed oxidation experiments of the products and by EDX analysis. We found that the Plasma-RES method can successfully generate doped graphene in situ as the urea and GO precursors simultaneously decompose and reduce in the discharge zone. When using the same amount of urea in the precursor mixture, samples obtained by Plasma-RES have higher surface area than those generated by RES, however, they contain a smaller nitrogen content.

The limited number of studies that focus on the size-dependent failure mechanisms of individual nanoparticles and their significance on epoxy composite material properties led to the twofold aim of this research: study the failure modes of nickel nanoparticles and determine the dependence of the mechanical properties of the Ni-epoxy composite on the size of the nickel particles used as reinforcement. Samples of spherical nickel nanoparticles were separated by size based on their densities and the resulting sections used as reinforcement in epoxy composites. The microstructural characterization of the nickel samples were performed on a Scanning Electron Microscope and the mechanical properties of the different Ni-epoxy composite pucks investigated using a nanoindenter. For the failure analysis investigation, an ultrasonic processor was used to induce damage to nickel nanoparticles of diverse sizes dispersed in a solvent. The corresponding effects of the treatment on the nanostructures were analyzed through X-ray diffraction techniques, to determine possible phase transformations, and Transmission Electron Microscopy, to analyze changes in the crystal lattice. Findings indicate that the hardness and Young’s Modulus values for the Ni-epoxy composites increase as filler particle size decreases and follows a normal Hall-Petch relation. The intense energy imparted by the ultrasonic process, along the particle-solvent interface, created a protective NiO coating in the Ni spherical nanoparticles. The latter seems to suppress the complete fracturing of the particle despite the creation of multiple lattice defects.

This thesis describes significant changes in the type and degree of localized corrosion for sensitized AA5083 under an applied tensile stress. AA5083 is an aluminum-magnesium alloy that experiences severe intergranular corrosion and intergranular stress corrosion cracking if sensitized. In this research, AA5083-H116 plates were cut into bend-bar samples along both the rolling and transverse directions, and then sensitized to two different levels using laboratory heat treatments of 7 and 30 days at 100°C. The sensitized samples were subjected to elastic tensile loading using a 4-point bend rig while being exposed to a 0.6 molar saltwater solution. Electrochemical polarization was performed on the tensile regions of the samples while under applied stress. Potentiodynamic scans showed that although sensitization causes the most change in electrochemistry, stress does shift the Tafel plot to be more stable when comparing the values for open circuit potential, but reduces the pitting potential of the passivating oxides. Confocal microscopy showed that samples with applied tensile stress produced a much higher density of localized corrosion, including pitting and intergranular corrosion than samples without applied tensile stress. The degree of corrosion damage was slightly higher for samples loaded in the transverse direction compared to samples loaded in the longitudinal direction.

The impact that biofouling has on a ship’s performance has long been recognized, since it increases the frictional resistance of the hull and can increase the ship’s fuel consumption. In this study, the spectrum of hydrophobic and antifouling surface patterns that can electrochemically be fabricated on HY-80 steel (alloy that is broadly used in shipbuilding for welded hull plates) is examined. After the fabrication of nanoscaled topographies, the optimum conditions for anodizing are determined by correlating the processing conditions with microstructural data. Characterization of the surface oxides was conducted by techniques such as Scanning Electron and Focused Ion Beam microscopy as well as identification of the formed phases by X-ray diffraction techniques. Hydrophobicity of the surfaces was examined by measuring the contact angle of deionized water on the HY-80 steel surface. These studies revealed the improved wetting behavior of the anodized surfaces. Thermogravimetric analysis along with quantitative examination of the biofouling on the specimens were studied after prolonged exposure to seawater and indicated a decrease in the corrosion rate of anodized surfaces.

This thesis presents research on the cold gas-dynamic spray process applied to the deposition of aluminum-copper alloy coatings. Cold spray deposition is a process utilized to create corrosion protection coatings and to perform additive repair for aluminum structures. This thesis utilized a series of Al-Cu binary alloy powders, from 2–5 weight percent copper and characterized their chemistry and microstructure. The powders were deposited using the cold spray approach to study the systematic increase of the alloying agent on the deposition process and coating characteristics. Deposition efficiency, critical velocity, coating thickness, hardness, porosity, and microstructure were all characterized as functions of carrier gas pressure, carrier gas temperature and feedstock powder copper composition. This thesis has demonstrated that all of the aluminum copper powders utilized can be successfully deposited via the low-pressure cold spray process with helium as the carrier gas. The copper content of the powders has a direct effect on the volume fraction of Al2Cu intermetallics, and on the coating hardness, while having no measurable effect on critical velocity for deposition or the coating thickness per pass.

This thesis presents research on the cold gas-dynamic spray process applied to the deposition of stainless steel coatings. Cold spray deposition is a relatively new process utilized to create corrosion protection coatings and to perform additive repair for large steel structures. This thesis aims to study the effectiveness of the low-pressure cold spray process on four, commercially available, austenitic stainless steel powders by characterizing both the powders and the resultant coatings. Particle velocimetry and fluid dynamics simulation were also utilized to study the in-flight characteristics of the powder. Notably, this thesis presents evidence that austenitic stainless steel can be successfully deposited via the low-pressure cold spray process. Substantial variability was observed in the commercially available austenitic stainless powders, particularly in the phase content, the particle size distribution, and the particle shape. These parameters had a large effect on the particle velocity and subsequent deposition characteristics. In fact, the PG-AMP- 10 powder, which possessed the highest ferrite fraction and had irregular particle shapes, achieved much higher velocities and greater deposition efficiency than the phase-pure and spherically-shaped S5001 powder.

A comprehensive set of processing-microstructure relationships is presented for friction stir welded oxide dispersion strengthened MA956 steel. Eight rotational speed/traverse speed combinations were used to produce friction stir welds on MA956 plates using a polycrystalline cubic boron nitride tool. Weld conditions with high thermal input produced defect-free, full- penetration welds. Electron backscatter diffraction results showed a significant increase in grain size, a persistent body centered cubic torsional texture in the stir zone, and a sharp transition in grain size across the thermo-mechanically affected zone sensitive to weld parameters. Micro- indentation showed an asymmetric reduction in hardness across a transverse section of the weld. This gradient in hardness was greatly increased with higher heat inputs. The decrease in hardness after welding correlates directly with the increase in grain size and may be explained with a Hall–Petch type relationship.

This thesis characterizes the residual stresses generated by friction stir welding of ODS steel MA956 as a function of heat index. The heat index of a weld is used to determine relative heat input among different friction stir welding conditions. It depends on a combination of the rotational speed and traverse, or welding speed of the tool through the metal. Higher rotational speeds and lower traverse speeds increase heat index and are expected to result in lower residual stresses than welds performed with lower heat index. Three conditions with varying heat indices were selected from high to low: 500 rpm/25 millileters per minute (mmpm), 400 rpm/50 mmpm and 400 rpm/100 mmpm. The full stress tensor was determined for points across these welds using x-ray diffraction. Longitudinal residual stresses approximately 90% of yield strength were observed for the lowest heat input condition. Stress profiles displayed the characteristic M shaped profile, and asymmetry between advancing and retreating stress peaks was limited, occurring mainly on the root of the weld. As expected, lowering the heat index of a weld increased the magnitude of residual stresses across the whole weld profile.

The Friction Stir Processing (FSP) and Friction Stir Welding (FSW) welding of nickel aluminum bronze (NAB) is used for a variety of naval applications. This paper investigates the beneficial effects of FSP on NAB passivity, and provides important benchmark data for future studies. Further enhancement of FSP NAB through application of LP will be discussed in subsequent papers, using the data presented here as a basis of comparison. This work shows that FSP has a beneficial effect on both the microstructure of this alloy, as well as on the integrity of the passive film formed in chloride electrolytes, including natural seawater. In addition to using a variety of characterization techniques to determine the effects of friction stir processing on microstructure, including scanning electron microscopy (SEM) with focused ion beam milling, we have used cyclic polarization (CP) and electrochemical impedance spectroscopy (EIS) to develop an understanding of passive film behavior for this material in the as-received state, as well as after friction stir processing. A variety of interfacial impedance models have been explored for fitting the data, including transmission line models. Results on this important alloy, before and after processing will be presented.

This thesis describes the microstructural and mechanical property changes associated with Friction Stir Processing (FSP) of HY-80 steel under dry and underwater conditions. HY-80 is a low-carbon alloy steel that is used in a quenched and tempered condition and is highly susceptible to hydrogen assisted cracking associated with conventional fusion welding. FSW/P (400 RPM/ 2 IPM) was conducted using a polycrystalline cubic boron nitride tool having a pin length of 6.35 mm. Two sets of processing runs were completed on HY-80 plates, 6.35 mm in thickness, one dry and the other under seawater. Analysis of the residual hydrogen content revealed little change in hydrogen content associated with FSW/P. Detailed microstructural characterization (optical and scanning electron microscopy) with emphasis on the differences in the distribution of constituent phases in the rolling, transverse and normal planes was carried out. Microstructural analysis of the “plan-view” section at the tool extraction sites of FSW/P samples was executed. Mechanical properties of these samples were evaluated by tensile, microhardness, and Charpy V-notch impact resistance tests. The results indicated that austenitization occurred within the stir zones and subsequent cooling influenced the final microstructure and properties. The thermomechanically affected zone displayed a gradual change in near-equiaxed austenitic grain size towards both the tool axis as well as the base plate with little grain shape change throughout. These results have been rationalized on the basis of expected temperature and deformation fields generated setup in these steel samples and the nature of phase transformations occurring in low carbon steels such as HY-80.

Microstructures produced by isothermal hot rolling of a NiAl bronze material were evaluated by quantitative microscopy methods and parameters describing the contributions of precipitate dispersions, grain size, solute content, and dislocation density to the yield strengths of the individual constituents of microstructure were determined. Models for the strengths of the individual constituents were combined to predict the temperature dependence of the yield strength as a function of hot rolling temperature, and the prediction was found to be in good agreement with measured yield strengths. The models were applied to microstructures in a stir zone produced by multipass friction-stir processing (FSP) and, again, found to predict measured yield strengths with high accuracy. Such models may aid in assessing the role of microstructure gradients produced during FSP and other processes.

The evolution of the stir zone microstructure during single-pass and multi-pass 'FSP of an as-cast NiAl bronze material was evaluated by optical and high-resolution scanning electron microscopy (SEM) methods, including orientation imaging microscopy (OIM). Deformation commences ahead of the tool as the local temperature exceeds the eutectoid temperature ("800'C) while subsequent recrystallization in the primary a is accompanied by dissolution of Kiv particles dispersed in this constituent. The recrystallized a grains remain equiaxed and appear annealed despite large displacements onward into the resulting stir zone (SZ). Characteristic shear texture components are retained in the thermomechanically affected zone (TMAZ) but the texture of the primary a becomes random after recrystallization and remains so into both single-pass and multipass SZs. Mechanisms to account for recrystallization and subsequent deformation are proposed.

Equivalent strains up to a value of ⊨2.7 were determined by evaluation of the shape changes of the phases in a duplex a(fcc)/b(bcc) microstructure formed ahead of the pin tool extraction site during the friction stir processing (FSP) thermomechanical cycle in a cast NiAl bronze alloy. Correlation of the local strains with volume fractions of the various microstructure constituents in this alloy shows that the concurrent straining of FSP results in acceleration of the a + b fi b reaction in the thermomechanically affected zone (TMAZ) ahead of the pin extraction site. The resulting volume fraction of b (as determined by the volume fraction of its transformation products formed during post-FSP cooling) corresponds closely to the volume fraction expected for the peak stir zone temperature measured separately by means of thermocouples embedded within the tool pin profile along the tool path. The stir zone (SZ) in this material exhibits near-equilibrium microstructures despite brief dwells near the peak temperature (Tpeak ⊨ 0.95 Tmelt), reflecting large local strains and strain rates associated with this process.

Novel iron-based amorphous metals, including SAM2X5 Fe(49.7)Cr(17.7)Mn(1.9)Mo(7.4)W(1.6)B(15.2)C(3.8)Si(2.4)), SAM1651 (Fe(48.0)Cr(15.0)Mo(14.0)B(6.0)C(15.0)Y(2.0)), and other compositions have been developed for use as corrosion-resistant coatings for spent nuclear fuel containers, as criticality control materials, and as ultra-hard corrosion-resistant material for ship applications. These amorphous alloys appear to have corrosion resistance comparable to (or better than) that of Ni-based Alloy C-22 (UNS # N06022), based on measurements of breakdown potential and corrosion rate in seawater. A variety of characterization tools, including scanning electron microscopy, cyclic polarization, linear polarization and electrochemical impedance spectroscopy, have been used to develop a thorough understanding of the corrosion performance of these alloys over prolonged exposure in seawater and concentrated brines at elevated temperature.

This final report details progress made on various topics related to advanced metallic, advanced metallic composites and ceramic materials. The development and sustainment of Air Force systems depends on both the optimal performance of traditional materials and the continued exploration of materials technologies. Major requirements driving the research into these new technologies include: 1) reducing the weight of engineering components of aircraft, 2) increasing the operating temperatures of engines, 3) providing advanced materials for thermal protection systems, and 4) producing geopolymer-based material for space mirror applications. Research was carried out three different classes of materials, advanced metallics, advanced metallic composites, and ceramics. In the latter case, both monolithic and fiber-reinforced materials were evaluated, along with geopolymers. The process-microstructure-property relationships were extensively and critically assessed for these material classes. Much of this research has been published elsewhere in the open literature as journal articles and papers.

An article and a method of making surface modified synthetic diamond substrates at temperatures below 500 deg C for electronic packaging applications are described. The article consists of a synthetic diamond substrate, the surface of which has been modified by providing an adherent thin coating of a ceramic (alumina) material so as to enable metallization of synthetic diamond by current industrial methods. The method of surtbce modification comprises deposition of a thin transition metal layer on the synthetic diamond substrate prior to low temperature reactive vapor deposition of aluminum followed by annealing in an oxygen atmosphere.

An article and a method of making surface modified synthetic diamond substrates at temperatures below 5000 C. for electronic packaging applications are described. The article consists of a synthetic diamond substrate, the surface of which has been modified by providing an adherent thin coating of a ceramic (alumina) material so as to enable metallization of synthetic diamond by current industrial methods. The method of surface modification comprises deposition of a thin transition metal layer on the synthetic diamond substrate prior to low temperature reactive vapor deposition of aluminum followed by annealing in an oxygen atmosphere.

Accurate lattice parameters of the tetragonal gamma-TiAl phase with the L1 structure have been determined by X-ray diffraction. The results showed that in binary alloys, the A parameter decreases while the C parameter increases with increasing A1 content. Integrated X-ray intensity were determined from annealed powder samples with powder size < 5 microns in order to estimate the temperature factors Difficulties associated with such evaluations due to the effects of extinction are also discussed. In addition, the 110, 111, and 200 structure factor amplitudes of gamma phase Ti-56at. % Al alloy were accurately determined from critical-voltage electron diffraction measurements. The Debye-Waller factors determined from X-ray experiments and the critical voltage experiments are compared and the results discussed.

This thesis presents research on the cold gas-dynamic spray process applied to the deposition of stainless steel coatings. Cold spray deposition is a relatively new process utilized to create corrosion protection coatings and to perform additive repair for large steel structures. This thesis aims to study the effectiveness of the low-pressure cold spray process on four, commercially available, austenitic stainless steel powders by characterizing both the powders and the resultant coatings. Particle velocimetry and fluid dynamics simulation were also utilized to study the in-flight characteristics of the powder. Notably, this thesis presents evidence that austenitic stainless steel can be successfully deposited via the low-pressure cold spray process. Substantial variability was observed in the commercially available austenitic stainless powders, particularly in the phase content, the particle size distribution, and the particle shape. These parameters had a large effect on the particle velocity and subsequent deposition characteristics. In fact, the PG-AMP- 10 powder, which possessed the highest ferrite fraction and had irregular particle shapes, achieved much higher velocities and greater deposition efficiency than the phase-pure and spherically-shaped S5001 powder., http://archive.org/details/thecoldgasdynami1094543994, Outstanding Thesis, Lieutenant Commander, United States Navy, Approved for public release; distribution is unlimited.

This thesis describes significant changes in the type and degree of localized corrosion for sensitized AA5083 under an applied tensile stress. AA5083 is an aluminum-magnesium alloy that experiences severe intergranular corrosion and intergranular stress corrosion cracking if sensitized. In this research, AA5083-H116 plates were cut into bend-bar samples along both the rolling and transverse directions, and then sensitized to two different levels using laboratory heat treatments of 7 and 30 days at 100°C. The sensitized samples were subjected to elastic tensile loading using a 4-point bend rig while being exposed to a 0.6 molar saltwater solution. Electrochemical polarization was performed on the tensile regions of the samples while under applied stress. Potentiodynamic scans showed that although sensitization causes the most change in electrochemistry, stress does shift the Tafel plot to be more stable when comparing the values for open circuit potential, but reduces the pitting potential of the passivating oxides. Confocal microscopy showed that samples with applied tensile stress produced a much higher density of localized corrosion, including pitting and intergranular corrosion than samples without applied tensile stress. The degree of corrosion damage was slightly higher for samples loaded in the transverse direction compared to samples loaded in the longitudinal direction., http://archive.org/details/theeffectofpplie1094547281, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

The limited number of studies that focus on the size-dependent failure mechanisms of individual nanoparticles and their significance on epoxy composite material properties led to the twofold aim of this research: study the failure modes of nickel nanoparticles and determine the dependence of the mechanical properties of the Ni-epoxy composite on the size of the nickel particles used as reinforcement. Samples of spherical nickel nanoparticles were separated by size based on their densities and the resulting sections used as reinforcement in epoxy composites. The microstructural characterization of the nickel samples were performed on a Scanning Electron Microscope and the mechanical properties of the different Ni-epoxy composite pucks investigated using a nanoindenter. For the failure analysis investigation, an ultrasonic processor was used to induce damage to nickel nanoparticles of diverse sizes dispersed in a solvent. The corresponding effects of the treatment on the nanostructures were analyzed through X-ray diffraction techniques, to determine possible phase transformations, and Transmission Electron Microscopy, to analyze changes in the crystal lattice. Findings indicate that the hardness and Young’s Modulus values for the Ni-epoxy composites increase as filler particle size decreases and follows a normal Hall-Petch relation. The intense energy imparted by the ultrasonic process, along the particle-solvent interface, created a protective NiO coating in the Ni spherical nanoparticles. The latter seems to suppress the complete fracturing of the particle despite the creation of multiple lattice defects., http://archive.org/details/sizedependentmec1094549612, Major, United States Army, Approved for public release; distribution is unlimited.

This thesis characterizes the residual stresses generated by friction stir welding of ODS steel MA956 as a function of heat index. The heat index of a weld is used to determine relative heat input among different friction stir welding conditions. It depends on a combination of the rotational speed and traverse, or welding speed of the tool through the metal. Higher rotational speeds and lower traverse speeds increase heat index and are expected to result in lower residual stresses than welds performed with lower heat index. Three conditions with varying heat indices were selected from high to low: 500 rpm/25 millileters per minute (mmpm), 400 rpm/50 mmpm and 400 rpm/100 mmpm. The full stress tensor was determined for points across these welds using x-ray diffraction. Longitudinal residual stresses approximately 90% of yield strength were observed for the lowest heat input condition. Stress profiles displayed the characteristic M shaped profile, and asymmetry between advancing and retreating stress peaks was limited, occurring mainly on the root of the weld. As expected, lowering the heat index of a weld increased the magnitude of residual stresses across the whole weld profile., http://archive.org/details/characterization1094534627, Outstanding Thesis, Ensign, United States Navy, Approved for public release; distribution is unlimited.

This thesis describes the microstructural and mechanical property changes associated with Friction Stir Processing (FSP) of HY-80 steel under dry and underwater conditions. HY-80 is a low-carbon alloy steel that is used in a quenched and tempered condition and is highly susceptible to hydrogen assisted cracking associated with conventional fusion welding. FSW/P (400 RPM/ 2 IPM) was conducted using a polycrystalline cubic boron nitride tool having a pin length of 6.35 mm. Two sets of processing runs were completed on HY-80 plates, 6.35 mm in thickness, one dry and the other under seawater. Analysis of the residual hydrogen content revealed little change in hydrogen content associated with FSW/P. Detailed microstructural characterization (optical and scanning electron microscopy) with emphasis on the differences in the distribution of constituent phases in the rolling, transverse and normal planes was carried out. Microstructural analysis of the “plan-view” section at the tool extraction sites of FSW/P samples was executed. Mechanical properties of these samples were evaluated by tensile, microhardness, and Charpy V-notch impact resistance tests. The results indicated that austenitization occurred within the stir zones and subsequent cooling influenced the final microstructure and properties. The thermomechanically affected zone displayed a gradual change in near-equiaxed austenitic grain size towards both the tool axis as well as the base plate with little grain shape change throughout. These results have been rationalized on the basis of expected temperature and deformation fields generated setup in these steel samples and the nature of phase transformations occurring in low carbon steels such as HY-80., http://archive.org/details/evaluationoffric109456892, Research Assistant, Naval Postgraduate School

This thesis presents research on the cold gas-dynamic spray process applied to the deposition of aluminum-copper alloy coatings. Cold spray deposition is a process utilized to create corrosion protection coatings and to perform additive repair for aluminum structures. This thesis utilized a series of Al-Cu binary alloy powders, from 2–5 weight percent copper and characterized their chemistry and microstructure. The powders were deposited using the cold spray approach to study the systematic increase of the alloying agent on the deposition process and coating characteristics. Deposition efficiency, critical velocity, coating thickness, hardness, porosity, and microstructure were all characterized as functions of carrier gas pressure, carrier gas temperature and feedstock powder copper composition. This thesis has demonstrated that all of the aluminum copper powders utilized can be successfully deposited via the low-pressure cold spray process with helium as the carrier gas. The copper content of the powders has a direct effect on the volume fraction of Al2Cu intermetallics, and on the coating hardness, while having no measurable effect on critical velocity for deposition or the coating thickness per pass., http://archive.org/details/processingmicros1094545887, Outstanding Thesis, Outstanding Thesis, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

The impact that biofouling has on a ship’s performance has long been recognized, since it increases the frictional resistance of the hull and can increase the ship’s fuel consumption. In this study, the spectrum of hydrophobic and antifouling surface patterns that can electrochemically be fabricated on HY-80 steel (alloy that is broadly used in shipbuilding for welded hull plates) is examined. After the fabrication of nanoscaled topographies, the optimum conditions for anodizing are determined by correlating the processing conditions with microstructural data. Characterization of the surface oxides was conducted by techniques such as Scanning Electron and Focused Ion Beam microscopy as well as identification of the formed phases by X-ray diffraction techniques. Hydrophobicity of the surfaces was examined by measuring the contact angle of deionized water on the HY-80 steel surface. These studies revealed the improved wetting behavior of the anodized surfaces. Thermogravimetric analysis along with quantitative examination of the biofouling on the specimens were studied after prolonged exposure to seawater and indicated a decrease in the corrosion rate of anodized surfaces., http://archive.org/details/engineeringofnan1094545934, Outstanding Thesis, Outstanding Thesis, Lieutenant, Hellenic Navy, Approved for public release; distribution is unlimited.