The present study compares needed prerequisites for the application of cavitation resistant bronzes by applying different coating techniques, such as cold spraying, HVOF spraying, warm spraying and arc spraying. By optimization to optimum cavitation resistance, the deposited coatings can increase the service life of ship rudders significantly and even serve as repair processes for ship propellers. The given overview aims to support the selection of processes when specifying the target properties to be set with regard to cavitation protection. By using high-pressure warm spraying and cold spraying, properties similar to those of cast nickel aluminum bronze were achieved, however at relatively high costs. In contrast, coatings produced by using HVOF and arc spraying have erosion rates that are only about four respectively three times higher as compared to cast nickel aluminum bronze, while far outperforming bulk shipbuilding steel. Hence, their properties should be sufficient for acceptable service life or docking intervals for ship rudder applications. Propeller repair might demand for better coating properties as obtained by cold spraying. With respect to costs, HVOF and arc spraying in summary might represent a good compromise to reach coating properties needed in application.

Thermal sprayed marine coatings in the marine environment usually encounter chloride-induced corrosion and microbiologically induced corrosion. Formation of microbial biofilm is crucial for subsequent attachment of large fouler and understanding the initiation and growth of the biofilm is essential for possibly controlling the occurring of biofouling. This paper reports the formation of Bacillus sp. bacterial biofilm on arc sprayed aluminum coatings and its effect on the corrosion behaviors of the coatings. Results show fast and pronounced attachment and colonization of the bacteria on aluminum coatings. The bacterial biofilm was systematically examined by CLSM, FESEM, and Raman spectroscopy. Electrochemical assessment revealed that the aluminum coating immersed in the bacteria-containing media showed higher corrosion resistance than the sterile samples. A model was proposed to explain how the microorganisms and their metabolic by-products protect the coatings against penetration of corrosive media. The results would give insight into design and fabrication of thermal sprayed coatings for enhanced anti-biocorrosion performances in the marine environment.

Bronze materials such as Ni-Al-bronze show exceptional performance against corrosion, erosive wear, and cavitation erosion due to their high fatigue strength and resistance to plastic deformation, and are thus used for ship propellers and in turbines, pumps, and other equipment where alternating stresses occur. Usually, the respective parts are cast, but in this study, a number of opportunities are evaluated to apply bronze as a coating to critical part surfaces. Initial experiments with cold gas spraying were promising enough to assess the use of warm spraying, a nitrogen-cooled HVOF process that provides similar particle impact velocities but higher particle temperatures, while still minimizing the effects of oxidation. The formation and performance of warm sprayed Ni-Al-bronze coatings was systematically investigated for different combustion pressures and nitrogen flow rates. Substrate preheating was also used to improve coating adhesion. The coatings obtained show low porosities, high strengths, and in some cases, cavitation resistance similar to that of the bulk material.

The present study investigates the microstructure and properties of cold spray coatings produced from gas-atomized CuAl10Fe5Ni5 powders. To obtain information relevant to ship rudder cavitation-erosion performance, GL-A shipbuilding steel, equivalent to S235, was chosen as the substrate material. Thick Cu-Al-bronze coatings were deposited on grit-blasted plates using a wide range of parameter sets with different powder treatments, nozzle geometries, gas and substrate temperatures, and particle impact conditions. Coating samples were examined via SEM and XRD analysis, cavitation tests were performed, and bond strengths were measured. Powder and single impact morphologies were also investigated and, along with coating properties and structures, are correlated with spraying conditions. The results indicate that cold sprayed bronze coatings have good potential for ship rudder protection.

This paper presents key findings from an ongoing study on the marine corrosion behavior of thermally sprayed zinc and aluminum coatings. Zn, Al, and Zn-Al layers of varied thickness were applied to twelve steel pipes by arc and flame spraying and subjected to different post-spray treatments such as sealing and painting. The pipes are mounted vertically on a test rig in the Pacific Ocean and have been inspected annually to record the appearance and thickness of the coatings. After 7 years, the Zn coatings began to show signs of degradation in the immersed portion of the pipe, although no such changes occurred with Al and Zn-Al coatings. After 18 years, heavily damaged sections of three pipes were removed and new pipe was welded in place. The repaired regions were coated with Al-5%Mg, which has performed well so far.

Damage of marine screw propeller parts made of aluminum bronze cast material caused by cavitation erosion is one of the serious problems. Erosion resistant thermal spray coating on aluminum-bronze material is expected to extend lifetime of such propellers. In this study, Cobalt-based alloy coatings sprayed by; (a) atmospheric plasma spraying (APS), (b) low pressure plasma spraying (LPPS) and (c) high velocity oxy-fuel (HVOF) spraying and aluminum bronze cast material were evaluated by cavitation erosion test using magnetostrictive cavitation test equipment. Fracture morphology of cavitation eroded coating surfaces were analyzed by surface observations with SEM and also the amount of volume loss was measured. Cobalt-based alloy coatings sprayed by LPPS exhibited superior cavitation erosion resistance compared to aluminum bronze cast material and coatings by APS and HVOF. Moreover, mechanical properties of Cobalt-based alloy coatings were investigated in detail by nanoindentation technique. It is found that cavitation erosion resistance of coatings is subjected to interparticle cohesive strength.

Hydrogen embrittlement in high strength marine structural steels can occur by improper cathodic protection. In this article the possibility of Hydrogen embrittlement (HE) in high strength steels caused by zinc and aluminium thermal sprayed (TS) coatings has been considered. Provided potential from the TS coatings in marine environments and permissible potential for performing cathodic protection and inhibiting HE has been described. Also effective parameters on HE and prevention methods for HE by thermal sprayed coatings has been reviewed. An effective method for quality stabilizing and potential regulating in anticorrosion TS coatings is utilization of the alloyed materials. Most used material for anticorrosion TS coatings is aluminium that provides relatively moderate potential and low current density and in particular situation can cause HE.

For thermal sprayed coatings, compactness of their constituent particles is required in many applications, e.g. to obtain impermeable anticorrosion coating in marine use. We investigated key factors to improve compactibility of deposited particles in HVOF sprayed coatings by condition measurements of spray particles. The results revealed that plastic deformability of the sprayed particles as well as their molten fraction was important to obtain the dense VHOF coatings.

This paper discusses the performance of arc-sprayed composite layers produced using aluminum oxide-filled wires. In tribological property testing, the composite layers show good non-slip behavior with a high coefficient of friction. They also exhibit excellent wear resistance, four to six times better than that of aluminum layers, owing to the presence of aluminum oxide particles dispersed throughout the metal matrix. Paper includes a German-language abstract.

Naval ship components are subject to extreme operating conditions while at sea, either during regular sailing periods and/or during training exercises. The Chilean Navy has employed thermal spray technology since the early 1960 decade. By setting up a joint cooperative program between the Chilean Navy industry and suppliers, it has been possible to start regaining confidence in thermal spraying and positioning the same as a "must" technology in regular naval maintenance work. This article presents a description of the Naval Components Reclamation Program and discusses the processes involved in hard chrome plating replacement in naval components. It provides a review of characteristic thermal spray applications developed by the Joint Naval Components Reclamation Program.

High Velocity Oxy-Fuel Thermal Spray has been used by the Navy for repairing components for several years with great success. This paper will discuss some of the applications being done, the results of these applications and where the technology will be utilized on the future. The Office of Naval Research in conjunction with Naval Research Laboratory and Naval Surface Warfare Center is investigating replacements for chrome plating. One of the technologies being looked at is HVOF Thermal Spray. This paper will discuss this program, new materials being developed and new applications being done. The superior physical characteristic of HVOF has increased the utility of this technology from mechanical components to aircraft and submarine components. Acceptance of these coatings at various levels at NAVSEA will be discussed and criteria established for these acceptances will be reviewed. The role of these coatings in ship repairs as well as the implications for new construction will be discussed. Specific examples of repairs will be shown and updated reports will be provided as to their service. Locations that have services available will be detailed and future growth of this technology within the Navy will be reviewed. A quick overview of similar emerging technologies will be provided. A highlight of the presentation will be an update of the repair done with HVOF Tungsten Carbide on the Rudder Rams on the USS Saipan.

The objective of this study is to develop viable surface-treatment technologies for offshore and underwater structures. The study focused on cavity formation, which is a prerequisite to underwater plasma spraying using a fluid-stabilized local dry-wet method. Factors affecting cavity formation that were investigated in the study include slit angles on protection tubes, jet velocity of water curtains, and clearances between protection tubes and plate surfaces. All plasma-sprayed coatings formed underwater were made with pure Ti wire and then assessed to determine the influence of various factors on cavity formation. Macroscopic examination of the coatings revealed neither cracks nor peelings. X-ray analysis confirmed that coatings consisted mostly of Ti phase.

For very large structures and parts in critical environments, a materials solution often cannot be found by using one material. The specific desired properties for those structures, like stiffness, ductility, high temperature stability, corrosion resistance, etc. are difficult to fulfill with only one material. In this case a solution may be found by using coatings and design their specific properties to replenish each other by their combination. The Thermal Spraying processes offer the necessary flexibility of producing thin to thick, ductile, soft to hard coatings while due to the wide range of process temperatures it is possible to process a wide range of materials, both as coating and structure. In this paper the some recent and important developments in Thermal Spraying to produce coatings for technical demanding structures will be described. These developments consist of High Power Plasma Spraying, powder- and process control development. To ensure process consistency during long spraying times and to apply reproducible coating quality a suitable process control is of great importance and the development of temperature control by Pyrometry and Thermography will be presented. The example will be drawn according to the application of a coating on a ball valve for off-shore and ship diesel engine parts (piston and valve).

Thermal spraying has been used to protect many steel structures from aqueous corrosion using Zinc and Aluminium, and to some extent their alloy coatings to provide galvanic protection. The lifetimes of the coatings can approach 50 years even when exposed in severe marine environments. Zinc coatings work by continuously sacrificing themselves and slowly dissipating over time. Aluminium coatings passivate more readily and form a barrier layer, the passivity makes them less able to protect damaged areas and to self heal. A new ternary coating system involving Aluminium, Zinc and Magnesium has been shown to be capable of providing both a passive barrier layer as well as being able to give galvanically active protection. Salt spray tests have shown that the resistance to red rust of these new coatings increases by 300% over similar thicknesses of the separate metal coatings. Processing by arcspray is straightforward and both adhesion and deposition efficiency are better than where Zinc is sprayed alone.