Abstract Thermal-sprayed titanium coatings were investigated as anodes for impressed current cathodic protection systems for steel reinforced concrete structures. The coatings were applied by twin-wire thermal-spraying using air and nitrogen as atomizing gases. The coatings were non-homogeneous due to oxidation and nitridation of the molten titanium with the atmospheric gases oxygen and nitrogen. The primary coating constituents were α-Ti (containing interstitial nitrogen and oxygen), γ-TiO and TiN. Nitrogen atomization produced coatings with less cracking, more uniform chemistry, and lower resistivity than air atomization.

Abstract Steel-reinforced concrete slabs coated with a thermal-sprayed titanium anode were used to simulate impressed current cathodic protection systems. The titanium anodes were activated with a cobalt nitrate catalyst and subjected to accelerated electrochemical aging representing approximately 23 years at 0.00215 A/m 2 (0.2 mA/ft 2 ). During the aging experiment, current was kept constant at 0.0215 A/m 2 (2 mA/ft 2 ), voltages were recorded, and water was applied periodically when voltages exceeded compliance levels. At the end of the experiment, coating resistivity, adhesion strength, and titanium-concrete interfacial chemistry were determined. Results show that the coating resistivity increases and adhesion strength decreases with electrochemical aging. Voltages for the slabs varied with the relative humidity. Electrochemical reactions at the titanium-concrete interface caused deterioration of the cement paste by leaching of calcium compounds. Accelerated aging results are compared to similar ones for an uncatalyzed titanium anode and to results from the Depoe Bay Bridge.

Abstract Corrosion behavior of a flame sprayed titanium coating sealed by some resins was investigated in 3.5% NaCl solution by an electrochemical polarization measurement and an immersion test. The composition and structure of the sprayed film was also analyzed by SEM and EPMA. Although an as-sprayed titanium had no resistance to the corrosion because of its porosity, the sprayed titanium sealed with epoxy or silicon resin showed an excellent resistivity against the chloride corrosion. In spite that almost half amount of the titanium changed to oxide, nitride and carbide through the gas flame spraying, the conversion of the metal to the compounds had little effect to decrease the corrosion resistivity. The sprayed and sealed titanium coating obtained by a conventional onsite thermal spraying is expected as an economical material for chloride containing environments.

Abstract The application of thermally sprayed coatings is often limited by their porosity as well as their low adhesion. A new approach for high energy beam surface treatment of thermally sprayed coatings is presented using simultanously a lower power level for continuous remelting and pulses of higher power in order to get coatings with good corrosion behaviour and improved adhesion. This technology is applied to titanium as well as to NiCr-coatings on steel substrates. The investigations prove that remelted thermally sprayed coatings with a smooth and dense surface layer, followed by a heat treated section of the coating and a reaction zone at the substrate/coating interface can be obtained. Therefore, a change in chemical composition of the coating is avoided, while at the same time the bond strength of the remelted coatings can be influenced by metallurgical reactions at the interface zone.

Abstract The covering of titanium implants by means gas-thermal spraying of hydroxyapatite powders is an actual scientific, technical and medical problem. Application of hydroxyapatite for these purposes is more preferable. However, the problem of its structural and cyclic strength under conditions of bioenvironment response determines of application areas of such coatings and reliability of them usage. Structure and phase composition of hydroxyapatite coating under plasma spraying on titanium substrates and their changing, caused as conditions of forming coating on its increasing, so and conditions of spraying an laminar and turbulent plasma streem were studied. Exact belief about the crystalline structure and phase composition of coating is obtained by methods electronic microscopy and X-ray analysis. Changing of coating structure after sintering in the vacuum and electron beam melting in the vacuum is discussed.

Abstract Tungsten carbide cobalt thermal spray coatings are used in the aircraft industry to reduce wear damage of lightweight metals such as titanium The performance and life of tungsten carbide (WC-Co) coated titanium materials depend on many factors. An important factor that has received increased attention in thermal spray research is the residual stresses in the coating and substrate. Residual stresses depend on the parameters of the application process. Parameters affecting residual stresses include the prespray treatment of the substrate material (grit blasting, shot peening) and the type of spray application process (HVOF, plasma arc) During the in-service life of a WC-Co coated material, residual stresses can change significantly. The goal of this work is to quantitatively evaluate the changes in residual stresses of the substrate and the WC-Co coating during various stages of processing. A destructive laboratory method, called the "Modified Layer Removal Method," was used to evaluate the through-thickness residual stresses of the WC-Co coating and the titanium substrate material. Residual stresses are determined for three conditions: (1) shot peened, (2) shot peened and grit blasted, and (3) shot-peened, grit blasted and thermal spray coated. The changes in the residual stresses are shown at selected stages during the processing history of the coated materials. Differences between residual stress levels at selected stages are identified and discussed. The effect of coating thickness and HVOF application process on the residual stress in the coating is also examined.