Stainless austenitic steels like the 316L (1.4404) are widely applied in various applications and were also used for surface protection using thermal spraying. The reason for this is the easy processability and the high corrosion resistance. Stainless austenitic steels typically contain the following alloying elements: The formation of an austenitic microstructure is achieved by nickel (Ni). The addition of chromium (Cr) lead to good corrosion resistance due to formation of an oxide layer. For resistance against pitting corrosion, molybdenum (Mo) can be added. Also, stainless austenites usually exhibit very low carbon and nitrogen contents to prevent chromium carbides and nitrides which reduces the corrosion resistance. However, both alloying elements cannot be classified as being detrimental in stainless austenites in general. In contrast high nitrogen contents can also be used to improve the chemical properties, especially the resistance against pitting corrosion. Finally, carbon and nitrogen lead to an increase in hardness of the thermal sprayed layer. Based on this knowledge, a high-strength austenite for thermal spraying was developed. The new high strength austenite was processed by HVAF spraying with different particle distributions and parameter variations. Resulting coatings were investigated regarding the microstructure, elemental composition, hardness and corrosion properties in comparison to the standard coating material 316L.

This study assesses the effectiveness of wire arc sprayed aluminum coatings for protecting welded super duplex stainless steel (UNS S32750) in subsea applications. Pitting and crevice corrosion tests were conducted at different potentials in recirculated synthetic seawater maintained at 90 °C with an acidity of 7.5-8.1 pH. After 90 days, the samples were examined, showing no signs of corrosion even in areas where coating defects were present.

Cold Gas Spray allows to extend the range of steel coating formulations in comparison with other thermal spraying techniques because the material doesn’t melt during process. The absence of processes of fast solidification implies the absence of tensile stresses in the coating and makes possible to obtain thick coatings becoming a new alternative to welding cladding processes for the restoration of surfaces with corrosion pitting, notched areas or welded zones with bad appearance and for the repair of porous casting, contractions or losses of tolerance, by applying located coatings. 17-4 PH steel is one of the most widely used precipitation hardening grades in the business, offering high strength with corrosion resistance similar to S30400 in most environments. While soft and ductile in the solution annealed condition, it is capable of high properties with a single precipitation or aging treatment. Characterized by good corrosion resistance, high hardness, toughness and strength. Commonly used in both aircraft and gas turbines, nuclear reactor, paper mill, oil field, and chemical process components. A study has carried out in Thermal Spray Center for the production and optimization of thick coatings of 17-4 PH steel (S17400) through Cold Gas Spray technology onto carbon steel substrates. The study concentrates in the determination of influence of spray parameters on coating properties.

HVOF-sprayed coatings (WC-17Co, WC-10Co-4Cr, Co-28Mo-17Cr-3Si) have been compared with various kinds of industrially manufactured hard chrome coatings (HCC), whose substrate preparation, deposition process, post deposition treatments greatly affect their characteristics. Microstructure, micromechanical properties, tribological behaviour and corrosion resistance (electrochemical polarization tests and Corrodkote test) have been studied. HVOF-sprayed cermets are harder but less tough than HCC, Co-28Mo-17Cr-3Si are less hard than HCC. Splats detachment causes a comparable or higher mass loss in three-body abrasion than HCC coatings. Forming a uniform surface film, cermet coatings definitely overcome HCC in two-body sliding, while Co-28Mo-17Cr-3Si has insufficient hardness to display good sliding wear resistance. HVOF coatings show no passivation in corrosive media but cermets posses more noble corrosion potentials than HCC, and undergo generalized corrosion in HNO 3 and HCl, with similar corrosion current densities (I C ). HCC passivate and resist well in HNO 3 0.1N, but undergo pitting corrosion in 0.1N HCl. Definitely different E C and I C are recorded for various HCC in HCl. HVOF-sprayed cermet coatings show lower I C in 0.1N HCl solution than several kinds of HCC. No visible damage occurs on HVOF-sprayed coatings after the Corrodkote test, while non de-hydrogenated HCC suffered pitting corrosion.

In this paper, the corrosion characteristics of two HVOF-sprayed coatings made with self-fluxing NiCrSiB powders are assessed in the as-sprayed condition. One of the coatings is also investigated after post-spray treatment with polymer sealing and after vacuum furnace fusion. It was found that cracking at lamellar boundaries dominates the corrosion behavior of the layers in the as-sprayed and sealed states, while pitting corrosion resulting from the failure of hard phases plays the main role in the melted layer. Paper includes a German-language abstract.