Under marine and coastal conditions, the degradation by corrosion of low-alloyed steels is generally observed. In order to overcome such important corrosion problems, the use of thermal spray coatings made of noble materials may be an attractive solution. 316 stainless steel thermal spray coating, an iron alloy coating, is often considered for corrosion protection because of its low material cost. Also, the high velocity oxy-fuel (HVOF) is often the selected coating process because it is known to provide coatings with a very low porosity level preventing the corrosive media to reach the substrate. The present paper compares the corrosion behavior of wrought 316 stainless steel with sprayed coatings made of the same alloy on 1020 mild steel. The corrosion behavior of materials is studied under salt fog conditions and with electrochemical techniques in brine simulating the marine environment. The coatings have been sprayed by HVOF under usual conditions. The results of this study demonstrate that the material behavior with regard to corrosion is process dependent . The HVOF sprayed stainless steel coating is much more sensitive to corrosion than wrought stainless steel. Corrosion product appearing on the samples is not only linked to the corrosion of the substrate by diffusion of the corrosive solution through pores but is also generated by intrinsic corrosion of coating itself. An enhanced sensitivity of the coating with regard to corrosion is attributed to the surface of particles or droplets, which are most likely degraded during the spraying process. However, thermal spray coatings having performances as good as wrought stainless steel can be obtained. In the present work, it is demonstrated that coatings obtained using vacuum plasma spray (VPS) have similar corrosion properties than wrought stainless steel in simulated marine environment. The industries considering corrosion protection of their components in marine environments by the use of stainless steel coatings must be aware of the reliability of their coatings. During the usual HVOF spray process, particles or droplets of stainless steel 316 are subject to important modification leading to a loss of performance against corrosion. Oxidation of alloying elements necessary to obtain a good stainless steel most likely occurs. However, the use of vacuum sprayed stainless steel coatings results to efficient protection against corrosion in marine environment.

This paper compares the corrosion resistance of electrolytic hard chrome plating and HVOF-sprayed WC-Co-Cr on two steel alloys used in landing gears. Test samples were evaluated by means of salt spray testing and electrochemical measurements. Post-test metallographic examinations were conducted to investigate the failure mode of the coatings. Test results are presented along with relevant findings and observations. Paper includes a German-language abstract.

The HVOF technology is well known to provide a wide variety of coating materials having excellent performance characteristics under different aggressive conditions such as wear, erosion by impact of particle and corrosion. Carbides, as a family, constitute a big segment of materials used by the thermal spray industry. Although their material properties may be well known since they are often used in wear or corrosive-wear industrial applications, aqueous corrosion of such coatings are not well characterized. Moreover, thermal spray process technology being in constant evolution, past literature on these coatings may not be directly applicable as newer produced coatings have higher adhesive and cohesive strength. Recent technology allows a better control on density and oxides content that are important parameters to consider for corrosion applications. The success of a coating is related to judicious material selection for various applications. However, the choice of the starting materials for producing a coating is often difficult since there is a lack of data on the corrosion performance of thermal spray coatings. The present paper addresses the performance of various carbide HVOF coatings in terms of corrosion rate and degradation mode in two corrosive environments — HCl and HNO3. Behavior of the coatings is compared using bulk SS316 and SS316 HVOF coating as a benchmark.

This paper evaluates four tungsten carbide basecoats produced by thermal spraying with a high speed flame spraying system as potential candidates to replace hard chrome in applications subject to abrasive and/or corrosive conditions. It investigates the potential of using WC-based cermet coatings deposited using high velocity oxy-fuel thermal spraying to replace electrodeposited hard chromium. The paper shows that WC-based thermally sprayed coatings are available to replace hard Cr in many applications. Salt spray tests and electrochemical measurements in synthetic sea water showed that the Cr-containing coatings had the highest corrosion resistance. These results indicated that 10Co-4Cr-WC could be the best coating candidate for conditions in which both abrasion and corrosion are present. Paper includes a German-language abstract.