This work evaluates the influence of yttrium on the heat and wear resistance of active arc sprayed (AAS) coatings produced using FeCrBAl cored wire. The AAS process differs from ordinary arc spraying in that it uses propane-air combustion products as a carrier gas instead of compressed air. This increases particle velocity and temperature and forms a reducing atmosphere that protects metal particles in flight and improves coating adhesion and porosity. Coating samples produced with different amounts of yttrium were characterized in terms of surface morphology, microstructure, phase composition, and hardness. They were also subjected to heat resistance, abrasive wear, and corrosion tests in which they performed better than typical wrought steels used in boilers.

This study compares the corrosion resistance of a wide range of coatings in a chlorine-containing atmosphere at elevated temperatures. Four HVOF-sprayed NiCr coating samples were produced and tested along with an iron-aluminide HVOF layer, a chromium diffusion layer, and a laser-treated HVOF NiCrMo layer. The investigators found that the structure of HVOF coatings has a major effect on corrosion resistance and that chlorine corrosion primarily attacks the substrate through cracks and interconnected networks of pores and oxides at splat boundaries. They also observed that laser melting increases corrosion resistance by homogenizing the coating structure. Paper includes a German-language abstract.

Zinc and aluminium coatings have been used widely to protect steel structures from corrosion in aggressive and hostile conditions. The more recent development of zinc 15wt% aluminium alloy in a wire form has demonstrated that arc-spray coatings can be produced with a resistance to red rust which is superior to that of the single metals. Competitive 'pseudo' alloy or composite coatings produced by co-spraying wires of zinc and aluminium have been shown to achieve resistance to salt spray conditions similar to this conventional alloy. Work described in this paper confirms these findings and goes on to demonstrate an additional advantage of co-spraying an aluminium -5wt% magnesium instead of aluminium with the zinc. The importance of providing a fine dispersion of the two phases in the 'pseudo' alloy is highlighted and an alternative method of providing a similar dispersion by using a 'cored' wire (e.g. Al-5wt%Mg wire in a zinc sheath) approach has been demonstrated. The importance of 'self sealing' in these coatings after the initial loss of zinc is discussed which is related to the coating microstructure and their electrochemical behaviour in chloride solutions.