Abstract

Two boron-rich Fe/Cr based gas atomised powders (Armacor M and Armacor C) have been thermally sprayed using the HVOF process and the resultant deposits subsequently characterised, using X-ray diffraction, scanning electron microscopy (SEM), plan view transmission electron microscopy (TEM), and microhardness measurements. The wear and corrosion characteristics of the two alloy coatings have also been investigated by three body abrasive wear (utilising cross-sectional TEM to examine the worn surfaces) and potentiodynamic corrosion testing respectively. Results from microstructural analysis of the as-sprayed deposits revealed the presence of small chromium-iron boride precipitates within a predominantly amorphous matrix in the Fe-based Armacor M coating. The Fe-Cr-based Armacor C coating, however, consisted mainly of regions of nano- and microcrystalline material interspersed with chromium boride precipitation. Iron-chromium oxides have been observed within both of the alloy coatings studied. Both of these alloys exhibit good abrasive wear resistance when compared with other metallic based HVOF sprayed coatings. Both Armacor M and Armacor C also exhibit extensive passivation on exposure to an acidic solution. The wear and corrosion test results are related to the microstructural observations.

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