Abstract
Abstract Wear resistant highly amorphous Fe 60 Cr 8 Nb 8 B 24 (at.%) coatings of about 280 μm thickness were prepared through high velocity oxygen fuel (HVOF) thermal spray process onto API 5L X80 steel substrate. Feedstock powders were produced by gas atomization with low purity precursors by modifying AISI 430 stainless steel with additions of niobium (Fe-Nb) and boron (Fe-B). It was found that the coatings were mostly amorphous with some embedded FeNbB and Fe 2 B borides. The formation of a large fraction of amorphous phase was attributed to the high cooling rates of molten droplets combined with a proper powder composition. The average Vickers hardness of the coating (HV 0.3 = 838 ± 23) was about four times higher than that of the API 5L X80 substrate (HV 0.3 = 222 ± 5). The excellent wear resistance of the amorphous coating in the pin-on-disc measurements was attributed to its large fraction of amorphous phase (~ 66%) with reinforcing hard Fe 2 B and FeNbB borides, high Vickers hardness, low oxygen content ( − 5 and 8.5 × 10 − 4 mm 3 ·N − 1 ·m − 1 , respectively). API 5L X80 steel exhibited dominant adhesive wear at low sliding speed and oxidative wear at high sliding speed. HVOF coatings presented oxidative wear regardless of the sliding speed.
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