High temperature corrosion and wear behavior of HVOF-sprayed coating of Al2O3-NiAl on AISI 304 stainless steel

Abstract

High velocity oxy-fuel (HVOF) technique was used to deposit an Al2O3-30(Ni20Al) coating on AISI 304 stainless steel substrate to improve its corrosion and wear performance at high temperature. First, thermal cycling tests at 750 and 850 °C were conducted in air atmosphere on both coated and uncoated stainless steel substrates to study the effectiveness of coating protection system at different exposure times (2, 6, 10 and 15 days). Then, high temperature corrosion and wear mechanisms were studied by SEM and XRD techniques. These analyses revealed that uncoated specimens were severely corroded but no oxidation on the coated substrates was detected. Oxide growth on the uncoated substrate was mainly formed by spinel (MnCr2O4 and FeCr2O4) and corundum (Fe2O3 and Cr2O3) type oxides. Meanwhile, these oxides were not found on the coated substrate. Wear rate of the coated specimen was found to be reduced from 6.9·10−4 to 8.3·10−5 mm3/N·m compared to that of the uncoated specimen. The exposure to high temperatures improved coating wear resistance: wear rate was four times lower in the coated sample exposed to high temperatures compared to that of the non-exposed coated sample due to the formation of a harder phase of NiO.