Oxidation Behaviour of HVOF Sprayed NiCrAlY and NiCrAlY-20SiC Coatings on T-91 Boiler Tube Steel
Gurmail Singh, Niraj Bala, Vikas Chawla
Abstract
In present study, the high temperature oxidation behavior of HVOF sprayed NiCrAlY alloy coating and NiCrAlY–20SiC composite coating on T-91 boiler tube steel has been investigated at elevated temperature of 900°C for 50 cycles. The kinetics of oxidation has been established with weight change measurements. Both coatings and uncoated material obeyed the parabolic law during oxidation studies. XRD, FE-SEM along with EDS, X-ray Mapping characterization tools were utilized to check phase formation, elemental distribution and microstructure. The study resulted that both coatings performed better in oxidizing environment due to the formation of protective oxides in coated surface, however in case of uncoated steel unprotective Fe2O3 oxide was formed which led to extensive spallation. Moreover the composite NiCrAlY–20SiC coating provided more resistance to high temperature oxidation than NiCrAlY alloy coating.