TiAIN & AICrN COATINGS ON T-91 STEEL BY PAPVD PROCESS FOR OXIDATION IN AIR & AQUEOUS CORROSION IN 3% NaCI

Abstract

The PAPVD process is applied for deposition of TiA1N & A1CrN coatings on T-91 boiler tube steel. The coated sample then studied for characterization before undergone the cyclic oxidation.SEM is used to measure thickness,AFM analysis was carried out to see the roughness and Microhardness test was done for hardness measurement at the interface and coating. Characterisation and oxidation behaviour of coatings after exposure to air at 900 ° C were studied under cyclic conditions. The thermo-gravimetric technique was used to establish kinetics of corrosion. XRD, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the corrosion products. The A1CrN coating on T-91 substrate was very effective in decreasing the corrosion rate in air at 900 °C after 50 cycles.Whereas the TiA1N coating on T-91 substrate was least effective.The uncoated sample shows eagerness to oxidation, with spalling after 50 cycles at 900 °C in air. Immersion test, corrosion chamber test and potentiodynamic test was carried to check the effectiveness of coated and uncoated samples.The corroded product then tested with FE SEM/EDAX to analyse the mode of corrosion.Pitting was observed in each case.Uncoated sample rapidally get corroded and TiA1N coated sample found less corroding than bare one.AlCrN coated sample was found excellent corrosion resistance after immersion & chamber test.The potentiodynamic test(both Linear & Tafel-tests) shows the effectiveness of A1CrN coating. iii