ROLE OF RARE AND REACTIVE ELEMENTS IN Cr3C2-25% (NiCr) COATING ON SUPERNI 600 BY D-GUN PROCESS IN SIMULATED BOILER ENVIRONMENT

Abstract

II igh temperature oxidation is the main cause for the degradation of materials used at elevated temperature which is responsible for the major shut down of turbines, boilers and incinerators used in large units. The superalloys are being employed in supereritical boilers and other energy generation and conversion systems. These superalloys have to withstand very severe environmental conditions during service. Thermal spray coatings find their wide application to increase the life of these superalloys and protecting them from severe degradable conditions like boilers, incinerators environment. Various thermal spray teclrniques are available to provide the coatings but in this study an attempt has been made to use Cr3C2-25%NiCr coating deposited by D-gtin technique on Supemi 600 alloy. Use of Cr.C'2-NiCr coating by 1)-gun technique is normally confined to improving the wear and erosion resistance. in this study CrzC'-NiCr coating and ('nCl_NiCr+0.4w1.%CeO2 have been used for providing utah temperature corrosion resistance to the superalloy Superni 600. These coating have been studied for oxidation and hot corrosion in moiten salt i.e. 75%Na2SO4-25'YoNaCl at 900°C under cyclic conditions. Sound and adherent coatings of 150-250 itni was obtained by fl-gun process. The effect of rare earth elements i.e. Ce was also observed. The bare and coated alloys were individually stthjected to cyclic oxidation and hot corrosion for IOU cycles. Weight change/area has been plotted against number of cycles and to monitor the oxidation kineucs, The scale ihrnied after oxidation and hot corrosion on the bare and coated alloys has been examined using FISFM'EDX. XRD, and Cross-sectional/Mapping analysis. D-gun sprayed Cr.C2-NiCr coating has contributed to increase in the oxidation resistance of coated superalloy.