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High‐temperature corrosion behavior of some post‐plasma‐spraying‐gas‐nitrided metallic coatings on a Fe‐based superalloy
Author(s) -
Chawla Vikas,
Sidhu Buta S.,
Rani Amita,
Handa Amit
Publication year - 2019
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.201910971
Subject(s) - materials science , nitriding , superalloy , corrosion , metallurgy , high temperature corrosion , coating , molten salt , fluidized bed , oxide , thermal spraying , composite material , layer (electronics) , microstructure , waste management , engineering
The objective of the present study is to propose a cost‐effective process for modifying commercially available coatings by gas nitriding using commonly available equipment and starting materials. Al–Cr and Ti–Al metallic coatings were deposited on Superfer 800H (Fe‐based superalloy) using a plasma spray process. Then the gas nitriding of the coatings was done in the lab and the parameters were optimized after conducting several trials on plasma‐sprayed‐coated specimens. Characterization and high‐temperature corrosion behavior of coatings after exposure to air and molten salt at 900°C were studied under cyclic conditions. Techniques like XRD, SEM/EDX, and X‐ray mapping analysis were used for the characterization of the coatings and analysis of the oxide scale. Both the coatings successfully protected the substrate and were effective in decreasing the corrosion rate when subjected to cyclic oxidation (Type‐I hot corrosion) at 900°C for 50 cycles in air and molten salt (a salt mixture of Na 2 SO 4 –60%V 2 O 5 dissolved in distilled water). Based on the findings of the present study, the coatings under study are recommended for tapplications to super‐heater and reheater tubes of boilers and all those surfaces that face fireside corrosion, such as fluidized beds, industrial waste incinerators, internal combustion engines, gas turbines or steam turbines, to provide protection against degradation in these environments. The cost of the product/process is approximately Rs. 0.62 per mm 2 in case of Al–Cr coating and Rs. 1.86 per mm 2 in case of Ti–Al coating.