Studies on erosion-corrosion behaviour of plasma sprayed Ni₃Al coating in a coal-fired thermal power plant environment at 540°C

Abstract

Purpose

The purpose of this study is to investigate the application of Ni₃Al coating for boilers and other power plant equipment, which suffer severe erosion-corrosion problems resulting in substantial losses. Currently, superalloys are being used to increase the service life of the boilers. Although the superalloys have adequate mechanical strength at elevated temperature, they often lack resistance to erosion-corrosion environments.

Design/methodology/approach

In this paper, the erosion-corrosion performance of plasma-sprayed nickel aluminide (Ni₃Al) coating on nickel- and iron-based superalloys have been evaluated by exposing them to the low temperature primary superheater zone of the coal-fired thermal power plant at the temperature zone of 540^°C for ten cycles of 100 h duration. The exposed products were analysed along the surface and cross-section using scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron micro probe analysis (EPMA).

Findings

The XRD, SEM and EPMA analyses have shown the formation of mainly NiO, NiAl₂O₄ and indicated the presence of Ni₃Al, Ni and Al₂O₃. In the boiler environment, Ni₃Al coating partially oxidizes and acts as a perfect barrier against erosion-corrosion of superalloys. The partially oxidised Ni₃Al coating remains intact even after 1,000 h cycle exposure.

Originality/value

The probable mechanism of attack for the plasma-sprayed Ni₃Al coating in the given boiler environment is presented.

Citation

Mishra, S.B., Chandra, K. and Prakash, S. (2017), "Studies on erosion-corrosion behaviour of plasma sprayed Ni₃Al coating in a coal-fired thermal power plant environment at 540°C", Anti-Corrosion Methods and Materials, Vol. 64 No. 5, pp. 540-549. https://doi.org/10.1108/ACMM-11-2015-1592