Degradation by high-temperature oxidation is one of the main failure modes of hot-section components in the gas turbines. No alloy is immune to hot corrosion attack indefinitely, although there are some alloy compositions that require long initiation time at which hot corrosion process moves from initiation stage to propagation stage. Understanding the behaviour of metals at elevated temperatures, especially their corrosion behaviour and to provide protective surface layers become an object of scientific investigation since long. The high temperature protecting coatings must be reliable, chemically and mechanically compatible with substrate, provide adequate environment resistance, and economically viable. Wide use of cobalt-based coatings has been reported because they combine several advantages such as abrasion, erosion and resistance to high temperature corrosive atmospheres. This paper briefly reviews the hot corrosion behaviour of cobalt-based coatings, including its properties and microstructure, as well as to review the performance of coatings on various substrates. The effect of thickness of coatings, residual stresses induced in substrates, porosity and pre and post heat treatment on the physical, mechanical and chemical characteristics of cobalt-based coatings have been reviewed with an aim to improve their high temperature corrosion resistance properties.

Comprehensive review of corrosion coatings have appeared regularly since early 1970, the purpose of this paper is not to recapitulate the published materials, but rather to focus on research trends and to point out some research prospectus.