The corrosion of carbon steel is major infrastructure degradation problem in practically all industries, including chemical materials, mineral, and petrochemical industries. Coating on carbon steel is one of the techniques which required improving corrosion resistance in extreme environments. In present work, NiCoCrAl was diffusion-coated onto low carbon steel by electrodeposition for NiCo and pack cementation for Cr and Al. The cross section of coated specimen was observed and analyzed using SEM and TEM. Two types of coating processes have been challenging the formation of bond-coat layer on carbon steel substrate with different temperature coating process. SEM and EDS results show that the coating comprises three layers: intermetallics zone of Ni (Al) and Al (Cr), interdiffusion zone of Ni (Co), and there is the substrate. By XTEM observation, it was found that γ (Ni,Fe) and ζ hexagonal structure were identified in all specimens. Orthorhombic structure with the Al3Ni was identified in specimen developed at temperature of 800OC. Further, the top surface of a 1000OC specimen has two phases of β-NiAl and ζ hexagonal structure. In order to understand the performance of two types coating system with different temperature process, oxidation test at temperature of 800OC for 100 hours has been carried out and the result shows that coating system which was developed at 800OC has better oxidation resistance compare to 1000OC coating system.
Abstract. Intermetalic coatings of NiCoCrAl have been successfully developed on low carbon steel substrate to improve oxidation resistance in extreme environments. The influence of oxidation temperature on the oxide scale formation was studied in the temperature range of 600-1000 C. The measurements were made in air under isothermal oxidation test for 100 h. The surface morphology showed that a cauliflower like structure developed entire the oxide scale of sample oxidized at 800 C and 1000 C, while partly distributed on the surface of sample oxidized at 600 C. The XRD analysis identified Cr 2 O 3 phase predominantly formed on the oxidized sample at 600 C and meta-stable Al 2 O 3 with several polymorphs crystalline structures : η, δ, θ, κ, and α-Al 2 O 3 at relatively high temperatures, i.e. 800 C and 1000 C. A Cross-sectional microstructure showed that complex and porous structures formed on the top surface of 600 C and 1000 C samples. In contrast, a very thin oxide scale formed on 800 C oxidized samples and it appeared to act as a diffusion barrier of oxygen to diffuse inward, hence could increase in the service life of carbon steel substrate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.