Protective Coatings for Austenitic Stainless Steels
Authors:Fatin Ismail, Armen Kvryan, Christopher Lopez, Zorineh Megerdichian, Sarah Phipps, Brian Stoops
Mentor:Dr. Vilupanur A Ravi, Professor and Chair, Department of Chemical and Materials Engineering, California State Polytechnic University Pomona
The need for materials to withstand highly corrosive environments at elevated temperatures has been ongoing for decades. Current industrial needs continue to demand materials solutions to difficult environmental problems, e.g., higher temperatures of operations in modern coal-burning plants, corrosion-resistant components for fuel cell assemblies and for solar energy conversion, corrosion resistant components for high temperature chemical processing, municipal waste burning, or petrochemical plants, etc. One of the approaches to combat corrosion at elevated temperatures is by the application of protective coatings to alloy substrates. Ongoing research at Cal Poly Pomona is focused on a coating process called halide-activated pack cementation. This technique involves the use of a master alloy, inert filler and a halide activator to coat a substrate. The objective of the current research is the investigation of process parameters affecting coating microstructure on austenitic stainless steel substrates. Coating results from different grades of austenitic stainless steels, e.g., 304, 309, etc., will be discussed. As an example, coatings on type 304 stainless steel grow in a parabolic manner. We have determined the value of the parabolic rate constants for the coating process at different temperatures. The kinetics of the coating process will be discussed with particular focus on temperature and time of processing. Microstructures obtained by optical and scanning electron microscopy will be presented and discussed along with surface analysis using X-ray diffraction. Microhardness results will also be presented to supplement the other coating characterization techniques. We will also point out the potential benefits of our approach for industrial applications.