Introduction: Waste-to-hydrogen technology requires the involvement of new material development and performance evaluation for Additive Manufacturing (AM). Metal 3D printing is a very good possible alternative and is delivering results visible in the circular economy environment. By using the AM technique, complex operations are avoided when combining the individual components, which is a typical disadvantage in obtaining composite materials; such samples are prepared with only one operation from the starting melt, which is chemically defined. Pyrolysis rotary kiln sealing rings are to be upgraded with several different in microstructure coatings in order to improve the surface performances. The surface topology is aimed to be fine, dense and smooth. Also, the target characteristics are a low friction coefficient and a high hardness value, suggesting enhanced wear resistance. For elevated temperatures, 900 oC is selected for cobalt-based superalloy Stellite types with particle reinforcement.
Method: Two possibilities for advanced materials obtainment are proposed with the Directed Energy Deposition Plasma Arc (DED-arc) and Laser Directed Energy Deposition (DED-LB). The shell of the rotary kiln sealing ring is to be made of stainless steel as the base, with the coating overlayed. Selected mixtures in powder form with defined composition are applied. For the DED-arc, commercially available Stellite 6 (Deloro Stellite® 6, GmbH, Germany) and 20 vol% WC particles with a grain size of 63 - 150 µm were employed. For the DED-LB, we employed TRIBALOY® T-800 (Kennametal StelliteTM) with 25 vol% TiC and a mesh size of -100/+325 (particle diameter between 45 and 150 µm). After the representative samples were metallurgically bonded with the base stainless steel, the relevant properties were obtained.
Results: Manufactured samples are compared in terms of microstructures and mechanical properties. Analysis of structure: Intermetallic carbides that formed on the cobalt basis make the composite harder and increase the plasticity in a defined direction. The hypoeutectic structures of Stellite 6 + 20%WC consist of dendrite and interdendrite eutectic. It is observed that with an increase in WC volume fraction, the size of the dendrites becomes finer and the amount of eutectic structure is increased. For the TRIBALOY® T-800 with TiC, we obtained relatively smaller grain sizes. The roughness values for the tested samples with WC were initially Ra=0.8 µm, increasing up to Ra=3.44 µm after the wear test, whereas for the TiC, it was slightly lower. Microhardness testing revealed increased values compared to the base stainless steels. Advanced sensor analysis with Acoustic Emission (AE) and Electrical Contact Resistance (ECR) also showed the properties of the new materials.
Conclusion: Customizable coatings with tailored properties were deposited by DED-arc and DED-LB. From the tests performed, a new technological procedure for obtainment is proposed for novel pyrolysis rotary kiln sealing rings. The microhardness, roughness, microstructure and abrasive wear-resistant response of the metallic composite material were examined in order to characterize the stable multiphase system.
Funding: The author acknowledges support from project BG16RFPR002-1.014-0005.
