Metallurgical, erosion, and sensitization performance of TiAlN monolayer and TiAlN/TiN multilayer ceramic coatings on AISI 304 boiler steel

In the present work, TiAlN monolayer and TiAlN/TiN multilayer ceramic coatings were deposited on AISI 304 austenitic stainless steel by plasma arc physical vapor deposition (PAPVD) process. The metallurgical, erosion, and sensitization performance of these coatings were compared with uncoated 304 boiler steel. Metallurgical studies depicted formation of Al and Ti nitrides on monolayer and multilayer coated steel surfaces, which resulted into higher nitriding at the surface and dense coating formation on boiler steel substrate. Multilayer film exhibited comparatively lesser porosity, lower surface roughness, and higher hardness than monolayer coated and uncoated steel. The erosion performance was evaluated at 30 degrees and 90 degrees besides 2 g/min and 3 g/min flow rates of Al2O3 erodent material for coated and uncoated steel substrate. Multilayer coated 304 steel possessed lower erosion wear rate as evaluated through lesser weight loss before and after erosive wear, smaller crater formation, and minimal adherence of erodent material along with lesser Fe content on eroded surface relative to monolayer coated and uncoated steel. Multilayer coated steel thermally aged at 750 degrees for 24 h had least degree of sensitization (DOS) compared to monolayer coated and uncoated aged boiler steel. Although monolayer coated steel performed better than uncoated one in erosion and sensitization performance but multilayer coating performance was best among all coated and uncoated steel used for present study. Thus, it was established that TiAlN/TiN multilayer coating on AISI 304 boiler steel has improved its metallurgical, erosion, and sensitization performance.