Isothermal oxidation behaviour of HVAF-sprayed Ni-based coatings
Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
High temperature corrosion of metallic materials in biomass and waste fired boilers, is a major challenge in utilization of green heat and power production from renewable fuels. Particularly, the pressure bearing parts such as superheater tubes and water walls are prone to extensive corrosion, and thereby limit the electrical efficiency of the boiler. A promising route to improve the durability of degradation-prone components, such as above, is applying a protective coating that has inherently better corrosion resistance. Without the need for improved mechanical stability, the coating material can primarily be optimized to ensure superior corrosion behaviour in the anticipated boiler environment.Thermal spray technique is proposed as a potential solution to insulate the components from the corrosive environment by applying a protective coating. In the present work, the oxidation behaviour of four Ni-based coatings, produced by high-velocity air fuel (HVAF) process is investigated. NiCr, NiAl, NiCrAlY and CorEr powders were used to spray on low-alloyed ferritic steel 16Mo3 substrate. Different HVAF process parameters were initially used to obtain optimized coatings in terms of high density and low porosity. The setting that generated the densest coating was selected and applied to succeeding spraying sessions. The austenitic stainless steels Sanicro 25, stainless steel 304L, as well as 16Mo3 were selected as the reference materials to compare the oxidation results. The coated and uncoated samples were exposed to an ambient air environment with a temperature of 600°C with different time intervals up to 168h. The oxidation behaviour of samples was investigated after different stages of heat exposure utilizing SEM/EDS and XRD analysis.The coatings were graded based on their oxidation performance in the test environment. The ranking for the coatings is (from the best to worst): NiCrAlY> NiAl> NiCr > CorEr. For the reference materials, the ranking is (from the best to worst): 304L>Sanicro 25> 16Mo3.
Place, publisher, year, edition, pages
2016. , 46 p.
HVAF, Oxidation, Boiler, Superheater, Coatings, NiCrAlY, NiCr, NiAl, CorEr, 304L, Sanicro 25, 16Mo3
Manufacturing, Surface and Joining Technology
IdentifiersURN: urn:nbn:se:hv:diva-9842Local ID: EXP800OAI: oai:DiVA.org:hv-9842DiVA: diva2:956686
Subject / course