Agglomerate sintered and blended NiCrAlY-Y 2 O 3 cermets were prepared from NiCrAlY and Y 2 O 3 powders by two process routes. The particle morphologies and powder characteristics of both cermets feedstock using for thermal spraying were investigated. Both types of NiCrAlY-Y 2 O 3 cermets and one commercial CoCrAlY-Y 2 O 3 cermets were HVOF thermal sprayed onto the stainless steel substrate to obtain coatings having a thickness about 100 microns. Porosity and thermal shock resistance of coatings were examined. Four thermal sprayed coatings were comparatively evaluated build-up resistance by contacting reaction with MnO, Fe 3 O 4 powders and manganese bearing carbon steel statically at high temperatures. The agglomerate sintered NiCrAlY-Y 2 O 3 coatings have good resistance to manganese oxide build-up but bad resistance to iron oxide build-up. The agglomerate sintered cermets coating has better build-up resistance than blended cermets coating.

Thermal spray coatings have been applied on furnace rolls in continuous annealing lines to improve product quality and prolong roll service life. The most common defects formed on working furnace rolls are oxide pickups. In this study, HVOF sprayed cermet coatings are used to duplicate pickups by reacting with iron and manganese oxides. The reactions are performed in a furnace at 900 °C with inert gas flow. After testing for eight days, large Mn-rich pickups were formed on the coatings while pickups without Mn were very small. Mn was shown to enhance the reaction between the coating and the iron oxide. Pickups from a furnace roll were also investigated and compared with the laboratory samples.

To increase the service life of a sink roll in a continuous galvanizing line has been an important issue in steel industry. It was shown that sink rolls are vulnerable to molten zinc corrosion and can be improved by thermal spraying with WC-Co coatings. Four WC-12Co thermal sprayed coatings were investigated in this study. Samples were immersed in Al-added zinc bath (460°C) for testing. The results show that the conventional coatings are more resistant to molten zinc corrosion than the nanostructured ones. It was also found that coatings containing η- phase have longer life in the zinc bath. Accumulation of Al on the coating surface was also observed.