High overlay coatings

Calorised Coatings The nickel- and cobalt-base superalloys of gas turbine blades, which operate at high temperatures, have been protected by coatings produced by cementation. Without such protection, the presence of sulphur and vanadium from the fuel and chloride from flying over the sea promotes conditions that remove the protective oxides from these superalloys. Pack cementation with powdered aluminium produces nickel or cobalt aluminides on the surfaces of the blade aerofoils. The need for overlay coatings containing yttrium have been necessary in recent times to deal with more aggressive hot corrosion conditions. 

The results of the studies with the model alloys have been used for optimisation of the overlay coating compositions for high strength, commercial ODS FeCrAl alloys. 

Developments in high-temperature corrosion and protection Overlay coating... 

In this section, the sensitivity characteristics of HRI-coated LPGs have been investigated to outline their dependence on the overlay thickness and mode order. In addition, the experimental results here presented provide the basic design criteria for the development of highly sensitive in fiber refractometers and chemical sensors for specific SRI ranges. 

The application process is also dependent on the type of project. Asphalt-rubber used as a seal coat is sprayed on the surface with equipment designed for asphalt-rubber s high viscosity and need for constant stirring to suspend the rubber. Hot mix projects require little special equipment as the asphalt-rubber is premixed with the aggregate and applied in the same manner as a standard overlay (29). 

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