Turbine blades and vanes are critical components of both steam and gas turbines.
To achieve optimum aerodynamic performance, the blades have an aerofoil shape and an optimal surface finish. During operation, the blades often move at a speed close to or exceeding the speed of sound, and are exposed to erosion from high-speed water droplet and solid particle impacts, which result in material loss and roughening of the turbine blade surface causing an increase in drag and loss of turbine efficiency. Blades and vanes often have to be replaced at maintenance intervals due to erosion and/or corrosion issues.
Gas turbine efficiency is often improved by introducing water mist into the gas flow at the turbine inlet to increase the mass flow and the efficiency of the compressor. Compressor blades operating with this inlet fogging can suffer from WDE, as can the last rows of steam turbine blades where expanding steam produces water condensation. WDE damages the leading, and sometimes trailing edges, of steam and gas turbine blades, increasing turbine rotation drag, reducing efficiency and incurring costly blade and vane maintenance.
Hardide-A and Hardide-T coatings significantly improve resistance to WDE, extending blade and vane life. In testing by the UK National Physical Laboratory (NPL), Hardide-A and Hardide-T showed at least a x10 fold longer WDE incubation stage compared with uncoated 410SS.
Unlike PVD coatings for turbine blades and vanes, Hardide coatings are also highly corrosion resistant being pore-free, 10x thicker and more ductile.
Enhanced high cycle fatigue performance is another important quality of Hardide coatings for gas and steam turbine blades. Some other hard coatings introduce significant fatigue debit reducing the loads or life of the coated blades by as much as 60%. Hardide-A coating shows minimal fatigue debit between +10% and -10% in both rotating bend and axial high cycle fatigue tests.