Yuk-Chiu Lau

Corrosion Potential Behavior in High-Temperature Water of Noble Metal-Doped Alloy Coatings Deposited by Underwater Thermal Spraying

Abstract The electrochemical corrosion potential (ECP) of type 304 (UNS S30400) stainless steel (SS) coated under water by hyper-velocity oxy-fuel (HVOF) and plasma-spray (PS) techniques using noble metal-doped powders was measured to evaluate the catalytic behavior in high-temperature water under various water chemistry conditions. Thermal-spray coatings of noble metal-doped powders exhibited catalytic behavior for the recombination of oxygen and hydrogen in high-temperature water, which caused ECP to decrease well below a critical value of −230 mVSHE for intergranular stress corrosion cracking (IGSCC) protection in water. This was observed in water containing various amounts of oxygen and hydrogen peroxide (H2O2) when stoichiometric excess hydrogen was present.

Development of Higher Temperature Abradable Seals for Gas Turbine Applications

Improving sealing between rotating and stationary parts in industrial turbines can significantly increase unit performance. Abradable seals are being developed to reduce blade-tip clearances where an abradable material is placed on the stationary shroud or casing opposite the rotating blade tips to reduce clearances with minimum risk to the turbine components during rubs. A newly developed metallic abradable material is a thermally sprayed coating on the first stage of gas turbine shrouds to reduce tip clearances; thereby, improving turbine power and efficiency by about 1/2 percent. This material is an improvement over currently available metallic abradables increasing the maximum operating temperature from 750°C to about 950°C with no special treatments required on the rotating blade tips. Initial engine field tests have shown the new material to be abradable and on target to meet life requirements.Copyright