Upgrading Marine Engine Materials for Future Navy Ships

U.S. Navy marine gas turbine engines serve as primarye and auxiliary power sources for several current classes of ships. Early observations noted in the 1960s and 1970s revealed severe corrosion attack on the first stage blade and vane components of a shipboard marine gas turbine engine that caused engine failure after only several hundred hours. In gas turbine development, there is always a drive and need to enhance the performance and life of engines. The virtues of using Ni-base superalloys in hot-section components has been well recognized and practiced as a means of substantial increase in turbine-inlet temperature, resulting in improvements in thermal efficiency, durability, and performance of engines. The USN shipboard environment (the marine environment) is high in salt laden air and water, coupled with air and fuel sulfur species that cause aggressive corrosion in gas turbine hot sections. Materials that can function in this environment are considered to be “Marinized”. Higher engine power density and pressure ratios for new engine designs will increase maximum blade, vane, and rotor metal temperatures from a mainly Low Temperature Hot Corrosion (LTHC) regime into both the High Temperature Hot Corrosion (HTHC) and Oxidation Corrosion regions. It is expected that future increased surface combatant loads and operational changes will require increased gas turbine operating temperatures and change the associated operating environment to one where Type I and Type II hot corrosion AND oxidation will be prevalent in newly anticipated operational profiles. The advanced gas turbine upgrade package will include better corrosion and oxidation resistant capability and/or higher temperature capable materials and their associated component overhaul methodologies. New materials need to be created and developed for use in more aggressive environments and higher temperature operations. The main cause of the shorter time between overhauls is the materials deterioration of the engine components associated with the hot section of the engine, e.g. turbine airfoils. The deterioration mechanisms are hot corrosion, with Type 1 hot corrosion mechanism becoming operative at the higher temperatures. The goal of this paper is to evaluate methods to enable running the engine at high power while getting back to the longer mean time between overhauls. The method to achieve the longer time is to evaluate and propose for implementation materials, which can withstand the higher temperatures and at the same time mitigate the operative corrosion mechanisms associated with marine environments.