Optimizing Coating Processes and Chemistries for Enhanced Hot Section, Low Cycle Fatigue (LCF) Life

ABSTRACT: Environmental protection coatings are required to provide oxidation and hot corrosion protection to hot section turbine components. Unfortunately, the current generation of such coatings can degrade the fatigue resistance of the coated alloy. It is increasingly recognized that, due to the detrimental effect of the coating on low cycle fatigue (LCF) performance, the LCF life of a coated superalloy, not the stress/creep rupture strength, limit the design of a turbine component. As a result, the development of a new generation of environmental coatings optimized to not only provide oxidation and corrosion resistance, but also to limit any detriment to the fatigue performance of the alloy would greatly improve the current state-of-the-art. Thus, a strong need exists to develop novel environmentally protective coatings that are also relatively ductile and strong, as well as coating deposition processes that provide defect-free and dense microstructures. In this work, advanced environmental coating compositions having high strength and toughness will be developed and applied onto engine components using an advanced vapor deposition approach. Additionally, the use of thermodynamic modeling approaches will be used to enable the coating compositions to be chemical activity matched to minimize inter-diffusion with the underlying substrate and retain performance during service. BENEFIT: The development of a strong, fatigue resistant, environmental coating that matches the temperature capabilities of third- and fourth-generation Ni-base alloys will allow reduced cooling flow in airfoil designs providing improved overall engine efficiency/higher thrust designs and hence, reduced specific fuel consumption (SFC). It will also provide improved component durability. Payoffs with a 50 degrees F temperature capability increase as sought in this program are considered to be highly significant by the gas turbine engine companies. Such an increase has been historically been achieved only after 10 to 15 years of extensive development effort in both design and material technologies. Several government and industry funded programs are aimed at developing turbines within the next ten years that will operate at firing temperatures about ~300 degrees F higher than the current generation of high-performance gas turbines. Such temperature requirements can be significantly aided by reducing to fatigue debit of the current environmental protection coatings to enable the current generation of nickel-based superalloys to be used to their full capability. This will lead to turbine engine performance benefits in future gas turbine engines resulting in very significant SFC reductions. Civilian transportation and power generation sectors will be aided as well as air and sea based military vehicles.