Advanced ceramic-coating development for industrial/utility gas turbines. Final report

A program was conducted with the objective of developing advanced thermal barrier coating (TBC) systems. Coating application was by plasma spray. Duplex, triplex and graded coatings were tested. Coating systems incorporated both NiCrAlY and CoCrAlY bond coats. Four ceramic overlays were tested: ZrO/sub 2/.8Y/sub 2/O/sub 3/; CaO.TiO/sub 2/; 2CaO.SiO/sub 2/; and MgO.Al/sub 2/O/sub 3/. The best overall results were obtained with a CaO.TiO/sub 2/ coating applied to a NiCrAlY bond coat. This coating was less sensitive than the ZrO/sub 2/.8Y/sub 2/O/sub 3/ coating to process variables and part geometry. Testing with fuels contaminated with compounds containing sulfur, phosphorus and alkali metals showed the zirconia coatings were destabilized. The calcium titanate coatings were not affected by these contaminants. However, when fuels were used containing 50 ppM of vanadium and 150 ppM of magnesium, heavy deposits were formed on the test specimens and combustor components that required frequent cleaning of the test rig. During the program Mars engine first-stage turbine blades were coated and installed for an engine cyclic endurance run with the zirconia, calcium titanate, and calcium silicate coatings. Heavy spalling developed with the calcium silicate system. The zirconia and calcium titantate systems survived the full test duration. It was concludedmore » that these two TBC's showed potential for application in gas turbines. Process variables and substrate composition were found to be critical and further work is required to relate them to coating performance.« less