Laboratory testing was conducted on air plasma sprayed (APS) and electron beam-physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) applied onto nickel alloy specimens. As-coated chemistry, microstructure, and bond strength of the TBC systems were evaluated. Cyclic oxidation tests that simulated industrial gas turbine environments were also conducted on the various thermal barrier coatings. This study evaluated the effects of ceramic and metallic coating compositions and application processes on coatings microstructure and performance. The relative cyclic performance of the TBC systems was determined from the laboratory tests.

The rhenium containing second generation single crystal alloy CMSX-4® was introduced for turbine blading in the Solar® Turbines Incorporated Mars® T-14000 engine in 1990. Based on the initial success with the first 4,000 hour engine test, the alloy was confirmed as bill of material for the stage 1 turbine blades in the T-14000 engine. Field experience has been excellent and there are now about 1,500,000 hours total accumulated engine time with several engines having completed their first overhaul cycle (Typically 30,000 hours). Use of this alloy is now being considered by Solar for other turbine airfoil components. This update provides the results of metallurgical evaluations on high time blades. A detailed analysis of the substrate and coating, microstructure following the 25,000 hours field exposure was conducted and the results reported herein. A brief discussion of the effect of PtAl coatings on fatigue properties is also included.

Tungsten carbide-12 wt.% cobalt (WC-12Co) coatings and chromium plating are used to provide wear resistant surfaces in gas turbine applications. These treatments provide surfaces with hardnesses greater than 60 Rockwell C. In addition, a surface finish better than 8 microinches RMS is required for optimum performance. To achieve this surface finish, diamond grinding is required. The diamond grinding step adds considerable cost to the product and economical benefits could be achieved if more conventional grinding techniques were incorporated. A program was initiated to develop an alternative thermal spray coating, with a target hardness lower than 60 Rockwell C, but high enough to provide the wear resistance required. Spray development was conducted on five commercially available materials using the Diamond Jet 2600 high velocity oxy-fuel process. Laboratory evaluation included coating microstructure, macro- and microhardness, bond strength, salt spray corrosion, and cyclic compression tests.