Advanced Coatings on Superalloy Blades and Vanes for Hot Corrosion and Oxidation Resistance D. K. Hanik, Q. 0. Shockley, and J. 0. Hodshire Allison Div., General Motors Corp. Mid-Year Meeting Chicago, III. May 19-23,1969 690480 Downloaded from SAE International by University of Wisconsin - Madison , Sunday, September 09, 2018690480 Advanced Coatings on Superalloy Blades and Vanes for Hot Corrosion and Oxidation Resistance D. K. Hanik, Q. 0. Shockley, and J. 0. Hodshire Allison Div., General Motors Corp. COATINGS FOR NICKEL BASE alloys employed as gas tur­ bine engine blade and vane components have now attained over 15 years of experience dating from the first experi­ mental tests and including more than a decade of production field service. Although the objectives of the first aluminum diffused surfaces were to improve resistance to thermal shock or thermal fatigue, as it is identified today, early work in the laboratory and under military flight experience rapidly established the further benefits of oxidation resistance: high temperature wear and fretting (1,2)*. All of these mech­ anisms of deterioration contributed to problems in leading/ trailing edge cracking. Certainly, this type of life-limiting behavior precluded a full utilization of useful creep/stress rupture life. In early burner (combustion case) designs, which were preeminently successful in developing severe turbine inlet vane hot spots, life of nozzle vane assemblies was measured in terms of a few hours. Further, the design philosophy favored aero­ dynamics performance in many configurations at the ex­ pense of high localized stresses and temperatures. The re­ sulting problems were enhanced by the difficulties associated with instrumenting engines to obtain operational test data which could substantiate abnormal environment. Neverthe­ less, this was the industry situation which prompted a dual and intense effort by the materials engineer to improve our alloys and provide a protective/compatible high temperature coating. NEED FOR A COATING Industry has advanced considerably in its applied tech­ nology so that cooled turbines are now specified to operate at least 5000 hr between major overhaul under turbine inlet temperatures exceeding 2100 F. Life-limiting hot corrosion typical of the blade assembly shown in Fig. 1, and the single blade, Fig. 2, illustrate the deterioration which prevents the achievement of durability design goals. *Numbers in parentheses designate References at end of paper. ABSTRACT The need for surface protection of nickel base alloys to prevent hot corrosion and/or sulfidation is discussed. Re­ sults of controlled engine test cycling and the rig testing of turbine blades are discussed to establish laboratory test correlation. The relative corrosion resistance of a number of commercial alloys is shown, and the response of these alloys to corrosion resistance with protective coating is covered in relation to their limitation in erosion/oxidation deterioration. Finally, some technology results and general methodology applied to electrophoretic processing for apply­ ing coatings of aluminum and combinations with chromium are described. The processing advantages and disadvantages of this coating process and general results are compared with present production. Downloaded from SAE International by University of Wisconsin - Madison , Sunday, September 09, 20182 TESTING PROGRAMS TO APPRAISE TECHNOLOGY IMPROVEMENT Test rigs, such as the laboratory unit shown in Fig. 3, have demonstrated the capability of producing a condition of hot corrosion functionally identical to that occurring on turbine components returned from service or subjected to sea salt ingestion engine test. The rig utilizes 8-16 airfoil shaped paddles or standard T56 engine turbine blades as specimens, and the test is con­ ducted in cycles. Each cycle consists of heating the rotating (1800 rpm) test specimens in a furnac