Fatigue crack growth (FCG) experiments were conducted on controlled variations of Type 7075 and 7050 aluminum alloys. Alloy FCG resistance was ranked under constant amplitude and simple variable amplitude load spectra. Fracture mechanics and fractographic approaches were used to interpret causes for variation in ranking of 7XXX aluminum alloy FCG resistance with loading conditions. The interpretation is built around clarification of a controlling FCG mechanism that is dependent upon interaction of microstructure and load history. This clarification represents a necessary first step toward knowing which microstructure or which design (test) procedure is optimum for a particular class of application, for example, fighter as opposed to bomber or transport aircraft.

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Thermal barrier coatings (TBC) have been used in jet engine combustors for over 15 years. However, it is only recently that they have been actively used in the harsh turbine environment on nozzle guide vane platforms. It is intended to use TBCs on vane airfoils, and on rotating turbine blades where the maximum payoff will be realized. Much work has been done in the last five years towards this goal. Problem areas that need to be addressed are as follows: 1. Prevent coating failure due to: a. thermal cycling of the ceramic layer. b. oxidation of the bond coat. c. erosion due to gas stream solid particles. d. deposition of gas stream molten debris. e. acid leaching of coating phase stabilizers. 2. Minimize performance losses due to rough coatings. 3. Insure consistent high quality coatings. This report will review some of the work done by Rolls-Royce that would hopefully allow an increased use of TBCs on turbine components in the future.

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