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The efficiency of axial flow compressors is greatly affected by the amount of air that leaks past the blade tips. It is desirable, therefore, to reduce the clearance between the compressor case and the rotating compressor blades as much as possible. One solution to the problem is to utilize a clearance coating in the compressor case at the blade tip paths Two methods for accomplishing this on both new and overhaul cases are discussed in detail.

Recently there have been many new developments in aluminum-base diffusion coatings as well as with other coating materials for protection of metal parts in high temperature oxidizing environments. Evaluation is described of many of these coatings on three separate laboratory test devices, for determining (1) resistance to erosion in a high velocity high temperature oxidizing atmosphere, (2) resistance to cracking and oxidation in a thermal fatigue test, and (3) sensitivity to light impact damage at elevated temperatures. Experience with diffused aluminum base coatings on some turbine engine components is discussed, and limitations of the evaluated coatings are cited.

The need for surface protection of nickel base alloys to prevent hot corrosion and/or sulfidation is discussed. Results 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 applying 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.