Corrosion Fatigue Behavior of Coated 4340 Steel for Blade Retention Bolts of the AH-1 Helicopter
The main rotor blade bolt for the 540 roto system (AH-1G, UH-1C, UH-1M helicopter) is proposed to be improved by the substitution of plasma-sprayed tungsten carbide coating on the outer shank for the present cadmium or chromium plate. The WC coating was originally suggested to reduce the costly machining and plating operations required to recondition blade retention bolts for the AH-1G helicopter. Fretting-induced corrosion resulted in significnet surface pitting on the bolts after less than 500 hours of service. Based on prior results with a similar configuration bld for the 240 rotor system, a WC-coated bolt is expected to last over 3000 hours (the approximately design life of the airframe) as compared to about 300 hours for current Cd-plated new production bolts and about 500 hours for Cr-plated reworked bolts. Thus a significant cost savings has been projected if bolt reconditioning and replacement is eliminated.
KeywordsFatigue Strength Fatigue Test Tungsten Carbide Corrosion Fatigue Fatigue Specimen
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