MECHANISMS OF FRETTING-FATIGUE OF TITANIUM-ALLOYS

The effect of continuous fretting in air at 20 degrees C on fatigue pe rformance has been studied for Ti-17 and Ti-6A1-4V, high strength tita nium alloys used for gas-turbine fan and compressor disks and blades, respectively. The effect of fretting was to reduce the fatigue stress limit from 700 MPa for plain fatigue to 200 MPa for fretting-fatigue. A number of models, supported by metallographic and fractographic evid ence, are proposed which explain (i) how the cyclic loading of individ ual asperities results in crack initiation; (ii) the formation of mult iple cracks; (iii) the existence of non-propagating cracks; and (iv) h ow fretting influences crack propagation once fatigue cracks have form ed. (C) 1997 Elsevier Science S.A.