Low-cycle fatigue of single crystals of α CuAl alloys

Abstract

Single slip oriented single crystals of CuAl alloys with aluminium contents of 2, 4, 7, 11 and 16 at.% were cycled at constant plastic strain amplitudes until fatigue failure. The cyclic response has been measured by monitoring the changes in hysteresis loop shape, energy absorption, and peak, average and saturation stresses. The results show that the initial cyclic hardening rates decrease and the saturation stresses increase with decreasing stacking fault energy (SFE). At lower SFE fatigue fracture may develop before saturation stresses are reached. The hysteresis loop shape, on the average, becomes more and more pointed with decreasing SFE and with decreasing strain amplitude within any one alloy. When compared with copper at the same plastic strain amplitudes the alloys containing 2 and 4 at.% copper can be characterized by slightly higher saturation stresses, more rectangular hysteresis loops and shorter fatigue life. Fatigue results obtained on the alloys containing 4 and 7 at.% copper suggest that within that alloy range there is a sharp improvement in fatigue performance. Further improvement in fatigue performance has been recorded with the alloys containing 11 and 16 at.% copper and these improvements are best explained by assuming reductions in crack propagation rates.