THE INFLUENCE OF CO ON CREEP DEFORMATION ANISOTROPY IN NI-BASE SINGLE-CRYSTAL SUPERALLOYS AT INTERMEDIATE TEMPERATURES

In order to investigate the influence of Co on creep deformation aniso tropy, some Ni-base single crystal superalloys have been creep tested at 800 degrees C and 735 MPa. It is found that, although Go-containing alloys have higher creep resistance when the tensile direction is wit hin 5 degrees of (100), they are much more sensitive to tensile orient ation than Go-free alloys, which have similar creep rupture lives for tensile orientations within 25 degrees of (100). It is revealed that f or Co-containing alloys the (111)(112) slip system is operative during first-stage creep, when heterogeneous deformation occurs. Also, the d egree of heterogeneous deformation correlates very well with creep rup ture lives. It may thus be concluded that Co is not essential in impro ving creep rupture properties of Ni-base superalloys. (C) 1997 Elsevie r Science S.A.