Multiaxial creep of a nickel-base directionally solidified alloy. 1st Report. Experiments and analysis on minimum creep-rate.

Abstract

Combined tension-torsion creep tests of a Ni-base directionally solidified alloy are performed at 850°C using thin-walled tubular specimens solidified directionally in the axial direction. It is observed that equivalent creep rate depends markedly on the ratio of shear stress to tensile stress under constant equivalent stress of the Mises-type, while noncoaxiality between stress and creep rape is relatively small. Minimum creep rates obtained in the experiments are examined in comparison with related analyses based on the crystallographic slip theory. It is shown that the minimum creep rates are simulated well if the {111} octahedral system is combined with the {100} cubic system. The former is active in tensile creep of the specimen, while the latter is in shear creep.