A study on bending deformation behavior of ni-based DS and SC superalloys

Abstract

Bending deformation behavior of Ni-based directionally solidified (DS) and single crystal (SC) superalloys was studied. For a DS superalloy, bending creep curves at 800, 850 and 900°C were obtained. As a result, the stress exponents for the steady-state creep displacement rates of the bending creep were found to show the almost same values as those for the steady-state creep strain rates of the tensile creep. It was also confirmed that activation energy for the bending creep corresponded to that for the tensile creep within the temperature range of this study. It can be concluded from these results that the bending creep behavior of DS superalloys can be deduced from the simple tensile creep test data because the correspondence of the deformation mechanism between the bending and the tensile creep was proven. For a SC superalloy, notable secondary orientation dependence of the steady-state creep displacement rates was observed at 750°C/950MPa. The specimen, whose slip system caused the 45°-shear-type slip, exhibited apparently faster creep displacement rate than the specimen, whose slip system caused the hinge-type deformation, even if their tensile/compressive directions were same. At 982°C/294MPa, secondary orientation dependence of the creep displacement rates was not significant while [011] specimens showed higher creep resistance than [001] specimens. The microstructural observations after bending creep tests provided interesting results that one type of raft-like microstructure observed in the tension side of [011] specimens was also found in the compression side of [001] specimens and another type of raft-like microstructure observed in the compression side of the [011] specimens was also found in the tension side of the [001] specimens.