THE EFFECT OF CYCLIC DEFORMATION ON THE ELASTIC-CONSTANTS IN A NICKEL SUPERALLOY

In order to determine residual stresses in engineering components from neutron-diffraction strain measurements it is necessary to use the appropriate elastic constants (Plane Specific Elastic Constants-PSEC's). These constants can be obtained by calibration measurements or by calculations using for example the Kroner model. This paper presents results that show the effect of cyclic plasticity on the PSEC's in a nickel-base superalloy from measurements made in TEST BEAM at ISIS at the Rutherford Appleton Laboratory, UK. A tensile sample was loaded in situ in the neutron beam. Elastic constants were obtained for the virgin material, then after one cycle of loading to 2% strain and finally after 5 cycles of loading to 5% strain. Stress-strain curves have been plotted for each crystallographic reflection investigated and elastic moduli calculated after each load cycle. The elastic constants obtained after cyclic plasticity are compared with the values obtained in the virgin material. It was found that the (3 1 1) reflection was unaffected by the cyclic loading and plastic deformation.