THE CRITICAL RESOLVED SHEAR-STRESS OF A SUPERALLOY AS A COMBINATION OF THOSE OF ITS GAMMA-MATRIX AND GAMMA'PRECIPITATES

The critical resolved shear stress (CRSS), tau(o), of peak-aged single crystals of the gamma'-hardened commercial nickel-base superalloy NIM ONIC 105 has been measured as a function of temperature T and orientat ion [hkl] of the compression axis. The same measurements have been car ried out for the two constituent phases of NIMONIC 105: for the single -phase gamma matrix and for the single-phase L1(2)- long-range ordered gamma' phase. The value of T ranged from 283 to 1150 K, and the follo wing orientations were studied: [001], [011], [(1) over bar 11], and [ (1) over bar 23]. The specimens were compression tested. The T, values of NIMONIC 105 and of the gamma' phase are anisotropic; the anisotrop y of NIMONIC 105 is similar to that of the gamma' phase, but less pron ounced. The tau(o), of the gamma phase is isotropic. The tau(o),values of the gamma and of the gamma' phase vary with T, whereas the tau(o), of NIMONIC 105 is nearly independent of T for 400 K less than or equa l to T less than or equal to 1000 K, A model is presented that relates the function tau(o) ([h, k, l], T) of NIMONIC 105 to the analogous fu nctions of its constituent gamma and gamma' phase.