EFFECT OF TEMPERATURE AND CRYSTAL ORIENTATION ON THE PLASTICITY (SLIP) EVOLUTION IN SINGLE CRYSTAL NICKEL BASE SUPERALLOY NOTCHED SPECIMENS

摘要

A comprehensive numerical investigation of plasticity (slip) evolution near notches was conducted at 28℃ and 927℃, for two crystallographic orientations of double-notched single crystal nickel base superalloys (SCNBS) specimens. The two specimens have a common loading orientation of < 001 > and have notches parallel to the < 010 > (specimen Ⅰ) and < 110 > (specimen Ⅱ) orientation, respectively. A three dimensional anisotropic linear elastic finite element model was employed to calculate the stress field near the notch of these samples. Resolved shear stress values were obtained near the notch for the primary octahedral slip systems ({111} < 110 > ) and cube slip systems ({100} < 110> ). The effect of temperature was incorporated in the model as changes in the elastic modulus values and the critical resolved shear stress (CRSS). The results suggest that the number of dominant slip systems (slip systems with the highest resolved shear stress) and the size and the shape of the plastic zones around the notch are both functions of the orientation as well as the test temperature. A comparison between the absolute values of resolved shear stresses near the notch at 28℃ and 927℃ on the {111} slip planes revealed that the plastic zone size and the number of activated dominant slip systems are not significantly affected by the temperature dependency of the elastic properties of the SCNBS, but rather by the change in critical resolved shear stress of this material with temperature. The load required to initiate slip was found to be lower in specimen II than in specimen I at both temperatures. Furthermore, at 927℃ the maximum resolved shear stress (RSS) on the notch surface was found to be greater on the {100} slip planes as compared with the {111} slip planes in both specimens. The results from this study will be helpful in understanding the slip evolution in SCNBS at high temperatures.