Orientation and temperature dependence of yielding and deformation behavior of a nickel-base single crystal superalloy

Single crystal nickel-base superalloy SRR99 with orientation near 〈0 0 1〉, 〈0 1 1〉 and 〈1 1 1〉 were tension tested at the temperature range from 20 to 900 °C. The experimental results showed that yielding strength of SRR99 alloy was anisotropic at all tested temperatures. The deformation mechanism was characterized by the matrix dislocation propagating on octahedral slip systems and shearing of γ′ particles by dislocation pairs, loops and superlattice stacking faults. Meanwhile, the cross-slip of screw dislocations within γ′ was thought to account for the tensile anisotropy. Fracture behavior was investigated by optical microscopy (OM) and scanning electron microscopy (SEM). It is of interest to note that the fracture surfaces of the three orientated samples tested at intermediate temperature indicate shearing rupture characteristic along {1 1 1} crystal plane.