Substituting Mo for Re in equal weight for Ni based single crystal superalloy

The effect of substituting Mo for Re in the equal weight on high temperature stress rupture properties of Ni based single crystal superalloys has been investigated. The 980 degrees C/ 250 MPa rupture life decreases with the substitution while the 1100 degrees C/ 137 MPa life keeps almost unchanged. Both the interface-strengthening effect, i.e. the gamma-gamma' lattice misfit, and the gamma-solid solution hardening effect are nearly fixed with the substitution, which contributes to the success of the substitution. Dislocations are found to shear into gamma'-precipitates and climb/glide via the interfaces. The 3D dislocation reconfiguration reveals the complex interaction between the gamma'-shearing dislocations, including pair-coupling structure, dislocation reaction and drag effect, which indicates that the plastic deformation of gamma'-precipitates is limited. Based on a constitutive model, the stresses rupture life is proportional to the reciprocal of effective diffusivity (1/D-eff), meaning that such dislocation's climb via the interfaces is the rate-determining step of creep. The substitution-induced reduction of 1/D-eff significantly diminishes with the temperature increasing, due to the Arrhenius equation where the effective diffusivity is strongly affected by temperature. According to this model, the substitution proves useful and the temperature dependence of its strengthening effect is rationalized.