Investigation of porosity in single-crystal nickel-base superalloys

Different types of microporosity were investigated in SC superalloys of 1{sup st}, 2{sup nd} and 3{sup rd} generation. It was shown that development of superalloys by increasing the total level of strongly segregating refractory elements, results in high microporosity forming during homogenization. A pronounced growth of microporosity, correlating with steady creep, was found after creep tests at high temperatures (1050-1100 C). It is proposed that mechanism for growth of this microporosity is dislocation climb transverse to the stress axis along the interfaces of the rafted {gamma}/{gamma}'-microstructure. Climb parallel to the stress axis is retarded by {gamma}'-rafts. Such anisotropic climb creates a powerful flux of vacancies agglomerating into pores by fast diffusion through the interfacial dislocation networks. (orig.)