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In this paper, the variation of gamma prime precipitates along the creep specimen from the end to the fracture surface was studied, on which a necking phenomenon was observed. The morphologies and chemical compositions of gamma prime precipitates of crept DD417G alloy under the condition of 1000°C/115 MPa were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning TEM, with energy diffraction spectrum and X-ray diffraction. The results indicate that with a negative gamma/gamma prime lattice misfit the superalloy gamma prime rafted structure formed perpendicular to the tensile loading axis, but in the necked zone, the gamma prime rafts are thickened significantly and no longer perpendicular to the tensile loading axis, but tend to parallel to the tensile loading axis. Based on element diffusion and lattice rotation theories, this phenomenon was discussed. From the observation and analysis of dislocation configurations, it is evident that the tertiary creep deformation is mainly controlled by dislocation shearing mechanism. And, some γ′ particles also precipitate from the matrix during the creep test. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of polycrystalline Ni76Al23Zr alloy was studied as a function of heat treatment, environment, and temperature. It was found that the tensile ductility was very sensitive to temperature, the alloy showing low ductility at temperatures from 700 to 1000°C both in air and vacuum. Environmental embrittlement could be alleviated for those specimens with elongated grains. The ductile transgranular fracture was explained by stress concentration at the intersection of slip bands and grain boundaries. It was also found that an oxide layer, formed during tensile testing at elevated temperature, affected the environmental embrittlement of Ni3Al(Zr) alloy. An adherent Al rich oxide film was effective in protecting the underlying alloy from oxygen penetration. [ABSTRACT FROM AUTHOR]