Influence of residual stresses on ageing precipitation behavior of alloy 718

Abstract

The interior residual stresses, which were generated at previous stages of forging and water quenching, exist as a pre-condition of γ″ precipitation during the subsequent thermal ageing. To clarify the issue, a refine investigation for the preferentially orientation of γ″ precipitates in Inconel 718 can be achieved by means of TEM, FE-SEM and small angel neutron scattering. Compared with the isotropic nucleation in the early stage of ageing, the preferential orientation during the coarsening process has a specific orientation-relationship, due to the volume diffusion of niobium atoms affected by elastic strain, with the load direction in a multiple crystal system. The inhomogeneity and anisotropy in microstructure give rise to a deterioration and anisotropy of mechanical properties.