A resistometric study of ageing in nimonic alloys (I). PE16

The Nimonic alloy PE16 is a candidate for use in a radiation environment in fast reactors. Williams and Fisher have investigated void-swelling in this alloy and have found it to be dependent upon the γ' precipitate present. In order to investigate the dependence of precipitation upon heat-treatment, the variation of the electrical resistivity with time on ageing PE16 at various temperatures between 580°C and 780°C has been measured. To account for the observed variation, a model based on nucleation and growth of γ' precipitates has been developed. This model allows for different scattering cross sections, and hence specific resistivities, of particles in small and large clusters. The rate constants for nucleation and growth are found to follow the usual Arrhenius behaviour with activation energies of 1.11 eV and 1.83 eV respectively. Specimens aged at different temperatures for varying times t, were viewed in the electron microscope. The observations have indicated that the precipitate diameter varies as $\text{(K}{}_2\text{t)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, where K₂ is the growth rate constant.