AGEING CHARACTERIZATION OF THE POWDER METALLURGY SUPERALLOY N18

The ageing process of the powder metallurgy superalloy N18 has been investigated. This alloy exhibits a two-phase microstructure with a long range L12 ordered multimodal J’ precipitation. N18 has been designed for high temperature turboengine disks applications. Superalloys however, are prone to microstructure evolution when sustained at high temperature since J’ precipitates are coarsening. A method based on scanning electron microscope (SEM) image analysis is developed to qualify and quantify the material ageing. Two kinds of ageing have been considered: material temperature exposure with and without mechanical loading application. A short term quantitative law considering precipitates size, ageing time and temperature is established. In addition a long term behavior in agreement with our measurements is suggested.