γ′ precipitation kinetics in the powder metallurgy superalloy N19 and influence of the precipitation latent heat

Onera – The French Aerospace Lab, 92322 Châtillon, France

^a Corresponding author: mikael.perrut@onera.fr

Abstract

The N18 superalloy, powder metallurgy processed, is used for high-pressure turbine disks of the Snecma M88 engine and has been extensively studied. The size distribution of its γ′ precipitates was first modelled in the late 1980's using a binary alloy model [1]. The precipitation model has been recently revised, upgraded in a pseudo-binary alloy model and used in a multi-scale mechanical model for the calculation of the fatigue life in low cycle fatigue conditions [2]. We here present how the new calibration of the pseudo-binary model for the N19 superalloy has been accelerated through the use of the Thermo-Calc^® software, its TCNI5 thermodynamic database and its MOBNI2 mobility database. On a more fundamental point of view, the influence of the γ > γ′ latent heat of precipitation on the microstructural parameters of quenched samples of N18 and N19 has been studied using this same model. We conclude on the very importance of taking into account the latent heat in a coupled thermal-microstructural model for correct numerical simulations of the precipitation process at each point of a superalloy sample or part.