Characterisation of γ' Precipitates in a Single Crystal Nickel Base Superalloy SC16 using SEM, TEM and SANS as Complimentary Measuring Tools

Abstract

Characterisation of the microstructure in nickel base superalloys is important for understanding and predicting the behaviour of these complex alloys. Large particle sizes of γ' precipitates in modern alloys, their regular arrangement in periodic arrays in the γ matrix and the complexity of the microstructure evolving under deformation at high temperatures, pose serious challenge to the precise characterisation of the microstructure. This necessitates the use of complementary measuring tools e.g. X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM), optical metallography etc. Small angle neutron scattering (SANS) is a useful modern technique, used to characterise fine precipitates and inhomogenities (< 50 nm) in materials. So far, established methodology does not exist for using SANS to characterise large particles like γ' precipitates in superalloys. In this paper we develop a model to analyse SANS intensity profiles from large (400nm) γ' precipitates and together with the help of complementary methods such as SEM and TEM, characterise them in a single crystal nickel base alloy SC16.