[3A3] Phase characterisation of nickel-based superalloys using ultrasound
J Jobling
Imperial College London, UK
Nickel-based superalloys are widely used across the engineering industry, due to their superior mechanical properties at elevated temperatures and excellent resistance to creep and fatigue under harsh working conditions. The microstructure of the material, influenced by phase composition and grain size, greatly affects these characteristics. A notable superalloy is Inconel 718, where the amount of the γ'' phase precipitated within the main γ matrix is most important for material performance – though other phases are also present, including the γ' and δ phases. Existing methods for material characterisation are destructive, expensive and time consuming (such as scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD)), as are techniques for determination of the fatigue life of components (which require surface preparation for hardness testing); hence, it would be highly beneficial to develop a non-destructive, rapid and reliable method enabling quick inspections for characterising a material’s microstructure to assess its suitability for a particular application or to tailor the properties to optimise a component’s design.
This talk discusses a non-destructive inspection method using ultrasound for phase characterisation of nickel-based superalloys. A novel technique, involving ultrasonic wave speed measurements with a spherical convolution theoretical framework, has been successfully demonstrated to be able to detect microstructural changes within both billet and powder metallurgy nickel-based superalloys. In contrast to existing characterisation techniques, this method requires minimal surface preparation and gives a statistical average over a volume (as opposed to surface or near-surface measurements only), thus greatly reducing the overall time of inspection. Ultrasonic measurement experiments using Inconel 718 comprised first a feasibility study, to demonstrate the capability of the spherical convolution technique in detecting phase changes, followed by experiments with dual-phase microstructures to investigate the accuracy of phase estimates using this technique, thus laying the foundations for the rapid phase characterisation of nickel-based superalloys. The ultrasonic test set-up has also been used to acquire attenuation measurements and hardness tests have also been carried out, with the aim of combining these streams of information as a useful materials characterisation framework for future inspections.
This talk discusses a non-destructive inspection method using ultrasound for phase characterisation of nickel-based superalloys. A novel technique, involving ultrasonic wave speed measurements with a spherical convolution theoretical framework, has been successfully demonstrated to be able to detect microstructural changes within both billet and powder metallurgy nickel-based superalloys. In contrast to existing characterisation techniques, this method requires minimal surface preparation and gives a statistical average over a volume (as opposed to surface or near-surface measurements only), thus greatly reducing the overall time of inspection. Ultrasonic measurement experiments using Inconel 718 comprised first a feasibility study, to demonstrate the capability of the spherical convolution technique in detecting phase changes, followed by experiments with dual-phase microstructures to investigate the accuracy of phase estimates using this technique, thus laying the foundations for the rapid phase characterisation of nickel-based superalloys. The ultrasonic test set-up has also been used to acquire attenuation measurements and hardness tests have also been carried out, with the aim of combining these streams of information as a useful materials characterisation framework for future inspections.
