Modelling the ultrasonic scatter of complex microstructures in heavy rotor forgings

Neumann, Daniel (2020). Modelling the ultrasonic scatter of complex microstructures in heavy rotor forgings. University of Birmingham. Eng.D.

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Abstract

This thesis sets out to establish a quantitative model of ultrasonic scattering caused by the martensitic microstructure associated with power generation steel. An established model from the literature, which is designed for pearlite microstructure, is extended for the martensitic model. A mechanism is established to predict the reflective ability of microstructural features based on their acoustical impedance and relative size, which is based on the principles of acoustic theory.

A series of samples are generated and quantified covering a range of microstructure feature sizes and phases, including pearlite, mixed martensite and bainite and fully martensitic microstructures. The measured attenuation of the generated samples is used to validate, and ultimately disprove the pearlitic scattering model and also the martensitic extension. The quantified microstructure is used in combination with expected (from orientation relationships) and measured (from EBSD measurements) crystallographic orientation mismatches of the martensitic microstructure features to estimate scattering significance based on the boundary reflectivity method. These predictions, and further hardness measurements, appear to be in agreement with other qualitative assessments of martensitic scatter mechanisms in the literature. The scattering associated with martensitic microstructure is shown to be dominated by prior austenite grain boundaries due to their size.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

Supervisor(s):