Inspection of additively manufactured components by spatially resolved acoustic spectroscopy

Dryburgh, Paul (2022) Inspection of additively manufactured components by spatially resolved acoustic spectroscopy. EngD thesis, University of Nottingham.

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This thesis presents the development of spatially resolved acoustic spectroscopy (SRAS) for the materials characterisation of new alloys and additive manufacturing specimens. SRAS is an acoustic microscopy technique that uses laser-generated and detected ultrasound to probe the material properties of crystalline specimens. Laser generation allows the surface acoustic wave velocity to be measured across the specimen and is a valuable tool for highlighting the grain structure. In anisotropic materials, inversion of the SAW velocity in multiple directions is used to determine the crystalline orientation.

SRAS measurements are presented in two notable additive manufacturing techniques, wire-arc additive and laser powder bed fusion. This section is focused on the study of prepared surfaces and utilises the powerful forward model for calculating SAW velocities to reveal pertinent information about material microstructure and, in turn, the build process. Examples include detecting the elimination of prior-beta microstructures in wire-arc specimens and the measurement of crystalline texture in high-silicon steel. These results demonstrate the power of SRAS as a materials characterisation tool in additive manufacturing, providing the ability to map the grain structure and extract critical crystalline information rapidly.

This analysis relies on accurate knowledge of the material elastic constants, and further results demonstrate the determination of crystallographic orientation is also highly sensitive to these values. Therefore, in this work, this inversion process is extended to allow the simultaneous determination of both orientation and elasticity from SAW velocity as measured by SRAS. In contrast to existing methods, this technique can be applied to polycrystalline specimens rather than specifically prepared single crystals, which are usually studied. Experimental results are presented for single-crystal nickel, along with more interesting polycrystalline CMSX-4 and titanium; the results show good agreement with electron backscatter diffraction measurements of crystallographic orientation and existing literature values for elastic constants. We believe this feature will significantly enhance the range of applications of SRAS and have a tangible and significant impact across materials and manufacturing sciences.

Having developed the technical case for the use of SRAS within additive manufacturing as a characterisation tool, the industrial case is considered. This focuses on the monetary and temporal consequences of a hypothetical SRAS inspection. This methodology is the basis for outlining the future potential of SRAS within the additive manufacturing sector. In the case of complex components where builds tend to fail (potentially due to an incorrect microstructure), there is a strong case for the integration of SRAS system in the build machine from a monetary viewpoint, along with the technical case developed above. Nevertheless, much work remains to be done in this field to realise SRAS within a functioning additive build system in the case of powder bed fusion.

Item Type: Thesis (University of Nottingham only) (EngD)
Supervisors: Clare, Adam T
Clark, Matt
Smith, Richard J
Li, Wenqi
Patel, Rikesh
Keywords: spatially resolved acoustic spectroscopy, SRAS, optics, photonics, additive manufacturing
Subjects: T Technology > TA Engineering (General). Civil engineering (General) > TA1501 Applied optics. Phonics
T Technology > TS Manufactures
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Electrical and Electronic Engineering
Item ID: 71831
Depositing User: Dryburgh, Paul
Date Deposited: 16 Feb 2023 13:17
Last Modified: 16 Feb 2023 13:37

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