Microstructural characterisation of laser shock peening processed commercially pure titanium

Mahmud, Uthman ORCID: 0009-0004-1121-508X (2024). Microstructural characterisation of laser shock peening processed commercially pure titanium. University of Birmingham. Ph.D.

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Abstract

Laser shock peening can be applied on a wide range of materials with real world applications, including many aerospace and automotive components. In this work, the microstructure evolution during laser shock peening of commercially pure titanium with large grain size (well exceeding 100 µm) was studied.

The study focused on the microstructural features observed as a result of laser shock between 1 and 20 times, with a beam of laser of 2 J power, 1.5 µm spot size and 10 ns pulse duration, giving a power density approximating 11.32 GW cm^-2. The samples were studied using optical profilometry, scanning electron microscopy, transmission Kikuchi diffraction, and transmission electron microscopy.

It was found that an increase in the number of shocks increases the plastic deformation zone underneath the shock spot. Twinning was observed in the 3, 5, 10 and 15 shock samples at a distance of 142 µm, 339 µm, 570 µm, and 805 µm, respectively from the surface. A similar increase in total twinning area was also observed. The near surface (typically ~10 µm) twins were identified to be of {101 ̅1} type, and the rest are primarily of {112 ̅1} type, extending to the afore mentioned depths. This is atypical for HCP structures, with the {112 ̅1} twin production most likely being a result of the large twin shear caused by the deformative shockwave. It is proposed that the near surface twins in the LSP without coating (LSPwC) regime are indicative of tensile residual stresses, and those found over the majority of the samples indicate compressive residual stresses, characterised by microstructural presentation.

The collection of findings in this study develops a picture of the mechanisms of deformation introduced through LSP, and the resultant microstructural analysis allows us to make assertions as to the reasons behind the effect on component performance. This contributes a step towards building a process parameter - mechanical property relationship, allowing us to predict the mechanical performance improvement of components as a result of laser inputs, based on the materials involved.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):