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Response of Ti Microstructure on Laser Forming

Admiraal, Jan (2018) Response of Ti Microstructure on Laser Forming. Master's Thesis / Essay, Applied Physics.


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In this research the microstructural and bending response to laser forming of commercially pure (CP) titanium grade 2 was studied using experimental and modelling methods. Emphasis was placed on the phase transformation during the laser forming process. The bending angle response is measured in situ for different processing parameters using 3D digital image correlation (DIC). The change in microstructure is observed using electron backscatter diffraction (EBSD). Finite element method (FEM) models are used to analyze the heat transfer and temperature inside the material and simulate the laser forming process. The thermal expansion of CP titanium grade 2 showed an increase in density during the α to β phase transformation. Evidence of small influence of the phase transformation, in dependence of the bending angle on the amount of delivered energy was found. The FEM models proved to be helpful for better understanding the heat transfer inside the metal sheet. A possible relation between the α − β phase transformation and the depth of the laser affected microstructure was found. DIC proved to be a strong instrument for in situ observation of laser bending. Experimental and simulation results suggest that the laser power has a larger influence on the final bending angle than the laser traverse speed. Sandblasted sheets show significantly higher final bending angle values, where grain size seems to have no influence. The laser bending process results show good repeatability. The final depth of the laser beam heat affected zone (LHAZ) strongly correlates with the final bending angle. The microstructure of the LHAZ consists of small refined grains at the top layer followed by large elongated grains. Deformation mechanisms slip and twinning were observed in the LHAZ, where the distribution depends on particular processing parameters. Large grains at the top layer of the LHAZ favour pyramidal first order <C+A> slip.

Item Type: Thesis (Master's Thesis / Essay)
Supervisor name: Ocelik, V. and Hosson, J.T.M. de
Degree programme: Applied Physics
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 31 Oct 2018
Last Modified: 01 Nov 2018 13:48

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