Author details

The residual stress: In all the forming processes analysed, changes in residual stress are greatly influenced by process specifications. In laser forming however these changes are dependent on the process parameters used, as these differ with each laser power. Thermal gradient influences the development of residual stresses. In mechanical forming changes in residual stress are determined by the complexity of the formed shape. It was envisaged at the beginning of the study that residual stress would be enhanced but the laser forming process made undesirable changes to the underlying residual stress distribution. According to Norton [5] good design requires that an engineer try to tailor the residual stresses to a minimum, not create negative effects on the strength and preferably to create positive effects. Fatigue failure is a tensile residual stress phenomenon. The laser forming process resulted in increased tensile residual stress in the specimens due to higher line energies. The use of lower line energies on CP grade 2 titanium results in no bending of the material, and therefore high tensile residual stress remains part of the process if there is forming to be done. The parent material and mechanically formed plates had low residual stress values which was an advantage during fatigue testing as these had a

Titanium Alloys - Novel Aspects of Their Manufacturing and Processing

Microstructure: The mechanical forming process has a minimal influence on the microstructure of CP grade 2 titanium plate specimens compared to the effects of laser forming. The laser forming process results in changes in grain size as thermal energy is increased. Changes in the microstructure influenced the mechanical

Beam interaction time: The beam interaction time is significant in the analysis of resulting mechanical properties as a result of the laser forming process. The time taken to heat up an area influences the mechanical properties and the microstruc-

Heat flux: The heat flux is significant in changes observed with titanium plates, and each laser power setting evaluated had a different reading, resulting in varying microstructures on the plates evaluated. The depth of laser penetration depends on

Laser power: An increase in laser power leads to the oxidation of the passive layer

Forming parameters: The changing of forming parameters in the laser forming of CP grade 2 titanium succeeded in obtaining optimum operating parameters (in the case of this research, a power of 2.5 kW, a line energy of 90 kJ/m and a scanning

Plates: Laser formed titanium plates should not be used in applications requiring prolonged fatigue life. The process is only beneficial in applications where hardness is a priority without a need for high fatigue life, and perhaps the process could be beneficial in military defence applications. Laser formed titanium plates do not

Process control: The process needs precision control of processing parameters as they play a major role in the final microstructural layout and mechanical properties. For good fatigue properties, thermo-mechanical/laser processing of titanium needs to be conducted using lower line energies but then these do not bend the

Nelson Mandela University (NMMU) for financial assistance and laboratory

on CP grade 2 titanium plates as a result of the concentrated thermal energy

bend to the same radius of curvature as proved in this study.

facilities. Mr. Victor Ngea-Njoume for technical assistance.

higher fatigue life.

ture of plate samples.

generated by the laser.

material.

44

Acknowledgements

properties of CP grade 2 titanium plates.

the amount of line energy generated.

velocity of 1.67 m/min) for titanium.

Kadephi Vuyolwethu Mjali<sup>1</sup> \* and Annelize Botes2,3

1 iThemba LABS—Laboratory for Accelerator Based Sciences, Somerset West, Cape Town, Western Cape, South Africa

2 Council for Scientific and Industrial Research (CSIR), Pretoria, South Africa

3 Department of Mechanical Engineering, Nelson Mandela University, Port Elizabeth, South Africa

\*Address all correspondence to: vuyo.mjali@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
