Product Code: ICAL09_1205

Direct Metal Deposition Melt Pool Temperature Distribution Control Through Novel Holographic Beam Shaping, Allowing Improved Mechanical and Corrosion Properties
Authors:
Matthew Gibson, Loughborough University; Loughborough Great Britain
John Tyrer, Loughborough University; Loughborough Great Britain
Rebecca Higginson, Loughbrough University; Loughborugh Great Britain
Presented at ICALEO 2009

The use of a laser beam to fuse a metal addition to the surface of a component for repair or direct manufacture has been adopted my many industries. However there are still issues to be overcome. Due to the high temperatures involved in the process and the complex materials utilised there are issues with mechanical weakness in the depositions caused by residual stress. Residual stresses are formed in the components due to differing rates of contraction upon cooling of the deposit. With a traditional process using a moving Gaussian beam the shape and intensity profile induces an uneven temperature distribution in the workpiece. The uneven temperature input leads to excessive heating in areas of the deposition and a varying rate of cooling, these affects lead to a weakened microstructure. A novel method for designing the time-temperature profile within the deposition is by customising the beam shape and intensity profile using Holographic Optical Elements (HOE). By controlling the beam shape and intensity and therefore the temperature profile in the material a designed microstructure has been induced. The improved microstructure provided by the HOE has increased the microhardness of the depositions along with the tensile strength properties. Removal of the large columnar grain structure caused by excessive heating and slow cooling leads to a deposition with an improved resistance to intergranular corrosion and reduced residual stress.