Conventional laser cladding systems use a focussing nozzle to direct the beam to the work piece, and by using either blown or pre placed powder, they are able to fuse the powder to the substrate. The shortfall of this process is that, once sectioned, a parabolic transverse profile is seen. This is due to the Gaussian irradiance distribution of the beam and no conventional optics can remedy the problem. Diffractive optical elements, however, can be designed for each process. Models of thermal conduction in the powder and the substrate can be utilised to produce a diffractive optical element specific to this operation. This enables a rectangular spot with a semi-idealised intensity cross section to be delivered to the work piece, reorganising 90% of the 1.2kW CO2 laser beam. When the diffractive optical element is applied to the laser cladding process, the resultant transverse clad profile is uniformly rectangular with a lack of ‘shoulder rounding’.
The laser cladding operation produced complex microstructures, which could not be satisfactorily categorised with optical microscopy. This lead to the simplification of the process by removing the powder. Autogenous bead on plate laser welds have therefore been manufactured, using both conventional optics and diffractive optical elements, in order to determine the solidification microstructure of 316L stainless steel. Optical microscopy, electron back-scatter diffraction (EBSD), energy dispersive spectroscopy (EDS), have been employed to assist in the characterisation of the complex microstructures produced.