The work presented in this thesis discovers that through the use of shaped laser beam
profiles the microstructure of the deposition can be modified. It has been seen that
though modifying the beam profile melt pool flow observed during the preposition
process has altered.
A number of problems have been identified with current laser deposition processes,
typically porosity, cracking and undesired deposition profile. The work identifies that
thermal profiles are a major factor influencing both the microstructure and deposition.
Methods for observing and measuring thermal profiles are explored.
A number of beam profiles are used in this study showing a number of effects on the
thermal profiles present during the deposition on Inconel 625 onto mild steel substrate.
EBSD and ESD analysis is used to examine the properties of the depositions. Further
imaging and analysis of melt pool flow during the process is undertaken using high
speed camera imaging, motion tracking and novel pyrometry techniques.
As was expected the use of modified beam profiles had an influence on the
microstructure of the depositions formed, large variations in grain size an orientation
were observed along with alloy element segregation. Through the melt pool imaging
techniques developed it was observed that the material transport mechanisms were
modified by the shaped laser beam dramatically reducing the material transport
velocity, indicating a reduced thermal gradient.
This work shows that through modifying the laser beam profile factors influencing the
quality of a resulting deposition can be changed. Through further work this principle
can be expanded to use the laser beam profile as an input factor to allow the used
design of deposition profiles.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.