The use of custom beam profiles in laser deposition

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.