Crack-free selective laser melting of silica glass: single beads and monolayers on the substrate of the same material

Selective laser melting (SLM) is recognized for additive manufacturing from metals and alloys. Application of this technique to ceramic materials could also be promising. However, ceramics are brittle and often crack during this process. Silica glass is promising for obtaining crack-free ceramic parts due to its extremely low thermal expansion coefficient. The carried out experiments are elementary steps of SLM. Powder of particles < 20 mu m is deposited on a thick substrate to form layers of thickness from 100 to 200 mu m. The obtained sandwich-like target is scanned with the laser beam of 10.6 mu m wavelength. Cracking of silica glass is not observed at laser treatment. The quality of the obtained single beads is very sensitive to the laser power and the scanning velocity. This indicates that consolidation of powder requires a narrow temperature interval. A precise control of laser parameters is necessary to maintain the temperature within this range. Such control can be difficult to attain for industrial SLM machines. The theoretical analysis of consolidation kinetics shows that the best solution of this problem would be using powder with smaller particle size. The beads of consolidated powder can be superposed to form a uniform layer on the substrate. The lower is the thickness of the powder layer, the better is the quality of the consolidated layer. This is because of more uniform heating of finer layers by laser.