Methods for evaluating particle coalescence and their implications in laser sintering

Abstract

An experimental study on the melt and coalescence of different Poly(aryl ether ketones) (PAEK) powders was carried out. The study consisted of evaluating individual particles and neck growth using a hot stage platform. Three different methods of assessing particles dimensions were evaluated, and the coalescence was compared for the grades on three different substrates: glass, glass coated silicone and amorphous PEKK films, the last substrate with the intent to relate with the laser sintering process. It was found that all individual particles shrink prior to melting, achieving up to 30% reduction in perimeter at temperatures just above melting. This shrinkage is followed by an increase in size, mostly driven by viscous flow. Shrinkage is expected to affect neck growth by delaying coalescence, as particles are pulled away whilst neck increases. This is a plausible explanation for why neck growth occurs at a lower rate than predicted by most coalescence models. The use of different substrates does not seem to affect particle coalescence or change in dimension. Viscosity and particle size influence overall particle behaviour and melt, whilst morphology and porosity do not have a great impact in particles coalescence.