Abstract
Understanding the complicated crystallization process is important for controlling the performance reproducibility and stability in high temperature-selective laser sintering (HT-SLS). Therefore, in this paper, the performance of HT-SLS processed polyetheretherketone (PEEK) is analyzed from the perspective of crystallization kinetics. It is found that each layer of sintered powder undergoes the dynamic non-isothermal crystallization promoted by cold powder coating (CPC) and the quasi-static isothermal crystallization during the part bed temperature (Tb) maintenance of HT-SLS. The kinetic analysis shows 321 °C is a theoretical Tb for PEEK. However, due to the great sensitivity to the temperature drop of CPC, the practical Tb is set around 332 °C, at which the 1/t1/2 approaches zero according to the extrapolated analysis of Hoffman-Lauritzen theory. The shrinkage is only caused by the dynamic non-isothermal crystallization of CPC, and the minimum powder feeding temperature is found to be 250 °C by Nakamura analysis. In addition, the quasi-static maintaining of Tb during HT-SLS can lead to extended planar subunit along c-axis, increased crystallite size perpendicular to (1 1 0) and (2 0 0), and higher mechanical strength.
Published Version
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