Effects of energy density on morphology and properties of selective laser sintered polycarbonate

Selective laser sintering (SLS) was used to prepare components from polycarbonate (PC) powder. The effects of energy density of the laser beam, ranging from 0.036 to 0.12 J mm^-2, on the physical density, tensile properties and morphology of the sintered specimens were investigated. At low energy density levels, the physical density and tensile strength of the specimens were found to increase with the increase in energy density. Smoke was observed when the components were sintered under an energy density above 0.09 J mm^-2, which suggests degradation of the PC powder. These specimens appeared slightly yellow and there was a reduction in the density and tensile strength. In specimens built under a low energy density, scanning electron microscopy (SEM) showed that slight fusion occurred at the surface of the PC particles. The individual particles could be identified and the voids between the particles were interconnected. The crack propagated between the particles during tensile fracture. When the energy density was high, the powder was fused thoroughly which allowed a more dense structure to be built. SEM also showed that fusion was more effective within the individual layers of the PC powder, whilst considerable amounts of voids were present between the layers. Therefore, the strength of the components normal to the layers is expected to be lower than the in-plane strength of the layers. Some wavy circular features were observed on the fracture surfaces of the specimens built under a high energy density. Such features are commonly found on the fracture surfaces of brittle plastics. The work forms a basis for the production of selective laser sintered PC functional products.