Micro selective laser sintering of silicon carbide

Abstract

Silicon carbide (SiC) is of high importance in modern industry due to its superior properties including low bulk density, high hardness, high thermal conductivity, and excellent thermal shock and corrosion resistance. However, the strong Si – C covalent bond, lack of liquid phase, and low self-diffusivity of SiC make it very difficult for the production of fully dense parts without sintering aids or external pressure. These difficulties can be bypassed with the implementation of selective laser sintering, which enables the generation of complex-shape, high-resolution SiC parts with structural integrity. Current sintering process normally involves a powder mixture of silicon carbide as a structural material and polymer as a binder material for the generation of the preforms. It is then further sintered in high-temperature furnace to achieve full densification. In general, liquid silicon infiltration process is accompanied during the furnace sintering in order to minimize porosity and thus, maintain structural stability and enhance material properties. However, excessive infiltration may lead to overfill of the structure, deteriorating the surface and small features. \nThe goal of the proposed research is to apply selective laser sintering technology to achieve additive manufacturing of SiC parts with micro scale resolution. The proposed work is focused on the development of a micro SLS system as well as the investigation of different methods for the freeform fabrication of SiC. More specifically, the objectives of this research are threefold. Firstly, a simulation model is developed to analyze the interaction between laser radiation and micron-sized powders. Ideal system and processing parameters are estimated from the model and analyzed with experimental results. Secondly, the design of a new micro selective laser sintering system that is capable of micro scale featuring resolution is proposed. Improvements in laser scanning system and powder coating and compaction processes are studied. Finally, a material-specific micro SLS process is developed for the generation of SiC parts with complex geometry, micro scale resolution, and structural integrity. Different binding mechanisms and sintering additives are studied to facilitate the process and enhance the porosity control.