Support free infiltration of selective laser sintered (SLS) silicon carbide preforms

Indirect selective laser sintered (SLS) silicon carbide objects have been successfully infiltrated with silicon. Selective laser sintering has several advantages over conventional manufacturing methods of silicon carbide parts including more greater geometrical freedom, lower process temperatures and pressures, cheaper starting materials, and higher geometrical tolerances. Post-processing of selective laser sintered silicon carbide objects entails binder conversion to carbon and subsequent silicon infiltration to create fully dense parts that include reaction-bonded silicon carbide. These objects exhibit an overfilling of silicon onto all surfaces, especially on the bottom and in corners. Geometrical studies and microscopy were used to characterize overfilling patterns. A metrology study and generation of an Ashby Densification map proved that shrinkage of the silicon carbide structure was not the cause of the overfilling. Further research and calculations determined that the origin of overfilling was the volume expansion on freezing of silicon. An attempt to infiltrate silicon carbide preforms with an alternate infiltrant was unsuccessful due to incompatible wetting characteristics. This method is advantageous for silicon carbide applications that require complex geometries and for which composite material is acceptable.