Warm isostatic pressing (WIPʹing) of GS44 Si3N4 FDC parts for defect removal

Fused deposition of ceramics (FDC) is one of the developing solid freeform fabrication (SFF) techniques. The successful production of high performance ceramics by the FDC process requires that no defects exist in the green parts. However, build defects, such as missing roads, poorly bonded layers or sub-perimeter voids can be encountered in improperly built FDC parts. In this study, a method known as WIPʹing (warm isostatic pressing) was evaluated for its ability to eliminate existing defects in GS44 Si3N4 green FDC parts. Analogous to CIPʹing (cold isostatic pressing), the green FDC parts were rubber bagged and loaded into a pressure chamber filled with water soluble oil at different temperatures, ranging from 30 to 90°C, at pressures of up to 35 MPa. X-Ray radiography results indicated that at temperatures above 70°C, WIPʹing was effective in closing the gaps of the intentionally placed void defects in FDC parts. However, WIPʹing above 70°C was not effective in healing the defects completely. The fracture strengths of FDC parts with intentional added defects, WIPʹed above 70°C were substantially lower than control samples.