Development of Improved Processing and Evaluation of Silicon Nitride

Abstract

The goals of this program are to develop and demonstrate significant improvements in processing methods, process controls, and nondestructive evaluation (NDE) which can be commercially implemented to produce high-reliability silicon nitride components for advanced heat engine applications at temperatures to 1370°C. Achievement of this goal is being sought by • The use of silicon nitride - 4% yttria composition which is consolidated by glass encapsulated HIP’ping. • The generation of baseline tensile strength data from an initial process route involving injection molding. • Fabrication of tensile test bars by colloidal techniques, e.g. injection molding and colloidal consolidation. • Identification of (critical) flaw populations through NDE and fractographic analysis of tensile bars. • Correlation of measured tensile strength with flaw populations and process parameters. • Minimization of these flaws through innovative improvements in process methods and controls. The program goals are: • mean room temperature tensile strength of 900 MPa and Weibull modulus of 20; • mean 1370°C fast fracture tensile strength of 500 MPa; • mean 1230°C tensile stress rupture life of 100 hours at 350 MPa. This report describes the progress made to date in developing injection molding and colloidal consolidation processes for the net shape forming (NSF) of tensile bars, nondestructive evaluation of processed material, and tensile testing of net shape bars in green and densified states.