Progress of previous work on reaction bonded and hot pressed silicon nitride materials technology is summarized. Improvements to the hot press bonding process resulted in a significant improvement in the yield of flaw-free hot press bonded rotors. Modulus of rupture and cold spin tests of rotor blade rings revealed the presence of undetected subsurface flaws in both the blades and the rim. Blade bend testing indicated that blade strength degraded during hot press bonding. An investigation of hot press bonding temperatures and time at temperature defined a region of zero microstructural and strength degradation. Using 19 hot press bondings, curves were generated defining the changes in color, porosity, hardness, phase and strength as a function of time and temperature. Improvements in injection molding of rotor blade rings were made utilizing an adaptive process control unit which controlled and monitored the injection velocity and die cavity pressure during the injection and hold portions of the molding cycle. Microfocus x-ray results indicated that high injection flowrates combined with low holding pressures in the die cavity reduced the number of subsurface void-type blade flaws. The detection of planar flaws in both green as-molded and nitrided blade rings revealed that this type flaw was only detectable after nitriding, indicating that it may only occur after burn out and/or nitriding. Approximately 30 experiments were conducted utilizing glass and/or metals as isostatic hot pressing media. Decomposition of the glass was minimized with vycor utilizing boron nitride as a barrier material. A reliability analysis was conducted for individual loading conditions. Recommendations for follow on work are presented. (ERA citation 04:039073)
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