Hot isostatic pressing (HIPing) without encapsulation has been investigated with sintered alpha silicon carbide plates and Modulus of Rupture (MOR) bars made by dry pressing and with MOR bars and gas turbine rotors made by injection molding. Early HIPing trials indicated that substantial density increases up to 99.5 percent of theoretical could be achieved. At least 98 percent densification was consistently attainable on components initially having greater than 95 percent density and less than about 1 percent open porosity. Several HIPing cycles were investigated by varying maximum temperature, maximum pressure, and their respective rates. Analysis of densities, MOR bar strength and Weibull modulus, and microstructures were used to assess the influence of HIPing parameters on material properties. Vacuum spin test results and room temperature flexural strength data on MOR bars cut from HIPed rotors were compared with results from pressureless sintered rotors. Although densities and flexural strength showed improvement, data on rotor spin-test performance were inconclusive. Emphasis is now being placed on optimizing the HIPing cycle for gas turbine rotors.

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