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Refractory nonmetallic materials are attractive for high-temperature structural applications, but in most instances the most promising materials have been produced only on a laboratory scale. This paper describes one such material and the efforts to scale up the processing procedures to an extent where practical structural components can be produced. The point of view is that of the designer rather than that of the materials engineer. The material is a multiphase body formed from zirconium diboride (ZrB2), molybdenum disilicide (MoSi2), and boron carbide (B4C) powders by means of cold pressing and sintering. The scale-up program, while following essentially standard procedures, was established to give more direct attention to user requirements than is normally the case with material scale-up activities. Early consideration of microstructural and chemical gradients, inspection requirements, and surface finish characteristics resulted from a close cooperation of the user and the material supplier. Throughout the scale-up effort, emphasis is being placed on maintaining similarity of the material as produced for test bars and for components. In this way, the designer is provided with a maximum of confidence in the characteristics to be expected from the material used for structural hardware. Control of sintering conditions, configuration of green shapes to be sintered, and machining procedures were identified as items of major importance for maintaining similarity. Electron microprobe techniques, radiographic and ultrasonic inspection techniques, and metallographic examination at high magnification provided valuable information regarding the degree of similarity obtained.
Anthony, F. M.
Chief, Bell Aerosystems Co., Buffalo, N. Y.