An Experimental Study of the Relationship between Microstructure and Mechanical Properties of a Ceramic Composite Fabricated by Selective Laser Sintering
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Alumina-ammonium phosphate powder blends were processed with Selective Laser Sintering. Ammoniumphosphate with a melting point of 190°C, acts as a binder when processed with a laser and holds the alumina (m.p. 2300°C) particles together to form a "green" body. When the green body is heat treated at 850°C for 6 hours, ammonium phosphate decomposes evolving ammonia and water vapor. Residual P205 reacts with alumina to form aluminum phosphate. This results in a composite of unreacted alumina with a coating of aluminum phosphate around the alumina particles. The variation of compressive strength of these low density ceramic composites was investigated in terms of the particle size distribution the amount of binder in the initial blend. It was observed that the strength depends on the relative density and initial blend composition and the critical flaw size. A constitutive equation was formulated to characterize the influence of the relative density, binder composition and the critical flaw size on the strength of the composite.