Effects of Shaping Conditions on the Microstructure and the Mechanical Property of the Al₂O₃-YAG Eutectic Composite Produced by Melting the Al₂O₃-YAP Eutectic Structure

Abstract

When the Al₂O₃-YAP metastable eutectic system was heated above the metastable eutectic temperature but below the equilibrium eutectic temperature, undercooled melt was formed. Solidification in the equilibrium path accompanied the melting of the metastable eutectic system, resulting in a fine and uniform eutectic structure. A novel solidification process using undercooled melt formation was developed. In this paper, the influences of the initial Al₂O₃-YAP eutectic particle size, forming pressure and holding time at the maximum temperature on the microstructure and/or the mechanical property of the Al₂O₃-YAG compact were examined to optimize the forming conditions. The Al₂O₃-YAG compact produced from the Al₂O₃-YAP eutectic particles with diameters less than 20 μm exhibited a higher flexural strength and the smaller porosity as compared to that produced from Al₂O₃-YAP eutectic particles with diameters ranging from 20 μm to 45 μm. The volume fraction of the porosity was approximately 4% under a forming pressure of 10 MPa and a holding time of 60 s. The flexural strength of the Al₂O₃-YAG compact decreased with the increase in the holding time due to the increase in the lamellar spacing. For Al₂O₃-YAP eutectic particles with diameters less than 20 μm, a low forming pressure of 10 MPa and a short holding time of 60 s were sufficient to synthesize a dense Al₂O₃-YAG compact. Thus, the solidification technique that uses undercooled melt produced by melting the Al₂O₃-YAP metastable eutectic system has good advantages for shaping.