Effects of Shaping Conditions on the Microstructure and the Mechanical Property of the Al_2O_3-YAG Eutectic Composite Produced by Melting the Al_2O_3-YAP Eutectic Structure

摘要

When the Al_2O_3 -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 Al_2O_3-YAP eutectic particle size, forming pressure and holding time at the maximum temperature on the microstructure and/or the mechanical property of the Al_2O_3-YAG compact were examined to optimize the forming conditions. The Al_2O_3-YAG compact produced from the Al_2O_3-YAP eutectic particles with diameters less than 20 mu m exhibited a higher flexural strength and the smaller porosity as compared to that produced from Al_2O_3-YAP eutectic particles with diameters ranging from 20 mu m to 45 mu m. The volume fraction of the porosity was approximately 4 percent under a forming pressure of 10MPa and a holding time of 60s. The flexural strength of the Al_2O_3-YAG compact decreased with the increase in the holding time due to the increase in the lamellar spacing. For Al_2O_3-YAP eutectic particles with diameters less than 20 mu m, a low forming pressure of 10 MPa and a short holding time of 60 s were sufficient to synthesize a dense Al_2O_3-YAG compact. Thus, the solidification technique that uses undercooled melt produced by melting the Al_2O_3-YAP metastable eutectic system has good advantages for shaping.